/* === PHYSL 210 — class-sourced cards & questions ===
   Auto-generated. Flashcards = audited Quizlet master (src:'quizlet') + lecture/notes gap-fill (src:'class').
   Questions = official sample-exam MCQs (src:'course'). Merged additively into the FLASHCARDS / QUESTIONS globals. */

const CLASS_FLASHCARDS = {"cell":[{"t":"Name 4 functions of the plasma membrane.","d":"Physical barrier, cell-to-cell communication, structural support, and transport (selectively permeable).","src":"quizlet"},{"t":"What is the structure of a biological membrane?","d":"A phospholipid bilayer (double layer of lipid molecules) with embedded proteins.","src":"quizlet"},{"t":"What lipids are found in the plasma membrane?","d":"Phospholipids, cholesterol, and glycolipids (all amphipathic).","src":"quizlet"},{"t":"What is an amphipathic molecule?","d":"A molecule that contains both polar (hydrophilic) and nonpolar (hydrophobic) regions.","src":"quizlet"},{"t":"What proteins do desmosomes and gap junctions each contain?","d":"Desmosomes contain cadherins, which link adjacent cells together; gap junctions are made of connexons.","src":"quizlet"},{"t":"Which organelles are surrounded by a double phospholipid membrane?","d":"The nucleus and the mitochondrion (the only two organelles with a double phospholipid membrane).","src":"quizlet"},{"t":"Give an example of a cell that has no nucleus.","d":"A red blood cell (mature RBCs lack a nucleus).","src":"quizlet"},{"t":"Give an example of a cell that has multiple nuclei.","d":"A skeletal muscle cell (multinucleate).","src":"quizlet"},{"t":"What type of transport is diffusion of particles through a membrane via a carrier protein?","d":"Facilitated diffusion (carrier-mediated). The carrier has a specific binding site for the transported substance and does not require energy input.","src":"quizlet"},{"t":"Give examples of passive transport (transport that does not require the direct input of energy).","d":"Simple diffusion, osmosis, channel-mediated facilitated diffusion, and carrier-mediated facilitated diffusion.","src":"quizlet"},{"t":"What does diffusion require?","d":"A concentration gradient. Substances move from a region of high concentration to a region of low concentration (down their concentration gradient).","src":"quizlet"},{"t":"How can materials be moved from a low to a high concentration?","d":"Active transport (primary and secondary), which uses energy to move a substance against its electrochemical/concentration gradient.","src":"quizlet"},{"t":"True or false: Diffusion uses the direct input of cellular energy.","d":"False. Diffusion is passive; molecules move down their concentration gradient (high to low) without energy input.","src":"quizlet"},{"t":"What type of transport is pinocytosis an example of?","d":"Endocytosis. The three types of endocytosis are phagocytosis, pinocytosis, and receptor-mediated endocytosis.","src":"quizlet"},{"t":"True or false: The Na+/K+ pump moves 3 sodium ions into the cell and 2 potassium ions out of the cell.","d":"False. The Na+/K+ pump moves 3 Na+ OUT of the cell and 2 K+ INTO the cell for each ATP hydrolyzed.","src":"quizlet"},{"t":"What type of transport is the engulfing of microbes by white blood cells an example of?","d":"Phagocytosis. It is used to bring large particles such as bacteria or cell debris into the cell, and is performed by white blood cells.","src":"quizlet"},{"t":"A white blood cell has engulfed a foreign pathogen by phagocytosis. Which organelle will now digest the contents of the vesicle?","d":"The lysosome. The phagosome fuses with a lysosome to form a phagolysosome, and lysosomal enzymes destroy the ingested substance.","src":"quizlet"},{"t":"Gated channels in the membrane can be opened by what factors?","d":"Voltage changes (voltage-gated), binding of a ligand (ligand-gated), or mechanical stress such as swelling/stretching (mechanically-gated).","src":"quizlet"},{"t":"How do active transport and passive transport differ?","d":"Active transport requires the input of energy and can move substances against (up) a gradient; passive transport requires no energy and moves substances down their gradient.","src":"quizlet"},{"t":"What physical properties determine whether a molecule will cross a membrane by simple diffusion?","d":"Size, polarity (polar vs. nonpolar / lipid solubility), and charge. Small, nonpolar, uncharged molecules cross easily; charged molecules cannot cross by simple diffusion regardless of size.","src":"quizlet"},{"t":"Define osmosis.","d":"The net movement of water from a region of low solute concentration to a region of high solute concentration (i.e., from high to low water concentration) across a selectively permeable membrane.","src":"quizlet"},{"t":"Which would most easily cross the membrane by simple diffusion: a large polar molecule, a positively charged ion, or a small lipid-soluble molecule?","d":"A small lipid-soluble molecule. Small, nonpolar, uncharged molecules cross the lipid bilayer; charged ions and large polar molecules do not.","src":"quizlet"},{"t":"Which driving force(s) affect the movement of an ion through a membrane channel: chemical, electrical, or both?","d":"Both. The electrical and chemical driving forces act on an ion; their sum is the electrochemical driving force.","src":"quizlet"},{"t":"What are the functions of the cytoskeleton?","d":"Maintain cell shape, mediate cell and organelle motility, and maintain the position of organelles within the cell.","src":"quizlet"},{"t":"Which organelle contains numerous vesicles and cisternae?","d":"The Golgi apparatus, consisting of stacked, flattened membrane-bound sacs (cisternae) with incoming and outgoing transport vesicles.","src":"quizlet"},{"t":"Name 3 properties of receptors.","d":"Specificity (specific binding site for a specific messenger), saturation, and affinity (they bind different messengers with different affinities).","src":"quizlet"},{"t":"Name 3 properties of G proteins.","d":"Composed of 3 subunits (alpha, beta, gamma); bind guanosine nucleotides (GTP/GDP); and are found at the cytosolic surface of the plasma membrane.","src":"quizlet"},{"t":"Which subunit of a G protein binds GDP/GTP?","d":"The alpha subunit (the beta and gamma subunits do not bind GTP/GDP).","src":"quizlet"},{"t":"Put these G-protein signaling steps in the correct order: activation of G proteins, response in a cell, binding of the first messenger to the receptor, alteration of effector protein activity.","d":"1) Binding of the first messenger to the receptor, 2) activation of G proteins, 3) alteration of effector protein activity, 4) response in the cell.","src":"quizlet"},{"t":"What is the role of calcium in signal transduction?","d":"It acts as a second messenger; it binds to and activates calmodulin (a cytosolic protein that is inactive until Ca2+ binds it).","src":"quizlet"},{"t":"Where are receptors for lipid-insoluble (water-soluble) chemical messengers located?","d":"On the extracellular surface of the plasma membrane, because they cannot diffuse across the hydrophobic core of the membrane.","src":"quizlet"},{"t":"Why are cells called selectively permeable?","d":"Because the plasma membrane allows some substances to cross the phospholipid bilayer but not others (most require specific transport proteins).","src":"quizlet"},{"t":"When a signal molecule binds a G-protein-linked receptor, what happens to the G protein?","d":"It becomes activated. First-messenger binding causes a conformational change in the receptor, and the GTP-bound alpha subunit becomes activated.","src":"quizlet"},{"t":"Glycolipids","d":"Amphipathic lipids with a carbohydrate chain attached; found exclusively in the outer leaflet of the plasma membrane; form the glycocalyx along with glycoproteins.","src":"class"},{"t":"What are the two types of membrane proteins, and how do they differ in their relationship to the bilayer?","d":"Integral (intrinsic) proteins are amphipathic and partially or fully span the phospholipid bilayer (transmembrane proteins); they comprise ~70% of all membrane proteins. Peripheral (extrinsic) proteins are NOT amphipathic and are attached only to the inner or outer surface of the membrane without penetrating the bilayer.","src":"class"},{"t":"Glycoproteins","d":"Membrane proteins with carbohydrates attached; found on the extracellular surface of the plasma membrane; form the glycocalyx together with glycolipids.","src":"class"},{"t":"Ribosomes: composition and types","d":"Non-membrane-bound organelles composed of a small and large subunit (each made of proteins and rRNA); the two subunits join prior to protein synthesis. Functional ribosomes are found either free in the cytoplasm or bound to the rough ER; proteins destined for secretion or membranes are made at the RER.","src":"class"},{"t":"Nucleolus","d":"A region within the nucleus that is the site of ribosomal RNA (rRNA) synthesis.","src":"class"},{"t":"Chromatin","d":"DNA and its associated proteins found in the nucleus; condenses to form chromosomes during cell division.","src":"class"},{"t":"What protein makes up each type of cytoskeletal filament?","d":"Microfilaments (actin filaments) — actin; Intermediate filaments — several proteins (e.g., keratin); Microtubules — tubulin.","src":"class"},{"t":"Aquaporins","d":"Water channel proteins (a type of channel-mediated facilitated diffusion) that allow water to move across membranes; found in tissues with high water permeability such as the kidneys.","src":"class"},{"t":"Receptor-mediated endocytosis","d":"A specific form of endocytosis in which binding of a ligand to its receptor recruits the cytoplasmic protein clathrin to the membrane; receptor-ligand complexes concentrate in a clathrin-coated pit that pinches off as a clathrin-coated vesicle. The vesicle can deliver contents to organelles, release contents outside the cell, or fuse with endosomes for sorting.","src":"class"},{"t":"What is the role of clathrin in receptor-mediated endocytosis?","d":"Clathrin is a cytoplasmic protein recruited to the inner membrane surface when a ligand binds its receptor; it lines the forming pit (clathrin-coated pit), concentrating receptor-ligand complexes. After the vesicle pinches off, clathrin is released from the vesicle.","src":"class"},{"t":"Steps of phagocytosis","d":"1. Recognition of substance to be ingested. 2. Attachment of phagocyte to the substance. 3. Pseudopodia surround substance and fuse to form a phagosome. 4. Phagosome fuses with a lysosome to form a phagolysosome. 5. Lysosomal enzymes destroy the ingested substance. 6. End products are released into the cell or expelled by exocytosis.","src":"class"},{"t":"What are the functions of exocytosis beyond secretion?","d":"Exocytosis secretes substances (e.g., hormones), releases waste products, and replenishes the plasma membrane by adding lipids and proteins when vesicles fuse with the membrane — balancing the membrane removed by endocytosis.","src":"class"},{"t":"Membrane potential (electrical driving force)","d":"A difference in electrical potential (voltage) across the cell membrane — also described as a separation of charge. It creates an electrical driving force that pushes or pulls charged substances across the membrane depending on their charge and the polarity of the membrane potential. Neutral substances are NOT affected by the electrical driving force.","src":"class"},{"t":"Electrochemical driving force","d":"The sum of the chemical (concentration) and electrical driving forces acting on an ion. The net direction of ion movement depends on the combined direction of these two forces.","src":"class"},{"t":"Why is mediated transport described as saturable, while simple diffusion is not?","d":"Mediated transport uses membrane proteins with a limited number of binding sites; once all sites are occupied, the transport rate plateaus no matter how much the concentration increases. Simple diffusion does not involve proteins or binding sites, so the rate keeps increasing with concentration.","src":"class"},{"t":"Signal transduction","d":"The sequence of events between the binding of a chemical messenger to a receptor and the production of a cellular response.","src":"class"},{"t":"Receptor affinity","d":"How strongly a receptor binds its messenger. High affinity = strong binding at low messenger concentrations; low affinity = weaker binding requiring higher messenger concentrations.","src":"class"},{"t":"First messenger vs. second messenger","d":"First messenger: an extracellular chemical messenger that binds to a membrane-bound receptor. Second messenger: a substance that enters or is generated inside the cytoplasm following first-messenger binding (e.g., cAMP, Ca²⁺).","src":"class"},{"t":"Receptor tyrosine kinase (enzyme-linked receptor)","d":"A membrane-bound receptor with intrinsic kinase activity. When a first messenger binds, the receptor autophosphorylates tyrosine residues; the resulting phosphotyrosines act as docking sites for cytoplasmic proteins, which are then activated by phosphorylation and relay the signal to produce a cellular response.","src":"class"},{"t":"How does a ligand-gated ion channel receptor produce a cellular response?","d":"A first messenger binds to the receptor component, causing an intrinsic ion channel in the same protein to open; ions flow through the channel and alter the electrical properties of the cell, producing a response. This is fast because the receptor and channel are a single protein.","src":"class"},{"t":"Gs vs. Gi proteins","d":"Gs (stimulatory G protein) activates its effector enzyme (e.g., adenylyl cyclase), increasing second-messenger production. Gi (inhibitory G protein) inhibits its effector enzyme, decreasing second-messenger production.","src":"class"},{"t":"cAMP second messenger system: steps from receptor to cellular response","d":"1. First messenger binds receptor → conformational change. 2. α-subunit of Gs releases GDP, binds GTP, and separates from βγ. 3. GTP-bound α-subunit activates adenylyl cyclase (membrane-bound enzyme). 4. Adenylyl cyclase converts ATP → cAMP. 5. cAMP activates protein kinase A (PKA). 6. PKA phosphorylates cellular proteins, altering their activity and producing a response.","src":"class"},{"t":"Calcium-induced calcium release","d":"When Ca²⁺ enters the cytoplasm from the ECF (via a ligand-gated or G-protein-linked channel), it binds to receptors on the ER (which stores Ca²⁺), triggering further Ca²⁺ release from the ER into the cytoplasm. This amplification step raises cytoplasmic Ca²⁺ enough to activate calmodulin.","src":"class"},{"t":"Calmodulin","d":"A cytosolic protein that is activated by Ca²⁺ (which acts as a second messenger); active calmodulin activates a calmodulin-dependent protein kinase, which phosphorylates cellular proteins to produce a response.","src":"class"},{"t":"How do tight junctions create cell polarity in epithelial cells?","d":"Tight junctions prevent integral membrane proteins and lipids from moving between the apical and basolateral surfaces of the cell. This allows different transport proteins to be maintained on each surface (e.g., Na⁺-dependent glucose transporter only on the apical side), giving the cell distinct apical and basolateral functions — a property called cell polarity.","src":"class"},{"t":"Sarcoplasmic reticulum","d":"The smooth ER (SER) in muscle cells, specialized for storing Ca²⁺ that is released to trigger muscle contraction.","src":"class"},{"t":"Cotransport vs. countertransport","d":"Cotransporters move two substances in the same direction across the membrane (e.g., Na⁺/glucose cotransporter). Countertransporters move two substances in opposite directions (e.g., Na⁺/H⁺ exchanger, where Na⁺ moves in while H⁺ moves out).","src":"class"}],"blood":[{"t":"What are the formed elements of blood?","d":"Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).","src":"quizlet"},{"t":"What is erythropoiesis?","d":"The formation (production) of red blood cells.","src":"quizlet"},{"t":"What is the role of a monocyte?","d":"Monocytes ingest (phagocytose) dead or damaged cells and help defend against infectious organisms; they leave the bloodstream and differentiate into tissue macrophages.","src":"quizlet"},{"t":"What is the role of an eosinophil?","d":"Destroy multicellular parasites and participate in allergic/immediate hypersensitivity reactions.","src":"quizlet"},{"t":"What is the role of a basophil?","d":"Participate in allergic (inflammatory) reactions; they are the blood counterparts of tissue mast cells and release histamine.","src":"quizlet"},{"t":"What term describes the sequence of responses that stops bleeding when blood vessels are injured?","d":"Hemostasis.","src":"quizlet"},{"t":"What is the loss of a large amount of blood from the blood vessels called?","d":"Hemorrhage.","src":"quizlet"},{"t":"Which blood type(s) have anti-A antibodies in their plasma?","d":"Type O and type B blood (type O has both anti-A and anti-B).","src":"quizlet"},{"t":"Which blood type(s) have anti-B antibodies in their plasma?","d":"Type O and type A blood (type O has both anti-A and anti-B).","src":"quizlet"},{"t":"What is the difference between Rh+ and Rh- blood?","d":"Rh+ blood has the Rh (D) antigen on the red blood cell membrane; Rh- blood lacks the Rh (D) antigen.","src":"quizlet"},{"t":"What is hemorrhagic anemia?","d":"Anemia caused by excessive loss of red blood cells through bleeding (e.g., injury, bleeding ulcers, or chronic menstruation).","src":"quizlet"},{"t":"What is hematocrit?","d":"The percentage of total blood volume occupied by packed red blood cells.","src":"quizlet"},{"t":"What would happen to red blood cells if the heme group could be removed from hemoglobin?","d":"They would not be able to bind oxygen. The heme group contains an iron atom that binds oxygen, so without heme, hemoglobin cannot carry oxygen.","src":"quizlet"},{"t":"What is hematopoiesis, and where does it occur after birth?","d":"Hematopoiesis is the process of formation of blood cells; after birth it occurs in the red bone marrow.","src":"quizlet"},{"t":"Platelets are formed from which cells?","d":"Megakaryocytes (platelets are pinched off from the cytoplasm of megakaryocytes).","src":"quizlet"},{"t":"For the ABO blood group, where are the antigens and where are the antibodies found?","d":"Antigens are found on the surface of red blood cells; antibodies are found in the plasma.","src":"quizlet"},{"t":"What molecule is involved in the breakdown (dissolution) of a clot?","d":"Plasmin, which breaks down insoluble fibrin strands into soluble fibrin degradation products.","src":"quizlet"},{"t":"What are the cells in red bone marrow that give rise to all the formed elements of blood called?","d":"Pluripotent hematopoietic stem cells.","src":"quizlet"},{"t":"What component of blood provides the major defense against invading bacteria and viruses?","d":"White blood cells (leukocytes).","src":"quizlet"},{"t":"Describe the structure of hemoglobin A.","d":"Hemoglobin has a non-protein part (heme) and a protein part (globin). Adult hemoglobin (HbA) is made of four globin chains (2 alpha and 2 beta). Each highly folded globin chain has a pocket holding a heme group, and at the center of each heme group is a ferrous (Fe²⁺) iron atom.","src":"quizlet"},{"t":"What is erythropoietin (EPO), where is it released from, and where does it act?","d":"EPO is a cytokine released from the kidneys; it acts on hematopoietic stem cells in the bone marrow to stimulate red blood cell production.","src":"quizlet"},{"t":"What is the name of the iron transport protein found in plasma?","d":"Transferrin.","src":"quizlet"},{"t":"What cells recycle old or worn-out red blood cells, and where does this occur?","d":"Macrophages, in the spleen (old/damaged RBCs are taken up by macrophages via phagocytosis).","src":"quizlet"},{"t":"What molecule is needed for the absorption of vitamin B12 in the small intestine?","d":"Intrinsic factor (a protein secreted by cells in the stomach wall), which forms a complex with vitamin B12 to allow its absorption.","src":"quizlet"},{"t":"What is acquired immunity, and what cells are involved?","d":"Acquired (adaptive/specific) immunity is immunity developed over time upon exposure to foreign pathogens or cells; it is mediated by lymphocytes (B and T cells).","src":"quizlet"},{"t":"What activates platelets during hemostasis?","d":"Exposed subendothelial collagen of the endothelial basement membrane, revealed when vessel injury disrupts the endothelial layer.","src":"quizlet"},{"t":"What is the first phase of hemostasis?","d":"Vascular spasm (vasoconstriction).","src":"quizlet"},{"t":"Hypoxia stimulates the kidneys to produce which hormone?","d":"Erythropoietin (EPO).","src":"quizlet"},{"t":"What is chemotaxis?","d":"The ability of white blood cells to move against a concentration gradient (low to high) in response to chemical (chemotactic) factors.","src":"quizlet"},{"t":"What is the formation of a blood clot known as?","d":"Coagulation.","src":"quizlet"},{"t":"What are the three Rs that all lymphocytes must be able to do?","d":"1) Recognize antigens in a specific manner; 2) Respond to antigens, bringing about their destruction; 3) Remember the first encounter with an antigen so they can respond better upon re-exposure.","src":"quizlet"},{"t":"Free, circulating antibodies provide which type of immunity?","d":"Humoral immunity (mediated by secreted, free-circulating antibodies in body fluids/humors).","src":"quizlet"},{"t":"Fibrinogen is converted to fibrin by which enzyme?","d":"Thrombin (the active enzyme that converts inactive fibrinogen to active fibrin).","src":"quizlet"},{"t":"How is protein C activated, and what proteins are involved?","d":"Thrombin binds to thrombomodulin (a protein on healthy endothelial cells); the bound thrombin then activates protein C.","src":"quizlet"},{"t":"Distinguish hematopoiesis, homeostasis, and hemostasis.","d":"Hematopoiesis is the formation of the formed elements of blood (blood cells); homeostasis is the maintenance of a stable internal environment; hemostasis is the stoppage of bleeding (prevention of blood loss).","src":"quizlet"},{"t":"What is serum, and how does it differ from plasma?","d":"Serum is plasma from which the clotting proteins (fibrinogen and other coagulation factors) have been removed after clot formation. Plasma is the full liquid portion of blood including all dissolved proteins.","src":"class"},{"t":"Thrombopoietin: what is it and what does it regulate?","d":"Thrombopoietin is a cytokine (hematopoietin) that regulates the production of platelets (thrombocytes) from megakaryocytes in the bone marrow.","src":"class"},{"t":"Why is carbon monoxide (CO) inhalation potentially fatal?","d":"Hemoglobin has ~200× greater affinity for CO than for O₂. CO binds tightly and is difficult to displace, preventing Hb from carrying O₂ and delivering it to tissues.","src":"class"},{"t":"What is polycythemia, and how does hematocrit reflect it?","d":"Polycythemia is an abnormally high number of red blood cells, which raises hematocrit above the normal range (~42% in females, ~47% in males). It increases blood viscosity and can impair circulation.","src":"class"},{"t":"What is aplastic anemia?","d":"Aplastic anemia is a type of anemia caused by damage to the bone marrow (e.g., by radiation or certain drugs), resulting in decreased production of red blood cells.","src":"class"},{"t":"What is hemolytic anemia?","d":"Hemolytic anemia results from increased breakdown (destruction) of red blood cells — caused by abnormal RBC shape (e.g., sickle cell disease) or immune reactions (e.g., mismatched blood transfusion).","src":"class"},{"t":"What happens to biliverdin after heme is broken down in the spleen?","d":"Biliverdin (green) is converted to bilirubin (yellow/brown), which is secreted into bile by the liver and enters the small intestine, eventually excreted in feces and urine.","src":"class"},{"t":"What is ferritin, and where is iron stored in the body?","d":"Ferritin is a storage protein that binds iron in the liver and spleen. The body's iron reserve is ~50% in hemoglobin, ~25% in other iron-containing proteins, and ~25% stored bound to ferritin.","src":"class"},{"t":"Distinguish active immunity from passive immunity.","d":"Active immunity is self-generated upon exposure to an antigen (or vaccination); it takes days–weeks to develop but lasts months–years. Passive immunity involves transfer of pre-formed antibodies (e.g., from mother to fetus); it is immediate but short-lived (weeks).","src":"class"},{"t":"What is immunological memory, and how do primary and secondary immune responses differ?","d":"Immunological memory is a feature of acquired immunity in which memory B and T cells retain specificity for a first antigen encounter. The primary response is slow and produces little antibody; the secondary response (re-exposure to the same antigen) is faster and produces far more antibody.","src":"class"},{"t":"What is antigen presentation, and which cells perform it?","d":"Antigen presentation is the process by which a host cell (macrophage or dendritic cell) engulfs a foreign protein, digests it into fragments, loads those fragments onto MHC proteins, and displays them on the cell surface to activate T cells.","src":"class"},{"t":"MHC I vs. MHC II: where is each found?","d":"MHC I proteins are expressed on virtually all nucleated cells. MHC II proteins are found specifically on antigen-presenting cells such as macrophages and dendritic cells.","src":"class"},{"t":"What triggers vasoconstriction (step 1 of hemostasis) after vessel injury?","d":"Vasoconstriction is triggered by: (1) pain receptors activating nerve endings at the cut site, (2) direct injury to vascular smooth muscle, and (3) release of serotonin from injured platelets, which acts as a vasoconstrictor.","src":"class"},{"t":"What are the contents of platelet alpha granules vs. dense granules?","d":"Alpha granules contain large molecules: von Willebrand factor (vWF), growth factors, some clotting factors, and cytokines. Dense granules contain small molecules: ADP, ATP, serotonin (5-HT), and Ca²⁺.","src":"class"},{"t":"What is the role of von Willebrand factor (vWF) in primary hemostasis?","d":"vWF is secreted by platelets and endothelial cells. It binds to exposed collagen at the site of vessel injury, changes conformation, and forms a bridge between the damaged vessel wall and platelets, mediating platelet adhesion.","src":"class"},{"t":"How does nitric oxide (NO) limit platelet plug formation?","d":"Adjacent undamaged endothelial cells release nitric oxide (NO), which inhibits platelet adhesion, activation, and aggregation, preventing the plug from spreading beyond the site of injury.","src":"class"},{"t":"How does low-dose aspirin reduce clot formation, and why is its effect on platelets permanent?","d":"Aspirin irreversibly inhibits both COX-1 (in platelets) and COX-2 (in endothelial cells). Because platelets have no nucleus, they cannot synthesize new COX-1, so thromboxane A₂ production is permanently blocked for the platelet's lifespan. Endothelial cells regenerate COX-2 and resume prostacyclin synthesis, maintaining an anti-hemostatic effect.","src":"class"},{"t":"What initiates the intrinsic coagulation pathway, and what is Factor XII's role?","d":"The intrinsic pathway is initiated by contact of Factor XII (Hageman factor) with negatively charged surfaces — exposed subendothelial collagen in vivo, or glass/artificial surfaces in vitro. Factor XII is activated to XIIa, which triggers the cascade leading to Factor Xa.","src":"class"},{"t":"What initiates the extrinsic coagulation pathway?","d":"External trauma ruptures the vessel wall, exposing tissue factor (TF, Factor III) — a transmembrane protein on extravascular cells — to circulating blood. Factor VII binds TF and is activated; the TF–VIIa complex then activates Factor X.","src":"class"},{"t":"What is thrombocytopenia?","d":"Thrombocytopenia is a deficiency in the number of platelets, which impairs primary hemostasis and can lead to excessive bleeding.","src":"class"},{"t":"What is hemophilia, and which clotting factor is deficient in classic hemophilia?","d":"Hemophilia is a hereditary bleeding disorder caused by deficiency of a clotting factor. Classic hemophilia A results from lack of Factor VIII (anti-hemophilic factor A), causing severe bleeding.","src":"class"},{"t":"What is agglutination in the context of blood transfusion?","d":"Agglutination is the clumping of red blood cells that occurs when antibodies in the recipient's plasma bind to mismatched antigens on donor RBCs, forming cross-linked complexes. It is followed by hemolysis (rupture of the RBCs).","src":"class"},{"t":"Why is blood type O the universal donor, and blood type AB the universal recipient?","d":"Type O RBCs carry no A or B antigens, so they will not be attacked by a recipient's anti-A or anti-B antibodies. Type AB individuals have no anti-A or anti-B antibodies in their plasma, so they will not attack donor RBCs of any ABO type.","src":"class"},{"t":"What is hemolytic disease of the newborn (HDN) and how is it prevented?","d":"HDN occurs when an Rh− mother, sensitized during a first Rh+ pregnancy, produces IgG anti-D antibodies that cross the placenta in a subsequent Rh+ pregnancy and destroy fetal RBCs, causing hemolysis, jaundice, and enlarged spleen. Prevention: injecting the mother with anti-Rh antibodies immediately after first delivery to neutralize fetal Rh+ RBCs before they can sensitize her immune system.","src":"class"},{"t":"What immunoglobulin class are ABO antibodies, and how are they produced?","d":"ABO antibodies (anti-A and anti-B) are naturally occurring antibodies of the IgM class, produced without prior exposure to the foreign blood type antigen.","src":"class"}],"nms":[{"t":"What is a motor unit, and what makes it the functional unit of the motor system?","d":"A motor unit is a single motor (efferent) neuron, its axon, and all of the muscle fibers it innervates. It is the functional unit of the motor system and represents the smallest increment of force that can be generated in a muscle.","src":"quizlet"},{"t":"How many presynaptic neurons innervate each skeletal muscle fiber?","d":"Each muscle fiber is innervated by only one presynaptic (motor) axon.","src":"quizlet"},{"t":"What protein makes up the thick filaments of muscle?","d":"Myosin. Thick filaments are composed of the contractile protein myosin.","src":"quizlet"},{"t":"Which ion triggers exposure of the myosin-binding sites on actin during cross-bridge cycling?","d":"Calcium (Ca2+). Ca2+ binds to troponin in the thin filament, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin.","src":"quizlet"},{"t":"Across a chemical synapse, what carries the signal across the synaptic cleft?","d":"Neurotransmitter molecules. They are released by exocytosis, diffuse across the synaptic cleft, and bind to receptors on the postsynaptic membrane.","src":"quizlet"},{"t":"What is synaptic integration?","d":"Integration is the process of summing all excitatory (EPSP) and inhibitory (IPSP) inputs to a postsynaptic neuron. This summation occurs at the axon hillock and determines the pattern of action potential output; if the net depolarization reaches threshold, the cell fires one or more action potentials.","src":"quizlet"},{"t":"Are GABA and glutamate excitatory or inhibitory neurotransmitters?","d":"GABA is inhibitory (opens Cl- channels, hyperpolarizing the cell) while glutamate is excitatory (opens Na+ channels, depolarizing the cell).","src":"quizlet"},{"t":"What is the resting membrane potential, and what is its approximate value in a neuron?","d":"The resting membrane potential (Em) is the steady electrical potential difference across the membrane of an unstimulated cell, in the absence of excitatory or inhibitory stimulation. In a neuron it is approximately -70 mV.","src":"quizlet"},{"t":"How can graded postsynaptic potentials trigger an action potential?","d":"By summation. Individual graded postsynaptic potentials (EPSPs) that are too small on their own can add together to depolarize the membrane to threshold and trigger an action potential.","src":"quizlet"},{"t":"In saltatory conduction, where is the nerve impulse regenerated along a myelinated axon?","d":"At the nodes of Ranvier. The action potential is regenerated only at the nodes (which contain voltage-gated Na+ channels) rather than at every point along the axon, so it jumps from node to node.","src":"quizlet"},{"t":"What is a synapse?","d":"A synapse is the specialized junction between a neuron and its target cell (another neuron, a muscle cell, or other effector) across which signals are transmitted.","src":"quizlet"},{"t":"Which properties describe an action potential?","d":"An action potential is all-or-none, actively propagated for long distances (regenerated along the membrane without decrement), and has a threshold and a refractory period. It is not graded and does not decay as it travels (unlike graded potentials).","src":"quizlet"},{"t":"What voltage-gated ion channels are clustered at the nodes of Ranvier and axon hillock?","d":"Voltage-gated sodium (Na+) channels. They are clustered at the nodes of Ranvier and at the axon hillock (both unmyelinated), and are absent from the myelinated internodal regions of the axon.","src":"quizlet"},{"t":"Why does an action potential conduct in only one direction along an axon?","d":"Because of the absolute refractory period. By the time the absolute refractory period of a region has ended, the action potential has moved far enough down the axon that it cannot re-depolarize the upstream membrane it just came from.","src":"quizlet"},{"t":"What part of a neuron is myelinated?","d":"The axon. Schwann cells ensheath axons in the PNS (one cell per myelin segment) and oligodendrocytes ensheath axons in the CNS.","src":"quizlet"},{"t":"What is temporal summation?","d":"Temporal summation is the adding together of postsynaptic potentials (EPSPs or IPSPs) from a single presynaptic neuron that arrive at different times — the presynaptic neuron fires repeatedly in succession — so the inputs overlap in time and sum to produce a larger potential change than a single input.","src":"quizlet"},{"t":"What is spatial summation?","d":"Spatial summation is the adding together of simultaneous postsynaptic potentials (EPSPs/IPSPs) produced by many different presynaptic neurons at different locations on a single postsynaptic neuron, producing a larger potential change than any single input.","src":"quizlet"},{"t":"Which ion triggers fusion of presynaptic vesicles and neurotransmitter release into the synaptic cleft?","d":"Calcium (Ca2+). Depolarization of the presynaptic terminal opens voltage-gated Ca2+ channels; the resulting Ca2+ influx causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter by exocytosis.","src":"quizlet"},{"t":"In a neuron at rest, is the inside more or less negatively charged than the outside?","d":"More negatively charged. At rest the inside of the neuron is negative relative to the positive outside (about -70 mV), maintained in part by the electrogenic Na+/K+ pump.","src":"quizlet"},{"t":"What is the neurotransmitter at the neuromuscular junction?","d":"Acetylcholine (ACh), which is excitatory. No inhibitory transmitters are released at the NMJ.","src":"quizlet"},{"t":"At the peak of the action potential, which ion's equilibrium potential does the membrane potential approach?","d":"Sodium (Na+). The large Na+ influx during depolarization drives the membrane potential toward the Na+ equilibrium potential, and the action potential peaks at about +30 mV.","src":"quizlet"},{"t":"What is the motor end plate?","d":"The motor end plate is the specialized region of the muscle fiber's plasma membrane that lies directly under the axon terminal of a motor neuron at the neuromuscular junction.","src":"quizlet"},{"t":"What is a neuron?","d":"A neuron is a nerve cell: a cell of the nervous system specialized to initiate, integrate, and conduct electrical signals. (A nerve cell is distinct from a nerve, which is a bundle of axons.)","src":"quizlet"},{"t":"What are the three general types of neurons?","d":"Afferent (sensory) neurons, which carry information from the periphery to the CNS; efferent (motor) neurons, which carry information from the CNS to the periphery; and interneurons, which carry information between neurons and lie entirely within the CNS.","src":"quizlet"},{"t":"What type of neuron is the afferent (sensory) neuron that carries muscle-stretch information to the CNS?","d":"A pseudo-unipolar cell. The afferent neuron in the stretch reflex is a pseudo-unipolar neuron.","src":"quizlet"},{"t":"In the stretch reflex, what kind of synaptic contact does the sensory afferent neuron make onto the motor neuron?","d":"Monosynaptic. The afferent neuron makes direct (monosynaptic) contact onto the efferent/motor neuron that innervates the quadriceps muscle. The stretch reflex is the only known monosynaptic reflex arc.","src":"quizlet"},{"t":"What cell myelinates an interneuron, and why?","d":"Oligodendrocytes, because an interneuron lies entirely within the CNS, and oligodendrocytes are the myelinating glia of the CNS.","src":"quizlet"},{"t":"What cell myelinates an efferent neuron, and why?","d":"Schwann cells, because the axons of an efferent (motor) neuron run in the peripheral nervous system, and Schwann cells are the myelinating glia of the PNS.","src":"quizlet"},{"t":"What two factors determine the speed at which an axon propagates an action potential?","d":"Axon diameter and myelination. The larger the axon diameter, the faster the propagation; myelinated axons propagate faster than unmyelinated axons.","src":"quizlet"},{"t":"Describe the withdrawal (flexor) reflex.","d":"A protective reflex in which a painful stimulus causes automatic withdrawal of the threatened body part. On the stimulated (ipsilateral) side it activates flexor muscles and inhibits extensors; it also has a contralateral component (crossed-extensor reflex). It is a polysynaptic reflex, involving at least one interneuron.","src":"quizlet"},{"t":"Describe the stretch reflex (e.g., the knee-jerk reflex).","d":"The stretch reflex is a monosynaptic, unilateral reflex that helps control posture and muscle length. The knee-jerk (patellar) reflex is a classic example; it is the only known monosynaptic reflex arc.","src":"quizlet"},{"t":"What makes up the central nervous system (CNS)?","d":"The CNS consists of the brain (cerebral cortex, cerebellum, and brainstem) and the spinal cord.","src":"quizlet"},{"t":"What is the peripheral nervous system (PNS)?","d":"The PNS is the portion of the nervous system outside the brain and spinal cord. It consists of the peripheral nerves (sensory and motor neuron axons) that connect the CNS to the rest of the body.","src":"quizlet"},{"t":"What proportion of cells and volume do neurons occupy in the CNS?","d":"Neurons make up only about 10% of the total number of cells in the CNS but occupy about 50% of its volume (they are larger than glia).","src":"quizlet"},{"t":"What are the two types of cells in the nervous system?","d":"Neurons and glial cells (glia). Glia are far more numerous (~90% of cells) but are smaller, so neurons and glia each occupy roughly half the volume.","src":"quizlet"},{"t":"What are the functions of glial cells (glia)?","d":"Glial cells support, nourish, and protect neurons. They produce myelin (oligodendrocytes in the CNS, Schwann cells in the PNS), help form and maintain the blood-brain barrier, buffer extracellular K+ and remove neurotransmitter (astrocytes), and guide neuronal growth especially during development.","src":"quizlet"},{"t":"What are afferent neurons?","d":"Afferent (sensory) neurons carry information from sensory receptors in the periphery to the CNS, entering via the dorsal roots. Their cell bodies lie outside the CNS (in the dorsal root ganglia), and they are excitatory.","src":"quizlet"},{"t":"What are efferent neurons?","d":"Efferent (motor) neurons carry information away from the CNS to the periphery, leaving the spinal cord via the ventral roots. They are excitatory.","src":"quizlet"},{"t":"What are interneurons?","d":"Interneurons are CNS neurons that lie entirely within the CNS (not found in the PNS). They communicate between neurons, intervening between sensory inputs and motor outputs, and can be either excitatory or inhibitory.","src":"quizlet"},{"t":"What do the dorsal roots of the spinal cord contain?","d":"The dorsal roots contain afferent (sensory) nerve fibers entering the spinal cord on its dorsal (posterior) side.","src":"quizlet"},{"t":"What do the ventral roots of the spinal cord contain?","d":"The ventral roots contain efferent (motor) fibers leaving the spinal cord on its ventral side, conveying motor output from both somatic and visceral (autonomic) motor neurons to the periphery.","src":"quizlet"},{"t":"What is a mixed peripheral nerve?","d":"A mixed peripheral (spinal) nerve carries both afferent and efferent fibers combined together within a single connective-tissue sheath.","src":"quizlet"},{"t":"Trace the components of a reflex loop/arc.","d":"A reflex arc (reflex loop) is circular: a stimulus activates a receptor, which activates an afferent fiber that enters the spinal cord through the dorsal root. This activates (often via an integrating center/interneurons) an efferent fiber that leaves through the ventral root and activates an effector (e.g., a muscle). Components: receptor, afferent pathway, integrating center, efferent pathway, effector.","src":"quizlet"},{"t":"What is the white matter of the spinal cord?","d":"White matter is the outer region of the spinal cord that surrounds the central (butterfly-shaped) gray matter. It is composed of myelinated axons (which give it its white appearance) and is organized into anterior, lateral, and posterior columns.","src":"quizlet"},{"t":"What is the gray matter of the spinal cord?","d":"Gray matter is the central, butterfly-shaped region of the spinal cord, composed largely of neuron cell bodies and unmyelinated processes. It is divided into dorsal horns (sensory), ventral horns (motor), and lateral horns.","src":"quizlet"},{"t":"What is the dorsal horn of the spinal cord?","d":"The dorsal (posterior) horn is the region of gray matter in the dorsal part of the spinal cord that receives sensory (afferent) input and connects with motor neurons in the ventral horn. Also called the posterior horn.","src":"quizlet"},{"t":"What is the ventral horn of the spinal cord?","d":"The ventral (anterior) horn is the gray matter in the front of the spinal cord that contains the cell bodies of motor (efferent) neurons. Also called the anterior horn.","src":"quizlet"},{"t":"What is the neuron cell body (soma)?","d":"The cell body (soma) is the part of the neuron that contains the nucleus.","src":"quizlet"},{"t":"What is the axon hillock?","d":"The axon hillock is the conical initial segment of the axon where it joins the cell body. It is the neuron's trigger zone: it integrates incoming EPSPs and IPSPs, and if the net depolarization reaches threshold it initiates the action potential.","src":"quizlet"},{"t":"From which part of a neuron are neurotransmitters released?","d":"From the axon terminals (synaptic terminals/knobs) at the end of the axon. They contain neurotransmitter in synaptic vesicles; Ca2+ influx during the action potential triggers neurotransmitter release by exocytosis. These terminals form the synaptic junction with the postjunctional cell.","src":"quizlet"},{"t":"What are dendrites?","d":"Dendrites are the branch-like extensions of a neuron specialized to receive information (from the periphery or from other cells), via activation of chemically or mechanically gated ion channels.","src":"quizlet"},{"t":"What is an axon (nerve fiber)?","d":"An axon is the long extension from the neuron cell body that propagates the nerve impulse (action potential) away from the cell body to its target cells, ending in branching synaptic terminals. Also called a nerve fiber.","src":"quizlet"},{"t":"What is a nerve?","d":"A nerve is a group of many nerve fibers (axons from numerous neurons) encased in connective tissue and traveling together in the peripheral nervous system. (Distinct from a single nerve cell/neuron.)","src":"quizlet"},{"t":"What do protein pumps do in the cell membrane?","d":"Protein pumps use active transport (energy) to move ions/substances across the membrane against their electrochemical gradient (from one side of the cell to the other).","src":"quizlet"},{"t":"What is an ion channel (and a leak channel)?","d":"An ion channel is a transmembrane protein that allows a specific ion to diffuse across the membrane down its concentration/electrochemical gradient. Leak channels are the simplest type: always open, selective for a particular ion (each ion has its own), allowing passive flow based on existing chemical and electrical gradients.","src":"quizlet"},{"t":"What is a ligand-gated ion channel (ionotropic receptor)?","d":"A ligand-gated ion channel is a gated transmembrane channel that stays closed until a specific signaling molecule (a ligand, such as a neurotransmitter) binds and changes the protein's shape to open the channel. Because the receptor itself is the channel, it is also called an ionotropic receptor.","src":"quizlet"},{"t":"What is a voltage-gated ion channel?","d":"A voltage-gated ion channel is an ion channel that opens or closes in response to changes in the membrane potential.","src":"quizlet"},{"t":"What does the Na+/K+ ATPase (sodium-potassium pump) do?","d":"It is an enzyme/pump that uses energy from hydrolysis of one ATP to pump three Na+ ions out of the cell and two K+ ions into the cell, against their gradients.","src":"quizlet"},{"t":"What does 'electrogenic' mean, and how is the Na+/K+ pump electrogenic?","d":"Electrogenic means producing a change in the electrical potential of a cell by net movement of charge. The Na+/K+ pump is electrogenic because it moves 3 Na+ out for every 2 K+ in, a net export of positive charge that makes the cell interior more negative and contributes directly to the membrane potential.","src":"quizlet"},{"t":"How do K+ leak channels and the K+ gradients help set the resting potential?","d":"K+ leak channels are always open and help establish the resting potential. The chemical gradient drives K+ out of the cell (K+ is high intracellularly), while the electrical gradient draws K+ in (the interior is negative). The net direction of K+ depends on the membrane potential relative to the K+ equilibrium potential (-90 mV).","src":"quizlet"},{"t":"What is the equilibrium potential for K+, and which way does K+ move above or below it?","d":"The equilibrium potential for K+ is -90 mV. At this potential there is no net K+ movement. If the membrane is more positive than -90 mV, K+ leaves the cell; if more negative than -90 mV, K+ enters the cell.","src":"quizlet"},{"t":"How do the gradients act on Na+ through Na+ leak channels at rest?","d":"Na+ leak channels are always open. At rest, both the chemical gradient (high extracellular Na+) and the electrical gradient (negative cell interior) drive Na+ into the cell.","src":"quizlet"},{"t":"What is the equilibrium potential of an ion, and how can it be calculated?","d":"The equilibrium potential of an ion is the membrane voltage at which the electrical force exactly balances the concentration (chemical) force, so there is no net movement of that ion. It can be calculated with the Nernst equation.","src":"quizlet"},{"t":"How does the K+/Na+ permeability ratio determine the resting membrane potential?","d":"The more permeant an ion, the more it pulls Em toward its own equilibrium potential. The greater the membrane's permeability to K+ relative to Na+, the closer the resting potential lies to the K+ equilibrium potential (-90 mV). If the ratio is small (relatively more Na+ permeability), the resting potential is pulled toward the Na+ equilibrium potential. At rest the membrane is ~50-100x more permeable to K+ than Na+, so the resting potential (-70 mV) is near EK.","src":"quizlet"},{"t":"What is an action potential (AP)?","d":"An action potential is a large, rapid, momentary reversal of the membrane potential, from about -70 mV to about +30 mV and back to resting over a few milliseconds. It is propagated by neurons and muscle cells, is all-or-none, and has a threshold and a refractory period.","src":"quizlet"},{"t":"How does an action potential propagate, and what determines its velocity?","d":"An AP self-propagates: Na+ influx at the active region carries positive charge that spreads (electrotonically) along the axon core to depolarize adjacent membrane to threshold, generating a new AP there. In most neurons it travels in one direction only (the refractory period prevents back-propagation). Velocity depends on fiber diameter (larger = faster) and myelination (myelinated = faster).","src":"quizlet"},{"t":"How does a specific stimulus initiate depolarization toward threshold?","d":"A specific physical or chemical stimulus disrupts the resting steady state by causing Na+-selective channels to open (e.g., a stimulus activates a stretch receptor). Na+ entry depolarizes the membrane toward threshold (approximately -50 mV); if threshold is reached, voltage-gated Na+ channels open and an action potential is triggered.","src":"quizlet"},{"t":"What is threshold (threshold potential)?","d":"Threshold is the membrane potential (approximately -50 mV) that an excitable cell must reach to fire an action potential; it is the minimum level of stimulation/depolarization required to trigger the impulse. A threshold stimulus is one just strong enough to depolarize the membrane to this level.","src":"quizlet"},{"t":"Both voltage-gated Na+ and K+ channels respond to depolarization, but how do their timings differ?","d":"Both are triggered by membrane depolarization, but voltage-gated Na+ channels open first because they respond rapidly, while the voltage-gated K+ channels are relatively slow ('sluggish') and open afterward, driving repolarization.","src":"quizlet"},{"t":"What is the absolute refractory period?","d":"The absolute refractory period is the time during/immediately after an action potential when the membrane cannot generate a second action potential in response to any stimulus, no matter how strong. It occurs because the voltage-gated Na+ channels are either already open or inactivated.","src":"quizlet"},{"t":"What is the relative refractory period?","d":"The relative refractory period follows the absolute refractory period: a second action potential is possible but requires a stronger-than-normal stimulus. During this time the voltage-gated K+ channels are still open and Na+ channels have returned to the resting state, leaving the membrane transiently hyperpolarized (farther from threshold).","src":"quizlet"},{"t":"What is myelin, and what does myelination do?","d":"Myelin is an insulating, lipid-rich (fatty) material made of layers of glial-cell plasma membrane wrapped around an axon. Myelination is the process of ensheathing an axon with myelin; it acts as an insulator that increases the speed of conduction (electrotonic spread) and enables saltatory conduction.","src":"quizlet"},{"t":"What are Schwann cells and where do they make myelin?","d":"Schwann cells are the myelinating glia of the peripheral nervous system (PNS); a single Schwann cell forms one myelin segment of one axon.","src":"quizlet"},{"t":"What are oligodendrocytes and where do they make myelin?","d":"Oligodendrocytes are the glial cells of the CNS that produce the myelin sheath around axons. A single oligodendrocyte myelinates several axons and several regions within a given axon.","src":"quizlet"},{"t":"What is proprioception?","d":"Proprioception is the sense of body position and limb movement: the cumulative sensory input to the CNS from mechanoreceptors (e.g., muscle spindles and Golgi tendon organs) that sense the position of the body and its parts relative to one another.","src":"quizlet"},{"t":"What is synaptic transmission?","d":"Synaptic transmission is the process by which one neuron communicates, at a synapse, with other neurons or with effectors such as muscle cells. It occurs via two types of synapses: electrical synapses and chemical synapses.","src":"quizlet"},{"t":"Describe electrical synaptic transmission and its properties.","d":"At an electrical synapse, two cells are directly connected by gap junctions (each channel is a connexon made of 6 connexin subunits). Local current/depolarization spreads passively and immediately between cells, transmission is bidirectional, and these synapses coordinate the simultaneous firing of large groups of neurons. They are inflexible (strength cannot be modulated) and always excitatory (no inhibition).","src":"quizlet"},{"t":"Describe directly-gated (ionotropic) chemical synaptic transmission step by step.","d":"When an action potential reaches the axon terminal, it opens voltage-gated Ca2+ channels; Ca2+ entry causes neurotransmitter-filled vesicles to fuse with the presynaptic membrane and release transmitter by exocytosis into the synaptic cleft. The neurotransmitter binds to ligand-gated (ionotropic) receptors on the postsynaptic membrane, producing a postsynaptic potential. The neurotransmitter is then removed from the receptor for degradation or recycling.","src":"quizlet"},{"t":"Describe indirectly-gated (metabotropic) chemical synaptic transmission.","d":"At an indirectly-gated (metabotropic) synapse, the receptor and the ion channel are separate proteins. The neurotransmitter binds a receptor that activates a second-messenger system via a G-protein cascade, producing effects with a slow onset that are long lasting.","src":"quizlet"},{"t":"What are postsynaptic potentials (PSPs) and their key properties?","d":"PSPs are graded potential changes in a postsynaptic neuron caused by neurotransmitter release. They can be excitatory (depolarizing, EPSP) or inhibitory (hyperpolarizing, IPSP), are graded (amplitude varies) and summate, spread passively in both directions with no refractory period, and decay (decrement) over space and time, unlike action potentials. They are small but relatively long-lasting (~10-20 ms or longer, longer than an AP), and they alter the probability that the postsynaptic cell fires an action potential.","src":"quizlet"},{"t":"What is an excitatory postsynaptic potential (EPSP), and how does an excitatory synapse work?","d":"An EPSP is a depolarizing graded potential in the postsynaptic neuron produced when an excitatory neurotransmitter (e.g., glutamate) opens channels permeable to Na+ (and K+); the net inward Na+ movement depolarizes the cell, bringing it closer to threshold and increasing the likelihood (or frequency) that it fires an action potential. A synapse that does this is an excitatory synapse.","src":"quizlet"},{"t":"What is an inhibitory postsynaptic potential (IPSP), and how does an inhibitory synapse work?","d":"An IPSP is a hyperpolarizing graded potential in the postsynaptic neuron produced when an inhibitory neurotransmitter (GABA or glycine) opens Cl- or K+ channels, making the cell interior more negative. This stabilizes/moves the membrane away from threshold, making the postsynaptic neuron less likely to fire (or reducing its firing frequency). A synapse that does this is an inhibitory synapse.","src":"quizlet"},{"t":"What are the excitatory neurotransmitters covered in this course?","d":"Glutamate (the major excitatory neurotransmitter in the CNS) and acetylcholine (excitatory at the neuromuscular junction).","src":"quizlet"},{"t":"What are the inhibitory neurotransmitters covered in this course?","d":"GABA (gamma-aminobutyric acid), the major inhibitory neurotransmitter in the brain, and glycine, the major inhibitory neurotransmitter in the spinal cord and brainstem. Both are amino acid neurotransmitters.","src":"quizlet"},{"t":"Can a single neuron be both excitatory and inhibitory? Which neuron types are which?","d":"No. A given neuron is either excitatory or inhibitory, never both. Afferent and efferent neurons are excitatory; interneurons can be either excitatory or inhibitory (but any single interneuron is only one of these).","src":"quizlet"},{"t":"What is smooth muscle and what does it do?","d":"Smooth muscle is involuntary muscle that forms the walls of hollow organs and tubes (blood vessels, stomach, intestines, urinary bladder, uterus, and airways of the lungs). It regulates blood flow through vessels, propels food through the GI tract, expels urine from the bladder, and changes airway diameter to regulate airflow (note: breathing itself is driven by skeletal muscles such as the diaphragm).","src":"quizlet"},{"t":"What is cardiac muscle?","d":"Cardiac muscle is striated, involuntary muscle found only in the heart; its contraction pumps blood through the heart into the circulation.","src":"quizlet"},{"t":"What is skeletal muscle?","d":"Skeletal muscle is striated, voluntary muscle that is attached to the skeleton.","src":"quizlet"},{"t":"What are the differences in synaptic transmission at the neuromuscular junction versus a central synapse?","d":"At the NMJ: transmission is only excitatory (acetylcholine; no inhibitory transmitters); each muscle fiber is innervated by only one presynaptic axon; and no summation is required (one action potential in the motor neuron generates one action potential in the muscle fiber), whereas central synapses require summation.","src":"quizlet"},{"t":"What is the neuromuscular junction?","d":"The neuromuscular junction is the synapse-like junction between the axon terminal of an efferent (motor) nerve fiber and a skeletal muscle fiber.","src":"quizlet"},{"t":"What are T-tubules (transverse tubules)?","d":"T-tubules are tubular infoldings of the muscle fiber's plasma membrane (sarcolemma) that penetrate into the cell; their lumen is continuous with the extracellular space. At rest the fiber interior is negative relative to the extracellular fluid/T-tubule lumen. The action potential propagates along the surface membrane and down the T-tubules into the fiber interior.","src":"quizlet"},{"t":"What is excitation-contraction coupling, and what is its mechanism?","d":"Excitation-contraction coupling is the sequence of events linking an action potential on the sarcolemma to activation of the myofilaments. The AP travels down the T-tubule and activates the voltage-gated DHP (dihydropyridine) receptor, which is physically coupled to the ryanodine receptor on the sarcoplasmic reticulum; this opens the SR Ca2+ channel, releasing Ca2+ from the lateral sacs into the cytosol to trigger contraction.","src":"quizlet"},{"t":"What is a muscle fiber?","d":"A muscle fiber is a single muscle cell. It contains myofibrils (the contractile elements made of actin and myosin) surrounded by sarcoplasmic reticulum, which stores and releases the Ca2+ needed for contraction; mitochondria lie between the myofibrils.","src":"quizlet"},{"t":"What is a myofibril, and what is the structure of a sarcomere?","d":"A myofibril is made of repeating sarcomeres bounded on either side by Z-lines (Z-disks). Within each sarcomere, thin filaments attach to the Z-lines, and thick filaments lie centrally between the Z-lines. The sarcomere is the basic contractile (structural) unit of striated muscle.","src":"quizlet"},{"t":"What are thin filaments composed of?","d":"Thin filaments are composed of actin (the major protein), plus the regulatory proteins troponin and tropomyosin.","src":"quizlet"},{"t":"What is the H zone of a sarcomere?","d":"The H zone is the narrow central region of the A band containing only thick filaments (the space between the opposing ends of the thin filaments). It narrows (shortens) as the muscle contracts and the sarcomere shortens.","src":"quizlet"},{"t":"What is actin?","d":"Actin is the major protein of the thin filaments. Globular (G-actin) subunits twist into a double-helical chain, and each subunit has a binding site for the myosin cross-bridge.","src":"quizlet"},{"t":"What is myosin and how does its head change with energy state?","d":"Myosin is the contractile protein of the thick filaments; each molecule has a long tail and two globular heads (cross-bridges) that bind actin. Each head has a binding site for actin and one for ATP. In the low-energy state the head is bound to ADP+Pi and is bent; hydrolysis of ATP (to ADP + Pi) puts the head into the high-energy ('cocked'/flat) state, ready to bind actin and perform the power stroke.","src":"quizlet"},{"t":"What is a cross-bridge?","d":"A cross-bridge is a myosin head/projection extending from the thick filament that is capable of binding the thin filament and exerting force on it, causing the filaments to slide past each other.","src":"quizlet"},{"t":"What is tropomyosin?","d":"Tropomyosin is a regulatory protein, a double-helical strand that wraps around the actin (thin) filament and covers the myosin-binding sites on actin in the resting/unactivated state, preventing cross-bridge binding.","src":"quizlet"},{"t":"What is troponin?","d":"Troponin is a regulatory protein bound to tropomyosin at regular intervals; it has a binding site for calcium. When Ca2+ binds, troponin undergoes a conformational change that moves tropomyosin away from the myosin-binding sites on actin, making them available.","src":"quizlet"},{"t":"What is the cross-bridge cycle and what are its steps?","d":"The cross-bridge cycle is the sequence of events between a cross-bridge binding actin, releasing, and reattaching during contraction: 1) Ca2+ release exposes the myosin-binding sites on actin (myosin is in its high-energy/cocked state, bound to ADP+Pi). 2) The energized cross-bridge binds actin. 3) Power stroke: the head pivots, sliding the thin filament toward the sarcomere center (H zone narrows), releasing ADP + Pi. 4) A new ATP binds the cross-bridge, causing it to detach from actin. 5) ATP is hydrolyzed, re-energizing/repositioning the head to the high-energy state. 6) When stimulation ends, Ca2+ is actively pumped back into the sarcoplasmic reticulum and tropomyosin re-covers the binding sites.","src":"quizlet"},{"t":"What are the properties of white (fast-twitch) muscle fibers?","d":"White muscle fibers are fast-twitch and produce intense but short-lasting, powerful contractions. They are large in diameter, rely on anaerobic glycolysis (producing lactic acid), have high glycogen, low myoglobin, few mitochondria, and poor blood supply, so they fatigue rapidly.","src":"quizlet"},{"t":"What are the properties of red (slow-twitch) muscle fibers?","d":"Red muscle fibers are slow-twitch and produce long-lasting, continuous contractions with high endurance. They rely on aerobic metabolism (Krebs cycle and oxidative phosphorylation), have high myoglobin (which has a higher O2 affinity than hemoglobin), many surrounding capillaries, numerous mitochondria, and are smaller in diameter, so they resist fatigue.","src":"quizlet"},{"t":"What is the afterhyperpolarization phase of an action potential?","d":"The afterhyperpolarization is the phase immediately after the action potential when the membrane potential transiently falls below (more negative than) the normal resting potential. It is caused by continued K+ efflux through the still-open voltage-gated K+ channels and the K+ leak channels, transiently driving Em toward the K+ equilibrium potential.","src":"quizlet"},{"t":"What is ATP (adenosine triphosphate)?","d":"ATP is a nucleotide that stores energy in high-energy phosphate bonds and transfers energy from metabolism to cell functions when broken down to ADP + inorganic phosphate (or to AMP + inorganic pyrophosphate). It occurs in all cells.","src":"quizlet"},{"t":"What is a bipolar cell (neuron)?","d":"A bipolar cell is a neuron with two extensions (one input branch and one output branch). Bipolar cells are specialized sensory neurons for special senses; in the retina, they convey information from photoreceptors to the retinal ganglion cells.","src":"quizlet"},{"t":"What is depolarization?","d":"Depolarization is a change in membrane potential toward zero, making the cell interior less negative than the resting potential.","src":"quizlet"},{"t":"What is an excitable membrane?","d":"An excitable membrane is a membrane capable of generating (producing) action potentials.","src":"quizlet"},{"t":"What is an electrochemical gradient?","d":"An electrochemical gradient is the combined driving force across a plasma membrane that determines whether an ion moves into or out of the cell. It is established by both the concentration difference and the electrical (membrane potential) difference across the membrane.","src":"quizlet"},{"t":"What is a gap junction?","d":"A gap junction is a structure made of protein channels (connexons) that link the cytoplasms of adjacent cells, allowing ions and small molecules to flow directly between the connected cells.","src":"quizlet"},{"t":"What is a graded potential?","d":"A graded potential is a membrane potential change of variable amplitude and duration that is conducted decrementally (decays with distance) and has no threshold and no refractory period.","src":"quizlet"},{"t":"What is a membrane potential (potential difference)?","d":"A potential difference is the voltage difference between two points due to separated charges of opposite sign. The membrane potential is the voltage difference between the inside and the outside of a cell.","src":"quizlet"},{"t":"What is a neurotransmitter?","d":"A neurotransmitter is a chemical messenger used by neurons to communicate with each other or with effectors.","src":"quizlet"},{"t":"What is a nicotinic receptor?","d":"A nicotinic receptor is an acetylcholine receptor that responds to nicotine. It is an ionotropic receptor found at the motor end plate of skeletal muscle and on the postganglionic neurons at autonomic ganglia.","src":"quizlet"},{"t":"What is a node of Ranvier?","d":"A node of Ranvier is a space between adjacent myelin-forming cells along a myelinated axon where the axonal plasma membrane is exposed to the extracellular fluid (and where voltage-gated Na+ channels are clustered).","src":"quizlet"},{"t":"What is repolarization?","d":"Repolarization is the change in membrane potential, just after the depolarization phase of an action potential, that returns it to a negative value, usually back to the resting membrane potential.","src":"quizlet"},{"t":"What is the somatic nervous system?","d":"The somatic nervous system is the component of the efferent (motor) division of the peripheral nervous system that innervates skeletal muscle.","src":"quizlet"},{"t":"What is a transmembrane protein?","d":"A transmembrane protein is a protein that spans the plasma membrane, containing both hydrophilic and hydrophobic regions. It often functions as a receptor or as an ion channel.","src":"quizlet"},{"t":"What is nervous (neural) communication?","d":"Nervous communication is fast signaling that uses electrical impulses (action potentials) conducted through neurons, with neurotransmitters mediating communication across synapses.","src":"quizlet"},{"t":"Equilibrium potential for Na+","d":"+55 mV. Na+ will always enter the cell unless the membrane potential rises above +55 mV.","src":"quizlet"},{"t":"What is a pseudo-unipolar neuron, and which neuron in the stretch reflex has this morphology?","d":"A pseudo-unipolar cell has a single process that bifurcates into a peripheral axon (to the muscle) and a central axon (to the CNS); the cell body sits at the branch point. The afferent (sensory) neuron of the stretch reflex is pseudo-unipolar, with its cell body in the dorsal root ganglion.","src":"class"},{"t":"What is a multipolar neuron, and which neurons in the stretch reflex circuit are multipolar?","d":"A multipolar neuron has multiple dendrites emanating from the cell body plus a single axon. Interneurons and the efferent (motor) neurons to the quadriceps and hamstrings are all multipolar cells.","src":"class"},{"t":"What are astrocytes and what do they do?","d":"Astrocytes are glial cells that physically and metabolically support neurons: they buffer extracellular K+, remove neurotransmitter from synaptic clefts, help maintain the blood–brain barrier, and play roles in signaling and information processing.","src":"class"},{"t":"What are microglia and what is their function?","d":"Microglia are glial cells that serve immune functions in the CNS; they are the resident immune cells of the central nervous system.","src":"class"},{"t":"What is a connexon, and how does it relate to connexins?","d":"A connexon is one half of a gap-junction channel; it is formed by 6 connexin protein subunits arranged in a ring. Two connexons (one from each cell) align to form a complete channel that directly links the cytoplasm of adjacent cells.","src":"class"},{"t":"What is one key functional difference between electrical and chemical synapses with respect to inhibition?","d":"Electrical synapses are always excitatory and cannot produce inhibition. Only chemical synapses can generate inhibitory postsynaptic potentials, because they can release inhibitory neurotransmitters (GABA or glycine).","src":"class"},{"t":"What are the approximate intracellular and extracellular concentrations of Na+ and K+ in a neuron?","d":"Extracellular: Na+ ~150 mM, K+ ~5 mM. Intracellular: Na+ ~15 mM, K+ ~150 mM. These gradients are maintained by the Na+/K+ ATPase.","src":"class"},{"t":"What is the approximate width of the synaptic cleft at a chemical synapse?","d":"The synaptic cleft at a chemical synapse is approximately 40 nanometers (40 nm) wide.","src":"class"},{"t":"What is membrane conductance (g), and how does it change during the depolarization and repolarization phases of an action potential?","d":"Conductance (g) is the rate at which ions travel through a channel. During depolarization, Na+ conductance rises sharply as voltage-gated Na+ channels open, then falls as they inactivate. During repolarization, K+ conductance increases as voltage-gated K+ channels open, then decreases as they close.","src":"class"},{"t":"How does a sensory stimulus initiate an action potential in an afferent neuron (e.g., in the stretch reflex)?","d":"Muscle stretch enlarges the sensory receptor, opening specialized Na+ channels in the receptor membrane. Na+ flows into the afferent neuron, causing a graded depolarization (receptor/generator potential). If this depolarization reaches threshold (~−50 mV), voltage-gated Na+ channels open and an action potential is generated.","src":"class"},{"t":"What is the threshold potential for a neuron, and how far is it from the resting membrane potential?","d":"Threshold is the membrane potential at which voltage-gated Na+ channels open and an action potential is initiated; it is typically 10–15 mV more depolarized than the resting membrane potential (approximately −50 mV, given a resting potential of −70 mV).","src":"class"},{"t":"What are the three states of a voltage-gated Na+ channel, and what distinguishes them?","d":"Closed (resting): activation gate closed, channel can be opened by depolarization. Open: activation gate open, Na+ flows in. Inactivated: inactivation gate closed; channel cannot open even with a strong stimulus — it must return to the closed (resting) state before it can open again.","src":"class"},{"t":"What is the dihydropyridine (DHP) receptor and what is its role in excitation–contraction coupling in skeletal muscle?","d":"The DHP receptor is a voltage-gated Ca²⁺ channel located in the T-tubule membrane. Its main role is as a voltage sensor: when an action potential travels down the T-tubule, the DHP receptor undergoes a conformational change that — via a physical foot process — opens the ryanodine receptor in the sarcoplasmic reticulum membrane, releasing Ca²⁺.","src":"class"},{"t":"What is the ryanodine receptor and where is it located?","d":"The ryanodine receptor is a large Ca²⁺ channel inserted in the membrane of the sarcoplasmic reticulum. In skeletal muscle it is physically coupled to the DHP receptor via a foot process; when the DHP receptor changes shape, the ryanodine receptor opens and Ca²⁺ rushes from the SR into the cytosol.","src":"class"},{"t":"How does excitation–contraction coupling differ between skeletal and cardiac muscle?","d":"In skeletal muscle, the DHP receptor is physically coupled to the ryanodine receptor via a foot process (no Ca²⁺ entry required to open SR channels). In cardiac muscle, there is no physical coupling; instead, Ca²⁺ enters through voltage-gated (L-type) Ca²⁺ channels and triggers additional Ca²⁺ release from the SR — a process called calcium-induced calcium release.","src":"class"},{"t":"What is the endomysium and what is its function in skeletal muscle?","d":"The endomysium is a membrane that surrounds each individual muscle cell (fiber). It electrically isolates muscle fibers from one another, ensuring that each fiber must be independently stimulated by its own neuromuscular junction.","src":"class"},{"t":"What is the sarcolemma?","d":"The sarcolemma is the plasma membrane of a muscle cell (fiber). An action potential propagates along the sarcolemma in all directions from the motor end plate and travels down the T-tubules to trigger Ca²⁺ release.","src":"class"},{"t":"What is the sarcoplasmic reticulum and what is its key role in muscle contraction?","d":"The sarcoplasmic reticulum (SR) is a specialized smooth ER network that surrounds myofibrils in muscle cells. It stores Ca²⁺; when an action potential travels down the T-tubule, Ca²⁺ is released from the SR into the cytosol to initiate cross-bridge cycling, and then actively pumped back into the SR (via an ATP-dependent pump) to allow relaxation.","src":"class"},{"t":"What is the sliding filament theory?","d":"The sliding filament theory describes skeletal muscle contraction: the thin (actin) filaments slide over the thick (myosin) filaments toward the center of the sarcomere, shortening the H zone and the sarcomere. The lengths of the individual filaments do not change — only the degree of overlap changes.","src":"class"},{"t":"Why does muscle relaxation depend on the absence of Ca²⁺ rather than an inhibitory neurotransmitter?","d":"At the NMJ only the excitatory neurotransmitter ACh is released; there is no inhibitory signal. Muscle relaxes because Ca²⁺ is actively pumped back into the sarcoplasmic reticulum (by an ATP-dependent pump), removing Ca²⁺ from troponin. This allows tropomyosin to re-cover the myosin-binding sites on actin, stopping cross-bridge cycling.","src":"class"},{"t":"What are the three roles of ATP in skeletal muscle contraction?","d":"1. Energizing the power stroke: ATP is hydrolyzed to ADP + Pi, putting the myosin head in its high-energy state ready to bind actin. 2. Disconnecting the cross-bridge: a new ATP molecule binds to the myosin head, causing it to release from actin. 3. Pumping Ca²⁺ back into the sarcoplasmic reticulum after contraction ends.","src":"class"},{"t":"What is myoglobin and what is its significance in muscle?","d":"Myoglobin is the primary oxygen-carrying protein of muscle tissue. Red (slow-twitch) muscle fibers contain large quantities of myoglobin, which stores oxygen for aerobic ATP synthesis; white (fast-twitch) fibers have reduced myoglobin and rely on anaerobic glycolysis instead.","src":"class"},{"t":"Compare postsynaptic potentials (PSPs) and action potentials (APs) in terms of amplitude, duration, location, and conduction.","d":"Amplitude: PSPs are graded (depolarizing or hyperpolarizing, ~0.2 mV each); APs are all-or-none (~100 mV). Duration: PSPs last milliseconds to seconds; APs last ~2–3 ms. Location: PSPs are evoked mainly on dendrites and soma; APs are initiated at the axon hillock and propagate down the axon. Conduction: PSPs are passive and decay with distance; APs are active and travel long distances without decrement.","src":"class"},{"t":"How does synaptic integration increase the complexity of behavior?","d":"Because the axon hillock continuously sums all incoming EPSPs and IPSPs, the same sensory stimulus can produce different motor responses depending on the balance of excitatory and inhibitory inputs at any moment. Increases or decreases in inhibition or excitation within a pathway allow one stimulus to generate entirely different behavioral outputs.","src":"class"},{"t":"Where are the cell bodies of sensory (afferent) neurons of spinal nerves located?","d":"The cell bodies of sensory neurons of spinal nerves are located in the dorsal root ganglion (DRG), which sits just outside the spinal cord along the dorsal root.","src":"class"}],"cns":[{"t":"The brain and spinal cord are protected by membranes known as:","d":"Meninges — three membranes: dura mater (tough outer layer), arachnoid (spidery intermediary mesh), and pia mater (delicate inner layer).","src":"quizlet"},{"t":"The brain's supporting cells are called:","d":"Glial cells (glia) — non-neuronal cells that support neurons and do not generate action potentials.","src":"quizlet"},{"t":"The large, highly convoluted outer surface of the brain is called the:","d":"Cerebral cortex — the thin outer shell of gray matter of the cerebrum, folded into peaks called gyri and grooves called sulci.","src":"quizlet"},{"t":"The centers of vision are located in which lobe of the cerebral cortex?","d":"The occipital lobe.","src":"quizlet"},{"t":"Name the four lobes of the cerebral cortex.","d":"Frontal, parietal, temporal, and occipital lobes.","src":"quizlet"},{"t":"Jane can speak but her speech is slurred after a brain injury. Which area is injured (Broca's or Wernicke's), and what is slurring of speech called?","d":"Broca's area (frontal lobe), which controls the motor aspects of speech. Lesions result in motor aphasia (slurred speech).","src":"quizlet"},{"t":"What are the elevated ridges and shallow grooves on the surface of the cerebral hemispheres called?","d":"The elevated ridges are called gyri; the shallow grooves are called sulci.","src":"quizlet"},{"t":"The term central nervous system (CNS) refers to the:","d":"The brain and spinal cord.","src":"quizlet"},{"t":"Cavities of the brain are called:","d":"Ventricles — an interconnected series of cavities filled with cerebrospinal fluid (CSF).","src":"quizlet"},{"t":"The outermost membrane surrounding the spinal cord (and brain) is the:","d":"Dura mater — the tough outer layer of the meninges.","src":"quizlet"},{"t":"Which glial cells help form the blood-brain barrier?","d":"Astrocytes (they also physically support neurons).","src":"quizlet"},{"t":"What is the main function of the cerebellum?","d":"Muscle coordination — the cerebellum controls movement, including motor timing, scaling, coordination, and learning.","src":"quizlet"},{"t":"What is the function of cerebrospinal fluid (CSF)?","d":"Bathes and supports (provides mechanical protection to) neural tissue and maintains electrolyte balance around neurons.","src":"quizlet"},{"t":"What two properties of receptive fields determine the ability to locate a stimulus?","d":"The size and density of the receptive fields of the receptors.","src":"quizlet"},{"t":"What is REM sleep also called, and what EEG rhythm does it resemble?","d":"Paradoxical sleep; its EEG resembles that of an alert, awake brain — beta rhythm.","src":"quizlet"},{"t":"Which type of glial cell lines the ventricles and produces cerebrospinal fluid?","d":"Ependymal cells. (Note: physically supporting neurons is the function of astrocytes, not ependymal cells.)","src":"quizlet"},{"t":"What do the ascending tracts form, and what type of information do they carry to the brain?","d":"The ascending tracts form the dorsal columns and carry sensory information to the brain.","src":"quizlet"},{"t":"The area of skin supplied by a pair of spinal nerves is called a:","d":"Dermatome.","src":"quizlet"},{"t":"What do Golgi tendon organs signal, and what do muscle spindles respond to?","d":"Golgi tendon organs signal muscle force (tension); muscle spindles respond to changes in muscle length (stretch).","src":"quizlet"},{"t":"A sensation combined with an understanding of its meaning is called:","d":"Perception.","src":"quizlet"},{"t":"True or false: Corticospinal tract (CST) neurons are two CNS synapses away from muscle.","d":"False. CST neurons make monosynaptic connections with spinal alpha motoneurons, so they are only one CNS synapse away from muscle — the 'final common path' from brain to muscle.","src":"quizlet"},{"t":"What is the role of adenosine in the sleep/wake cycle?","d":"It stimulates (activates) the sleep center, which in turn inhibits orexin-producing neurons, reducing wakefulness.","src":"quizlet"},{"t":"Which region includes all parts of the cerebral cortex that act together to control muscle movement?","d":"The sensorimotor cortex (comprising the somatosensory cortex and the motor cortex).","src":"quizlet"},{"t":"Does orexin promote wakefulness or sleep?","d":"Wakefulness — orexins help maintain the awake state.","src":"quizlet"},{"t":"What is the difference between a primary motivated behavior and a secondary motivated behavior?","d":"Primary motivated behavior is directly related to homeostasis. Secondary motivated behavior is not directly related to homeostasis — it is influenced by habit, learning, intellect, and emotions (often hedonistic/for enjoyment).","src":"quizlet"},{"t":"What is the function of oligodendrocytes in the CNS?","d":"Oligodendrocytes form myelin sheaths around neuronal axons, electrically insulating segments of axons and increasing their conduction velocity.","src":"class"},{"t":"What is the function of microglia?","d":"Microglia are scavenger cells in the CNS that ingest bacteria and cellular debris, mediating immune responses in the brain and spinal cord.","src":"class"},{"t":"What is the choroid plexus and what does it do?","d":"The choroid plexus is a network of capillaries lined by specialized epithelial cells in the ventricles; it produces cerebrospinal fluid (CSF) at a fairly steady rate.","src":"class"},{"t":"What is hydrocephalus and what causes it?","d":"Hydrocephalus ('water on the brain') occurs when reabsorption of CSF is blocked, causing CSF to accumulate and increase pressure in the cavities of the CNS; treated surgically with drainage tubes.","src":"class"},{"t":"Why can dopamine not be used directly to treat Parkinson's disease, and what is used instead?","d":"Dopamine cannot cross the blood-brain barrier; its precursor L-dopa (levodopa) is used instead because it can cross the BBB and is then converted to dopamine in the brain.","src":"class"},{"t":"What is the role of the thalamus?","d":"The thalamus acts as an integrating center and relay station: almost all sensory information from lower parts of the CNS is transmitted through the thalamus on its way to the cerebral cortex, and it can 'shape' sensory information passing through it.","src":"class"},{"t":"What is the function of the hypothalamus?","d":"The hypothalamus plays a key role in homeostasis and behavioral drives, including appetite, sex function, and endocrine integration; it also includes the posterior portion of the pituitary gland.","src":"class"},{"t":"What is the corpus callosum?","d":"The corpus callosum is a large bundle of nerve fibers (myelinated axons) that connects the left and right cerebral hemispheres, ensuring communication between them.","src":"class"},{"t":"What is the substantia nigra and why is it clinically important?","d":"The substantia nigra is an area in the midbrain rich in dopaminergic neurons that is part of the basal nuclei and enables movement and coordination. Degeneration of its pars compacta (SNpc) neurons causes Parkinson's disease.","src":"class"},{"t":"What are the functions of the pons?","d":"The pons serves as a relay station connecting the cerebrum and cerebellum, and it assists in the coordination of breathing (along with the medulla oblongata).","src":"class"},{"t":"What are the functions of the medulla oblongata?","d":"The medulla oblongata is where the brainstem connects to the spinal cord; it contains autonomic centers controlling involuntary visceral functions including cardiovascular, respiratory, and digestive regulation.","src":"class"},{"t":"What are the three horns of spinal cord gray matter and what does each contain?","d":"The dorsal (posterior) horn contains interneurons on which afferent sensory neurons terminate; the ventral (anterior) horn contains cell bodies of efferent motor neurons supplying skeletal muscles; the lateral horn contains cell bodies of autonomic neurons supplying smooth muscle, cardiac muscle, and exocrine glands.","src":"class"},{"t":"What are central pattern generators?","d":"Central pattern generators are neural circuits in the spinal cord that generate the rhythmic motor commands underlying repetitive movements such as walking and breathing, without requiring continuous input from higher brain centers.","src":"class"},{"t":"What are the three classes of movement generated by motor systems?","d":"1. Reflexes — rapid, stereotyped, involuntary responses; 2. Rhythmic motor behaviors — initiated and terminated voluntarily but continue automatically once activated (e.g., walking, breathing); 3. Voluntary movements — complex, intentional movements (e.g., swinging a baseball bat).","src":"class"},{"t":"Distinguish upper motor neurons (UMNs) from lower motor neurons (LMNs).","d":"UMNs originate in the primary motor cortex or brainstem nuclei and send signals down descending tracts, synapsing onto LMNs. LMNs originate in the ventral horn of the spinal cord (or cranial nerve nuclei in the brainstem) and directly innervate skeletal muscles to produce movement.","src":"class"},{"t":"What is the corticobulbar tract (CBT) and what does it control?","d":"The CBT is a pyramidal tract that runs from the primary motor cortex to nuclei in the midbrain, pons, or medulla (brainstem), where it synapses on cranial nerve lower motor neurons. It controls voluntary movement of the muscles of the head, face, tongue, and neck.","src":"class"},{"t":"What is the extrapyramidal system and what is its primary function?","d":"The extrapyramidal system consists of brainstem pathways that do not pass through the medullary pyramids. It coordinates the large muscle groups of the trunk and proximal limbs for posture, locomotion, and involuntary/automatic motor control.","src":"class"},{"t":"What EEG rhythm is present during alert wakefulness, and how does it change during relaxed wakefulness?","d":"Alert wakefulness produces high-frequency, low-amplitude beta rhythm. During relaxed wakefulness, the EEG transitions to alpha rhythm (lower frequency, higher amplitude).","src":"class"},{"t":"What characterizes NREM sleep on the EEG, and how many stages does it have?","d":"NREM (slow-wave) sleep is characterized by high-amplitude, low-frequency waves (theta and delta rhythms). It has three stages: N1 (light sleep, theta/delta waves begin), N2 (random larger amplitude waves), and N3 (deep sleep, dominant theta and delta activity).","src":"class"},{"t":"What is the suprachiasmatic nucleus (SCN) and what role does it play in the sleep-wake cycle?","d":"The SCN is located in the anterior hypothalamus and serves as the circadian pacemaker. In the morning it activates orexin-producing neurons to promote wakefulness; in the evening it regulates melatonin secretion to prepare for sleep.","src":"class"},{"t":"What is long-term potentiation (LTP) and why is it significant?","d":"LTP is a process in which frequently used synapses increase in effectiveness over time; it involves AMPA and NMDA receptor activity at glutamatergic synapses. LTP is the fundamental cellular mechanism underlying learning and memory.","src":"class"},{"t":"What are the two hallmark neuropathological features of Alzheimer's disease?","d":"1. Senile (amyloid) plaques — extracellular deposits of beta-amyloid (Aβ) protein clumped between nerve cells; 2. Neurofibrillary tangles — intracellular accumulations of hyperphosphorylated tau protein that disrupt axonal transport, leading to neuronal degeneration.","src":"class"},{"t":"What is lateral inhibition and what does it accomplish in sensory processing?","d":"Lateral inhibition is a mechanism by which strongly stimulated neurons suppress the activity of neighboring, less-activated neurons. It sharpens contrast and focuses ascending sensory signals onto the center of the stimulus, improving spatial acuity and stimulus localization.","src":"class"},{"t":"What are labeled line codes, and how do they explain phantom limb pain?","d":"Labeled line codes are a 1:1 association between a specific receptor/afferent pathway and a particular sensation (e.g., signals arriving at the somatosensory cortex are always perceived as touch). Phantom limb pain occurs because remaining afferent fibers, when stimulated, still transmit their labeled modality to the cortex even though the peripheral receptor is absent after amputation.","src":"class"},{"t":"Distinguish tonic (slowly adapting) from phasic (rapidly adapting) sensory receptors.","d":"Tonic receptors generate action potentials throughout the duration of a stimulus, providing continuous monitoring (e.g., Merkel's corpuscles, Ruffini corpuscles, free nerve endings). Phasic receptors fire only briefly at the onset or change of a stimulus and then cease firing, signaling change rather than sustained stimulation (e.g., Pacinian corpuscles, Meissner's corpuscles).","src":"class"},{"t":"What is the limbic system and what are its primary functions?","d":"The limbic system is an interconnected group of forebrain structures (including the hippocampus, amygdala, hypothalamus, thalamus, basal ganglia, and cingulate gyrus) involved in behavioral and emotional responses: learning, emotion, visceral functions (appetite, sex), fight-or-flight responses, and endocrine integration.","src":"class"},{"t":"What is the role of the amygdala?","d":"The amygdala is a limbic structure involved in emotional responses, particularly fear and fight-or-flight reactions, as well as the emotional aspects of learning and memory.","src":"class"}],"ans":[{"t":"Are the effects of the autonomic divisions (and their neurotransmitters) always excitatory or always inhibitory?","d":"No. Neither division is purely excitatory or inhibitory. Both the sympathetic and parasympathetic systems can have excitatory or inhibitory effects, and norepinephrine/epinephrine (like ACh) can excite or inhibit a target depending on the target tissue, the neurotransmitter released, and the receptor it binds (a metabotropic, G-protein-coupled mechanism).","src":"quizlet"},{"t":"Does the adrenal medulla release epinephrine and norepinephrine as hormones or as neurotransmitters?","d":"As hormones. Because they are released directly into the bloodstream, epinephrine (~80%) and norepinephrine (~20%) act as hormones.","src":"quizlet"},{"t":"What is the primary function of the parasympathetic nervous system?","d":"To maintain homeostasis (the constancy of the internal environment); it dominates 'rest and digest' housekeeping functions such as digestion.","src":"quizlet"},{"t":"How do the lengths of sympathetic preganglionic and postganglionic fibers compare?","d":"Short preganglionic fibers; long postganglionic fibers.","src":"quizlet"},{"t":"How do the lengths of parasympathetic preganglionic and postganglionic fibers compare?","d":"Long preganglionic fibers; short postganglionic fibers.","src":"quizlet"},{"t":"What are the two major neurotransmitters released by autonomic nervous system neurons?","d":"Acetylcholine and norepinephrine.","src":"quizlet"},{"t":"During the 'rest and digest' response, which division of the autonomic nervous system dominates?","d":"The parasympathetic division.","src":"quizlet"},{"t":"How are the effects of sympathetic and parasympathetic stimulation of the salivary glands described?","d":"Cooperative — both divisions act together to change the type and volume of saliva produced.","src":"quizlet"},{"t":"Name three target tissues innervated only by the sympathetic nervous system (exceptions to dual innervation).","d":"The adrenal medulla, sweat glands, and most blood vessels.","src":"quizlet"},{"t":"True or false: Varicosities are found on both preganglionic and postganglionic autonomic fibers.","d":"False. Varicosities are found only on postganglionic fibers (of both the sympathetic and parasympathetic divisions).","src":"quizlet"},{"t":"Where are the cell bodies of postganglionic autonomic neurons located?","d":"Outside the CNS, in the autonomic ganglia (not in the brain or spinal cord).","src":"quizlet"},{"t":"Where is acetylcholine used as a neurotransmitter?","d":"At neuromuscular junctions and at all autonomic ganglia — both sympathetic and parasympathetic. ACh is the neurotransmitter released at every autonomic ganglion.","src":"quizlet"},{"t":"Acetylcholine binds to which two classes of receptors?","d":"Nicotinic and muscarinic (cholinergic) receptors.","src":"quizlet"},{"t":"What term describes axons from numerous preganglionic neurons forming synapses with a single postganglionic neuron?","d":"Convergence.","src":"quizlet"},{"t":"What neurotransmitters and hormones bind alpha and beta adrenergic receptors?","d":"Norepinephrine and epinephrine (NE/E).","src":"quizlet"},{"t":"The cell bodies of sympathetic preganglionic fibers are found in which regions of the spinal cord?","d":"The thoracic and lumbar regions (T1–L2).","src":"quizlet"},{"t":"Where are nicotinic receptors found within the autonomic nervous system?","d":"On the cell bodies of postganglionic neurons at all autonomic ganglia (both sympathetic and parasympathetic).","src":"quizlet"},{"t":"List the five components of a reflex arc in order.","d":"Receptor (sensor) → afferent/sensory pathway → integrating center (brain or spinal cord) → efferent/motor pathway → effector (tissue/organ).","src":"quizlet"},{"t":"How does the somatic nervous system's efferent pathway differ from the ANS efferent pathway?","d":"The somatic nervous system uses a single neuron from the CNS to skeletal muscle (always excitatory). The ANS uses a two-neuron chain (preganglionic + postganglionic) connected by a ganglion, targeting smooth muscle, cardiac muscle, and glands; effects can be excitatory or inhibitory.","src":"class"},{"t":"What are the two types of sympathetic ganglia, and where is each located?","d":"Paravertebral ganglia (sympathetic trunk/chain): run parallel to the spinal cord on either side of the vertebral column. Collateral ganglia (prevertebral ganglia): located in front of the vertebral column, close to abdominal viscera; include the celiac, superior mesenteric, and inferior mesenteric ganglia.","src":"class"},{"t":"What are the three pathways a sympathetic preganglionic fiber can take after leaving the spinal cord?","d":"1. Synapse immediately with a postganglionic neuron in the sympathetic ganglion at the same level. 2. Travel up or down the sympathetic chain and synapse in a ganglion at a different level. 3. Pass through the chain without synapsing and continue as a splanchnic nerve to a collateral (prevertebral) ganglion.","src":"class"},{"t":"White ramus communicans vs. grey ramus communicans","d":"White ramus communicans: the branch carrying a myelinated preganglionic fiber from the spinal nerve into the sympathetic ganglion (white = myelin). Grey ramus communicans: the branch carrying an unmyelinated postganglionic fiber back out of the ganglion into the spinal nerve (grey = no myelin).","src":"class"},{"t":"What is the only set of ganglia in the parasympathetic nervous system, and where are they located?","d":"Terminal ganglia — situated on or very close to (sometimes within the walls of) the target organ. Because the ganglion is so near the organ, the preganglionic fiber is long and the postganglionic fiber is short.","src":"class"},{"t":"What percentage of all parasympathetic fibers does the vagus nerve (cranial nerve X) carry?","d":"Approximately 75% of all parasympathetic fibers travel in the vagus nerve, innervating thoracic and upper abdominal organs.","src":"class"},{"t":"Autonomic tone","d":"A background level of activity maintained simultaneously by both the sympathetic and parasympathetic divisions. The two divisions are activated reciprocally: when one increases activity, the other decreases, allowing precise control of target organ function.","src":"class"},{"t":"Give an example of antagonistic dual innervation.","d":"Heart: sympathetic stimulation increases heart rate and force of contraction; parasympathetic stimulation decreases heart rate and force of contraction. GI tract: sympathetic decreases motility and secretions; parasympathetic increases motility and secretions.","src":"class"},{"t":"What is an example of cooperative dual innervation in the male reproductive system?","d":"The parasympathetic division mediates erection (dilation of blood vessels); the sympathetic division mediates emission. Both divisions work together to complete the reproductive response.","src":"class"},{"t":"What is the biosynthetic pathway for norepinephrine (NE) in a sympathetic varicosity?","d":"Tyrosine (amino acid) is taken up into the varicosity → converted to DOPA → converted to dopamine → dopamine is taken up into vesicles → converted to NE, where it is stored until release.","src":"class"},{"t":"How is the action of norepinephrine (NE) terminated at the sympathetic nerve terminal?","d":"Primarily by reuptake: the intact NE molecule is taken back up into the varicosity and repackaged into vesicles for future release. A small amount diffuses away and is broken down by enzymes in surrounding tissues.","src":"class"},{"t":"How is acetylcholine (ACh) synthesized, and how is it removed from the synaptic cleft?","d":"Synthesis: acetyl-CoA + choline, catalyzed by choline acetyltransferase; ACh is packaged into vesicles. Removal: acetylcholinesterase cleaves ACh into choline + acetate; choline is recycled back into the nerve terminal via a carrier; acetate breaks down to CO₂ and water.","src":"class"},{"t":"Describe the structure of the NN nicotinic receptor and what happens when ACh binds.","d":"The NN receptor is an ionotropic (ligand-gated ion channel) receptor made of 5 subunits arranged in a ring with a central pore; it has 2 alpha subunits bearing the ACh binding sites. ACh binding to both alpha subunits opens the channel, allowing Na⁺ (and K⁺) to flow through; the larger Na⁺ influx depolarizes the postganglionic neuron, producing an EPSP that triggers an action potential.","src":"class"},{"t":"NM vs. NN nicotinic receptors: where is each found and what does each bind?","d":"NM (nicotinic muscle): found on skeletal muscle at the neuromuscular junction; binds ACh released from somatic motor neurons. NN (nicotinic nerve): found on the cell bodies of postganglionic neurons at all autonomic ganglia (both SNS and PSNS) and on the adrenal medulla; binds ACh released from preganglionic fibers.","src":"class"},{"t":"What is the structure and mechanism of muscarinic and adrenergic receptors?","d":"Both are metabotropic G-protein–coupled receptors with 7 transmembrane-spanning domains. Ligand binding (ACh for muscarinic; NE/E for adrenergic) activates a G protein, which modulates a membrane enzyme or ion channel, generating a second messenger cascade that produces either excitation or inhibition of the target tissue.","src":"class"},{"t":"What receptor on sweat glands and blood vessels of skeletal muscle binds the ACh released by sympathetic postganglionic fibers?","d":"Muscarinic receptors — even though the fiber is sympathetic, those specific postganglionic terminals release ACh, which binds muscarinic receptors on sweat glands and on the blood vessels of skeletal muscle.","src":"class"},{"t":"What is divergence in the ANS, and how does it differ between the SNS and PSNS?","d":"Divergence: a small number of presynaptic neurons synapse with a larger number of postsynaptic neurons (spreading out of information). SNS has a higher degree of divergence (ratio up to 1:20), producing diffuse, mass-discharge responses. PSNS divergence is lower (ratio ~1:3), producing more localized, organ-specific responses.","src":"class"},{"t":"What are the three CNS integrating centers for autonomic reflexes and what does each control?","d":"Spinal cord (sacral region): integrates reflexes such as urination, defecation, and erection (modulated by higher brain centers). Medulla oblongata (brainstem): major ANS reflex center for cardiovascular, respiratory, and digestive activity (blood pressure, salivation, swallowing, vomiting). Hypothalamus: the head ganglion of the ANS; integrates and commands autonomic functions including temperature regulation.","src":"class"},{"t":"What are the sympathetic effects on the eyes, lungs, and bladder during fight-or-flight?","d":"Eyes: pupil dilation, adjustment for far vision. Lungs: dilation of bronchioles and inhibition of mucus secretion. Bladder: smooth muscle relaxation — prevents voiding (urine retention).","src":"class"},{"t":"What are the parasympathetic effects on the eyes, lungs, and bladder during rest-or-digest?","d":"Eyes: pupil constriction, adjustment for near vision. Lungs: constriction of bronchioles and stimulation of mucus secretion. Bladder: smooth muscle contraction — promotes voiding.","src":"class"},{"t":"Why does the somatic nervous system use ionotropic (NM nicotinic) receptors on skeletal muscle rather than metabotropic (muscarinic) receptors?","d":"Ionotropic receptors always produce excitation (Na⁺ influx → action potential → contraction), ensuring that every motor command reliably causes muscle contraction. Muscarinic (metabotropic) receptors can be excitatory or inhibitory depending on the G-protein pathway, which would be unreliable for voluntary movement.","src":"class"}],"ss":[{"t":"Rods and cones (photoreceptors) are found in which part of the eye?","d":"The retina (located against the back of the eye, behind the lens).","src":"quizlet"},{"t":"Which part of the eye regulates the amount of light entering the eye?","d":"The iris, which controls the size of the pupil and thus the amount of light passing into the eyeball.","src":"quizlet"},{"t":"What is the optic chiasm?","d":"The region at the base of the brain where the two optic nerves meet and some of their axons cross to the opposite side.","src":"quizlet"},{"t":"What is accommodation (of the eye)?","d":"The ability of the eye to change lens shape (via the ciliary muscles) to focus on close objects.","src":"quizlet"},{"t":"What are the sensory receptors of the auditory system, and in which part of the ear (outer/middle/inner) are they found?","d":"Hair cells; they are located in the inner ear (within the cochlear duct).","src":"quizlet"},{"t":"On what structure are the hair cells of the auditory system found?","d":"The organ of Corti (within the cochlear duct).","src":"quizlet"},{"t":"What is the function of the bones of the middle ear (malleus, incus, and stapes)?","d":"They act as levers and amplify sound, transmitting vibrations to the fluid of the inner ear.","src":"quizlet"},{"t":"Which structure of the inner ear contains the organ of Corti?","d":"The cochlea (its cochlear duct houses the organ of Corti).","src":"quizlet"},{"t":"Order the path of light from the cornea to the photoreceptors (cornea, photoreceptors, retina, lens, vitreous humor, aqueous humor).","d":"Cornea → aqueous humor → lens → vitreous humor → retina → photoreceptors.","src":"quizlet"},{"t":"Which photoreceptor functions best in bright light and is responsible for color vision?","d":"The cone.","src":"quizlet"},{"t":"The auditory cortex is found in which lobe of the brain?","d":"The temporal lobe.","src":"quizlet"},{"t":"What type of graded potential do sensory receptors generate in response to a stimulus?","d":"Receptor potentials.","src":"quizlet"},{"t":"Are Meissner's corpuscles rapidly or slowly adapting receptors?","d":"Rapidly adapting mechanoreceptors.","src":"quizlet"},{"t":"Name 4 factors important for localizing the site of a stimulus.","d":"Size of the receptive field, density of sensory receptors in the receptive field, overlapping receptive fields, and lateral inhibition.","src":"quizlet"},{"t":"How does receptor density affect two-point discrimination?","d":"The more densely packed the sensory receptors are, the greater the two-point discrimination.","src":"quizlet"},{"t":"Proprioception (kinesthesia)","d":"The sense of posture and movement; awareness of the position of body parts and muscle contraction in space. Mediated by a mix of joint and tendon stretch receptors. Distinct from somatosensation — individuals who lose proprioception can still move limbs but cannot control them precisely.","src":"class"},{"t":"What does the Merkel's corpuscle respond to, and what is its adaptation type?","d":"Responds to touch and pressure; it is a slowly adapting mechanoreceptor. It generates a receptor potential that decays slightly but persists throughout the entire duration of the stimulus.","src":"class"},{"t":"What does the Pacinian corpuscle respond to, and what is its adaptation type?","d":"Responds to vibration and deep pressure; it is a rapidly adapting mechanoreceptor.","src":"class"},{"t":"What does the Ruffini corpuscle respond to, and what is its adaptation type?","d":"Responds to skin stretch; it is a slowly adapting mechanoreceptor.","src":"class"},{"t":"Free neuron endings — what types of stimuli do they detect, and what is their adaptation rate?","d":"Free neuron endings are located close to the skin surface and include nociceptors (pain), thermoreceptors (temperature), and mechanoreceptors (touch/pressure). They are slowly adapting.","src":"class"},{"t":"Why are rapidly adapting receptors functionally useful?","d":"They filter out unimportant, continuous stimuli. For example, they signal when you sit in a chair or put on a shirt (stimulus onset/offset) but do not fire continuously during the duration of contact — preventing the CNS from being flooded with irrelevant information.","src":"class"},{"t":"Lateral inhibition","d":"A mechanism that sharpens stimulus localization. When a central afferent neuron is stimulated, it activates inhibitory interneurons (releasing glycine or GABA) that suppress activity in flanking afferent neurons. This amplifies the contrast between the stimulated region and its periphery, helping the brain identify the precise site of a stimulus. Occurs in somatosensation and vision, but not the auditory system.","src":"class"},{"t":"Anterolateral system (spinothalamic tract) — what information does it carry and where does it cross?","d":"Carries pain and temperature information. The first synapse is in the dorsal horn of the spinal cord (ipsilateral side); the secondary neuron crosses immediately to the contralateral side of the spinal cord and ascends to synapse in the thalamus, which then projects to the somatosensory cortex.","src":"class"},{"t":"Dorsal column system — what information does it carry and where does it cross?","d":"Carries fine touch and mechanoreception information. The sensory neuron ascends ipsilaterally up the spinal cord to the brainstem, where the first synapse occurs. The secondary neuron then crosses at the level of the brainstem and synapses in the thalamus, which projects to the somatosensory cortex.","src":"class"},{"t":"Where is the somatosensory cortex located?","d":"In the parietal lobe, posterior to the central sulcus and the primary motor cortex. It is the main region for processing somatic (body) sensory information.","src":"class"},{"t":"What determines how large a body region's representation is in the somatosensory cortex?","d":"The density of sensory receptor innervation. More densely innervated regions (e.g., fingers, lips, face) occupy larger cortical areas; sparsely innervated regions (e.g., trunk, back) occupy smaller areas.","src":"class"},{"t":"What is the primary structure responsible for refraction in the eye?","d":"The cornea. It is primarily responsible for bending (refracting) light waves as they enter the eye; the lens then fine-tunes the focus by changing shape.","src":"class"},{"t":"How does the autonomic nervous system control pupil size?","d":"The iris is innervated by the autonomic nervous system. Parasympathetic innervation causes the pupil to constrict; sympathetic innervation causes the pupil to dilate.","src":"class"},{"t":"Myopia (nearsightedness) — cause and correction","d":"Caused by an eyeball that is too long, so the image is focused in front of the retina. Corrected with concave (diverging) lenses to reduce refraction, or by laser surgery.","src":"class"},{"t":"Hyperopia (farsightedness) — cause and correction","d":"Caused by an eyeball that is too short, so the image is focused behind the retina (insufficient refraction). Corrected with convex (converging) lenses to increase refraction, or by laser surgery.","src":"class"},{"t":"Presbyopia","d":"Age-related loss of elasticity of the lens (due to breakdown of ciliary muscles) resulting in the inability to accommodate for near vision. Typically occurs around age 45.","src":"class"},{"t":"Glaucoma — cause and consequence","d":"Caused by buildup of aqueous humor leading to increased intraocular pressure. The pressure pushes back on the lens → vitreous humor → retina, damaging photoreceptors. There is no successful treatment; damage to photoreceptors is progressive.","src":"class"},{"t":"Cataracts — cause and treatment","d":"Age-related clouding of the lens caused by accumulation of cellular debris as lens cells die. Treated by surgically removing the lens and replacing it with a synthetic (silicone) lens, which cannot accommodate.","src":"class"},{"t":"Which cells in the visual pathway are the first to generate action potentials?","d":"Retinal ganglion cells. Photoreceptors and bipolar cells only undergo graded potentials because they lack voltage-gated sodium channels; retinal ganglion cells possess these channels and are the first cells where action potentials can be initiated.","src":"class"},{"t":"Key difference between ON-pathway and OFF-pathway bipolar cells regarding glutamate receptors","d":"ON-pathway bipolar cells have inhibitory (metabotropic) glutamate receptors — glutamate hyperpolarizes them. OFF-pathway bipolar cells have excitatory (ionotropic, non-selective cation channel) glutamate receptors — glutamate depolarizes them.","src":"class"},{"t":"What does the OFF visual pathway signal, and when is it active?","d":"The OFF pathway signals the absence of light. It generates action potentials in the dark (no light) and is suppressed when light is present. OFF bipolar cells are excited by glutamate released from depolarized photoreceptors in the dark.","src":"class"},{"t":"Where is the visual cortex located?","d":"In the occipital lobe. Visual information travels from the retina → optic chiasm → lateral geniculate nucleus (thalamus) → visual cortex in the occipital lobe.","src":"class"},{"t":"What is the lateral geniculate nucleus?","d":"A relay nucleus in the thalamus that receives input from the retinal ganglion cells (via the optic nerve/tract) and projects to the primary visual cortex in the occipital lobe.","src":"class"},{"t":"How are sound frequency (pitch) and amplitude (loudness) determined by a sound wave?","d":"Frequency (pitch) is determined by the number of zones of compression per unit time (or distance between zones); a faster vibration produces a higher pitch. Amplitude (loudness) is determined by the pressure difference between zones of compression and rarefaction — more air molecules packed in a zone of compression = louder sound.","src":"class"},{"t":"Name the three fluid-filled compartments of the cochlea and identify the fluid in each.","d":"Scala vestibuli (top) — filled with perilymph; scala tympani (bottom) — filled with perilymph; cochlear duct (middle) — filled with endolymph. The sensory hair cells of the organ of Corti are located in the cochlear duct.","src":"class"},{"t":"How does basilar membrane location relate to sound frequency detection?","d":"Different regions of the basilar membrane vibrate maximally at different frequencies. Hair cells at the region of peak vibration are most mechanically deformed, and the CNS interprets the pattern of hair cell stimulation as a specific sound frequency (basis of tonotopy).","src":"class"},{"t":"How do hair cells depolarize in response to sound?","d":"Movement of the basilar membrane bends the stereocilia. Bending toward the tallest stereocilium opens mechanically-gated K+ channels. Because endolymph has a high K+ concentration relative to the hair cell interior, K+ flows into the cell, depolarizing it. This generates a graded potential and triggers glutamate release onto afferent neurons of the vestibulocochlear nerve.","src":"class"},{"t":"What is the vestibulocochlear nerve?","d":"The cranial nerve (CN VIII) that carries auditory information from the hair cells of the organ of Corti to the brainstem. Cochlear nerve fibers synapse with interneurons in the brainstem, which relay information through the thalamus to the auditory cortex in the temporal lobe.","src":"class"},{"t":"How does a cochlear implant restore hearing?","d":"An external audio sensor (worn on the outside of the head) picks up sounds and converts them to electrical impulses. Electrodes bypass the outer, middle, and inner ear and directly electrically stimulate the vestibulocochlear nerve, which carries auditory signals to the cortex. It is used when the auditory machinery of the ear is non-functional.","src":"class"},{"t":"Central (descending) control of sensory pathways","d":"Sensory signals are subject to extensive modification before reaching higher CNS levels. Descending pathways from the cortex activate inhibitory interneurons that synapse onto afferent neurons or projection neurons, 'gating' sensory input (e.g., continuously inhibiting pain pathways to some degree). Removal of cortical inhibition amplifies the response to a given sensory stimulus.","src":"class"}],"cardio":[{"t":"What are the three layers of the heart wall (from outer to inner)?","d":"Epicardium (visceral pericardium), myocardium (muscular wall), and endocardium (endothelium covering the inner surfaces of the heart and heart valves).","src":"quizlet"},{"t":"What are the layers of the pericardial sac?","d":"The fibrous pericardium and the serous pericardium. The serous pericardium has two layers: the parietal pericardium and the visceral pericardium (epicardium).","src":"quizlet"},{"t":"Which single layer both lines the pericardium and forms the outermost wall of the heart?","d":"The visceral pericardium (also called the epicardium) — the innermost layer of the serous pericardium that covers the outer surface of the heart.","src":"quizlet"},{"t":"What term describes the force of a fluid pushing against a surface?","d":"Hydrostatic pressure — the pressure exerted by a fluid.","src":"quizlet"},{"t":"Where is the bicuspid (mitral) valve located, and what blood flow does its disorder impair?","d":"The bicuspid (mitral) valve is the left AV valve, located between the left atrium and the left ventricle. A bicuspid valve disorder impairs blood flow between the left atrium and left ventricle.","src":"quizlet"},{"t":"If the Purkinje system is damaged, conduction of electrical impulses through which structures is impaired?","d":"The ventricles. Purkinje fibers have fast conduction velocity and diffuse distribution, allowing the left and right ventricular myocytes to depolarize and contract nearly simultaneously.","src":"quizlet"},{"t":"In which heart chamber is the myocardium thickest?","d":"The left ventricle. Its wall is thicker than the right ventricle because it must develop higher pressures to pump blood through the systemic circulation.","src":"quizlet"},{"t":"What property, unique to cardiac muscle, allows cardiac cells to generate their own action potentials?","d":"Autorhythmicity (automaticity) — the ability of cardiac muscle to contract in the absence of neural or hormonal stimulation, driven by action potentials it generates itself.","src":"quizlet"},{"t":"Influx of which ion produces the rapid depolarization phase of the fast cardiac action potential?","d":"Sodium (Na+), moving in through fast voltage-gated Na+ channels. (In the 'slow' action potential, rapid depolarization is instead carried by Ca2+.)","src":"quizlet"},{"t":"Which portion of the ECG corresponds to ventricular repolarization?","d":"The T-wave, an upward deflection representing repolarization of the ventricles.","src":"quizlet"},{"t":"Which portion of the ECG corresponds to atrial repolarization?","d":"None. Atrial repolarization occurs while the ventricles are depolarizing and is too small an electrical event to be recorded at the surface of the skin (it is masked by the QRS complex).","src":"quizlet"},{"t":"Which phase of the cardiac cycle refers to ventricular relaxation with no change in blood volume?","d":"Isovolumetric ventricular relaxation — all heart valves are closed, so the ventricle relaxes with no change in volume.","src":"quizlet"},{"t":"During which phase does most blood enter the ventricle, and are the atria in systole or diastole at that time?","d":"Most blood enters during passive ventricular filling, while the atria are in diastole (relaxed). This passive filling provides about 70% of the blood volume to the ventricles.","src":"quizlet"},{"t":"What causes the first heart sound ('lub')?","d":"Closure of the atrioventricular (AV) valves at the beginning of ventricular systole.","src":"quizlet"},{"t":"What is the term for the force the heart must overcome to eject blood?","d":"Afterload — the tension (arterial pressure) against which the ventricle must eject blood; the load imposed on the ventricle when it contracts.","src":"quizlet"},{"t":"What happens to preload when venous return increases?","d":"Preload increases. Greater venous return raises the volume of blood filling the ventricle, increasing end-diastolic volume (EDV) and thus the load/stretch on the myocardium before contraction.","src":"quizlet"},{"t":"What is the difference between stroke volume and cardiac output?","d":"Stroke volume is the volume of blood ejected by each ventricle during systole (~70–75 mL). Cardiac output is the amount of blood pumped by each ventricle in one minute (cardiac output = stroke volume × heart rate).","src":"quizlet"},{"t":"Across which blood vessels does the largest drop in mean arterial pressure occur?","d":"The arterioles. The large pressure drop is due to their high resistance.","src":"quizlet"},{"t":"What is diastolic pressure?","d":"The minimum arterial (blood) pressure, reached at the end of ventricular diastole — just before the next ventricular ejection (systole) begins.","src":"quizlet"},{"t":"What is the effect of parasympathetic activation on the pacemaker potential and heart rate?","d":"It decreases the slope of the pacemaker potential (slower depolarization), which decreases heart rate. It reduces F-type channel permeability and hyperpolarizes cells by increasing K+ permeability.","src":"quizlet"},{"t":"As the distance from the heart increases, what happens to mean arterial pressure?","d":"It decreases. Mean arterial pressure (MAP) falls as the distance from the heart increases.","src":"quizlet"},{"t":"What do baroreceptors respond to?","d":"Changes in pressure. They detect mean arterial pressure and pulse pressure as the vessel walls stretch or relax, with the degree of stretch directly proportional to pressure.","src":"quizlet"},{"t":"Which is the only vein in the body that transports oxygen-rich blood?","d":"The pulmonary vein (along with pulmonary venules), which carries highly oxygenated blood from the lungs to the left atrium.","src":"quizlet"},{"t":"True or false: The spread of cardiac excitation speeds up at the AV node.","d":"False. Conduction slows at the AV node (AV nodal delay) — it takes ~100 milliseconds for the impulse to pass through the AV node to the Bundle of His.","src":"quizlet"},{"t":"What is the effect of parasympathetic stimulation on the AV node?","d":"It decreases conduction through the AV node, increasing AV nodal delay — so it takes longer for the impulse to pass through the AV node into the ventricles.","src":"quizlet"},{"t":"Which structure prevents backflow of blood from the ventricles into the atria?","d":"The chordae tendineae (part of the AV valve apparatus with the cusps and papillary muscles), which prevent eversion of the AV valves into the atria during ventricular contraction.","src":"quizlet"},{"t":"List the valves, in order, through which blood flows from the vena cava through the heart.","d":"Tricuspid valve → pulmonary semilunar valve → bicuspid (mitral) valve → aortic semilunar valve.","src":"quizlet"},{"t":"Where in the brain are the cardiovascular centers located?","d":"In the medulla oblongata (the medullary cardiovascular center).","src":"quizlet"},{"t":"Which cell type is found in the walls of both arterioles and capillaries?","d":"Endothelial cells. The endothelium lines all vessels (and is continuous with the heart's endocardium); capillaries are just one endothelial cell thick.","src":"quizlet"},{"t":"Blood colloid osmotic pressure favors fluid movement in which direction, and what causes it?","d":"It favors fluid movement into the capillaries, and is due to nonpermeating plasma proteins inside the capillaries.","src":"quizlet"},{"t":"Along the length of a capillary, is there more filtration or reabsorption?","d":"More filtration than reabsorption. The transition point between filtration and reabsorption lies closer to the venous end of the capillary.","src":"quizlet"},{"t":"Poiseuille's equation: which variable has the greatest effect on resistance to blood flow, and why?","d":"Vessel radius (r), because resistance is inversely proportional to r raised to the 4th power (R = 8Lη/πr⁴). Very small changes in vessel diameter therefore produce large changes in resistance.","src":"class"},{"t":"Frank-Starling mechanism","d":"An intrinsic cardiac mechanism by which increased end-diastolic volume (EDV) causes increased stretch of ventricular sarcomeres, producing a greater force of contraction and a larger stroke volume. It matches the output of both ventricles and operates independently of neural or hormonal input.","src":"class"},{"t":"End-diastolic volume (EDV)","d":"The volume of blood in each ventricle at the end of ventricular diastole (after the ventricles have finished filling). It determines the preload on the ventricle.","src":"class"},{"t":"End-systolic volume (ESV)","d":"The volume of blood remaining in each ventricle at the end of ventricular systole (after ejection). The ventricles do not empty completely; SV = EDV − ESV.","src":"class"},{"t":"Ejection fraction (EF)","d":"The fraction of end-diastolic volume ejected with each contraction: EF = SV/EDV. Under normal resting conditions the ejection fraction is 50–75%. Increased contractility (e.g., sympathetic stimulation) raises the ejection fraction.","src":"class"},{"t":"Isovolumetric ventricular contraction","d":"The first phase of ventricular systole in which the ventricles contract but all valves (AV and semilunar) remain closed. Ventricular pressure rises while ventricular volume stays constant; muscle develops tension but cannot shorten.","src":"class"},{"t":"Isovolumetric ventricular relaxation","d":"The first phase of ventricular diastole in which all valves remain closed and the ventricles relax. Ventricular volume is constant while ventricular pressure drops, until it falls below atrial pressure and the AV valves open.","src":"class"},{"t":"What opens the semilunar valves, and during which phase of the cardiac cycle does ejection occur?","d":"When ventricular pressure exceeds arterial pressure (a forward pressure gradient), the semilunar valves open and ventricular ejection begins. This is the ventricular ejection phase of systole. The AV valves remain closed throughout ejection.","src":"class"},{"t":"What causes the second heart sound ('dub'), and what does it signify?","d":"Closure of the semilunar (aortic and pulmonary) valves, caused by a backward pressure gradient when ventricular pressure falls below arterial pressure. It signifies the onset of ventricular diastole.","src":"class"},{"t":"Afterload","d":"The tension against which the ventricle must eject its blood; closely related to arterial pressure. As afterload increases, the period of isovolumetric contraction is prolonged and stroke volume decreases. It is increased by high arterial blood pressure, high vascular resistance, or a stenotic semilunar valve.","src":"class"},{"t":"What is contractility, and how does sympathetic stimulation alter it?","d":"Contractility is the strength of ventricular contraction at any given EDV. Sympathetic stimulation increases contractility by phosphorylating proteins in the excitation-contraction coupling pathway (L-type Ca²⁺ channels, ryanodine receptor, troponin, etc.), increasing SV and ejection fraction. Parasympathetic stimulation does not affect ventricular contractility because the ventricles receive little or no parasympathetic innervation.","src":"class"},{"t":"Calcium-induced calcium release (CICR) in cardiac muscle","d":"During the plateau phase of the cardiac action potential, Ca²⁺ enters the cytoplasm through L-type Ca²⁺ channels in the sarcolemma and T-tubules. This Ca²⁺ binds to ryanodine receptors on the SR, opening their intrinsic channels and releasing a larger amount of Ca²⁺ from the SR (~95% of cytosolic Ca²⁺). Unlike skeletal muscle, there is no physical coupling between the L-type channel and the ryanodine receptor in cardiac muscle.","src":"class"},{"t":"How is Ca²⁺ removed from the cytoplasm to allow cardiac muscle relaxation?","d":"L-type Ca²⁺ channels close; Ca²⁺-ATPases on the SR pump Ca²⁺ back into the SR (major route); and a Na⁺/Ca²⁺ exchanger in the sarcolemma removes Ca²⁺ from the cell. Reduced cytosolic Ca²⁺ causes Ca²⁺ to dissociate from troponin, blocking the actin–myosin interaction and allowing relaxation.","src":"class"},{"t":"Why can cardiac muscle not undergo tetanus?","d":"The absolute refractory period of ventricular muscle (~250 ms) lasts almost as long as the contraction itself. During this period, fast voltage-gated Na⁺ channels are inactivated and cannot reopen regardless of stimulus strength, so the muscle cannot be re-excited. This prevents summation and tetanus, ensuring the ventricles relax and refill between beats.","src":"class"},{"t":"Cardiac syncytium and all-or-none property","d":"Cardiac muscle cells are connected by gap junctions at intercalated discs, allowing action potentials to spread from cell to cell. The heart has two functional syncytia (atrial and ventricular). When one myocyte is excited, all cells in the syncytium respond — either all myocytes contract or none do (all-or-none property).","src":"class"},{"t":"Function of the cardiac fibrous skeleton","d":"The fibrous skeleton (made of dense connective tissue) physically separates the atria from the ventricles, electrically insulates them by blocking direct spread of action potentials, and provides attachment points for the valve leaflets and cardiac muscle. The only electrical connection between atria and ventricles is the AV node and Bundle of His.","src":"class"},{"t":"Chordae tendineae and papillary muscles: function in the AV valve apparatus","d":"Chordae tendineae are fibrous cords that attach the edges of the AV valve leaflets to papillary muscles projecting from the ventricular wall. When the ventricle contracts, the papillary muscles also contract, pulling the chordae tendineae taut. This prevents the AV valves from everting (opening backwards) into the atrium under the high ventricular pressure. The papillary muscles do not open or close the valves — valve movement is passive, driven by pressure gradients.","src":"class"},{"t":"Coronary blood flow: during which phase of the cardiac cycle is it greatest, and why?","d":"Coronary blood flow is greatest during diastole. During systole, ventricular contraction compresses the coronary vessels and nearly stops flow. During diastole, when the myocardium is relaxed, the vessels are no longer compressed and flow through the coronary arteries peaks.","src":"class"},{"t":"Cardiac tamponade","d":"Compression of the heart chambers due to excessive accumulation of fluid in the pericardial cavity (e.g., from pericarditis). It limits the heart's movement and decreases ventricular filling, reducing stroke volume and cardiac output.","src":"class"},{"t":"AV node escape rhythm: if the SA node is damaged, what rate does the AV node pace the heart?","d":"If the SA node is damaged, the AV node can generate action potentials to drive the ventricles, but at a slower intrinsic rate of approximately 40–60 beats/minute (compared to 60–100 beats/minute for the SA node).","src":"class"},{"t":"Partial vs. complete AV node block: how do they differ on the ECG?","d":"In partial AV node block, only every other (or occasional) atrial impulse is transmitted to the ventricles; every second P-wave is not followed by a QRS complex or T-wave. In complete AV node block, no atrial impulses reach the ventricles; there is no synchrony between P-waves and QRS complexes, so atria and ventricles beat independently.","src":"class"},{"t":"Mean arterial pressure (MAP): equation and major determinants","d":"MAP = CO × TPR, where CO is cardiac output and TPR is total peripheral resistance. TPR is determined primarily by arteriolar resistance. Factors that alter CO or TPR will alter MAP.","src":"class"},{"t":"Pulse pressure","d":"Pulse pressure (PP) = systolic pressure − diastolic pressure. It reflects the pulsatile nature of arterial blood pressure. As distance from the heart increases, pulse pressure decreases and eventually disappears at the level of the arterioles; no pressure oscillations are seen in capillaries.","src":"class"},{"t":"Active hyperemia","d":"A local control mechanism that increases blood flow to an organ or tissue when its metabolic activity increases. Increased metabolism alters local chemical conditions (e.g., decreased O₂, increased CO₂/metabolites) surrounding arterioles, causing arteriolar smooth muscle to vasodilate and increase blood flow. No nerves or hormones are involved.","src":"class"},{"t":"Mechanisms of venous return","d":"Three mechanisms increase venous return: (1) sympathetic venoconstriction — sympathetic neurons contract venous smooth muscle, increasing venous pressure and driving blood toward the heart; (2) skeletal muscle pump — skeletal muscle contractions compress veins, raising venous pressure; (3) respiratory pump — inspiration increases venous return to the heart.","src":"class"},{"t":"Why do veins serve as blood volume reservoirs?","d":"Veins are highly distensible (compliant) and can store large amounts of blood at low pressures. Approximately 60% of total blood volume is in the venous system at rest. Because they expand easily with little elastic recoil, they act as capacitance vessels and reservoirs.","src":"class"},{"t":"Atrial kick","d":"The final phase of ventricular filling caused by atrial contraction. Atrial systole propels the remaining ~30% of blood into the already-relaxed ventricles, completing filling. The ventricles are still in diastole during this phase.","src":"class"}],"gi":[{"t":"What are the major processes/functions of the GI tract?","d":"Secretion, digestion, absorption, and motility (with elimination of feces as a fifth function). The digestive system also performs immune/host-defense functions.","src":"quizlet"},{"t":"Define digestion.","d":"The breaking down of large food molecules into small, absorbable molecules, accomplished by digestive enzymes and other chemicals (acid, bile detergents), aided by motility.","src":"quizlet"},{"t":"Define absorption.","d":"The movement of the products of digestion (plus water and small nutrients) from the GI lumen across the epithelium into the internal environment. Most nutrients enter the blood capillaries; fats and fat-soluble nutrients enter lymphatic vessels (lacteals).","src":"quizlet"},{"t":"Define excretion/elimination as a GI function.","d":"Elimination of non-absorbed material (feces are mostly bacteria plus undigested/unabsorbed food) and of hydrophobic wastes excreted via the bile (e.g., cholesterol/steroids, some drugs).","src":"quizlet"},{"t":"How does the GI tract function in host defense?","d":"The lumen is a barrier to the outside environment, and the tract has a highly developed immune system (produces antibodies, has lymphatic nodules, and fights ingested microorganisms; stomach acid kills many).","src":"quizlet"},{"t":"List the functions of the digestive system.","d":"Digestion, absorption, excretion/elimination, and host defense (immune functions). (Ingestion and hepatic metabolic transformation/detoxification are also functions.)","src":"quizlet"},{"t":"What are the components (organs) of the GI tract?","d":"Mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine, and anus.","src":"quizlet"},{"t":"What are the accessory organs/tissues of the GI tract?","d":"Salivary glands, liver, gallbladder, and exocrine pancreas. They are not part of the tract but secrete substances into it via ducts.","src":"quizlet"},{"t":"What is the functional role of the mouth in digestion?","d":"Chewing mechanically breaks large food pieces into smaller particles, mixes them with salivary secretions, and forms a bolus.","src":"quizlet"},{"t":"What are the functions of the stomach?","d":"Stores food; mechanically churns/grinds and chemically (acid + pepsin) partially digests macromolecules (begins protein digestion); partially sterilizes food (acid kills bacteria); controls the rate chyme enters the small intestine; and secretes intrinsic factor (needed for B12 absorption).","src":"quizlet"},{"t":"What is the role of the small intestine?","d":"It is the major site of digestion and absorption: brush-border (apical) enzymes provide catalytic surfaces and villi/microvilli provide a large absorptive surface where most macromolecules are digested and absorbed.","src":"quizlet"},{"t":"What is the lumen of the GI tract, and is it inside or outside the body?","d":"The lumen is the interior space of the tube. It is continuous with the external environment, so its contents are technically OUTSIDE the body. The luminal (apical) surface is highly folded to increase surface area.","src":"quizlet"},{"t":"What muscle types form the esophagus vs. the rest of the GI tract?","d":"Skeletal muscle surrounds the upper third of the esophagus; smooth muscle surrounds the lower two-thirds and the rest of the GI tract.","src":"quizlet"},{"t":"What are the four layers (tunics) of the GI tract wall, from lumen outward?","d":"1) Mucosa, 2) submucosa, 3) muscularis externa, 4) serosa.","src":"quizlet"},{"t":"What are the three layers of the mucosa?","d":"Epithelium, lamina propria, and muscularis mucosa.","src":"quizlet"},{"t":"What is an epithelium?","d":"Tissue that covers all body surfaces, lines all body cavities, and forms most glands. It may be a single layer (simple epithelium) or multiple layers (stratified epithelium); the GI epithelium is a single layer.","src":"quizlet"},{"t":"What does stratified squamous epithelium consist of, and what is its function?","d":"Numerous layers (stratified) of flattened cells (squamous); it serves a protective function (e.g., protecting underlying tissue, as in the esophagus).","src":"quizlet"},{"t":"Why are epithelial cells described as polarized, and what keeps their transporters separated?","d":"They have distinct apical and basolateral membranes that contain different ion channels and transport proteins. Tight junctions seal the cells and confine transporters to their respective surfaces, keeping the two domains functionally distinct.","src":"quizlet"},{"t":"What is the apical (luminal) surface of an epithelial cell?","d":"The surface that faces the lumen of the tube (also called the luminal membrane).","src":"quizlet"},{"t":"What is the basolateral surface of an epithelial cell?","d":"The surface (basal + lateral) opposite the apical membrane; it rests on the basement membrane, is adjacent to blood vessels (blood/serosal side), and faces away from the lumen.","src":"quizlet"},{"t":"What are the functions of the GI epithelial layer?","d":"Selective absorption/secretion of nutrients, ions, and water across the surface, and (via tight junctions) acting as a selective barrier that prevents free passage of harmful substances.","src":"quizlet"},{"t":"What two pathways can a substance use to cross an epithelial layer?","d":"The paracellular pathway (between adjacent cells, through tight junctions) and the transcellular pathway (through the cell).","src":"quizlet"},{"t":"Describe the paracellular pathway across the intestinal epithelium.","d":"Diffusion BETWEEN adjacent epithelial cells; limited by tight junctions, which allow only small ions and water to diffuse through to a limited degree.","src":"quizlet"},{"t":"Describe the transcellular pathway across the intestinal epithelium.","d":"A substance crosses THROUGH the cell: it enters across the apical membrane, diffuses through the cytosol, and exits across the basolateral membrane, by diffusion and/or mediated transport (transport proteins).","src":"quizlet"},{"t":"What is the lamina propria?","d":"A layer of loose connective tissue beneath the epithelium (part of the mucosa, separated from underlying tissue by the muscularis mucosa). It contains small blood vessels, neurons, lymphatic vessels (the villus lacteal), and immune/inflammatory cells.","src":"quizlet"},{"t":"What is the muscularis mucosa?","d":"A thin layer of smooth muscle beneath the lamina propria, involved in small movements of the mucosal surface (e.g., moving the villi). It is NOT responsible for gross GI motility (that is the muscularis externa).","src":"quizlet"},{"t":"What is the submucosa?","d":"The connective-tissue layer beneath the mucosa; it contains blood vessels, lymphatic vessels, and a network of neurons called the submucosal plexus.","src":"quizlet"},{"t":"What is the muscularis externa?","d":"The layers of smooth muscle outside the submucosa that provide the force for moving/mixing GI contents. It has a thick inner circular layer and a thinner outer longitudinal layer, with the myenteric plexus between them. (The stomach has three layers.)","src":"quizlet"},{"t":"Describe the circular muscle layer of the muscularis externa.","d":"Its fibers are oriented in a circular pattern around the tube; it is the relatively THICK INNER layer, and its contraction narrows (closes) the lumen.","src":"quizlet"},{"t":"Describe the longitudinal muscle layer of the muscularis externa.","d":"It is the thinner OUTER layer; its contraction shortens the tube (controls segment length) rather than narrowing the lumen.","src":"quizlet"},{"t":"What is the serosa?","d":"The thin outermost connective-tissue layer of the GI tract wall; thin sheets of connective tissue connect it to the abdominal wall and suspend the tract in the body cavity.","src":"quizlet"},{"t":"What is a villus, and what does it contain?","d":"A fingerlike projection of the small-intestinal mucosa that increases surface area. Each villus is covered by a single layer of epithelial cells whose apical membranes bear microvilli (brush border).","src":"quizlet"},{"t":"What is a crypt (intestinal gland)?","d":"An invagination of the epithelium into the underlying mucosa (at the base of the villi). Stem cells here divide and the daughter cells differentiate as they migrate up the villus.","src":"quizlet"},{"t":"What three structures amplify the surface area of the small intestine?","d":"Circular folds (folds of Kerckring), villi, and microvilli (brush border); together they increase surface area about 600-fold.","src":"quizlet"},{"t":"What are lacteals and what is their function?","d":"Lacteals are the small lymphatic vessels in the lamina propria of the intestinal villi. They are important for fat absorption: most fat absorbed in the small intestine (as chylomicrons) enters the lacteals rather than the blood capillaries.","src":"quizlet"},{"t":"Which two GI processes are regulated by the neural plexuses/reflexes?","d":"Secretion and motility.","src":"quizlet"},{"t":"What four luminal stimuli initiate the reflexes that regulate GI secretion and motility?","d":"1) Distension of the wall by luminal volume, 2) osmolarity of the contents, 3) acidity/pH of the contents, and 4) concentration of specific digestion products (monosaccharides, fatty acids, peptides, amino acids).","src":"quizlet"},{"t":"What is a nerve plexus in the GI tract?","d":"A network of neurons in the wall of the GI tract; the two are the submucosal plexus and the myenteric plexus.","src":"quizlet"},{"t":"What is the enteric nervous system (intrinsic neural regulation)?","d":"The GI tract's own local (intrinsic) neural control, a division of the autonomic nervous system. It lies entirely within the gut wall, contains the myenteric and submucosal plexuses, controls motility and secretion, and can mediate reflexes (short reflexes) independently of the CNS.","src":"quizlet"},{"t":"Where is the myenteric plexus located and what does it influence?","d":"Located between the circular and longitudinal muscle layers of the muscularis externa; it influences smooth muscle activity and motility.","src":"quizlet"},{"t":"Where is the submucosal plexus located and what does it influence?","d":"Located in the submucosa, with neurons projecting to the mucosa; it influences gland function and secretory activity.","src":"quizlet"},{"t":"Through what system does extrinsic regulation of the GI tract occur?","d":"Through the autonomic nervous system (sympathetic and parasympathetic fibers), which enter the tract and synapse with neurons in both plexuses (long reflexes), allowing the CNS to influence motility and secretion.","src":"quizlet"},{"t":"Compare parasympathetic vs. sympathetic effects on the GI tract (extrinsic neural regulation).","d":"Parasympathetic ('rest and digest') input generally increases motility/segmentation and secretion; sympathetic input generally decreases them. Exception: both branches stimulate salivary secretion (parasympathetic produces the greater, more watery response).","src":"quizlet"},{"t":"Define endocrine signaling.","d":"A chemical messenger (hormone) is secreted into the blood by an endocrine cell/gland and carried by the blood to relatively distant target cells; GI hormones participate in feedback control and may have multiple targets.","src":"quizlet"},{"t":"Define neurocrine (neurotransmitter) signaling.","d":"A neuron produces an electrical signal that triggers release of a neurotransmitter, which diffuses through the extracellular fluid to act on a nearby neuron or effector (target) cell (it is not released into the blood).","src":"quizlet"},{"t":"Define paracrine signaling.","d":"A cell releases a substance into the extracellular (interstitial) fluid, where it diffuses to act on neighboring cells. It is not released into the blood (unlike a hormone), and paracrine agents are generally inactivated locally.","src":"quizlet"},{"t":"Define autocrine signaling.","d":"A cell secretes a substance into the extracellular fluid that acts back on the very cell that secreted it.","src":"quizlet"},{"t":"What is exocrine secretion?","d":"Secretion released into a duct, from which it exits the body or enters the lumen of another organ (e.g., the intestine), without being released into the blood (contrast endocrine, which is ductless and secretes into blood).","src":"quizlet"},{"t":"What is peristalsis?","d":"A progressive (wavelike) wave of muscle contraction that travels in one direction along a segment of the GI tract, compressing the lumen behind the bolus and forcing the contents ahead (toward the anus). It is the main propulsive force (e.g., in swallowing and esophageal transit).","src":"quizlet"},{"t":"What is segmentation, where does it occur, and what does it accomplish?","d":"Rhythmic, stationary contraction and relaxation of intestinal segments, occurring mainly in the small intestine, with little net movement toward the large intestine. It mixes chyme with digestive secretions/enzymes, brings it into contact with the absorptive epithelium, and slowly advances material, giving time for absorption.","src":"quizlet"},{"t":"What provides the force for intestinal motility, and what does it accomplish?","d":"Contraction and relaxation of the two muscle layers of the muscularis externa (inner circular + outer longitudinal) move and mix the GI contents along the tract.","src":"quizlet"},{"t":"What are pacemaker cells of the GI tract and what do they generate?","d":"Specialized cells (in the longitudinal smooth muscle layer) that spontaneously and continuously undergo depolarization-repolarization cycles called slow waves, which constitute the basic electrical rhythm of the gut.","src":"quizlet"},{"t":"How do slow waves behave, and how do they trigger contraction?","d":"At rest, the membrane potential drifts up and down (slow waves) due to regular ion-flux variation, too small to cause contraction. With excitatory neural/hormonal input, slow waves are depolarized above threshold, firing action potentials; the number of action potentials per wave determines the strength of contraction.","src":"quizlet"},{"t":"How are slow waves propagated between the muscle layers of the GI tract?","d":"Through gap junctions (conducted along the longitudinal layer and inducing slow waves in the overlying circular layer).","src":"quizlet"},{"t":"What determines the frequency of GI smooth muscle contractions?","d":"The intrinsic basic electrical rhythm (slow waves generated by pacemaker cells), which remains essentially constant.","src":"quizlet"},{"t":"What determines the force (strength) of GI smooth muscle contractions?","d":"Excitatory neural and hormonal input (e.g., gastrin; parasympathetic increases, sympathetic decreases) to the smooth muscle, which sets the number of action potentials fired per slow wave. (Frequency is unchanged; only force is altered.)","src":"quizlet"},{"t":"What are the three phases of GI (neural/hormonal) control, and where is each stimulus perceived?","d":"Cephalic phase (head), gastric phase (stomach), and intestinal phase (small intestine); each is named for the location of the stimulus that initiates it.","src":"quizlet"},{"t":"How is the cephalic phase initiated and mediated?","d":"Initiated by stimulation of receptors in the head (sight, smell, taste, chewing, and emotional state); the efferent reflexes are mediated mainly by parasympathetic (vagal) neurons that activate neurons in the GI nerve plexuses, ultimately stimulating gastric acid secretion.","src":"quizlet"},{"t":"Describe the gastric phase: its stimuli, mediators, and the role of gastrin vs. acetylcholine.","d":"Initiated by four stimuli in the stomach (distension, acidity, amino acids, peptides). Responses are mediated by short and long neural reflexes and by the hormone gastrin. Gastrin is the hormonal (endocrine) signal; acetylcholine is the neurotransmitter released by parasympathetic/plexus neurons. The gastric phase is the major stimulatory phase for acid secretion: food/peptides cause G cells to release gastrin into the blood, which acts on parietal cells to increase acid production.","src":"quizlet"},{"t":"Describe the intestinal phase: its stimuli and mediators.","d":"Initiated by stimuli in the small intestine (duodenum): distension, acidity, osmolarity, and digestive products. It is mediated by short and long neural reflexes and by the hormones secretin, CCK, and GIP (secreted by small-intestinal enteroendocrine cells). It is mainly inhibitory toward the stomach (enterogastrones secretin and CCK reduce gastric acid secretion and motility).","src":"quizlet"},{"t":"What is neuropeptide Y (NPY)?","d":"A hypothalamic neurotransmitter (neuropeptide) that stimulates appetite and hunger.","src":"quizlet"},{"t":"What is ghrelin, where is it released, and what does it do?","d":"A polypeptide synthesized and released mainly from enteroendocrine cells in the stomach during fasting/low-calorie states; it increases hunger/food intake by stimulating NPY and other neuropeptides in the hypothalamic feeding centers.","src":"quizlet"},{"t":"Where is leptin produced?","d":"By adipocytes (fat/adipose tissue), released in proportion to the amount of stored fat.","src":"quizlet"},{"t":"Where is insulin produced and how does it affect food intake?","d":"Produced by the pancreas (islet beta cells); it acts as a satiety signal that reduces food intake.","src":"quizlet"},{"t":"What stimulates thirst (water intake)?","d":"Increased plasma osmolarity, decreased extracellular fluid (plasma) volume, and dryness of the mouth/throat. GI 'metering' of ingested water also acts to prevent overhydration.","src":"quizlet"},{"t":"What does increased plasma osmolarity stimulate, and what is the result?","d":"It stimulates thirst and the release of vasopressin (antidiuretic hormone, ADH) via hypothalamic osmoreceptors; vasopressin increases renal water reabsorption (water conservation at the kidney).","src":"quizlet"},{"t":"How does a significant decrease in blood volume restore arterial pressure?","d":"It lowers blood pressure, sensed by arterial baroreceptors; reflexively, sympathetic outflow increases and parasympathetic outflow decreases, raising heart rate and causing vasoconstriction to restore arterial pressure toward normal.","src":"quizlet"},{"t":"Where are the intrarenal baroreceptors located, and what do juxtaglomerular cells do?","d":"Within the kidneys: the juxtaglomerular (granular) cells in the walls of the afferent arterioles are pressure-sensitive (act as intrarenal baroreceptors/pressure receptors), secreting more renin when renal pressure falls.","src":"quizlet"},{"t":"What product of the renin-angiotensin system acts on the hypothalamus to increase thirst?","d":"Angiotensin II (the active product of the renin-angiotensin system).","src":"quizlet"},{"t":"What are the three pairs of salivary glands?","d":"Parotid, submandibular, and sublingual glands.","src":"quizlet"},{"t":"What is saliva composed of?","d":"Water, bicarbonate (HCO3-), digestive enzymes (amylase and lipase), the glycoprotein mucin (in mucus), and antimicrobial factors (lysozyme and lactoferrin).","src":"quizlet"},{"t":"What is mucus composed of?","d":"An aqueous (watery), glycoprotein-rich secretion: water plus mucin (the glycoprotein). It is produced by epithelial cells throughout the GI tract and is protective/lubricating.","src":"quizlet"},{"t":"What is the function of salivary lysozyme?","d":"It destroys/breaks down bacterial cell walls (antibacterial).","src":"quizlet"},{"t":"What is the function of lactoferrin?","d":"An iron-binding protein that chelates iron, depriving bacteria of the iron they require and thereby inhibiting bacterial growth/multiplication.","src":"quizlet"},{"t":"What are the functions of saliva?","d":"Moistens and lubricates food for swallowing; initiates digestion of polysaccharides and triglycerides (amylase, lipase); dissolves food molecules so they can reach taste chemoreceptors; protects against harmful bacteria (lysozyme, lactoferrin); and buffers/neutralizes acids from food and bacterial metabolites.","src":"quizlet"},{"t":"Which ion gives saliva its alkaline/buffering character?","d":"Bicarbonate (HCO3-), which neutralizes/buffers acids in food and bacterial metabolites.","src":"quizlet"},{"t":"What are myoepithelial cells?","d":"Specialized contractile cells in certain exocrine glands; their contraction forces the gland's secretion through the ducts.","src":"quizlet"},{"t":"How is salivary secretion regulated?","d":"By both sympathetic and parasympathetic neurons (there is no hormonal regulation); the parasympathetic pathway is dominant, producing the greater response.","src":"quizlet"},{"t":"How is swallowing initiated?","d":"Swallowing is a complex reflex initiated when pressure receptors in the walls of the pharynx are stimulated by food/drink forced to the rear of the mouth by the tongue.","src":"quizlet"},{"t":"What is the pharynx?","d":"The passage at the back of the throat that is common to both air and food; it branches into the esophagus (to the stomach) and the larynx (airway).","src":"quizlet"},{"t":"What is the larynx?","d":"The air passage between the pharynx and the trachea; it is the 'voice box' because it houses the vocal cords.","src":"quizlet"},{"t":"What is the glottis?","d":"The area around the vocal cords (in the larynx) and the space between them; through it air passes the vocal cords.","src":"quizlet"},{"t":"What is the epiglottis and what does it do?","d":"A flap of tissue that tilts backward to cover the glottis during swallowing, preventing food from entering the trachea (aspiration) and reaching the lungs.","src":"quizlet"},{"t":"Describe the esophagus.","d":"A tube that passes through the thoracic cavity, penetrates the diaphragm, and joins the stomach. Skeletal muscle surrounds the upper third; smooth muscle the lower two-thirds. It does not contribute significantly to digestion or absorption; its function is to move food and drink to the stomach by peristalsis.","src":"quizlet"},{"t":"Where is the upper esophageal sphincter located and what is it made of?","d":"A ring of skeletal muscle surrounding the esophagus just below the pharynx.","src":"quizlet"},{"t":"Where is the lower esophageal sphincter located, what is it made of, and what does it prevent?","d":"A ring of smooth muscle at the junction where the esophagus joins the stomach; it maintains a barrier that prevents gastric (acidic) contents from refluxing into the esophagus.","src":"quizlet"},{"t":"What causes heartburn (gastroesophageal reflux)?","d":"An inefficient or incompletely closed lower esophageal sphincter allowing gastric contents into the esophagus; promoted by a large meal and by increased abdominal pressure (e.g., obesity, late pregnancy).","src":"quizlet"},{"t":"What are the major regions of the stomach: fundus, body, and antrum?","d":"The fundus and body are the upper part (thinner muscle layer) and secrete mucus, pepsinogen, and HCl. The antrum is the lower part with a thicker smooth-muscle layer; it mixes and grinds food and secretes mucus, pepsinogen, and gastrin.","src":"quizlet"},{"t":"What is the pyloric sphincter and where is it located?","d":"A ring of contractile smooth muscle between the antrum (lower stomach) and the duodenum (entry to the small intestine); it controls gastric emptying.","src":"quizlet"},{"t":"What causes the pyloric sphincter to close during gastric emptying?","d":"A peristaltic wave that begins in the body of the stomach and produces a stronger contraction as it reaches the antrum, which both mixes contents and closes the pyloric sphincter.","src":"quizlet"},{"t":"What is gastric motility important for?","d":"Mechanically breaking down and mixing food: peristaltic waves and retropulsion generate shear forces that disperse food particles into smaller bits and mix the chyme.","src":"quizlet"},{"t":"What are the three major exocrine secretions of the stomach, and where is pepsinogen secreted?","d":"Mucus, HCl (acid), and pepsinogen, each secreted by a different cell type. Pepsinogen is secreted by chief cells in the stomach.","src":"quizlet"},{"t":"What is the function of the protective mucus secretion in the stomach?","d":"Mucus (with trapped HCO3-) forms a protective coating (gastric mucosal barrier) that shields the stomach epithelium from luminal acid and pepsin, preventing self-digestion.","src":"quizlet"},{"t":"What are the functions of HCl in the stomach?","d":"Denatures dietary proteins (exposing sites for enzymes such as pepsin) and disrupts connective-tissue networks; activates pepsinogen to pepsin; and partially sterilizes food by killing most ingested bacteria.","src":"quizlet"},{"t":"What is a zymogen, and how does this apply to pepsinogen and pepsin?","d":"A zymogen (proenzyme) is an inactive enzyme precursor: it is synthesized and stored in an inactive form and must be activated before it can act. Pepsinogen is the inactive precursor of pepsin, secreted by chief cells; it is activated to pepsin by the acidic luminal pH of the stomach (autocatalytically). Pepsin then initiates protein digestion.","src":"quizlet"},{"t":"What are the minor secretions of the stomach and their classifications?","d":"Intrinsic factor (from parietal cells, for B12 absorption), gastrin (endocrine, from G cells), histamine (paracrine, from ECL cells), and somatostatin (paracrine, from D cells).","src":"quizlet"},{"t":"How much absorption occurs in the stomach, and what can be absorbed there?","d":"Very little nutrient absorption occurs in the stomach (its epithelium cannot transport most ions or molecules, and it has a small surface area). Alcohol and small amounts of water can be absorbed across the stomach wall.","src":"quizlet"},{"t":"Describe the mechanism of HCl secretion (acidification of the lumen) by the parietal cell.","d":"Carbonic anhydrase generates H+ and HCO3- from CO2 + H2O; an apical H+/K+-ATPase pumps H+ into the lumen (and K+ into the cell, which leaks back via K+ channels); HCO3- exits across the basolateral membrane in exchange for Cl- (Cl-/HCO3- exchanger); Cl- enters the lumen via apical Cl- channels.","src":"quizlet"},{"t":"What controls acid secretion by regulating the H+/K+-ATPase, and what are the four chemical messengers involved?","d":"Chemical messengers control the transfer and insertion of H+/K+-ATPase pumps from intracellular vesicles into the parietal-cell plasma membrane. Parietal cells have receptors for four messengers: gastrin, acetylcholine (ACh), and histamine stimulate insertion and acid secretion; somatostatin inhibits acid secretion.","src":"quizlet"},{"t":"What is gastrin's role in gastric acid secretion?","d":"A gastric hormone released by G cells (a major controller of acid secretion); it stimulates insertion of the H+/K+-ATPase into the parietal-cell membrane, increasing HCl production.","src":"quizlet"},{"t":"What is acetylcholine's role in gastric acid secretion?","d":"A neurotransmitter released (via increased parasympathetic activity) from plexus neurons; it stimulates insertion of the H+/K+-ATPase into the parietal-cell membrane, increasing acid secretion.","src":"quizlet"},{"t":"What is histamine's role in gastric acid secretion?","d":"A paracrine substance released by ECL cells; it stimulates insertion of the H+/K+-ATPase into the parietal-cell membrane, increasing acid secretion (and potentiates the response to gastrin and ACh).","src":"quizlet"},{"t":"What is somatostatin's role in gastric acid secretion?","d":"A paracrine substance released by D cells; it inhibits acid (HCl) secretion and inhibits the release of gastrin and histamine. Its release is stimulated by increased gastric acidity (negative feedback).","src":"quizlet"},{"t":"How is pepsinogen secretion regulated?","d":"Pepsinogen is released by chief cells as an inactive precursor; its secretion is stimulated mainly by the enteric nervous system and parallels HCl secretion; it is activated to pepsin by the acidic luminal pH.","src":"quizlet"},{"t":"What is the 'alkaline tide' produced by the stomach?","d":"When parietal cells pump H+ (acid) into the lumen, HCO3- (base) moves across the basolateral membrane into the blood; the resulting base added to blood leaving the stomach is the alkaline tide.","src":"quizlet"},{"t":"What is the 'acid tide' produced by the pancreas?","d":"Pancreatic duct cells secrete HCO3- (base) into the duct lumen while the H+ (acid) produced enters the blood; the acid added to blood leaving the pancreas is the acid tide (mirror image of the gastric alkaline tide).","src":"quizlet"},{"t":"Which enzyme catalyzes formation of carbonic acid from CO2 and water?","d":"Carbonic anhydrase (CO2 + H2O → H2CO3, which dissociates to H+ and HCO3-).","src":"quizlet"},{"t":"What are the causes (triggers) of vomiting, and where is the vomiting center?","d":"Triggers include GI disturbances (distension, irritation, infection), chemoreceptor detection of toxins in the brain or GI tract, inner-ear input and motion sickness (rotating head movements), increased intracranial pressure, intense pain, and tactile stimulation of the throat. The vomiting (emetic) center is located in the medulla oblongata of the brainstem.","src":"quizlet"},{"t":"What are the benefits (adaptive value) of vomiting?","d":"It removes ingested harmful or toxic substances before they are absorbed, and the accompanying nausea conditions the individual to avoid future ingestion of such noxious substances.","src":"quizlet"},{"t":"What are the negative consequences of excessive vomiting?","d":"Dehydration, electrolyte (ion) imbalance, and metabolic alkalosis (from loss of stomach acid); repeated acid exposure can also erode tooth enamel.","src":"quizlet"},{"t":"What is metabolic alkalosis (e.g., from vomiting)?","d":"A rise in arterial plasma pH (decreased H+ concentration) from a nonrespiratory cause; a common cause is persistent vomiting with loss of H+ as HCl from the stomach.","src":"quizlet"},{"t":"What are peptic ulcers, where do they occur, and what causes them?","d":"Ulcers are erosions (damage) of the GI mucosa, occurring where tissue is exposed to acid and pepsin: the stomach, lower esophagus, and duodenum. Cause is an imbalance between aggressive factors (acid + pepsin) and protective factors (mucus + HCO3-); a major cause is Helicobacter pylori infection (gastritis leading to chronic inflammation and erosion); other factors include genetics, drugs, alcohol, and bile salts.","src":"quizlet"},{"t":"What are the treatments for peptic ulcers?","d":"Antibiotics to suppress Helicobacter pylori; proton-pump inhibitors (H+/K+-ATPase inhibitors, e.g., omeprazole, lansoprazole); and H2 histamine-receptor antagonists (e.g., cimetidine).","src":"quizlet"},{"t":"Is the pancreas an exocrine or endocrine gland?","d":"Both: it has exocrine functions (secretes HCO3- and digestive enzymes into the duodenum) and endocrine functions (secretes hormones such as insulin and glucagon into the blood). Only the exocrine functions are directly involved in GI digestion.","src":"quizlet"},{"t":"What is the exocrine pancreas responsible for?","d":"It is the source of most enzymes needed to digest macromolecules and secretes HCO3- into the duodenum to neutralize stomach acid (which would otherwise inactivate the pancreatic enzymes).","src":"quizlet"},{"t":"What is the role of the endocrine pancreas?","d":"It is not involved in GI digestion; it produces hormones (insulin and glucagon from the islets of Langerhans) that regulate organic metabolism throughout the body.","src":"quizlet"},{"t":"Describe the anatomy of the exocrine pancreas.","d":"Acinar cells and duct cells secrete their products (enzymes and HCO3-) across the apical/luminal surface into ducts that converge into the main pancreatic duct, and the secretions ultimately enter the small intestine (duodenum).","src":"quizlet"},{"t":"Describe the anatomy of the endocrine pancreas.","d":"A ductless gland: endocrine cells (islets of Langerhans) surround capillaries and secrete hormones (e.g., insulin from beta cells) across the basolateral surface, diffusing into the blood.","src":"quizlet"},{"t":"What is the sphincter of Oddi (hepatopancreatic sphincter)?","d":"The sphincter where the common bile duct and the main pancreatic duct converge and empty into the duodenum; it regulates release of both bile (liver/gallbladder) and pancreatic secretions into the small intestine. CCK causes it to relax for bile release.","src":"quizlet"},{"t":"What are the two exocrine cell types of the pancreas and what does each secrete?","d":"Acinar cells produce and secrete digestive enzymes (by exocytosis of zymogen-containing vesicles); duct cells secrete HCO3- (to neutralize gastric acid) and water into the duct lumen.","src":"quizlet"},{"t":"Why is pancreatic juice alkaline?","d":"Because of its HCO3- content, which neutralizes the acidic chyme entering the duodenum from the stomach (HCO3- and water are secreted by the duct cells).","src":"quizlet"},{"t":"What are the digestive enzymes of pancreatic juice, and how do proteolytic enzymes work?","d":"Enzymes secreted by acinar cells digest fat, polysaccharides, proteins, and nucleic acids and are essential for macromolecule digestion. Proteolytic enzymes break proteins down (ultimately to amino acids), are secreted as inactive zymogens, and are activated in the duodenum.","src":"quizlet"},{"t":"What channel is defective in cystic fibrosis, affecting pancreatic HCO3- secretion?","d":"The CFTR (cystic fibrosis transmembrane conductance regulator), a Cl- channel; its mutation reduces pancreatic HCO3- secretion.","src":"quizlet"},{"t":"Which enteroendocrine cells of the small intestine secrete secretin, and what triggers its release?","d":"Enteroendocrine cells of the small intestine secrete secretin in response to acid reaching the duodenum/small intestine.","src":"quizlet"},{"t":"What is secretin and what does it do?","d":"A hormone released into the blood that acts on pancreatic duct cells to stimulate HCO3- secretion (the primary stimulant for HCO3- secretion).","src":"quizlet"},{"t":"Which enteroendocrine cells secrete CCK, what triggers its release, and what does CCK do?","d":"Enteroendocrine cells of the small intestine secrete CCK in response to fatty acids and amino acids (products of fat and protein digestion). CCK is released into the blood and acts on pancreatic acinar cells (not duct cells) to stimulate secretion of digestive enzymes (stored as inactive zymogens).","src":"quizlet"},{"t":"How do secretin and CCK affect the stomach (as enterogastrones)?","d":"They act on the stomach to reduce gastric acid secretion and gastric motility. (They inhibit acid secretion and motility directly; they do not inhibit gastrin secretion — gastrin release is inhibited by acid in the stomach and by somatostatin.)","src":"quizlet"},{"t":"What are the phases of pancreatic exocrine secretion and which is the major one?","d":"Cephalic, gastric, and intestinal phases. The intestinal phase is the major phase (drives most pancreatic secretion); the cephalic and gastric phases are minor contributors (via parasympathetic input).","src":"quizlet"},{"t":"What is the gallbladder and what does it do?","d":"A small sac located underneath the liver that stores and concentrates bile between meals.","src":"quizlet"},{"t":"What are the two blood supplies to the liver, and what does each carry?","d":"1) Hepatic artery (systemic arterial route): fully oxygenated, comparatively nutrient-poor blood. 2) Hepatic portal vein (portal route): nutrient-rich, oxygen-poor venous blood that has already perfused the stomach, pancreas, small intestine, and large intestine (their capillaries drain into it).","src":"quizlet"},{"t":"What is the hepatic portal circulation?","d":"A portal system of two capillary beds in series: nutrient-rich, oxygen-poor venous blood that has already perfused the GI tract (stomach, intestines), spleen, and pancreas drains via the hepatic portal vein into the liver (the liver's major blood supply) before returning to the heart/general circulation. The liver also receives oxygenated blood from the hepatic artery.","src":"quizlet"},{"t":"What does it mean that most organs are perfused 'in parallel' while the liver is perfused 'in series'?","d":"In parallel: systemic arteries branch so each organ independently receives a fraction of the freshly oxygenated blood pumped by the left ventricle. In series: the liver is predominantly perfused by portal blood that has already passed through another organ's (the GI tract's) capillary bed before reaching it.","src":"quizlet"},{"t":"Describe the structure of a hepatic lobule.","d":"The functional unit of the liver: a central vein runs through its center, and portal triads are located within the lobule at its periphery/corners.","src":"quizlet"},{"t":"What does a portal triad consist of?","d":"Branches of the bile duct, the hepatic portal vein, and the hepatic artery.","src":"quizlet"},{"t":"What are hepatocytes?","d":"Liver cells that take up and process nutrients/wastes (modifying or detoxifying substances) and secrete into the bile canaliculi (forming a canalicular network that drains into the bile ducts).","src":"quizlet"},{"t":"What are the functions of the liver?","d":"Exocrine secretion of bile; metabolism and storage of nutrients; deactivation/detoxification of substances; and production of circulating (plasma) proteins.","src":"quizlet"},{"t":"What are the major components of bile?","d":"Bile salts (bile acids), cholesterol, HCO3-/salts and water, phospholipids, bile pigments (e.g., bilirubin), and organic waste products/trace metals.","src":"quizlet"},{"t":"How and where are bile salts (bile acids) made, and what is their role?","d":"Synthesized by hepatocytes in the liver from cholesterol; they are amphipathic molecules that act as biological detergents in the emulsification of dietary fat.","src":"quizlet"},{"t":"What is emulsification and what does it require?","d":"The breakup of large lipid droplets into many small droplets, increasing surface area for lipase action. It requires (1) mechanical disruption of the droplets and (2) amphipathic emulsifying agents (bile salts and phospholipids) that coat the small droplets and prevent re-aggregation.","src":"quizlet"},{"t":"What is pancreatic lipase and where does it act?","d":"The major fat-digesting enzyme; it is water-soluble, so it can act only at the surface of lipid droplets.","src":"quizlet"},{"t":"In what form are the products of fat digestion held in the small intestine?","d":"In micelles, which keep the insoluble products soluble.","src":"quizlet"},{"t":"What are micelles made of?","d":"Bile salts, fatty acids, monoglycerides, and phospholipids (with small amounts of fat-soluble vitamins and cholesterol in the core).","src":"quizlet"},{"t":"How are bile acids conserved (enterohepatic circulation), and what are the steps?","d":"Bile salts are recycled via the enterohepatic circulation: (1) secreted by hepatocytes (and stored/concentrated in the gallbladder) into the duodenum for fat digestion; (2) reabsorbed in the ileum into the hepatic portal blood; (3) transported back into hepatocytes and re-secreted into bile.","src":"quizlet"},{"t":"By what transport mechanisms are bile salts reabsorbed in the ileum and taken back into hepatocytes?","d":"Both by Na+-coupled secondary active transport: ileal reabsorption uses Na+-coupled transporters, and hepatocyte uptake from portal blood is secondary active transport coupled to Na+.","src":"quizlet"},{"t":"Why are fatty acids and monoglycerides resynthesized into triglycerides inside the enterocyte?","d":"Resynthesis (in the smooth ER) lowers cytosolic free fatty acid/monoglyceride concentrations, maintaining the diffusion gradient from the lumen into the cell, and packages the lipid (as triglyceride) into chylomicrons for transport.","src":"quizlet"},{"t":"What are chylomicrons and what do they contain?","d":"Extracellular fat droplets (~1 micron) formed in the enterocyte; they contain triglycerides plus other lipids: phospholipids, cholesterol, and fat-soluble vitamins.","src":"quizlet"},{"t":"How and why are chylomicrons absorbed into the lymphatic system rather than blood capillaries?","d":"Chylomicrons pass into lacteals (lymphatic vessels in the villi) because the lacteals have large pores between endothelial cells ('leakier'), whereas the blood capillary basement membrane blocks the large chylomicrons.","src":"quizlet"},{"t":"What are the plasma and intracellular iron-binding proteins, and what is ferritin?","d":"Transferrin is the plasma iron-transport/binding protein. Ferritin is the intracellular iron-binding protein that stores iron (the storage form), found in enterocytes and especially the liver.","src":"quizlet"},{"t":"What are the three sections of the small intestine?","d":"Duodenum, jejunum, and ileum.","src":"quizlet"},{"t":"What are the major functions of the small intestine?","d":"Digestion of ingested macromolecules into small molecules and absorption of the resulting nutrients (small molecules such as vitamins and minerals are absorbed intact; macromolecules cannot cross the epithelium and must first be broken down).","src":"quizlet"},{"t":"What are the functions of the duodenum?","d":"Mixes pancreatic digestive enzymes and bile with food; is the main site of nutrient absorption (carbohydrate, protein, fat; also iron and calcium); and releases the hormones secretin and CCK into the blood.","src":"quizlet"},{"t":"What is the function of the jejunum?","d":"Continued digestion and absorption (most chyme is fully digested and absorbed in the duodenum and part of the jejunum).","src":"quizlet"},{"t":"What is the function of the ileum?","d":"Absorption of vitamin B12 (with intrinsic factor) and reabsorption of bile salts.","src":"quizlet"},{"t":"What are the epithelial cell types of the small intestine?","d":"Absorptive epithelial cells (enterocytes), goblet cells, and enteroendocrine cells.","src":"quizlet"},{"t":"What are enteroendocrine cells of the small intestine?","d":"Cells that secrete GI hormones, including secretin and CCK (and GIP), into the blood.","src":"quizlet"},{"t":"What do goblet cells secrete and why?","d":"They secrete mucus into the lumen, where it lubricates and protects the inner surface of the intestinal wall.","src":"quizlet"},{"t":"What is the brush border, and what are enterocytes (absorptive cells)?","d":"The brush border is the layer of small projections (microvilli) on the apical surface of the small-intestine epithelial cells; it is the major absorptive surface. Enterocytes are these absorptive cells, bearing microvilli (the brush border) on their apical membrane.","src":"quizlet"},{"t":"What is a brush-border enzyme?","d":"An enzyme anchored to the brush-border (apical) membrane of the small-intestine epithelial cells, with its catalytic activity facing the lumen (e.g., it digests luminal disaccharides).","src":"quizlet"},{"t":"What is starch broken down into, and by which enzyme?","d":"Amylase breaks starch (a polysaccharide) into the disaccharide maltose plus a mixture of short, branched chains of glucose molecules.","src":"quizlet"},{"t":"What is maltose broken down into, and by which enzyme?","d":"Maltose is hydrolyzed to glucose by the brush-border disaccharidase maltase. (Sucrase digests sucrose; lactase digests lactose.)","src":"quizlet"},{"t":"Which form of carbohydrate can be absorbed, and which monosaccharides are absorbed?","d":"Only monosaccharides can be absorbed (disaccharides/polysaccharides must first be digested to monomers). The monosaccharides absorbed are glucose, galactose, and fructose.","src":"quizlet"},{"t":"How are glucose and galactose transported across the enterocyte (apical and basolateral)?","d":"Apical: secondary active transport via the Na+-dependent sodium-glucose cotransporter (SGLT). Basolateral: facilitated diffusion via GLUT transporters.","src":"quizlet"},{"t":"How is fructose transported across the enterocyte (apical and basolateral)?","d":"By facilitated diffusion via GLUT transporters at both the apical and basolateral membranes.","src":"quizlet"},{"t":"What breaks down triglycerides, and into what products?","d":"Pancreatic lipase breaks triglycerides down into monoglycerides and free fatty acids.","src":"quizlet"},{"t":"By which enzymes are proteins broken down in the small intestine?","d":"Pancreatic proteases trypsin and chymotrypsin (the major active pancreatic proteases) break peptide bonds within proteins/polypeptides to form peptide fragments.","src":"quizlet"},{"t":"Which enzymes complete protein digestion to free amino acids, and how do carboxypeptidase and aminopeptidase differ?","d":"Carboxypeptidases (pancreatic) split off the terminal amino acid from the carboxyl (C-terminal) end; aminopeptidases (brush-border enzymes on the apical membrane) split off from the amino (N-terminal) end.","src":"quizlet"},{"t":"How are free amino acids vs. small peptides absorbed across the apical membrane?","d":"Free amino acids enter the enterocyte by secondary active transport coupled to Na+; di- and tripeptides enter by secondary active transport coupled to the H+ gradient.","src":"quizlet"},{"t":"What happens to absorbed peptides inside the enterocyte, and how do amino acids exit the cell?","d":"Inside the cytosol, intracellular peptidases hydrolyze the di-/tripeptides to free amino acids; the amino acids then leave the enterocyte by facilitated diffusion across the basolateral membrane into the interstitial fluid (then the blood).","src":"quizlet"},{"t":"Why is control of intestinal fluid important for GI function?","d":"Adequate luminal fluid permits contact between food and digestive enzymes, allows digested nutrients to diffuse to absorption sites, and keeps contents fluid for transit without damaging the epithelium.","src":"quizlet"},{"t":"Which intestine absorbs the greater volume of fluid?","d":"The small intestine (about 80% of the ~8000 mL/day entering it is absorbed there, far more than the large intestine).","src":"quizlet"},{"t":"In the small intestine, where does water absorption vs. secretion occur?","d":"Water absorption occurs along the villi (absorptive epithelium); water secretion occurs at the base of the villi (the crypt region). In the large intestine, absorption occurs at the crypts/surface because its mucosa lacks villi.","src":"quizlet"},{"t":"Which direction must the osmotic gradient favor for intestinal absorption vs. secretion?","d":"Inward (lumen to interstitium/blood) for absorption; outward (interstitium to lumen) for secretion. Water follows solute movement by osmosis.","src":"quizlet"},{"t":"Which electrolytes are most important for intestinal water transport?","d":"Na+, Cl-, and HCO3- (water follows their net movement by osmosis).","src":"quizlet"},{"t":"On what does small-intestinal water absorption depend, and how is the gradient generated?","d":"On Na+ gradients. The transepithelial Na+ gradient is established by the primary active Na+/K+-ATPase; this gradient also drives secondary active (Na+-coupled) nutrient uptake (e.g., SGLT at the apical membrane). Water follows the net Na+ movement by osmosis.","src":"quizlet"},{"t":"On what does small-intestinal water secretion depend?","d":"On apical Cl- secretion through the CFTR channel; water then follows into the lumen by osmosis.","src":"quizlet"},{"t":"What does cAMP do in intestinal secretory cells?","d":"cAMP acts as a second messenger; in intestinal secretory cells it increases the opening of the apical Cl- channel (CFTR), driving Cl- (and osmotic water) secretion.","src":"quizlet"},{"t":"What is the migrating myoelectric complex (MMC) and what is its purpose?","d":"After most of a meal is absorbed, segmentation ceases and is replaced by the MMC, a pattern of peristaltic activity. It moves undigested material from the small intestine into the large intestine and prevents bacteria from remaining in the small intestine long enough to overgrow.","src":"quizlet"},{"t":"Which hormone regulates (initiates) the MMC?","d":"Motilin (an intestinal hormone); feeding inhibits its release, and it stimulates MMCs via the enteric and autonomic nervous systems.","src":"quizlet"},{"t":"What is lactose intolerance and how does it affect water absorption?","d":"An inability to fully digest lactose, so lactose concentration stays high in the small intestine; because water absorption requires prior solute absorption to create an osmotic gradient, the unabsorbed lactose prevents some water from being absorbed (osmotic effect, causing diarrhea).","src":"quizlet"},{"t":"What causes cholera (secretory diarrhea)?","d":"A bacterium that releases a toxin which stimulates cAMP production in the secretory cells at the base of the intestinal villi, increasing apical Cl- channel opening and Cl- secretion, with osmotic water flow into the lumen (secretory diarrhea).","src":"quizlet"},{"t":"What is the purpose of motility of the large intestine?","d":"Mixing and retaining contents for optimal salvage (absorption) of fluid, ions, and useful products of bacterial metabolism; achieved by segmentation and by propulsion (mass movements toward the rectum).","src":"quizlet"},{"t":"What initiates the process of defecation?","d":"Mass movement of large-intestine contents into the rectum; the resulting sudden rectal distension initiates the neurally mediated defecation reflex.","src":"quizlet"},{"t":"Are all gastric gland cell types found in every region of the stomach?","d":"No. Cell distribution is region-dependent (e.g., parietal cells are mostly in the body/fundus; D and G cells are located primarily in and around the glands of the antrum).","src":"quizlet"},{"t":"What is the location and function of mucous (mucus) cells of the gastric gland?","d":"Located at the luminal end (opening) of the gastric gland; they secrete a protective coating of mucus (and HCO3-) that protects the stomach lining from acid and self-digestion.","src":"quizlet"},{"t":"What are the location, secretions, and features of the parietal (oxyntic) cell?","d":"Secretes HCl (acid) and intrinsic factor. Found mostly in the body and fundus of the stomach (not the antrum). Has an apical membrane modified with canaliculi to increase surface area, and many mitochondria to produce the ATP needed for active acid secretion (H+/K+-ATPase).","src":"quizlet"},{"t":"What is the function of canaliculi in parietal cells?","d":"These invaginations of the apical membrane increase the surface area of parietal cells, maximizing secretion of acid and intrinsic factor into the stomach lumen.","src":"quizlet"},{"t":"What are the location, secretion, and activation of the chief cell's product?","d":"Chief cells are found in gastric glands throughout the stomach (all regions) and secrete pepsinogen, the inactive precursor of pepsin. Pepsinogen is activated to pepsin by the acidic pH of the stomach lumen.","src":"quizlet"},{"t":"What are the location and secretion of enteroendocrine (G) cells?","d":"Found in the gastric glands of the antrum; these enteroendocrine cells, called G cells, secrete gastrin.","src":"quizlet"},{"t":"What are the location and secretion of enterochromaffin-like (ECL) cells?","d":"Scattered throughout the tubular gastric glands or surrounding tissue (shown in the body gland); releases the paracrine substance histamine, which stimulates acid secretion.","src":"quizlet"},{"t":"What are the location and secretion of D cells?","d":"Scattered throughout the gastric glands but located primarily in and around the glands of the antrum; secretes the polypeptide somatostatin.","src":"quizlet"},{"t":"Is the large intestine shorter or longer than the small intestine?","d":"Shorter. The large intestine is shorter than the small intestine; its surface is not convoluted and its mucosa lacks villi.","src":"quizlet"},{"t":"What is the ileocecal valve?","d":"A sphincter (ring of circular smooth muscle) between the ileum and the cecum, separating the small and large intestines.","src":"quizlet"},{"t":"What is the function of the appendix?","d":"A small, fingerlike projection extending from the cecum; it may participate in immune function and serve as a reservoir for healthy bacteria that can repopulate the large intestine when illness alters the bacterial population.","src":"quizlet"},{"t":"What are the functions of the large intestine (colon)?","d":"Primary function: store and concentrate fecal material before defecation. It concentrates undigested material by absorbing most remaining ions and water (forming feces; if material remains long, nearly all water is absorbed, leaving hard pellets), and also absorbs some potentially useful products of bacterial metabolism.","src":"quizlet"},{"t":"What is the function of the rectum?","d":"It serves as a reservoir for feces, which accumulate and distend it until the defecation reflex is triggered and the rectum contracts to expel feces via the anus.","src":"quizlet"},{"t":"The anus is composed of which two sphincters?","d":"1) Internal anal sphincter: smooth muscle, involuntary. 2) External anal sphincter: skeletal muscle, under voluntary control.","src":"quizlet"},{"t":"Describe the bacterial ecosystem of the large intestine and what it does.","d":"Colonic bacteria metabolize undigested polysaccharides (fiber) into short-chain fatty acids that are absorbed into the blood; produce small amounts of vitamins (especially vitamin K) that are absorbed into the blood; and produce gas (flatus) by fermenting undigested polysaccharides.","src":"quizlet"},{"t":"Which type of nutrients (water-soluble or fat-soluble) does the blood supply transport from the intestine?","d":"Water-soluble nutrients. These enter intestinal capillaries and the hepatic portal vein, whereas absorbed fats/fat-soluble nutrients are taken up by lymphatic lacteals.","src":"quizlet"},{"t":"In the enterohepatic circulation, how are bile salts taken up from portal blood into hepatocytes?","d":"By secondary active transport coupled to Na+.","src":"quizlet"},{"t":"Where are melanocortin-releasing POMC neurons located, and what does melanocortin do?","d":"POMC neurons are located in the arcuate nucleus of the hypothalamus; melanocortin reduces food intake (anorexigenic effect via MC4R activation).","src":"quizlet"},{"t":"What are the tonicity and pH of saliva?","d":"Saliva is hypotonic and slightly alkaline (due to HCO3- secretion by ductal cells; stimulated saliva reaches pH ~8).","src":"quizlet"},{"t":"Ductal cells","d":"Modify the primary (isotonic) saliva produced by acinar cells by reabsorbing Na+ and Cl- and secreting K+ and HCO3-. Because the duct epithelium has low water permeability, the resulting final saliva is both alkaline and hypotonic.","src":"quizlet"},{"t":"What are the properties of the tight junctions between acinar cells?","d":"They are leaky, allowing paracellular passage of Na+ (and water), which enables the isotonic primary secretion to form.","src":"quizlet"},{"t":"What is the key property of the tight junctions in ductal cells?","d":"They are impermeable to water, preventing its reabsorption and thereby maintaining the hypotonic nature of final saliva.","src":"quizlet"},{"t":"Where are all components of saliva first secreted?","d":"Into the lumen of the acinus (acinar lumen), forming the isotonic primary secretion.","src":"quizlet"},{"t":"What is the primary secretion from acinar cells, and what is its tonicity?","d":"An isotonic, plasma-like fluid rich in NaCl; it is isotonic (similar in concentration to plasma).","src":"quizlet"},{"t":"What does the primary (acinar) secretion contain?","d":"Na+, Cl-, K+, HCO3-, and water — a plasma-like isotonic ionic composition (~145–160 mM Na+, 5–10 mM K+, 120–130 mM Cl-, pH ~7.5).","src":"quizlet"},{"t":"How do ductal cells act on the primary secretion to produce final saliva?","d":"They modify it by reabsorbing Na+ and Cl- and secreting K+ and HCO3-, converting the isotonic primary saliva into hypotonic, alkaline final saliva.","src":"quizlet"},{"t":"Where is the feeding center located, and what happens when it is activated or lesioned?","d":"The feeding center is in the lateral hypothalamus. Activation increases hunger (food intake). Animals with lesions in this region become aphagic (stop eating) and lose weight.","src":"quizlet"},{"t":"Where is the satiety center located, and what happens when it is activated or lesioned?","d":"The satiety center is in the ventromedial hypothalamus. Activation produces feelings of fullness (satiety). Animals with lesions in this area become hyperphagic and obese.","src":"quizlet"},{"t":"What are the effects of orexigenic factors?","d":"They increase food intake (appetite-stimulating effects).","src":"quizlet"},{"t":"What are the effects of anorexigenic factors?","d":"They decrease food intake or cause loss of appetite (appetite-suppressing effects).","src":"quizlet"},{"t":"Where is peptide YY (PYY) released from, and what does it do?","d":"Released by enteroendocrine L-cells of the intestine (ileum and colon) postprandially to reduce food intake (suppress appetite and promote satiety).","src":"quizlet"},{"t":"Paneth cells","d":"Specialized secretory cells located at the base of intestinal crypts of Lieberkühn that secrete antibacterial peptides (defensins, lysozyme, and other antimicrobial proteins) to protect the GI tract from pathogenic bacteria and help regulate the intestinal microbiome.","src":"quizlet"},{"t":"What structural features does the large intestine lack, and what does it have instead?","d":"The large intestine lacks villi but has crypts (crypts of Lieberkühn).","src":"quizlet"},{"t":"What are the four epithelial cell types generated from stem cells in the large intestine?","d":"1. Absorptive cells (colonocytes) — do not contain brush border enzymes.\n2. Goblet cells — abundant.\n3. Paneth cells — absent in adults (very few or absent).\n4. Endocrine cells — very few (~1% of epithelium).","src":"quizlet"},{"t":"Crypt of Lieberkühn","d":"A tubular invagination of the intestinal epithelium into the underlying lamina propria, present in both the small and large intestine. Serves as the site of cell proliferation and renewal, and contains stem cells, goblet cells, Paneth cells (small intestine), and enteroendocrine cells.","src":"quizlet"},{"t":"How is divalent iron (Fe2+) absorbed into the enterocyte?","d":"Via active transport through the apical membrane using divalent metal transporter 1 (DMT1), located on the brush-border membrane of duodenal enterocytes.","src":"quizlet"},{"t":"Neurocrine regulation (GI)","d":"A type of GI regulation in which postganglionic neurons of the enteric nervous system release a neurotransmitter (e.g., VIP, GRP, enkephalins) that acts on nearby neurons or effector cells (smooth muscle, glands) close to the site of release.","src":"quizlet"},{"t":"Where are the hypothalamic feeding center and satiety center located?","d":"The feeding center is in the lateral hypothalamic area; the satiety center is in the ventromedial hypothalamus.","src":"quizlet"},{"t":"What are the consequences of lesions to the feeding center vs. the satiety center?","d":"Lesions to the feeding center (lateral hypothalamus) cause an animal to become aphagic (anorexic, weight loss). Lesions to the satiety center (ventromedial hypothalamus) cause an animal to become hyperphagic and obese.","src":"quizlet"},{"t":"Gastric phase","d":"The phase of gastric secretion triggered when food enters the stomach. Stomach distension and amino acids/peptides activate G cells to release gastrin, stimulating acid production. This is the major phase, accounting for ~60% of total gastric acid secreted.","src":"quizlet"},{"t":"What are the three cell types that compose salivary glands?","d":"1. Acinar cells — secrete the primary (initial) saliva containing enzymes, mucus, and electrolytes.\n2. Ductal cells — line the duct network and modify the electrolyte composition of saliva as it passes through.\n3. Myoepithelial cells — wrap around acini and intercalated ducts; contract to propel saliva through the duct system.","src":"quizlet"},{"t":"Acinar cells","d":"The secretory end-piece cells of salivary glands that produce and secrete the initial (primary) saliva — an isotonic fluid containing enzymes (e.g., salivary amylase, peroxidase), mucus, and electrolytes — before it is modified by ductal cells.","src":"quizlet"}],"resp":[{"t":"What is lung compliance?","d":"The change in lung volume produced by a given change in transpulmonary pressure (CL = ΔVL / ΔPtp). It reflects how easily the lungs expand (stretchability); compliance is the inverse of stiffness.","src":"quizlet"},{"t":"How does lung compliance affect the work of breathing?","d":"High compliance = more easily stretched (less stiff), so less work is needed to expand the lungs. Low compliance = stiffer lung, requiring a greater transpulmonary pressure and more muscular effort to achieve a given expansion.","src":"quizlet"},{"t":"What is elastic recoil (elasticity) of the lungs?","d":"The tendency of the stretched lung to oppose further stretching and return to a smaller size. Even at rest the lungs contain air, yet their natural tendency is to collapse because of elastic recoil.","src":"quizlet"},{"t":"Do the lungs or the chest wall naturally tend to collapse vs. expand, and what keeps them from doing so?","d":"At rest, the lungs naturally tend to collapse (inward elastic recoil) while the chest wall naturally tends to expand (outward recoil). These opposing recoil tendencies balance each other and create a subatmospheric intrapleural pressure that holds the lungs open and prevents either structure from fully collapsing or bursting.","src":"quizlet"},{"t":"What is negative (subatmospheric) intrapleural pressure, and why does it exist?","d":"Intrapleural pressure is below atmospheric (about -4 mmHg at rest). It arises because the lung's inward elastic recoil and the chest wall's outward recoil pull the pleural surfaces slightly apart; since the intrapleural fluid cannot expand, the pressure falls below atmospheric. This negative pressure holds the lungs open. Because of gravity, intrapleural pressure is less negative at the base of the lung than at the apex.","src":"quizlet"},{"t":"What is the anatomical dead space (conducting zone)?","d":"The volume of the conducting airways (trachea, bronchi, bronchioles, and terminal bronchioles) that contain no alveoli and do not exchange gases with the blood — about 150 mL. The large conducting airways (trachea and bronchi) are held open by cartilage rings and resist collapse.","src":"quizlet"},{"t":"For every 500 mL breath, how many mL do not participate in gas exchange?","d":"About 150 mL stays in the conducting airways (anatomical dead space) and does not reach the alveoli for gas exchange.","src":"quizlet"},{"t":"In what order does inspired air pass through the airways?","d":"Nasal/oral cavities → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.","src":"quizlet"},{"t":"What makes up the upper airway, and what does it do?","d":"The nose, mouth, pharynx, and larynx. It conducts air to the lower airway, protects the lower airways, and warms, filters, and humidifies inspired air.","src":"quizlet"},{"t":"Which airways are cartilaginous vs. non-cartilaginous?","d":"Cartilaginous (contain cartilage rings): the trachea and bronchi. Non-cartilaginous: bronchioles (terminal and respiratory), alveolar ducts/sacs, and alveoli — the bronchioles are the first branches that no longer contain cartilage.","src":"quizlet"},{"t":"What are respiratory bronchioles?","d":"Airways that branch from the terminal bronchioles and are the first airways to have alveoli attached to their walls; they mark the beginning of the respiratory (gas-exchange) zone.","src":"quizlet"},{"t":"What are alveolar sacs?","d":"Grape-like clusters of two or more alveoli that share a common duct/opening, consisting entirely of alveoli.","src":"quizlet"},{"t":"What are alveoli and what is their purpose?","d":"Tiny, hollow, thin-walled sacs continuous with the airway lumens that are the site of gas exchange. Their walls are lined mainly by flat type I alveolar cells with interspersed type II cells, and contain capillaries, alveolar pores, and macrophages.","src":"quizlet"},{"t":"Which airway structures are susceptible to collapse when surrounding pressure increases, and which collapse first?","d":"The small conducting airways (bronchioles) and alveoli. During forced expiration, the rise in intrapleural pressure compresses the small airways, so bronchioles collapse before alveoli. The large cartilage-supported bronchi and trachea resist collapse; surfactant helps prevent alveolar collapse.","src":"quizlet"},{"t":"What is the function of type I alveolar cells?","d":"They are thin, flat epithelial cells that line most of the alveolar surface, forming the extremely thin barrier across which O2 and CO2 rapidly diffuse between alveolar air and capillary blood.","src":"quizlet"},{"t":"What is the function of type II alveolar cells?","d":"They produce (secrete) pulmonary surfactant, a phospholipid-rich substance that lowers surface tension and helps prevent alveolar collapse.","src":"quizlet"},{"t":"What are the immune cells in the alveoli?","d":"Alveolar macrophages — they engulf and destroy inhaled particles and bacteria that reach the alveoli.","src":"quizlet"},{"t":"What is a right-to-left (anatomic) shunt?","d":"An anatomic shunt in which venous (deoxygenated) blood passes from the right to the left side of the heart without going through the lung (e.g., via a patent foramen ovale), bypassing gas exchange. The shunted blood lowers arterial O2 (hypoxemia).","src":"quizlet"},{"t":"What are the nonrespiratory functions of the lungs?","d":"1) Conditioning inhaled air (warming, moistening, and filtering/defense via cilia, mucus, and macrophages); 2) influencing arterial concentrations of biologically active substances (removing some via the pulmonary capillary endothelium, producing others such as angiotensin II); 3) acting as a filter that traps small blood clots from the systemic venous circulation, preventing arterial emboli.","src":"quizlet"},{"t":"Which of the following is NOT a function of the respiratory system: regulation of blood pH, phonation, CO2 elimination, defense against microbes, or regulation of blood pressure?","d":"Regulation of blood pressure. Respiratory functions include providing O2, eliminating CO2, regulating blood pH, forming speech sounds (phonation), and defending against inhaled microbes — but not regulating blood pressure.","src":"quizlet"},{"t":"What happens to thoracic cavity volume and the diaphragm during normal vs. forced inspiration?","d":"Thoracic cavity volume increases and the diaphragm contracts and moves downward. In forced inspiration the volume increase is even larger because accessory muscles (e.g., sternocleidomastoid, scalenes) are recruited; the diaphragm still moves down.","src":"quizlet"},{"t":"What happens to thoracic cavity volume and the diaphragm during normal vs. forced expiration?","d":"Thoracic cavity volume decreases and the diaphragm relaxes and moves upward. Normal expiration is passive; in forced expiration, contraction of the abdominal and internal intercostal muscles actively decreases thoracic volume further and pushes the diaphragm higher.","src":"quizlet"},{"t":"What does the chest wall (and diaphragm) do when thoracic pressure is decreased vs. increased?","d":"To decrease pressure: the diaphragm contracts downward and the chest wall expands, increasing thoracic volume (inspiration). To increase pressure: the diaphragm relaxes upward and the chest wall recoils/contracts, decreasing thoracic volume (expiration).","src":"quizlet"},{"t":"By Boyle's law, what happens to thoracic/alveolar pressure when thoracic cavity volume decreases greatly?","d":"The pressure greatly increases. By Boyle's law, decreasing the lung volume compresses the gas and raises alveolar pressure; a large decrease in volume produces a large rise in pressure.","src":"quizlet"},{"t":"What is Boyle's law?","d":"At constant temperature, the pressure exerted by a fixed number of gas molecules is inversely proportional to the volume of the container (P and V are inversely proportional).","src":"quizlet"},{"t":"What are the static properties of the lung?","d":"Properties measured under no-airflow (static) conditions — at the end of inspiration and expiration when there is no airflow. Transpulmonary pressure governs the static properties of the lungs.","src":"quizlet"},{"t":"What is another name for the pleural space?","d":"The intrapleural space (or pleural cavity) — the thin, fluid-filled space between the visceral and parietal pleura.","src":"quizlet"},{"t":"What is the pleural sac?","d":"A completely closed, double-layered sac (visceral pleura against the lung, parietal pleura against the thoracic wall) that surrounds each lung and separates it from the thoracic wall; the two layers are separated by a thin film of intrapleural fluid.","src":"quizlet"},{"t":"What is the barometric (atmospheric) pressure at sea level?","d":"760 mmHg.","src":"quizlet"},{"t":"What is the equation for airflow, and what are its two pressures?","d":"F = (Palv − Patm) / R, where F is bulk airflow, Palv is alveolar pressure (inside the lung), Patm is atmospheric/barometric pressure (outside), and R is airway resistance. Airflow is driven by the pressure difference Palv − Patm and is inversely proportional to airway resistance.","src":"quizlet"},{"t":"What must the respiratory system do to generate airflow out (expiration)?","d":"Raise alveolar pressure above atmospheric (Palv > Patm). This is done by decreasing thoracic/lung volume, which (by Boyle's law) compresses the alveolar gas so air flows outward.","src":"quizlet"},{"t":"What must the respiratory system do to generate airflow in (inspiration)?","d":"Lower alveolar pressure below atmospheric (Palv < Patm). This is done by increasing thoracic/lung volume, which (by Boyle's law) drops the alveolar pressure so air flows inward.","src":"quizlet"},{"t":"Why is ventilation (movement of air in and out of the lungs) alternating in direction?","d":"Air moves because alveolar pressure is alternately less than atmospheric (inspiration) and greater than atmospheric (expiration).","src":"quizlet"},{"t":"What is transpulmonary pressure (Ptp), and why is it useful?","d":"The transmural ('across the wall') pressure acting on the lungs: Ptp = Palv − Pip (alveolar pressure minus intrapleural pressure). It is a determinant of lung size — the degree of lung expansion is proportional to Ptp — so it indicates lung volume. If Ptp falls to 0, the lung tends to collapse.","src":"quizlet"},{"t":"When is intrapleural pressure equal in magnitude and opposite in sign to transpulmonary pressure?","d":"Under static (no-airflow) conditions, when alveolar pressure (Palv) = 0. Since Ptp = Palv − Pip, when Palv = 0, then Ptp = −Pip.","src":"quizlet"},{"t":"What are the pressures and airflow at the end of a normal (unforced) expiration?","d":"Static condition with no airflow: alveolar pressure (Palv) = 0 (equals atmospheric); intrapleural pressure (Pip) is subatmospheric (about −4 mmHg); transpulmonary pressure (Ptp ≈ +4 to +5 mmHg) exactly opposes lung elastic recoil. Flow = 0.","src":"quizlet"},{"t":"What are the pressures, volume, and airflow at the end of inspiration?","d":"Static condition: airflow = 0 and lung volume is maximal for the breath; alveolar pressure (Palv) = 0 (equals atmospheric); intrapleural pressure (Pip) is at its most subatmospheric for the cycle (about −6 to −7.5 mmHg); transpulmonary pressure (Ptp ≈ +7 mmHg) is highest of the cycle, balanced by greater lung elastic recoil.","src":"quizlet"},{"t":"Which has the greater lung volume: end inspiration or end expiration?","d":"End inspiration. Lung volume rises during inspiration and peaks at end inspiration, then falls during expiration.","src":"quizlet"},{"t":"When is alveolar pressure equal to 0 (atmospheric) and airflow equal to 0?","d":"At both the end of inspiration and the end of expiration. Whenever there is no airflow and the airways are open to the atmosphere, alveolar pressure equals atmospheric (0). Airflow is non-zero only during dynamic inspiration and expiration.","src":"quizlet"},{"t":"What is a pneumothorax?","d":"Air in the pleural space. Atmospheric air entering the intrapleural space raises intrapleural pressure toward 0, eliminating the transpulmonary pressure that holds the lung open, so the lung partially or completely collapses (lung volume decreases as pleural air increases).","src":"quizlet"},{"t":"What is a spirometer / spirometry?","d":"An apparatus (and the measurement) for recording inspired and expired lung volumes, classically via displacement in water. Note: residual volume, functional residual capacity, and total lung capacity cannot be measured by spirometry.","src":"quizlet"},{"t":"What is tidal volume (Vt), and what is a typical value?","d":"The amount of air inhaled or exhaled in one breath during normal quiet breathing; typically about 500 mL (of which ~150 mL is anatomical dead space).","src":"quizlet"},{"t":"What is inspiratory reserve volume (IRV)?","d":"The amount of air, in excess of a normal tidal inspiration, that can be inhaled with maximum effort.","src":"quizlet"},{"t":"What is expiratory reserve volume (ERV)?","d":"The amount of air, in excess of a normal tidal expiration, that can be exhaled with maximum effort.","src":"quizlet"},{"t":"What is residual volume (RV), and why do we have it?","d":"The volume of air remaining in the lungs after a maximal (forced) expiration (~1200 mL). It keeps the alveoli inflated between breaths so the lungs are never completely emptied; the residual air mixes with fresh air on the next inspiration, preserving the gas-exchange surface.","src":"quizlet"},{"t":"What is vital capacity (VC), and what does it equal?","d":"The maximal volume of air that can be exhaled after a maximal inspiration. VC = tidal volume + inspiratory reserve volume + expiratory reserve volume (VC = TV + IRV + ERV).","src":"quizlet"},{"t":"What is inspiratory capacity (IC)?","d":"The maximal volume of air that can be inhaled after a normal tidal expiration. IC = tidal volume + inspiratory reserve volume (TV + IRV).","src":"quizlet"},{"t":"What is functional residual capacity (FRC)?","d":"The volume of air remaining in the lungs after a normal tidal expiration. FRC = expiratory reserve volume + residual volume (ERV + RV).","src":"quizlet"},{"t":"What is total lung capacity (TLC), and what does it equal?","d":"The maximum amount of air the lungs can contain (~5900 mL, ~6 L). TLC = residual volume + vital capacity = TV + IRV + ERV + RV.","src":"quizlet"},{"t":"Are lung capacities the sum of two or more lung volumes?","d":"Yes. The capacities (IC, FRC, VC, TLC) are each sums of two or more of the four distinct lung volumes (TV, IRV, ERV, RV).","src":"quizlet"},{"t":"What is minute (total) ventilation, and what is a typical resting value?","d":"The total volume of air moved into or out of the lungs per minute = tidal volume × respiratory rate (VE = VT × RR). A typical resting value is ~6000 mL/min (500 mL × 12 breaths/min).","src":"quizlet"},{"t":"What is alveolar ventilation, and why is it always less than minute ventilation?","d":"The volume of fresh air reaching the alveoli per minute = (tidal volume − dead space) × respiratory rate. It is always less than minute ventilation because some inspired air stays in the conducting airways (dead space) and never reaches the alveoli. Alveolar ventilation is the more important factor for the effectiveness of gas exchange.","src":"quizlet"},{"t":"What is dead space ventilation?","d":"The volume of inspired air per minute that does not reach the alveoli for gas exchange = anatomical dead space × respiratory rate (e.g., 150 mL/breath × 12 breaths/min = 1800 mL/min).","src":"quizlet"},{"t":"What is respiratory rate (RR)?","d":"The number of breaths per minute; a typical resting value is ~12 breaths/min (normal resting range ~12–20).","src":"quizlet"},{"t":"What factors determine pulmonary ventilation?","d":"The pressure difference driving airflow, lung compliance (stretchability), and airway resistance.","src":"quizlet"},{"t":"What is tachypnea?","d":"Rapid breathing (an increased breathing rate).","src":"quizlet"},{"t":"What is hyperventilation?","d":"Ventilation increased relative to metabolism — i.e., alveolar ventilation too great for the amount of CO2 being produced — so that arterial/alveolar PCO2 falls below normal. It is not synonymous with simply 'increased ventilation' (e.g., the increased ventilation of moderate exercise is not hyperventilation).","src":"quizlet"},{"t":"What is hyperpnea?","d":"An increase in the depth and/or rate of breathing in which ventilation rises in proportion to increased metabolism/CO2 production (e.g., during exercise) — so, unlike hyperventilation, it does not lower PCO2.","src":"quizlet"},{"t":"Why does filling the lung with saline (vs. air) give the greatest compliance?","d":"Filling the alveoli with liquid eliminates the air-water interface and thus the surface tension, which is the major determinant of lung compliance. With surface tension removed, the lung is much easier to expand, so compliance is greatest. (Surfactant works similarly by lowering surface tension.)","src":"quizlet"},{"t":"Why is the first breath of a newborn the most difficult?","d":"In utero the lungs are filled with fluid, so there is no air-water surface tension. The first inflation of the newly air-filled lungs must overcome the high surface tension of the air-water interface, which requires great effort.","src":"quizlet"},{"t":"What is surface tension, and why does it occur at an air-water interface?","d":"Surface tension is the attractive (cohesive) force between water molecules at an air-water interface that causes the water lining to resist stretching — like a stretched balloon tending to shrink. Interior water molecules are pulled equally in all directions, but surface molecules experience a net inward pull because there is no water above them, making the liquid surface resistant to stretching.","src":"quizlet"},{"t":"What is pulmonary surfactant, and how does it lower surface tension?","d":"A detergent-like mixture of phospholipids and proteins secreted by type II alveolar cells. Its major phospholipid inserts its hydrophilic end into the alveolar water layer while its hydrophobic ends face the air, forming a monomolecular layer that reduces cohesive forces between water molecules at the interface. This lowers surface tension, increases lung compliance (easier expansion), and stabilizes alveoli of different sizes.","src":"quizlet"},{"t":"What is emphysema, and does it increase or decrease compliance?","d":"A chronic obstructive disease (classically from smoking) marked by destruction of alveolar walls and loss of elastic tissue, so adjacent alveoli fuse into fewer, larger sacs. This increases compliance (easy to inflate), but the loss of elastic recoil and collapse of small airways during expiration make it hard to exhale, and the reduced alveolar surface area impairs gas exchange.","src":"quizlet"},{"t":"What is pulmonary fibrosis, and does it increase or decrease compliance?","d":"Thickening and scarring of lung connective tissue (excessive tissue destruction and repair), producing rigid, stiff alveoli. This decreases compliance (a restrictive pattern), making the lungs hard to inflate; the thickened alveolar walls also impair gas diffusion.","src":"quizlet"},{"t":"How does gas cross the blood-gas (alveolar-capillary) barrier?","d":"By diffusion down its partial-pressure gradient across the thin alveolar-capillary membrane. In the lung, O2 diffuses from alveoli into blood and CO2 diffuses from blood into alveoli.","src":"quizlet"},{"t":"State Fick's law of gas diffusion across the respiratory membrane.","d":"The volume of gas diffusing across the membrane per unit time is proportional to the surface area, the diffusion constant (D), and the partial-pressure difference across the membrane (P_alveolar − P_capillary), and inversely proportional to membrane thickness. Vgas = (area × D × ΔP) / thickness, where D = solubility / √(molecular weight).","src":"quizlet"},{"t":"Does a thicker diffusion membrane increase or decrease gas diffusion?","d":"It decreases diffusion. Increased membrane thickness (e.g., from fibrosis or pulmonary edema) impairs gas exchange, consistent with Fick's law (diffusion is inversely proportional to thickness).","src":"quizlet"},{"t":"Does a patient with pulmonary edema have more or less effective diffusion surface area?","d":"Less. In pulmonary edema, fluid accumulates in and around the alveoli (some alveoli fill with fluid), decreasing the total surface area available for gas diffusion and impairing gas exchange.","src":"quizlet"},{"t":"What is the purpose of gas exchange?","d":"To provide O2 for aerobic cellular respiration — O2 is the final electron acceptor in the mitochondria — and to remove the metabolic waste CO2 (and the H+ it generates) from the blood via the lungs.","src":"quizlet"},{"t":"What is the composition of dry air at sea level vs. at high altitude (e.g., top of Mt. Everest)?","d":"The fractional composition is the same at all altitudes: ~79% nitrogen and ~21% oxygen, with very small amounts of water vapor, CO2, and inert gases. Only the total barometric pressure differs (760 mmHg at sea level vs. ~253 mmHg atop Mt. Everest), so the air is still ~21% oxygen at altitude.","src":"quizlet"},{"t":"How does altitude affect breathing and oxygenation?","d":"Higher altitude means lower atmospheric (barometric) pressure, which lowers the partial pressure of inspired and alveolar O2, reducing O2 uptake into the blood.","src":"quizlet"},{"t":"State Dalton's law of partial pressures.","d":"In a mixture of gases, each gas exerts its pressure independently of the others, so the total pressure of the mixture equals the sum of the individual (partial) pressures. The partial pressure of a gas = its fractional concentration × total pressure (e.g., atmospheric PO2 = 0.21 × 760 = 160 mmHg).","src":"quizlet"},{"t":"What is the composition and key partial pressures of alveolar air?","d":"Approximately 75% nitrogen, ~14% oxygen, ~6% water vapor, ~5% carbon dioxide. Compared with atmospheric air, CO2 and water vapor are higher. Key partial pressures: alveolar PO2 ≈ 105 mmHg, PCO2 = 40 mmHg, PH2O ≈ 47 mmHg.","src":"quizlet"},{"t":"What are the partial pressures of O2 and CO2 in atmospheric air?","d":"Atmospheric PO2 = 160 mmHg (0.21 × 760) and atmospheric PCO2 = 0.3 mmHg.","src":"quizlet"},{"t":"What is the partial pressure of CO2 in alveolar air?","d":"40 mmHg.","src":"quizlet"},{"t":"What are the PO2 and PCO2 of alveolar air, pulmonary veins, and systemic arteries?","d":"Alveolar PO2 ≈ 105 mmHg, PCO2 ≈ 40 mmHg. Pulmonary vein and systemic arterial blood: PO2 ≈ 100 mmHg (about 5 mmHg lower than alveolar) and PCO2 ≈ 40 mmHg.","src":"quizlet"},{"t":"What are the PO2 and PCO2 of pulmonary arterial / systemic venous (mixed venous) blood?","d":"PO2 = 40 mmHg and PCO2 = 46 mmHg (pulmonary arteries carry systemic venous blood). In the lung, the alveolar-to-blood gradients are ~65 mmHg for O2 (alveolar 105 vs. blood 40) and ~6 mmHg for CO2 (blood 46 vs. alveolar 40), driving gas exchange.","src":"quizlet"},{"t":"What are the PO2 and PCO2 in cells/tissues, and what gradients drive gas exchange there?","d":"Cellular PO2 is < 40 mmHg (mitochondrial PO2 < 5 mmHg) and cellular PCO2 is > 46 mmHg. Across the tissues, the ~60 mmHg O2 gradient (arterial 100 vs. venous 40) drives O2 into cells and the ~6 mmHg CO2 gradient (venous 46 vs. arterial 40) drives CO2 out; CO2 needs only a small gradient because it is far more soluble than O2.","src":"quizlet"},{"t":"What is the difference between alveolar PO2 and systemic arterial PO2, and why?","d":"Alveolar PO2 ≈ 105 mmHg and systemic arterial PO2 ≈ 100 mmHg — a difference of about 5 mmHg. Arterial PO2 is slightly lower mainly because of ventilation-perfusion inequality (largely from gravitational effects on blood-flow distribution in the upright lung), plus a small normal physiological shunt.","src":"quizlet"},{"t":"What does equilibration mean for gas exchange in the pulmonary capillaries?","d":"Net diffusion of O2 and CO2 ceases when the pulmonary capillary partial pressures become equal to those in the alveoli. The blood leaving the capillaries then has essentially the same PO2 (~100 mmHg) and PCO2 (~40 mmHg) as alveolar air.","src":"quizlet"},{"t":"How is gas transported to peripheral tissues, and in what forms?","d":"In the blood. O2 and CO2 have limited solubility in plasma, so red blood cells carry both on hemoglobin: O2 binds hemoglobin and CO2 is also carried bound to Hb and (chiefly) converted to soluble bicarbonate. As gas is removed from plasma, more diffuses in, and all the reactions are reversible.","src":"quizlet"},{"t":"What is pulmonary blood flow (perfusion) and its role in gas exchange?","d":"Bulk flow of blood from higher to lower pressure (F = ΔP/R). In the lung, perfusion carries systemic venous blood through the pulmonary capillaries, where O2 is taken up from and CO2 released into the alveoli. Matching this blood flow to alveolar ventilation determines the efficiency of gas exchange.","src":"quizlet"},{"t":"What measures the actual amount of oxygen carried in the blood (as opposed to percent saturation), and what is it made of?","d":"Oxygen content (oxygen-carrying capacity) — the total O2 dissolved in plasma plus that bound to hemoglobin in red blood cells (~200 mL O2 per liter of arterial blood, i.e., ~20 mL/dL at PO2 100 mmHg). About 2% is dissolved and ~98% is Hb-bound; it depends on hematocrit, not just percent saturation.","src":"quizlet"},{"t":"What percent of hemoglobin is saturated in arterial vs. mixed venous blood, and at what PO2?","d":"Arterial blood: ~98% (almost 100%) saturated at PO2 ≈ 100 mmHg. Mixed venous blood: ~75% saturated at PO2 ≈ 40 mmHg. The normal operating range of the dissociation curve is thus about 75–98% saturation.","src":"quizlet"},{"t":"What is mixed venous blood?","d":"Blood in the pulmonary artery — a mixture of venous blood returning from all the systemic veins to the right side of the heart. It has PO2 ≈ 40 mmHg, PCO2 ≈ 46 mmHg, is ~75% Hb-saturated, and carries ~15 mL O2/dL.","src":"quizlet"},{"t":"What is the most important factor determining percent hemoglobin saturation, and what is the shape of the oxygen-hemoglobin dissociation curve?","d":"The most important factor is the blood (arterial) PO2. The oxygen-hemoglobin dissociation curve is sigmoidal (S-shaped).","src":"quizlet"},{"t":"Where on hemoglobin does oxygen bind?","d":"To the iron (Fe2+) atom within each of the four heme groups of the hemoglobin molecule.","src":"quizlet"},{"t":"Does pH (acidity) affect oxygen binding to hemoglobin? Which factors shift the O2-Hb dissociation curve to the right?","d":"Yes — pH affects O2 binding. An increase in H+ (acidity), PCO2, temperature, and 2,3-DPG concentration all shift the curve to the right, decreasing hemoglobin's affinity for O2 (more unloading). Decreases in these factors shift it left, increasing affinity.","src":"quizlet"},{"t":"Does hemoglobin carry more O2 at higher or lower temperature, and what is normal body temperature?","d":"Lower temperature increases hemoglobin's affinity for O2 (left shift), so it holds (carries) more O2 at any given PO2; higher temperature lowers affinity (right shift), unloading more O2 to tissues. Normal body temperature is 37°C.","src":"quizlet"},{"t":"At a given PO2 (e.g., 40 mmHg), is hemoglobin more or less saturated in a hyperthermic (high-temperature) state, and why?","d":"Less saturated. Increased temperature shifts the dissociation curve to the right, lowering Hb affinity for O2 at any given PO2, so more oxygen is released (unloaded) to the tissues.","src":"quizlet"},{"t":"Is hemoglobin more saturated in acidotic or alkalotic conditions?","d":"Alkalotic. Decreased acidity (higher pH) shifts the dissociation curve to the left, increasing hemoglobin's affinity for O2, so saturation is higher at a given PO2.","src":"quizlet"},{"t":"During exercise, is hemoglobin more or less saturated, and why?","d":"Less. Exercising tissue produces increased CO2, H+ (acidity, e.g., lactic acid), and heat, which lower Hb affinity for O2 (right shift), so more oxygen is unloaded and diffuses into the tissues.","src":"quizlet"},{"t":"In what three forms is CO2 transported in the blood, and in what proportions?","d":"1) Dissolved in plasma and erythrocyte cytosol (~10%); 2) bound to hemoglobin as carbaminohemoglobin (~25–30%); 3) as bicarbonate (HCO3−) (~60–65%, formed mainly in red blood cells via carbonic anhydrase).","src":"quizlet"},{"t":"What enzyme catalyzes the reaction of CO2 and water, and what are the reactions of CO2 in blood?","d":"Carbonic anhydrase catalyzes (in both directions) the reaction CO2 + H2O ⇌ H2CO3 (carbonic acid). H2CO3 then dissociates rapidly and non-enzymatically into HCO3− (bicarbonate) + H+. The full reversible chain is: CO2 + H2O ⇌ H2CO3 ⇌ HCO3− + H+.","src":"quizlet"},{"t":"Is the CO2 → carbonic acid → bicarbonate reaction slow or fast in plasma vs. erythrocytes, and why?","d":"The first step (CO2 + H2O → H2CO3) is rate-limiting and very slow without carbonic anhydrase. It is fast in erythrocytes, which contain carbonic anhydrase, but slow in plasma, where the enzyme is absent. Thus most CO2 processing (bicarbonate formation) occurs inside red blood cells, and only a small amount of CO2 stays dissolved in plasma.","src":"quizlet"},{"t":"What is the chloride (Hamburger) shift?","d":"An antiporter exchange across the red blood cell membrane in which bicarbonate (HCO3−) moves out of the erythrocyte into the plasma in exchange for chloride (Cl−) moving in, maintaining electroneutrality. Removing HCO3− (a product) drives the CO2 → HCO3− reaction forward, allowing more CO2 to be taken up.","src":"quizlet"},{"t":"What is the Haldane effect?","d":"Deoxyhemoglobin has a greater affinity for H+ and CO2 than oxyhemoglobin does. So as hemoglobin unloads O2 in the tissues, it binds (buffers) more H+ and takes up more CO2; conversely, oxygenation in the lungs promotes release of H+ and CO2.","src":"quizlet"},{"t":"What is the Bohr effect?","d":"Increased H+ (and CO2) generated as blood passes through metabolizing tissues lowers hemoglobin's affinity for O2 (right shift), promoting O2 release/unloading to the tissues. H+ binding to oxyhemoglobin increases oxygen unloading; the H+ comes mainly from the carbonic acid/bicarbonate reaction.","src":"quizlet"},{"t":"How does hemoglobin act as a buffer in CO2/H+ transport?","d":"Deoxyhemoglobin has a high affinity for H+ and binds (buffers) most of the H+ generated as CO2 is converted to bicarbonate, so only a little H+ remains free (venous blood pH 7.36 vs. arterial 7.40). Removing this H+ product also pulls the CO2 → HCO3− + H+ reaction forward, increasing CO2 uptake.","src":"quizlet"},{"t":"What are the effects of CO2 accumulation in the blood?","d":"Retained CO2 generates H+ (via CO2 + H2O → H2CO3 → HCO3− + H+), lowering pH and producing respiratory acidosis.","src":"quizlet"},{"t":"How does a change in alveolar ventilation affect blood CO2?","d":"Increased alveolar ventilation removes (lowers) CO2; decreased alveolar ventilation (hypoventilation) retains (raises) CO2.","src":"quizlet"},{"t":"What is a normal blood pH?","d":"About 7.4 (normal arterial/extracellular range 7.35–7.45; arterial pH = 7.40, venous = 7.36).","src":"quizlet"},{"t":"What type of control governs the respiratory system, and where is the rhythm generator located?","d":"Automatic rhythmic control. The respiratory rhythm generator (pre-Bötzinger complex) in the medulla oblongata sets an automatic basal breathing rhythm, which is modulated according to changing demands signaled by PO2, PCO2, and H+.","src":"quizlet"},{"t":"Which CNS component controls the respiratory system?","d":"The brainstem — specifically the medulla oblongata (with input from the pons). It contains the medullary respiratory (inspiratory) center and the central chemoreceptors; the medullary inspiratory neurons drive spinal motor neurons that activate the respiratory muscles (diaphragm via the phrenic nerves, and intercostals).","src":"quizlet"},{"t":"What controls ventilation (the breathing control centers and their inputs)?","d":"The primary control centers are in the medulla (and pons). Key inputs come from central and peripheral chemoreceptors (stimulated by increased H+/PCO2 and, for peripheral receptors, decreased PO2), plus airway irritant receptors and protective pulmonary stretch receptors.","src":"quizlet"},{"t":"What are the two types of chemoreceptors in the respiratory system?","d":"Peripheral (arterial) chemoreceptors and central chemoreceptors.","src":"quizlet"},{"t":"Where are the peripheral chemoreceptors located and what do they sense?","d":"In the carotid bodies (at the bifurcation of the common carotid arteries) and the aortic bodies (on the aortic arch). They monitor arterial blood and are stimulated by a significantly decreased PO2 (hypoxia, threshold ~60 mmHg), increased H+, and increased PCO2. Their chemosensing cells (glomus/type I cells) couple to afferent nerves and act quickly, providing excitatory input to the medullary inspiratory neurons to increase ventilation.","src":"quizlet"},{"t":"What are central chemoreceptors sensitive to?","d":"Located in the medulla, they are directly sensitive to an increase in H+ concentration of the brain extracellular fluid (not arterial blood). Because CO2 readily crosses the blood-brain barrier and raises brain ECF H+ (while blood H+ crosses very slowly), they are indirectly sensitive to increased arterial PCO2, and so respond mainly to CO2-driven (respiratory) acidosis. They account for ~70% of the ventilatory response to increased PCO2.","src":"quizlet"},{"t":"Which crosses the blood-brain barrier readily: CO2 or H+?","d":"CO2 crosses the blood-brain barrier readily; H+ crosses very slowly. This is why central chemoreceptors respond mainly to CO2 (which raises brain ECF H+) rather than to blood H+ directly.","src":"quizlet"},{"t":"How does ventilation depend on brain (medullary) extracellular fluid pH?","d":"As brain extracellular fluid pH decreases (H+ increases), the central chemoreceptors are stimulated, reflexively increasing alveolar ventilation.","src":"quizlet"},{"t":"How do arterial acid-base changes affect brain (medullary) extracellular fluid pH?","d":"Respiratory changes affect it readily: CO2 diffuses rapidly across the blood-brain barrier, so a change in arterial PCO2 changes brain ECF H+/pH. Metabolic (non-CO2) changes in arterial H+ have little effect, because H+ crosses the blood-brain barrier only very slowly.","src":"quizlet"},{"t":"What is hypercapnia?","d":"Excess (increased) arterial CO2 (increased arterial PCO2).","src":"quizlet"},{"t":"How do respiratory acidosis and metabolic acidosis differ?","d":"Respiratory acidosis: decreased pH driven by a primary rise in arterial PCO2 (CO2 retention from hypoventilation). Metabolic acidosis: decreased pH from a cause other than a primary change in PCO2 (uncompensated, arterial CO2 is essentially unchanged).","src":"quizlet"},{"t":"What is respiratory alkalosis?","d":"A rise in blood pH due to hyperventilation, which decreases arterial PCO2 and therefore H+ concentration.","src":"quizlet"},{"t":"What is metabolic alkalosis?","d":"An elevation of pH (decreased H+) from a cause other than a primary change in PCO2 — usually an excessive loss of acid (e.g., loss of gastric H+ from vomiting). Arterial CO2 is not the primary driver.","src":"quizlet"},{"t":"What is respiratory compensation for acid-base disturbances?","d":"Adjusting ventilation to change arterial PCO2 and thereby H+/pH. For example, in acidosis, increased ventilation removes CO2, lowering H+ concentration back toward normal; in alkalosis, hypoventilation raises PCO2 to restore H+.","src":"quizlet"},{"t":"What is ventilation-perfusion coupling (the V/Q ratio)?","d":"The matching of alveolar ventilation (airflow) to pulmonary capillary blood flow (perfusion), expressed as the ratio VA/Q. Proper matching of ventilation to perfusion in each alveolus optimizes the efficiency of gas exchange; any mismatch is termed ventilation-perfusion inequality.","src":"quizlet"},{"t":"Are ventilation and perfusion ever perfectly equal, and what is a normal lung unit?","d":"No — there is always a small ventilation-perfusion mismatch, even in healthy lungs (causing the normal ~5 mmHg alveolar-arterial O2 gradient). A normal lung unit has both ventilation and perfusion present (V/Q ≈ 1), in contrast to dead-space and shunt units.","src":"quizlet"},{"t":"What is the ventilation-perfusion relationship in a dead-space unit?","d":"Ventilation but no perfusion (ventilated alveoli with no blood supply, e.g., due to a blood clot) — V/Q ratio = infinity. This is wasted ventilation.","src":"quizlet"},{"t":"What is the ventilation-perfusion relationship in a shunt unit?","d":"Perfusion but no ventilation (blood flows past unventilated/collapsed alveoli) — V/Q ratio = 0. Mixed venous blood bypasses gas exchange, so poorly oxygenated blood enters the left heart and systemic circulation, causing hypoxemia (low arterial PO2). Arterial PCO2 usually does not rise, because the hypoxemia reflexively stimulates increased ventilation that offsets the shunt's effect on PCO2.","src":"quizlet"},{"t":"What is a silent lung unit and what is hypoxic pulmonary vasoconstriction?","d":"A silent unit is a lung region with neither ventilation nor perfusion. A decrease in alveolar PO₂ in a poorly ventilated region causes local pulmonary arteriolar vasoconstriction, diverting blood flow away from the poorly ventilated area toward well-ventilated alveoli, which improves ventilation-perfusion matching.","src":"quizlet"},{"t":"How do gravity and posture affect ventilation and perfusion in the lung?","d":"In the upright lung, both ventilation and perfusion are greater at the base than the apex because of gravity, with perfusion (blood flow) affected more steeply than ventilation. This regional ventilation-perfusion inequality lowers arterial PO₂ by about 5 mmHg in healthy people.","src":"quizlet"},{"t":"What is diffusion limitation of gas exchange?","d":"A condition in which blood PO₂ fails to equilibrate with alveolar PO₂ by the time blood leaves the pulmonary capillary, reducing oxygen uptake. In a healthy lung, O₂ equilibration is normally complete within about the first third of the capillary; it can fail when the diffusion barrier is abnormal (e.g., fibrosis, pulmonary edema) and/or when capillary transit time is shortened by increased blood flow (e.g., during exercise), lowering arterial PO₂.","src":"quizlet"},{"t":"How does CO₂ equilibration in the pulmonary capillary compare to O₂?","d":"CO₂ equilibrates with alveolar PCO₂ (~40 mmHg), but the partial-pressure change is in the opposite direction (blood PCO₂ falls from 46 to 40 mmHg as O₂ rises from 40 to ~100 mmHg), so its equilibration curve is reversed. CO₂ diffuses even more rapidly than O₂ because it is more soluble.","src":"quizlet"},{"t":"What is minute ventilation, and how do respiratory rate and tidal volume each affect it?","d":"Minute ventilation (V̇E) = tidal volume × respiratory rate. Both directly affect minute ventilation: increasing either one increases V̇E. However, increasing breathing rate (shallow, rapid breathing) is less efficient than increasing tidal volume because a fixed volume of each breath goes to anatomical dead space — so increases in rate raise dead-space ventilation proportionally more than they raise alveolar ventilation.","src":"quizlet"},{"t":"How does surfactant affect surface tension as alveolar size changes?","d":"As an alveolus gets smaller, surfactant molecules on its surface become more concentrated (less spread out), which reduces surface tension. This helps equalize pressure between small and large alveoli, stabilizing them and preventing small alveoli from collapsing into large ones.","src":"quizlet"},{"t":"Which gas law explains alveolar pressure changes during breathing (when moles of gas are constant)?","d":"Boyle's Law (P₁V₁ = P₂V₂). At constant temperature, a fixed number of gas molecules in a larger volume exerts less pressure, and in a smaller volume exerts more pressure. This is the principle driving alveolar pressure changes during inspiration and expiration.","src":"quizlet"},{"t":"What is a pressure-volume loop in the context of respiratory mechanics?","d":"A graphical representation of the relationship between lung volume and transpulmonary pressure (or alveolar pressure) during the breathing cycle. Lung compliance (CL = ΔV/ΔP) is the slope of this curve; a steeper slope indicates higher compliance.","src":"quizlet"},{"t":"What governs the rate of gas diffusion across the alveolar membrane?","d":"Gas diffusion across the alveolocapillary membrane is governed by the partial pressure gradient of the gas on the two sides of the membrane, the surface area available, and the thickness of the diffusion barrier. Diffusion ceases when partial pressures on both sides are equal.","src":"quizlet"},{"t":"What is perfusion limitation of gas exchange?","d":"A condition in which the rate of gas uptake into blood is limited by blood flow (perfusion) rather than by diffusion across the alveolar membrane. In healthy individuals at rest, O₂ equilibrates between alveolar air and capillary blood well before the blood reaches the end of the capillary, meaning blood flow (perfusion) is the limiting factor for total O₂ uptake.","src":"quizlet"},{"t":"What is an anatomic right-to-left shunt?","d":"A condition in which mixed venous (deoxygenated) blood from the right side of the heart bypasses ventilated alveoli and passes directly to the left side of the heart, reducing arterial PO₂. An example is a patent foramen ovale (PFO) — a hole between the right and left atria. The shunted blood never gets oxygenated, so it lowers the O₂ content of arterial blood.","src":"quizlet"},{"t":"What happens in the thoracic cavity during inspiration?","d":"During inspiration, the diaphragm contracts and moves downward, increasing thoracic volume. By Boyle's law, alveolar pressure falls below atmospheric pressure, causing air to flow into the lungs. Intrapleural pressure becomes more subatmospheric, increasing transpulmonary pressure and expanding the lungs.","src":"quizlet"},{"t":"What happens in the thoracic cavity during forced expiration?","d":"During forced expiration, contraction of internal intercostal and abdominal muscles decreases thoracic volume. This raises alveolar pressure above atmospheric, driving air out of the lungs. The increase in intrapleural pressure during forced expiration also compresses small conducting airways, decreasing their radii.","src":"quizlet"},{"t":"What are the two forms of respiration?","d":"1) Internal (cellular) respiration: utilization of oxygen in the metabolism of organic molecules by cells.\n2) Pulmonary (external) respiration: the exchange of oxygen and carbon dioxide between an organism and the external environment, which is the subject of respiratory physiology.","src":"quizlet"},{"t":"Where in the airways does gas exchange begin?","d":"Gas exchange begins at the respiratory bronchioles, which are the first airways to have alveoli attached to their walls. The region from the respiratory bronchioles onward is called the respiratory zone.","src":"quizlet"},{"t":"Where does the vast majority of gas exchange occur in the lungs?","d":"The vast majority of gas exchange occurs at the alveolar ducts and alveolar sacs, which are located in the respiratory zone beyond the respiratory bronchioles. These structures have the greatest alveolar surface area.","src":"quizlet"},{"t":"What is a right-to-left intrapulmonary shunt?","d":"A condition in which blood perfuses alveoli that receive no ventilation (e.g., collapsed alveoli). The blood passes through the lung without being oxygenated, mixing with oxygenated blood in the pulmonary veins and lowering arterial PO₂. Arterial PCO₂ usually does not increase because the hypoxemia reflexively stimulates increased ventilation.","src":"quizlet"},{"t":"What is one non-respiratory function of the lungs related to blood clots?","d":"The lungs act as a sieve that traps and dissolves small blood clots (thrombi) generated in the systemic circulation, preventing them from reaching the systemic arterial blood and occluding vessels in other organs.","src":"quizlet"},{"t":"Due to gravity, how does blood-vessel filling differ between the top and bottom of the lung?","d":"Gravity increases the filling of blood vessels at the bottom of the lung relative to the top, contributing to a regional difference in blood-flow distribution. This ventilation-perfusion inequality causes the PO₂ of pulmonary venous (systemic arterial) blood to be approximately 5 mmHg less than average alveolar PO₂.","src":"quizlet"},{"t":"Why does perfusion (blood flow) increase as you go from the top to the bottom of the lung?","d":"Gravity: upright posture increases the filling of blood vessels at the bottom of the lung, so perfusion is greater at the lung base than at the apex.","src":"quizlet"},{"t":"What happens to H+ generated in the RBC by the carbonic anhydrase-catalyzed reaction?","d":"CO₂ + H₂O is converted to H₂CO₃, then to HCO₃⁻ + H⁺ in the erythrocyte (catalyzed by carbonic anhydrase). The H⁺ produced is buffered by deoxyhemoglobin (forming HbH), so venous blood becomes only slightly more acidic than arterial blood. Carbaminohemoglobin forms by a separate reaction (CO₂ binding to globin amino groups).","src":"quizlet"},{"t":"How is CO₂ distributed when it exits the tissues and enters the bloodstream?","d":"~10% remains dissolved in plasma and erythrocyte cytosol.\n~25–30% enters erythrocytes and combines with hemoglobin amino groups to form carbaminohemoglobin.\n~60–65% enters erythrocytes and is converted to HCO₃⁻ via carbonic anhydrase (CO₂ + H₂O → H₂CO₃ → HCO₃⁻ + H⁺); most HCO₃⁻ then moves into plasma via the chloride shift.","src":"quizlet"},{"t":"What is diffusion impairment in terms of gas exchange?","d":"A condition in which blood PO₂ and alveolar PO₂ fail to equilibrate, caused by thickening of the alveolar membranes or a decrease in their surface area.","src":"quizlet"},{"t":"Where is the respiratory rhythm generator located, and what do the central chemoreceptors (CCRs) do?","d":"The respiratory rhythm generator is located in the pre-Bötzinger complex of the ventral respiratory group (VRG) and sets the basal respiratory rate. The central chemoreceptors, located in the medulla, provide excitatory synaptic input to the medullary inspiratory neurons (they do not drive the rhythm generator itself).","src":"quizlet"},{"t":"What is the relative importance of central vs. peripheral chemoreceptors in the ventilatory response to increased PCO₂?","d":"Both peripheral and central chemoreceptors stimulate the medullary inspiratory neurons to increase ventilation in response to increased PCO₂/H⁺. The central chemoreceptors are the more important of the two, accounting for about 70% of the increased ventilation. The peripheral chemoreceptors respond faster to arterial changes, but central chemoreceptors dominate the overall CO₂ response.","src":"quizlet"},{"t":"What happens to hemoglobin's affinity for O₂ in a state of acidosis (increased H+)?","d":"Increased H⁺ (acidosis) decreases hemoglobin's affinity for oxygen, shifting the oxygen-hemoglobin dissociation curve to the right. This promotes unloading (release) of O₂ in the tissues; it does not decrease blood O₂ levels per se, but makes O₂ less tightly bound so more is delivered to tissues.","src":"quizlet"},{"t":"Does ventilation follow Boyle's law?","d":"Yes. The chest wall and diaphragm change lung volume, and those volume changes cause the alveolar pressure changes (by Boyle's law, P₁V₁ = P₂V₂ at constant temperature) that drive airflow into or out of the lungs.","src":"quizlet"},{"t":"Which factor has the greatest named clinical effect on hemoglobin-oxygen affinity: pH or temperature?","d":"pH (via the Bohr effect). Decreased pH (increased H⁺ or PCO₂) is the primary named mechanism by which hemoglobin's affinity for oxygen is reduced and oxygen is unloaded to tissues. Temperature also decreases O₂ affinity when elevated, but pH/CO₂ changes (the Bohr effect) are emphasized as the dominant physiological regulator of O₂ unloading at active tissues.","src":"quizlet"},{"t":"What is the difference between perfusion limitation and diffusion limitation of gas exchange?","d":"Perfusion limitation: gas exchange equilibrium between alveolar air and capillary blood is reached before blood exits the alveolar capillary, so blood flow (perfusion) is the factor limiting total O₂ uptake — this is normal at rest. Diffusion limitation: the alveolar-capillary membrane is too thick (e.g., fibrosis, pulmonary edema) or transit time is too short (e.g., heavy exercise) for equilibration to be completed, so the diffusion barrier itself limits gas transfer.","src":"quizlet"},{"t":"What is a glomus cell?","d":"The glomus cell (type I cell) is the principal chemosensory cell of the carotid and aortic bodies. It resembles a neuron, detects changes in arterial PO₂, PCO₂, and pH, and releases neurotransmitters in response to hypoxia to initiate reflex increases in ventilation and sympathetic tone.","src":"quizlet"},{"t":"When glomus cells are activated (stimulated by low O₂, high CO₂, or low pH), what do they do?","d":"Glomus cells depolarize and release neurotransmitters that activate afferent fibers of the carotid sinus branch of cranial nerve IX (glossopharyngeal nerve), relaying signals to the brainstem respiratory and cardiovascular centers. This triggers increased ventilation (hyperventilation) and sympathetic activation.","src":"quizlet"},{"t":"How does residual volume arise?","d":"During maximal forced expiration, pleural pressure exceeds airway pressure in small, non-cartilaginous (non-supported) airways, causing them to collapse. This traps air distal to the closure point in the alveoli. The volume of air remaining in the lungs after all small airways have collapsed is the residual volume.","src":"quizlet"},{"t":"On a static pressure-volume diagram, does deflation have more or less compliance than inflation?","d":"More compliance. During deflation (expiration), a greater lung volume is maintained for a given transpulmonary pressure than during inflation — meaning less pressure is required per unit volume change. This is reflected by the deflation limb sitting to the upper-left of the inflation limb on the P-V curve.","src":"quizlet"},{"t":"On a static pressure-volume diagram, do the curves of inflation and deflation superimpose on each other?","d":"No. The inflation (inspiration) and deflation (expiration) curves do not overlap; they form a loop. The deflation limb lies above and to the left of the inflation limb at any given lung volume, reflecting that less pressure is needed during deflation than during inflation to maintain the same volume. This separation is called hysteresis.","src":"quizlet"},{"t":"What is hysteresis in the context of lung mechanics?","d":"Hysteresis is the phenomenon in which the pressure-volume relationship of the lung differs between inflation (inspiration) and deflation (expiration), producing a loop rather than a single curve. At any given lung volume, less pressure is required during deflation than inflation. It arises mainly from alveolar surface tension forces (overcome by surfactant) and alveolar recruitment/derecruitment.","src":"quizlet"},{"t":"Hysteresis (lungs): how does compliance differ between inhalation and exhalation?","d":"At any given lung volume, the lung exhibits higher compliance (more volume per unit pressure) during exhalation than during inhalation. The pressure-volume curves for inhalation and exhalation do not superimpose, forming a loop whose area represents energy dissipated per breath.","src":"quizlet"},{"t":"What is the diffusion coefficient for gas diffusing through a liquid or membrane?","d":"The effective diffusion rate depends on solubility divided by the square root of molecular weight (combining Fick's law and Graham's law). This combined factor is sometimes called Krogh's diffusion coefficient (K = α × D, where α is solubility and D is the free diffusion coefficient, which itself varies as 1/√MW). CO₂ diffuses ~20× faster than O₂ across the alveolar membrane mainly because its solubility is ~24× greater, despite CO₂ being heavier.","src":"quizlet"},{"t":"Why do you survive longer when drowning in cold water than in warm water?","d":"Cold water induces hypothermia, which dramatically reduces cellular metabolic demand (approximately 5–7% per °C reduction in body temperature). This lowers tissue oxygen requirements, slowing the onset of hypoxic cell damage and extending survival time. Cold water also triggers the diving reflex (apnea, bradycardia, peripheral vasoconstriction), which redistributes blood to the heart and brain. Note: hypothermia also shifts the oxyhemoglobin dissociation curve leftward (increased Hb-O₂ affinity), which is a separate effect from reduced O₂ consumption.","src":"quizlet"}],"renal":[{"t":"What is the functional unit of the kidney, and what are its two parts?","d":"The nephron (~1 million per kidney). Each nephron consists of a renal corpuscle (the initial filtering component) and a renal tubule that extends from it.","src":"quizlet"},{"t":"What two structures make up the renal corpuscle?","d":"The glomerulus (a compact tuft of capillary loops) and Bowman's capsule (the surrounding fluid-filled capsule into which the glomerulus protrudes). The combination of a glomerulus and a Bowman's capsule constitutes a renal corpuscle.","src":"quizlet"},{"t":"What is the composition of Bowman's capsule?","d":"It is mostly Bowman's (capsular) space, a fluid-filled space; its visceral layer is composed of podocytes.","src":"quizlet"},{"t":"What are podocytes?","d":"Epithelial cells of Bowman's capsule that wrap around the glomerular capillaries; their foot-process extensions interdigitate to create filtration slits through which fluid passes into Bowman's space.","src":"quizlet"},{"t":"Name the segments of the renal tubule in order.","d":"Proximal convoluted tubule → proximal straight tubule → descending limb of the loop of Henle → thin then thick ascending limb of the loop of Henle → distal convoluted tubule → connecting tubule → collecting duct (cortical → outer medullary → inner medullary collecting duct).","src":"quizlet"},{"t":"What are the two regions of the kidney, and where are all the renal corpuscles located?","d":"The outer renal cortex and the inner renal medulla. The cortex contains all of the renal corpuscles (of both cortical and juxtamedullary nephrons).","src":"quizlet"},{"t":"Differentiate cortical and juxtamedullary nephrons by loop length and vascular supply.","d":"Cortical nephrons (~85%) have short loops of Henle that do not penetrate deep into the medulla; their efferent arterioles give rise to peritubular capillaries. Juxtamedullary nephrons (~15%) have long loops of Henle that plunge deep into the medulla; their efferent arterioles give rise to the long looping vasa recta. The juxtamedullary loops generate the hyperosmotic medullary interstitial gradient.","src":"quizlet"},{"t":"Name the three types of capillaries in the nephron and which maintains the medullary osmotic gradient.","d":"Glomerular capillaries, peritubular capillaries, and the vasa recta. The vasa recta (which loop into the medulla alongside juxtamedullary nephrons) maintain the medullary osmotic gradient via countercurrent exchange.","src":"quizlet"},{"t":"What is the function of the vasa recta?","d":"They are hairpin-loop capillaries that supply blood to the medulla and are highly permeable to solute and water; their countercurrent-exchange structure minimizes washout of the hyperosmotic medullary interstitial gradient.","src":"quizlet"},{"t":"What three layers make up the glomerular filtration barrier, and what does each restrict?","d":"(1) Fenestrated capillary endothelium — holds back blood cells but lets plasma through. (2) Basement membrane (basal lamina) — restricts larger proteins by size and charge. (3) Podocytes with filtration slits between their foot processes — restrict medium-sized proteins. Fluid filters across the endothelium, then the basement membrane, then between the podocyte foot processes.","src":"quizlet"},{"t":"Why are large plasma proteins such as albumin held back from the filtrate? (2 reasons)","d":"(1) Size selectivity: the renal corpuscle restricts movement of high-molecular-weight substances. (2) Charge selectivity: the filtration pathways in the corpuscular membranes are negatively charged and oppose the movement of plasma proteins, which are mostly also negatively charged.","src":"quizlet"},{"t":"How does the negative charge of the glomerular filtration barrier affect filterability of macromolecules?","d":"The filtration pathways are negatively charged, so they oppose (hinder) filtration of negatively charged (anionic) macromolecules such as plasma proteins. For a given size, anionic macromolecules are filtered less readily than neutral or cationic ones. (Small inorganic ions are freely filtered regardless of charge.)","src":"quizlet"},{"t":"What two components make up the juxtaglomerular apparatus (JGA)?","d":"The macula densa and the juxtaglomerular (JG) cells.","src":"quizlet"},{"t":"Describe the macula densa.","d":"A patch of cells in the wall of the ascending limb of the loop of Henle where it becomes the distal convoluted tubule (part of the JGA). It senses the amount of Na+/NaCl in the tubular fluid flowing past it; decreased Na+ delivery causes release of paracrine factors that diffuse to the nearby JG cells, activating them to release renin.","src":"quizlet"},{"t":"Describe the juxtaglomerular (JG) cells.","d":"Secretory cells in the wall of the afferent arteriole that synthesize, store, and secrete renin (an enzyme). They are also pressure-sensitive, acting as intrarenal baroreceptors that respond to stretch (afferent arteriolar pressure reflecting plasma volume).","src":"quizlet"},{"t":"What is the cell-free fluid containing only low-molecular-weight solutes that enters Bowman's space called?","d":"The glomerular filtrate, also called an ultrafiltrate.","src":"quizlet"},{"t":"What is micturition?","d":"Urination — the process of intermittently ejecting stored urine from the bladder to the outside of the body.","src":"quizlet"},{"t":"What are the major components of the urinary system?","d":"Kidneys, ureters, bladder, and urethra, plus the renal artery (perfusing) and renal vein (draining) the kidneys.","src":"quizlet"},{"t":"How do the kidneys help regulate blood volume and pressure?","d":"They regulate (1) water concentration and fluid volume and (2) inorganic ion concentration (composition), excreting just enough water and ions to keep body amounts within a narrow range. Regulating fluid volume is how they influence blood volume and pressure.","src":"quizlet"},{"t":"Where is the functional unit of the kidney found?","d":"The nephron is the functional unit; its renal corpuscles are located in the renal cortex (the loops of Henle and collecting ducts extend into the renal medulla). Note: it is the renal cortex, not the adrenal cortex.","src":"quizlet"},{"t":"Identify the key vascular and tubular structures of the nephron.","d":"Peritubular capillaries, glomerulus, collecting duct, afferent arteriole, and vasa recta. Note: the glomerulus (the capillary tuft) is distinct from Bowman's capsule (the fluid-filled capsule that surrounds it) — together they form the renal corpuscle.","src":"quizlet"},{"t":"What is mean arterial pressure (MAP)?","d":"The average pressure driving blood forward through the arteries into the tissues over the entire cardiac cycle. MAP = cardiac output × total peripheral resistance (CO × TPR).","src":"quizlet"},{"t":"What fraction of resting cardiac output goes to the kidneys, and why do kidneys receive such high blood flow?","d":"About 20% (~950–1000 mL/min of ~5000 mL/min). This large flow supports the very high GFR and the energy-intensive active Na+ reabsorption powered by Na+/K+-ATPase, which has a high O2 demand.","src":"quizlet"},{"t":"What are the three basic renal processes?","d":"Glomerular filtration, tubular reabsorption, and tubular secretion.","src":"quizlet"},{"t":"Define glomerular filtration and tubular secretion as routes by which a substance can enter the tubular lumen.","d":"A substance can gain entry to the tubular lumen (and be excreted) by glomerular filtration, by tubular secretion, or both. Filtration moves substances from the glomerular capillaries into Bowman's space; secretion moves them from peritubular plasma into the lumen.","src":"quizlet"},{"t":"What is tubular reabsorption, and in which direction does it move substances?","d":"Movement of a substance from the tubular lumen to the peritubular capillary plasma (lumen → blood). Once in the tubule, a substance can be partially or completely reabsorbed rather than excreted. Urinary excretion is the fluid that leaves at the end of the tubule.","src":"quizlet"},{"t":"Where does filtration occur in the nephron?","d":"At the renal corpuscle — plasma is filtered from the glomerular capillaries into Bowman's space (glomerular filtration).","src":"quizlet"},{"t":"Where does tubular reabsorption occur?","d":"Reabsorption (movement from the tubular lumen to peritubular capillary plasma) occurs at various sites along the entire tubule, with the proximal tubule responsible for the bulk of reabsorption.","src":"quizlet"},{"t":"Where does tubular secretion occur?","d":"Secretion (movement from peritubular plasma or the tubular cell into the tubular lumen) occurs at various sites along the tubule depending on the substance — it is not restricted to the distal convoluted tubule.","src":"quizlet"},{"t":"What is the difference between excretion and secretion in the renal system?","d":"Excretion is the appearance of a substance in the urine (its loss from the body). Tubular secretion is specifically the movement of a substance from the peritubular capillary plasma (or generated within the tubular cell) into the tubular lumen.","src":"quizlet"},{"t":"What is the equation for the amount of a substance excreted in the urine?","d":"Amount excreted = amount filtered + amount secreted − amount reabsorbed. (This applies to any substance, including urea.)","src":"quizlet"},{"t":"If a substance excreted in urine is less than its filtered load, what has occurred? If greater?","d":"Less than the filtered load: net tubular reabsorption has occurred. Greater than the filtered load: net tubular secretion has occurred.","src":"quizlet"},{"t":"Conservation of mass: what is the relationship between arterial input, venous output, and urine output in the kidney?","d":"Arterial input = venous output + urine output. Most of what enters via the renal artery returns to the blood via the renal vein (reabsorbed), and only a small fraction leaves as urine — so the claim that 'everything that goes in comes out as urine' is false.","src":"quizlet"},{"t":"What forces favor glomerular filtration, and what forces oppose it?","d":"Favoring filtration: glomerular capillary hydrostatic pressure, P_GC (~60 mmHg). Opposing filtration: fluid pressure in Bowman's space, P_BS (~15 mmHg), and the osmotic force due to plasma protein, π_GC (~29 mmHg). The protein concentration in Bowman's space is so low that π_BS is considered zero.","src":"quizlet"},{"t":"Calculate the net glomerular filtration pressure and explain why filtration occurs.","d":"Net filtration pressure = P_GC − P_BS − π_GC = 60 − 15 − 29 = 16 mmHg (outward, favoring filtration). Filtration occurs because the high glomerular capillary pressure exceeds the sum of the opposing forces. Net filtration pressure is normally positive but can fall to or below zero in pathological states.","src":"quizlet"},{"t":"How does net glomerular filtration pressure initiate urine formation?","d":"It forces an essentially protein-free filtrate of plasma out of the glomerulus into Bowman's space and then down the tubule toward the renal pelvis.","src":"quizlet"},{"t":"What is a normal glomerular capillary hydrostatic pressure (P_GC) versus the net filtration pressure?","d":"P_GC is ~60 mmHg. The net glomerular filtration pressure is much lower (~16 mmHg) because it equals P_GC (60) minus Bowman's space pressure (15) minus the plasma protein osmotic force (29).","src":"quizlet"},{"t":"What are the Starling forces governing net filtration pressure across a capillary?","d":"The four factors determining net filtration pressure (NFP) across a capillary: NFP = P_c + π_IF − P_IF − π_c, where P_c is capillary hydrostatic pressure, π_IF is interstitial-fluid osmotic force, P_IF is interstitial hydrostatic pressure, and π_c is capillary plasma-protein osmotic force.","src":"quizlet"},{"t":"What is glomerular filtration rate (GFR)?","d":"The volume of fluid filtered from the glomeruli into Bowman's space per unit time — the standard index of overall kidney function.","src":"quizlet"},{"t":"What is a normal GFR, and how is it clinically estimated?","d":"About 125 mL/min (180 L/day) in a 70 kg person — the entire plasma volume is filtered ~60 times a day. GFR is not fixed but is physiologically regulated. Creatinine clearance (~125 mL/min) is used clinically to approximate GFR.","src":"quizlet"},{"t":"What factors determine/influence GFR?","d":"Net glomerular filtration pressure, the permeability of the corpuscular membrane, and the surface area available for filtration. GFR is physiologically regulated mainly by neural and hormonal input to the afferent and efferent arterioles (which change net filtration pressure) and by neural/humoral input to the mesangial cells (whose contraction reduces capillary surface area).","src":"quizlet"},{"t":"Describe mesangial cells and their effect on GFR.","d":"Modified smooth muscle cells that surround the glomerular capillary loops; they are a distinct (third) cell type, not part of the JGA. Their contraction decreases the surface area of the capillaries, decreasing GFR at any given net filtration pressure.","src":"quizlet"},{"t":"What two things do changes in renal arteriolar resistance alter?","d":"Renal blood flow and GFR (via changes in glomerular capillary hydrostatic pressure, Pᴳᶜ).","src":"quizlet"},{"t":"How does increased afferent arteriolar resistance (constriction) affect Pᴳᶜ, GFR, renal blood flow, and blood flow to other organs?","d":"Decreased glomerular capillary pressure (Pᴳᶜ), decreased GFR, decreased renal blood flow, and increased blood flow to other organs (flow diverted).","src":"quizlet"},{"t":"How does increased efferent arteriolar resistance (constriction) affect Pᴳᶜ, GFR, and renal blood flow?","d":"Increased glomerular capillary pressure (Pᴳᶜ) and increased GFR (efferent constriction 'dams back' blood in the glomerular capillaries), but decreased renal blood flow.","src":"quizlet"},{"t":"If renal arterial pressure rises but GFR stays constant, what accommodates this? (autoregulation)","d":"Increased constriction (increased resistance) of the afferent arteriole. Afferent constriction lowers glomerular capillary pressure (Pᴳᶜ), offsetting the rise in renal arterial pressure so Pᴳᶜ and GFR remain roughly constant.","src":"quizlet"},{"t":"Describe three mechanisms responding to an increase in mean arterial pressure in the afferent arteriole.","d":"(1) Passive/'normal': increased pressure → increased Pᴳᶜ → increased GFR. (2) Myogenic regulation: increased pressure stretches arteriolar smooth muscle → reflex constriction/increased resistance → Pᴳᶜ and GFR restored toward normal. (3) Tubuloglomerular feedback: increased GFR → increased flow/NaCl past the macula densa → paracrine (adenosine) release → afferent constriction → GFR restored.","src":"quizlet"},{"t":"What is the filtered load of a substance, and what is its formula?","d":"The total amount of a nonprotein (or non-protein-bound) substance filtered into Bowman's space per unit time. Filtered load = GFR × plasma concentration of the substance.","src":"quizlet"},{"t":"What is the filtered load of glucose (textbook example)?","d":"180 g/day (GFR 180 L/day × plasma glucose 1 g/L = 180 g/day).","src":"quizlet"},{"t":"What fraction of plasma is filtered, and what happens to filtered water?","d":"About 20% of the plasma entering the glomerulus filters into Bowman's space (this ~20% is the filtration fraction); the rest leaves via the efferent arteriole. Of the ~180 L of water filtered per day, ~99% is reabsorbed so that only a small fraction (~1.5–1.8 L) is excreted.","src":"quizlet"},{"t":"What are the two processes that mediate tubular reabsorption?","d":"(1) Mediated (transcellular) transport — the major route, requiring transport proteins in the tubular cell membranes. (2) Diffusion across the tight junctions between tubular cells — a minor, paracellular route.","src":"quizlet"},{"t":"By what route does Na+ cross the tubular epithelium during reabsorption?","d":"Transcellular (transepithelial) transport: Na+ first crosses the apical (luminal) membrane into the cell, then crosses the basolateral membrane into the interstitial fluid.","src":"quizlet"},{"t":"Describe the two-step mechanism of Na+ reabsorption.","d":"(1) Na+ moves 'downhill' (passively) into the tubular cell across the apical membrane through channels/transporters. (2) Na+ is actively transported 'uphill' out of the cell across the basolateral membrane by Na+/K+-ATPase. Na+ is actively reabsorbed in all segments except the descending limb of the loop of Henle, and is never secreted.","src":"quizlet"},{"t":"How does Na+ move from the interstitial fluid into the peritubular capillary plasma (the final step of reabsorption)?","d":"By a combination of diffusion and bulk flow.","src":"quizlet"},{"t":"How is Cl- reabsorbed in the tubule relative to Na+?","d":"Cl- reabsorption is coupled to/driven by active Na+ reabsorption; Cl- can follow passively down the electrical gradient created by Na+ movement (and via cotransporters such as NKCC in the loop of Henle).","src":"quizlet"},{"t":"What is the relationship between renal O2 consumption and Na+ reabsorption?","d":"Most renal energy (and thus O2) use supports active Na+ reabsorption via Na+/K+-ATPase, so as O2 consumption increases, Na+ reabsorption increases.","src":"quizlet"},{"t":"How is glucose reabsorbed in the proximal tubule? (two transporters)","d":"Apical/luminal: secondary active Na+-glucose cotransport (SGLT) — Na+ moving down its gradient pulls glucose into the cell against its gradient. Basolateral: facilitated diffusion via the GLUT carrier. Na+ is then pumped out basolaterally by Na+/K+-ATPase.","src":"quizlet"},{"t":"What is normal glucose clearance, and what happens to all filtered glucose?","d":"Glucose clearance is normally zero because all filtered glucose is completely reabsorbed (none appears in the urine in a healthy kidney).","src":"quizlet"},{"t":"Which classes of substances are handled as 'filtration plus complete reabsorption'?","d":"Nutritionally valuable organic nutrients such as glucose and amino acids are filtered and then completely (100%) reabsorbed in the healthy kidney.","src":"quizlet"},{"t":"Which substances undergo filtration plus partial reabsorption?","d":"Electrolytes/inorganic ions (e.g., Na+) are filtered then largely but not completely reabsorbed, leaving a small amount excreted.","src":"quizlet"},{"t":"Which substances undergo filtration plus secretion?","d":"Organic anions/acids (e.g., PAH, para-aminohippurate) and organic bases are filtered and also actively secreted into the tubule.","src":"quizlet"},{"t":"Of the major solutes, which is filtered in the greatest mass per day?","d":"Sodium (Na+) — ~630 g/day filtered, the largest of the tabulated solutes (vs. glucose 180 g, urea 54 g).","src":"quizlet"},{"t":"Among Na+, glucose, and urea, which has the smallest filtered mass, greatest excreted mass, and lowest percent reabsorbed?","d":"Urea — it has the smallest filtered mass (~54 g), the greatest excreted mass (~30 g), and the lowest percent reabsorbed (~44%), because waste-product reabsorption is relatively incomplete.","src":"quizlet"},{"t":"What is transport maximum (Tm)?","d":"The maximum rate at which a mediated-transport system in the renal tubule can transport (e.g., reabsorb) a substance per unit time, reached when the transport-protein binding sites become saturated. If the filtered load exceeds the Tm, the excess substance is excreted in the urine.","src":"quizlet"},{"t":"What happens to glucose above the renal threshold?","d":"When plasma glucose exceeds its renal threshold, glucose begins to appear in the urine (glucosuria), because the filtered load exceeds the tubular transport maximum for reabsorption.","src":"quizlet"},{"t":"Why does glucose appear in the urine in diabetes mellitus?","d":"In sustained hyperglycemia, the capacity to reabsorb glucose is normal, but the greatly increased filtered load exceeds the tubular reabsorptive transport maximum, so glucose spills into the urine.","src":"quizlet"},{"t":"What is familial (renal) glucosuria?","d":"Appearance of glucose in the urine due to a genetic mutation/abnormality in the Na+-glucose cotransporter that normally mediates active glucose reabsorption in the proximal tubule (also called benign glucosuria).","src":"quizlet"},{"t":"What is a normal fasting plasma glucose concentration?","d":"About 70–110 mg/dL (fasting reference range).","src":"quizlet"},{"t":"How is urea reabsorbed, and on what does it depend?","d":"Water reabsorption in the proximal tubule increases the urea concentration inside the tubular lumen above that of the interstitial fluid/peritubular capillaries; urea then diffuses down its concentration gradient out of the lumen. Thus urea reabsorption is dependent on (passive, follows) water reabsorption.","src":"quizlet"},{"t":"What is tubular secretion?","d":"The movement of substances from the peritubular capillaries (or the tubular cell) into the tubular lumen — the third process in urine formation. The most important secreted substances are H+ and K+; organic anions (e.g., choline, creatinine) and foreign chemicals (e.g., penicillin) are also secreted. It requires active transport and is usually coupled to Na+ reabsorption.","src":"quizlet"},{"t":"What is renal clearance, and what is its formula?","d":"The volume of plasma from which a substance is completely removed ('cleared') by the kidneys per unit time. Clearance of S (Cs) = (Us × V) / Ps, where Us = urine concentration, V = urine flow rate, Ps = plasma concentration. Units are volume of plasma per unit time (mL/min or L/h).","src":"quizlet"},{"t":"What do clearance measurements tell us when compared to GFR?","d":"Clearance compares the filtered amount with the amount excreted to infer tubular handling: clearance > GFR means the substance undergoes net tubular secretion; clearance < GFR means it undergoes net tubular reabsorption.","src":"quizlet"},{"t":"How are renal clearance and GFR related?","d":"Clearance reflects the net of filtration plus secretion minus reabsorption for a substance, whereas GFR is the filtration rate at the glomerulus alone. They coincide only for an ideal marker (e.g., inulin) that is filtered but neither reabsorbed nor secreted.","src":"quizlet"},{"t":"Why is inulin used to measure GFR?","d":"Inulin is a polysaccharide (from plants, not made by the body) that is freely filtered but neither reabsorbed, secreted, nor metabolized by the tubule. Therefore the amount excreted equals the amount filtered, and its clearance equals the GFR (Cᴵₙ = GFR = Uᴵₙ × V / Pᴵₙ).","src":"quizlet"},{"t":"What are the criteria for an ideal GFR marker?","d":"The substance must be (1) freely filterable at the glomeruli, (2) neither reabsorbed nor secreted by the tubules, (3) not synthesized, broken down, or accumulated by the kidney, and (4) physiologically inert (not toxic, no effect on renal function).","src":"quizlet"},{"t":"Why is creatinine clearance a useful clinical index of GFR?","d":"Creatinine is an endogenous waste product of muscle metabolism that is filtered and not reabsorbed; it undergoes only a small amount of secretion, so creatinine clearance slightly overestimates GFR but is close enough (and far more practical than an inulin test) to be highly useful clinically.","src":"quizlet"},{"t":"What is renal plasma flow (RPF)?","d":"The total amount of plasma (blood minus red-cell volume) that passes through both kidneys per unit time — plasma flow, not whole-blood flow.","src":"quizlet"},{"t":"Describe the division of labor: what is the role of the proximal tubule?","d":"It reabsorbs most of the filtered water and nonwaste plasma solutes (about two-thirds, ~65–67%, of Na+ and water reabsorption occurs here). With K+ as a major exception, it is also the major site of solute secretion. It is the single most important segment for NaCl and water reabsorption.","src":"quizlet"},{"t":"What is the role of the loop of Henle in tubular processing?","d":"It creates the medullary osmotic gradient (countercurrent multiplier) and reabsorbs relatively large quantities of the major ions, with comparatively less water.","src":"quizlet"},{"t":"What is the role of the distal convoluted tubule and collecting ducts?","d":"These distal segments perform the fine-tuning of water and solute excretion, adjusting reabsorption (and, in a few cases, secretion) to set the final urine composition; most homeostatic controls act on these more distal segments.","src":"quizlet"},{"t":"What substances are mostly reabsorbed by the proximal tubule?","d":"Ions (Na+, K+, Cl-, Ca2+, HCO3-), glucose, amino acids, water-soluble vitamins, urea, and water — the bulk of filtered reabsorption.","src":"quizlet"},{"t":"What substance is the key example secreted by the proximal tubule?","d":"H+ (secreted via the Na+/H+ countertransporter). The proximal tubule is actually the major site of solute secretion overall, with K+ as the main exception.","src":"quizlet"},{"t":"Which transporters are in the early proximal convoluted tubule?","d":"Apical (lumen): Na+/glucose and Na+/amino-acid cotransporters (bringing Na+ and the organic solute into the cell), the Na+/H+ countertransporter (Na+ in, H+ out to lumen), and aquaporin water channels. Basolateral: Na+/K+-ATPase (3 Na+ out, 2 K+ in), a K+ channel, aquaporins, and a Na+-HCO3- cotransporter moving Na+ and HCO3- into the interstitium.","src":"quizlet"},{"t":"What is reabsorbed and secreted by the descending limb of the loop of Henle?","d":"Reabsorbed: water (the descending limb is highly permeable to water and reabsorbs it passively by osmosis; it does not reabsorb NaCl and has no active ion transport). Secreted: essentially none (no active solute secretion is attributed to it).","src":"quizlet"},{"t":"What is reabsorbed and secreted by the thick ascending limb of the loop of Henle?","d":"Reabsorbed: ions — Na+, Cl-, K+ (via the Na+-K+-2Cl- cotransporter, NKCC), plus Mg2+ and Ca2+ paracellularly; it is impermeable to water. Secreted: none net (apical K+ movement is a recycling process to sustain the NKCC, not true secretion).","src":"quizlet"},{"t":"Which transporters are in the thick ascending limb?","d":"Apical (lumen): the Na+-K+-2Cl- cotransporter (NKCC) bringing Na+/K+/2Cl- into the cell, an apical K+ channel that recycles K+ back to the lumen, and a Na+/H+ countertransporter; the segment is impermeable to water (no apical aquaporins). Basolateral: Na+/K+-ATPase, a K+ channel, and a Cl- channel.","src":"quizlet"},{"t":"Which substance is recycled in the thick ascending limb, and why?","d":"K+ — it is recycled across the apical membrane between the NKCC (Na+-K+-2Cl- cotransporter) and an apical K+ channel. Without this recycling, the lumen would run out of the K+ needed to sustain the NKCC.","src":"quizlet"},{"t":"What is reabsorbed and secreted by the distal convoluted tubule?","d":"Reabsorbed: ions — Na+ and Cl- (via the Na+-Cl- cotransporter) and Ca2+; the segment is relatively impermeable to water (water reabsorbed only under downstream vasopressin control). Secreted: K+ and H+.","src":"quizlet"},{"t":"What is reabsorbed and secreted by the collecting duct?","d":"Reabsorbed: Na+, water (vasopressin-dependent), urea (medullary collecting duct), and various ions. Secreted: K+ (the cortical collecting duct is the main site of regulated K+ secretion) and H+ (by intercalated cells).","src":"quizlet"},{"t":"What hormone upregulates Na+ reabsorption in the cortical collecting duct?","d":"Aldosterone (it increases Na+ reabsorption and K+ secretion there).","src":"quizlet"},{"t":"What type of reabsorptive environment does the kidney create?","d":"One that favors water reabsorption: active solute (mainly Na+) reabsorption establishes osmotic gradients that drive substantial water reabsorption, so that >99% of filtered water is normally reabsorbed.","src":"quizlet"},{"t":"What are the two sources of body water gain?","d":"(1) Water ingested in liquids and food. (2) Water produced from the oxidation of organic nutrients (metabolic water).","src":"quizlet"},{"t":"What are the avenues of body water loss?","d":"Four sites lose water to the external environment: skin, respiratory airways (insensible loss), gastrointestinal tract, and urinary tract — plus menstrual flow as a fifth route in women. (Sweat is a subset of skin loss.)","src":"quizlet"},{"t":"Through what channels does water move across tubular membranes?","d":"Aquaporins — water channels through which water moves by diffusion (osmosis).","src":"quizlet"},{"t":"On what is tubular water reabsorption dependent?","d":"On Na+ reabsorption: water reabsorption is passive (by osmosis) and is driven by the osmotic gradient set up by active Na+ reabsorption.","src":"quizlet"},{"t":"Where is the bulk of water reabsorbed, and how?","d":"About two-thirds (~67%) of filtered water is reabsorbed in the proximal tubule. Aquaporins are constitutively present in high numbers in these cells, so water is reabsorbed passively (by osmosis driven by Na+ reabsorption) almost as fast as Na+.","src":"quizlet"},{"t":"Where in the nephron is essentially no water reabsorbed?","d":"The ascending limb of the loop of Henle, which reabsorbs NaCl but is impermeable to water; the distal convoluted tubule is likewise relatively impermeable to water (water is normally not reabsorbed there unless vasopressin acts downstream at the collecting ducts). This water impermeability of the ascending limb underlies the countercurrent multiplier.","src":"quizlet"},{"t":"Which tubular segments have water permeability under physiological (hormonal) control?","d":"Only the cortical and medullary collecting ducts; their water permeability is controlled by vasopressin (ADH).","src":"quizlet"},{"t":"Which hormone regulates water reabsorption, and what does it act on?","d":"Vasopressin (antidiuretic hormone, ADH), a peptide hormone from the posterior pituitary. It regulates water reabsorption by controlling the insertion of a specific aquaporin (AQP2) into the apical membrane of the collecting-duct cells.","src":"quizlet"},{"t":"Which aquaporin is in the proximal tubule, and which are in the collecting duct?","d":"AQP1 is the constitutively expressed aquaporin of the proximal tubule. In the collecting duct, AQP2 is the apical, vasopressin-regulated channel, while AQP3 and AQP4 are on the basolateral membrane.","src":"quizlet"},{"t":"How does ADH/vasopressin regulate AQP2 insertion into the apical membrane?","d":"Via cAMP/protein kinase A (PKA): vasopressin binding raises intracellular cAMP, activating PKA, which phosphorylates proteins that increase fusion of pre-made AQP2-containing cytosolic vesicles with the apical membrane. (It is not via gene transcription — AQP2 is pre-formed and stored in vesicles.)","src":"quizlet"},{"t":"Are the basolateral aquaporins (AQP3/AQP4) regulated by ADH?","d":"No — the basolateral aquaporins are constitutively active and are not regulated by vasopressin.","src":"quizlet"},{"t":"What does ADH/vasopressin increase?","d":"Water permeability of the collecting ducts (by inserting AQP2 channels into the apical membrane), thereby increasing water reabsorption and decreasing urine volume.","src":"quizlet"},{"t":"What role does the collecting duct play during dehydration vs. overhydration?","d":"During dehydration (high vasopressin) it becomes water-permeable, reabsorbing water to rehydrate the body (small, concentrated urine). During overhydration (low vasopressin) it is water-impermeable, excreting the excess water (large, dilute urine).","src":"quizlet"},{"t":"What is the most important factor determining how much water is excreted, and how is it controlled?","d":"The rate of water reabsorption (water excretion = volume filtered (GFR) - volume reabsorbed). This is controlled physiologically by vasopressin (ADH); total-body water is regulated mainly by reflexes that alter vasopressin secretion.","src":"quizlet"},{"t":"Describe the production and control of ADH/vasopressin.","d":"Vasopressin is a peptide hormone produced by hypothalamic neurons (the supraoptic and paraventricular nuclei) and secreted from the posterior pituitary. Osmoreceptors in the hypothalamus sense increased plasma osmolarity and reflexively increase its secretion. Its mechanism is to alter the water permeability of the luminal (apical) membrane of collecting-duct cells.","src":"quizlet"},{"t":"What is diuresis, and what happens to the collecting duct in the absence of ADH?","d":"Diuresis is a large urine flow from any cause. Without vasopressin, the collecting-duct cells are almost impermeable to water (minimal apical AQP2), so very little water is reabsorbed and a large volume of water is excreted (water diuresis).","src":"quizlet"},{"t":"What is central diabetes insipidus?","d":"Failure of the hypothalamic neurons to synthesize or release vasopressin from the posterior pituitary, leading to a large volume of dilute urine.","src":"quizlet"},{"t":"What is water (nonosmotic) diuresis?","d":"Increased urine flow in which only excess water is excreted without an increase in solute excretion (e.g., from low vasopressin). It is not necessarily accompanied by equivalent solute loss.","src":"quizlet"},{"t":"What is osmotic diuresis?","d":"Increased urine flow resulting from a primary increase in solute excretion, where the unreabsorbed solute retains water in the tubular lumen. Example: uncontrolled diabetes mellitus, where filtered glucose that escapes reabsorption causes osmotic diuresis (with thirst and increased drinking).","src":"quizlet"},{"t":"What is the effect of increased ADH (e.g., from water deprivation, pain, hot weather, or shock)?","d":"Antidiuresis: water reabsorption by the collecting ducts increases, and a small volume of highly concentrated urine is excreted. Water deprivation raises plasma osmolarity, stimulating osmoreceptors, which increase ADH release, increasing renal water retention and thirst.","src":"quizlet"},{"t":"What is the effect of decreased ADH (e.g., from excess water intake or alcohol)?","d":"Water diuresis: water reabsorption falls and a large volume of dilute (hypoosmotic) urine is excreted. Excess water intake lowers plasma osmolarity, inhibiting osmoreceptors and ADH secretion; ethanol also inhibits vasopressin release.","src":"quizlet"},{"t":"How are total-body sodium and extracellular fluid volume related?","d":"Total-body sodium (the amount of Na+) is closely linked to extracellular fluid volume: because Na+ and its anions make up ~90% of extracellular solutes, changes in total-body sodium produce proportional changes in ECF (and plasma) volume. (It is the amount of Na+, not its concentration, that determines volume.)","src":"quizlet"},{"t":"What two cardiovascular variables change when total-body sodium changes?","d":"Blood (plasma) volume and blood pressure. Low total-body sodium leads to low plasma volume and decreased cardiovascular pressures.","src":"quizlet"},{"t":"What mainly determines plasma osmolarity?","d":"Plasma Na+ concentration — because Na+ (with its associated anions) accounts for ~90% of extracellular solutes, plasma osmolarity is dominated by plasma Na+.","src":"quizlet"},{"t":"How is Na+ handled by the nephron, and what is the equation for Na+ excretion?","d":"Na+ is freely filtered and actively reabsorbed but never secreted. Therefore: Na+ excreted = Na+ filtered - Na+ reabsorbed. Total-body sodium varies only a few percent even though intake and loss range widely; excretion is physiologically regulated by changing Na+ reabsorption.","src":"quizlet"},{"t":"How is low plasma sodium/volume handled short-term vs. long-term?","d":"Short-term: baroreceptors initiate reflexes that decrease GFR and increase Na+ reabsorption. Long-term: aldosterone promotes Na+ reabsorption (more important than GFR control long-term); renin and angiotensin II are required for aldosterone secretion.","src":"quizlet"},{"t":"What hormone is central to the long-term handling of low sodium, and what does it require?","d":"Aldosterone promotes Na+ reabsorption; its secretion requires angiotensin II (produced via the renin-angiotensin system) acting on the adrenal cortex.","src":"quizlet"},{"t":"How does atrial natriuretic peptide (ANP) respond to high plasma sodium/volume?","d":"ANP increases Na+ (and water) excretion: it acts on tubular segments to inhibit Na+ reabsorption, acts on renal blood vessels to increase GFR, and directly inhibits aldosterone secretion.","src":"quizlet"},{"t":"Where is ANP synthesized and secreted, and what stimulates its secretion?","d":"ANP is synthesized and secreted by cells in the cardiac atria. Its secretion is stimulated by increased plasma volume/total-body sodium, with the specific direct stimulus being increased atrial distension (not a change in Na+ concentration itself).","src":"quizlet"},{"t":"Describe aldosterone: its source, trigger, and main action.","d":"A steroid hormone secreted by the adrenal cortex. Low plasma volume/low sodium triggers its release (via angiotensin II). It stimulates Na+ reabsorption in the late distal tubule (distal convoluted tubule) and cortical collecting ducts.","src":"quizlet"},{"t":"What are the three actions of aldosterone on Na+?","d":"(1) Induces synthesis of Na+ transport proteins (channels and pumps); (2) stimulates Na+ reabsorption; (3) reduces Na+ excretion. (It acts slowly because it alters gene expression and protein synthesis.)","src":"quizlet"},{"t":"Aldosterone-driven Na+ reabsorption in the cortical collecting duct is linked to secretion of what ion?","d":"K+. Aldosterone simultaneously stimulates Na+ reabsorption and enhances K+ secretion in the cortical collecting duct.","src":"quizlet"},{"t":"What three factors regulate aldosterone secretion?","d":"(1) Dietary Na+ content and (2) total-body sodium status (low sodium raises it, high sodium lowers it), which act by changing (3) plasma angiotensin II, which acts directly on the adrenal cortex to stimulate aldosterone secretion.","src":"quizlet"},{"t":"What effect does high vs. low Na+ intake have on aldosterone secretion?","d":"High Na+ intake -> low aldosterone secretion. Low Na+ intake or Na+ depletion -> high aldosterone secretion.","src":"quizlet"},{"t":"Where is renin secreted, and what is the renin-angiotensin system pathway?","d":"Renin is an enzyme secreted by the juxtaglomerular cells of the JGA. Pathway: angiotensinogen --(renin)--> angiotensin I --(ACE)--> angiotensin II --> stimulates aldosterone secretion (and constricts arterioles). This system regulates blood pressure and fluid balance.","src":"quizlet"},{"t":"What is the main action of angiotensin II on blood vessels?","d":"It is a potent constrictor of arterioles, increasing peripheral resistance and thereby raising arterial blood pressure.","src":"quizlet"},{"t":"Trace the cascade triggered by NaCl depletion through to Na+ excretion.","d":"NaCl depletion -> increased renin secretion -> increased plasma renin -> increased angiotensin I -> increased angiotensin II -> increased aldosterone release -> increased plasma aldosterone -> increased Na+ transporter synthesis/insertion -> increased Na+ reabsorption -> DECREASED Na+ excretion.","src":"quizlet"},{"t":"What three inputs to the JG cells trigger renin secretion?","d":"(1) Increased renal sympathetic nerve activity (via extrarenal baroreceptor reflexes); (2) decreased renal arterial pressure sensed as decreased stretch of the JG cells (intrarenal baroreceptors); (3) decreased NaCl delivery/concentration sensed by the macula densa.","src":"quizlet"},{"t":"How does stretch of the JG cells affect renin release?","d":"Decreased stretch (low circulating volume/low renal arterial pressure) stimulates renin release; increased stretch (higher pressure/volume) inhibits renin release.","src":"quizlet"},{"t":"What is the most important trigger for aldosterone release?","d":"The renin-angiotensin system (angiotensin II acting on the adrenal cortex).","src":"quizlet"},{"t":"What are baroreceptors, and where are they located?","d":"Stretch-sensitive nerve endings/cells that respond to pressure. Locations: carotid sinus and aortic arch (arterial), major veins/atria (venous/cardiac), and intrarenal (the JG cells of the juxtaglomerular apparatus).","src":"quizlet"},{"t":"How do baroreceptors work?","d":"They sense changes in cardiovascular pressure/stretch (reflecting blood volume and peripheral resistance). A change in blood pressure changes stretch, which changes the frequency of nerve impulses; this afferent information is processed centrally (medulla oblongata/brainstem) and adjusts autonomic (ANS) outflow.","src":"quizlet"},{"t":"What initiates the short-term regulation of low plasma volume (reflecting low sodium)?","d":"Cardiovascular baroreceptors — they sense the lower pressures and initiate reflexes that decrease GFR and increase Na+ reabsorption.","src":"quizlet"},{"t":"What do intrarenal baroreceptors (JG cells) sense?","d":"Decreased intrarenal (afferent arteriolar) pressure — when kidney blood pressure falls, the JG cells are stretched less and secrete more renin.","src":"quizlet"},{"t":"What is the equation for K+ excretion?","d":"K+ excreted = K+ filtered - K+ reabsorbed + K+ secreted. (K+ is freely filtered, mostly reabsorbed, with regulated secretion in the cortical collecting duct.)","src":"quizlet"},{"t":"Where is most filtered K+ reabsorbed, and where is urinary K+ regulated?","d":"Most filtered K+ is reabsorbed in the proximal tubule and loop of Henle. Urinary K+ is regulated mainly by K+ secretion into the tubule by cells of the distal and (especially cortical) collecting ducts — changes in K+ excretion are due mainly to changes in secretion by this segment.","src":"quizlet"},{"t":"How is K+ secreted in the cortical collecting duct?","d":"K+ is pumped into the cell across the basolateral membrane by Na+/K+-ATPase and then diffuses into the tubular lumen through apical K+ channels; this secretion is coupled to Na+ reabsorption in the segment.","src":"quizlet"},{"t":"What is hyperkalemia, and why are K+ deviations dangerous?","d":"Hyperkalemia is excess K+ in the blood (extracellular fluid); hypokalemia is a decrease. Deviations in extracellular K+ can cause cardiac arrhythmias and abnormalities of skeletal-muscle contraction and neuronal conduction — potentially life-threatening.","src":"quizlet"},{"t":"What controls homeostasis of K+ in the body?","d":"The aldosterone-secreting cells of the adrenal cortex, which are directly sensitive to extracellular K+: increased plasma K+ stimulates aldosterone, which enhances K+ secretion in the cortical collecting duct. (Plasma K+ also acts directly on the cortical collecting duct.)","src":"quizlet"},{"t":"How do changes in extracellular K+ alter aldosterone and urinary K+ excretion?","d":"Increased extracellular K+ -> stimulates aldosterone production -> MORE K+ secreted/excreted in urine. Decreased extracellular K+ -> decreased aldosterone production -> LESS K+ excreted in urine.","src":"quizlet"},{"t":"What is intracellular fluid?","d":"The fluid contained inside all the cells of the body.","src":"quizlet"},{"t":"What is extracellular fluid, and what are its components?","d":"Fluid outside the cells; it is composed of plasma (the noncellular portion of blood) plus interstitial fluid. Total ECF volume = plasma volume + interstitial fluid volume.","src":"quizlet"},{"t":"What is interstitial fluid?","d":"The fluid that lies around and between cells, in the space known as the interstitium.","src":"quizlet"},{"t":"What is osmosis?","d":"The net movement of water across a semipermeable membrane (permeable to water but not solutes) from a region of high water concentration to a region of lower water concentration.","src":"quizlet"},{"t":"What is osmotic pressure?","d":"The opposing pressure that must be applied to a solution to prevent (stop) the net flow of water into it by osmosis.","src":"quizlet"},{"t":"In an isotonic solution, how do the osmolarities inside and outside the cell compare?","d":"They are the same — the cell neither swells nor shrinks. (Isotonic solutions have the same concentration of nonpenetrating solutes as normal extracellular fluid.)","src":"quizlet"},{"t":"What does hypertonic mean in terms of osmolarity?","d":"The outside environment has a higher osmolarity (of nonpenetrating solutes) than the inside of the cell, so water leaves the cell and it shrinks.","src":"quizlet"},{"t":"What determines the tonicity of a solution?","d":"The concentration of non-penetrating solutes relative to the cell interior (not total osmolarity). Penetrating solutes that readily cross the membrane do not contribute to tonicity.","src":"quizlet"},{"t":"What is the body's volatile acid, and how is it eliminated?","d":"CO2 (the source of carbonic acid). CO2 + H2O react (via carbonic anhydrase) to form H2CO3, which dissociates into HCO3- and H+. The reaction is reversible: H+ generated in the tissues is reincorporated into water in the lungs, where CO2 is exhaled as a gas. This contrasts with nonvolatile acids.","src":"quizlet"},{"t":"Give examples of nonvolatile acids.","d":"Phosphoric acid and sulfuric acid (generated mainly by protein catabolism), plus lactic acid and several other organic acids — organic and inorganic acids from sources other than CO2.","src":"quizlet"},{"t":"Which nonvolatile acid is produced during exercise?","d":"Lactic acid (produced during severe exercise or hypoxia).","src":"quizlet"},{"t":"What is the normal pH range of extracellular fluid, and what pH range is fatal?","d":"Normal ECF pH is 7.35–7.45 (about 7.4, slightly alkaline). A pH outside the range of 6.8–7.8 is incompatible with life if maintained.","src":"quizlet"},{"t":"What is acidosis, and what is alkalosis?","d":"Acidosis: arterial plasma H+ concentration is increased above normal (pH < 7.4) — gain of H+ exceeds loss. Alkalosis: arterial plasma H+ concentration is decreased below normal (pH > 7.4) — loss of H+ exceeds gain.","src":"quizlet"},{"t":"Why are metabolic reactions sensitive to H+ concentration?","d":"Because H+ influences the tertiary structure (shape) of proteins such as enzymes; even small pH changes alter protein shape and thus function.","src":"quizlet"},{"t":"What are the four sources of H+ ion gain?","d":"(1) Generation of H+ from CO2; (2) production of nonvolatile acids from the metabolism of proteins and other organic molecules; (3) gain of H+ due to loss of HCO3- in diarrhea or other nongastric GI fluids; (4) gain of H+ due to loss of HCO3- in the urine.","src":"quizlet"},{"t":"What are the four sources of H+ ion loss?","d":"(1) Utilization of H+ in the metabolism of various organic anions; (2) loss of H+ in vomitus; (3) loss of H+ (primarily as H2PO4- and NH4+) in the urine; (4) hyperventilation (loss of CO2).","src":"quizlet"},{"t":"What is a buffer?","d":"Any substance that can reversibly bind H+ (it can release H+ as well as bind it).","src":"quizlet"},{"t":"Where is most H+ buffered?","d":"By extracellular and intracellular buffers — most H+ is bound by buffers in both compartments.","src":"quizlet"},{"t":"What is the major extracellular buffer system, and what are the major intracellular buffers?","d":"Major extracellular buffer system: CO2/HCO3-. Major intracellular buffers: phosphates and proteins (e.g., hemoglobin as an intracellular protein buffer).","src":"quizlet"},{"t":"Where is H+ generated as blood passes through the body?","d":"In the peripheral tissues — CO2 from oxidative metabolism reacts (CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+) to generate H+ as blood passes through peripheral tissues.","src":"quizlet"},{"t":"What two organ systems together balance H+ within a narrow range, and what is each one's timing role?","d":"The kidneys and the lungs (respiratory system). The respiratory response is rapid (minutes) — a short-term role — while the kidneys respond slowly (hours to days) and are ultimately responsible for eliminating the imbalance (long-term/ultimate balancers).","src":"quizlet"},{"t":"What are three respiratory causes of an H+ (acid-base) imbalance?","d":"Hyperventilation, hypoventilation, and respiratory malfunction.","src":"quizlet"},{"t":"How is ventilation adjusted when an H+ imbalance is due to a non-respiratory cause?","d":"Ventilation is reflexively altered to help compensate for (oppose) the imbalance.","src":"quizlet"},{"t":"How do increases and decreases in arterial H+ affect ventilation?","d":"An increased arterial H+ concentration stimulates ventilation (lowering arterial PCO2 and, by mass action, reducing H+). A decreased H+ concentration inhibits ventilation (raising PCO2 and H+).","src":"quizlet"},{"t":"Why is losing H+ from the body equivalent to gaining HCO3-?","d":"Loss of H+ drives the CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+ reaction to the right (mass action), generating HCO3-; conversely, adding HCO3- to plasma lowers plasma H+ just as if H+ had been removed. So gaining HCO3- is the same as losing H+.","src":"quizlet"},{"t":"In alkalosis, what is the kidney's homeostatic response?","d":"The kidneys excrete large quantities of HCO3- (bicarbonate), which raises plasma H+ back toward normal and restores acid-base balance.","src":"quizlet"},{"t":"In acidosis, what is the kidney's homeostatic response?","d":"The kidney tubular cells produce new HCO3- and add it to the plasma (they do not excrete HCO3-), which lowers plasma H+ back toward normal.","src":"quizlet"},{"t":"On what does HCO3- reabsorption depend?","d":"On tubular H+ secretion: HCO3- reabsorption is an active process (not done conventionally) in which secreted H+ combines in the lumen with filtered HCO3-.","src":"quizlet"},{"t":"Normally, how much filtered HCO3- is reabsorbed, and where?","d":"Normally all filtered HCO3- is reabsorbed (except in response to alkalosis), preventing loss of HCO3- in the urine. Reabsorption occurs in the proximal tubule, the ascending loop of Henle, and the cortical collecting ducts.","src":"quizlet"},{"t":"Why does the H+ transport mechanism vary among tubular segments?","d":"Because, depending on the tubular segment, H+ secretion is achieved by different combinations of primary H+-ATPase pumps, primary H+/K+-ATPase pumps, and Na+/H+ countertransporters.","src":"quizlet"},{"t":"What is mechanism 1 for adding new HCO3- to plasma in acidosis (when secreted H+ exceeds luminal HCO3-)?","d":"(1) The extra secreted H+ binds to a filtered nonbicarbonate buffer, mainly HPO4²-, and is excreted as H2PO4-. (2) The HCO3- generated within the tubular cell diffuses into the plasma. (3) Net result: a net gain of HCO3- by the plasma.","src":"quizlet"},{"t":"What is mechanism 2 for adding new HCO3- to plasma in acidosis (glutamine metabolism / ammonium excretion)?","d":"Mainly proximal-tubule cells take up glutamine from the glomerular filtrate or peritubular plasma; NH4+ and HCO3- are formed inside the cells; NH4+ is secreted via Na+/NH4+ countertransport into the lumen and excreted; the HCO3- is added to the plasma.","src":"quizlet"},{"t":"What is respiratory acidosis?","d":"Acidosis from decreased ventilation (hypoventilation / CO2 retention, e.g., in emphysema), causing increased blood PCO2 and H+. The kidney compensates by secreting H+ and adding new HCO3- to the blood, lowering plasma H+; urine becomes acidic.","src":"quizlet"},{"t":"What is respiratory alkalosis?","d":"Alkalosis from hyperventilation (excessive CO2 elimination, e.g., at high altitude), causing decreased blood PCO2 and H+. The kidney compensates by excreting HCO3-; urine becomes alkaline.","src":"quizlet"},{"t":"Can the kidneys excrete both acidic and basic urine?","d":"Yes — the kidneys can excrete acidic urine (lowest attainable pH ~4.4, in acidosis) or alkaline/basic urine (pH > 7.4, in alkalosis).","src":"quizlet"},{"t":"What is metabolic acidosis, and what are its causes and consequences?","d":"Increased plasma H+ from causes such as diarrhea (loss of HCO3-), severe exercise (lactic acid), and uncontrolled diabetes mellitus (ketones). It causes a reflexive increase in ventilation (hyperventilation) and increased renal H+ secretion.","src":"quizlet"},{"t":"What is metabolic alkalosis, and what are its cause and consequences?","d":"Decreased plasma H+, occurring after prolonged/persistent vomiting (loss of H+ as HCl from the stomach). It causes a reflexive decrease in ventilation (hypoventilation) and increased renal HCO3- excretion.","src":"quizlet"},{"t":"How does the loop of Henle create a hyperosmotic medullary interstitium (countercurrent multiplication)?","d":"In the loop of Henle, opposing (countercurrent) flows in the descending and ascending limbs, combined with active NaCl reabsorption in the water-impermeable ascending limb, set up a transverse ~200 mOsm/L gradient between the interstitium and the ascending-limb fluid. This 'single effect' is multiplied along the length of the loop, so osmolarity rises from ~300 mOsm/L at the top to as high as ~1400 mOsm/L at the bottom (bend) of the loop.","src":"quizlet"},{"t":"Through which limb of the loop of Henle is water reabsorbed, and where is salt reabsorbed?","d":"Water is reabsorbed passively (by osmosis) only through the thin descending limb, which is highly permeable to water. NaCl is reabsorbed through the thick ascending limb, which is impermeable to water (so no water follows the salt).","src":"quizlet"},{"t":"What is the mechanism of water reabsorption in the large distal tubule and collecting duct?","d":"Passive (osmosis). In the collecting ducts, vasopressin inserts AQP2 into the apical membrane, and AQP3/AQP4 on the basolateral membrane carry water into the interstitium. (The distal convoluted tubule itself is relatively impermeable to water.)","src":"quizlet"},{"t":"What happens to tubular fluid osmolarity in the descending limb vs. the ascending limb of the loop?","d":"In the descending limb the fluid becomes concentrated (water leaves into the hyperosmotic interstitium). In the ascending limb the fluid is diluted (NaCl leaves but water cannot follow), so the fluid entering the distal convoluted tubule is hypoosmotic (~100 mOsm/L, more dilute than plasma).","src":"quizlet"},{"t":"At what point in the nephron does tubular fluid first become dilute (hypoosmotic)?","d":"In the thick ascending limb of the loop of Henle — NaCl is reabsorbed while water cannot follow, so the fluid entering the distal convoluted tubule is hypoosmotic (~100 mOsm/L).","src":"quizlet"},{"t":"What is the osmolarity of tubular fluid leaving the proximal tubule, and why?","d":"Isosmotic with plasma (~300 mOsm/L), because the proximal tubule reabsorbs Na+ and water in the same proportions (isosmotic reabsorption).","src":"quizlet"},{"t":"In the presence of ADH, what osmolarity does fluid in the cortical collecting duct reach?","d":"Isosmotic (~300 mOsm/L) with the cortical interstitial fluid/peritubular plasma. Vasopressin makes the duct water-permeable, so water leaves the hypoosmotic fluid until it equilibrates at ~300 mOsm/L.","src":"quizlet"},{"t":"Why does water move out of the medullary collecting duct, and what is the result?","d":"The high osmolarity established in the medullary interstitium (by the loop countercurrent multiplier and urea trapping) draws water out of the medullary collecting duct (when vasopressin is present), concentrating the duct fluid/urine (up to ~1400 mOsm/L). In water diuresis the fluid stays dilute.","src":"quizlet"},{"t":"How does the vasa recta help countercurrent exchange and preserve the medullary gradient?","d":"(1) The vasa recta form hairpin loops acting as countercurrent exchangers, so solute/water diffusing out of the descending vessel is largely reversed in the ascending vessel, minimizing washout. (2) Total blood flow through all vasa recta is only a small percentage of total renal blood flow, limiting washout of the hypertonic interstitium. (3) They are freely permeable to ions, urea, and water, which move in/out by diffusion (with bulk-flow uptake of reabsorbed salt and water), maintaining the steady-state gradient.","src":"quizlet"},{"t":"Why does the kidney need to produce concentrated urine?","d":"To save water by producing hyperosmotic urine, minimizing the rate of dehydration during limited water intake — a major determinant of survival with limited water.","src":"quizlet"},{"t":"What are the five mechanisms that maintain the hyperosmotic medullary environment?","d":"(1) Countercurrent anatomy and opposing fluid flow in the loops of Henle of juxtamedullary nephrons; (2) reabsorption of NaCl in the ascending limbs; (3) impermeability of those ascending limbs to water; (4) trapping of urea in the medulla; (5) hairpin loops of the vasa recta to minimize washout.","src":"quizlet"},{"t":"Describe the recycling and trapping of urea (with percentages).","d":"~50% of filtered urea is reabsorbed in the proximal tubule; the remaining 50% enters the loop of Henle and is secreted back into the thin limbs by facilitated diffusion, so ~100% enters the distal tubule. ~30% is reabsorbed from the distal tubule + cortical collecting duct, and ~55% from the medullary collecting duct (aided by ADH); only ~5% diffuses into the vasa recta with the rest secreted back into the loop. Recycling plus minimal vasa-recta uptake maintains high medullary osmolarity; ~15% of originally filtered urea is excreted.","src":"quizlet"},{"t":"Where in the nephron is urea most important to osmolality, and how much does it contribute?","d":"In the inner medulla — urea trapped there by recycling contributes at least about half of the solute (osmolarity) of the medullary interstitium.","src":"quizlet"},{"t":"What kind of flow occurs between the descending and ascending limbs of the loop of Henle?","d":"Countercurrent flow — the opposing flows in the two limbs form the countercurrent multiplier system.","src":"quizlet"},{"t":"What happens to loop-of-Henle osmolarity during water diuresis vs. antidiuresis?","d":"In both states, osmolarity rises along the descending limb (water leaves into the hyperosmotic interstitium) then falls below isosmotic in the water-impermeable ascending limb (NaCl reabsorbed via NKCC). The descending-limb peak osmolarity is higher in antidiuresis (vasopressin increases medullary urea trapping) and lower in water diuresis.","src":"quizlet"},{"t":"What happens to osmolarity in the distal convoluted tubule during water diuresis vs. antidiuresis?","d":"The fluid in the distal convoluted tubule is hypoosmotic (below isosmotic) in both states, because vasopressin does not act before the collecting ducts. The fluid does not return to isosmotic until the cortical collecting duct (during antidiuresis).","src":"quizlet"},{"t":"What is the normal isosmotic (plasma) osmolarity level?","d":"About 300 mOsm/L (plasma osmolarity typically 285–300 mOsmol/L, rounded to ~300).","src":"quizlet"},{"t":"By the end of the collecting duct, what two states can the urine be in?","d":"Either dilute (hypoosmotic, with low vasopressin) or concentrated (hyperosmotic, with high vasopressin).","src":"quizlet"},{"t":"What is the most concentrated and most dilute urine the kidney can produce?","d":"Maximal urinary concentration is ~1400 mOsmol/L (almost five times plasma osmolarity); the dilute extreme is very hypoosmotic, far below the ~300 mOsmol/L of plasma.","src":"quizlet"},{"t":"What does a very dilute urine (e.g., ~30–120 mOsmol/L) indicate?","d":"Overhydration / water diuresis — a hypoosmotic urine (well below the ~300 mOsmol/L of plasma) reflects low vasopressin. (Dehydration instead produces concentrated, hyperosmotic urine up to ~1400 mOsmol/L.)","src":"quizlet"},{"t":"At what osmolarity is urine excreted during water diuresis vs. antidiuresis?","d":"Water diuresis (low vasopressin): dilute, hypoosmotic urine far below 300 mOsmol/L. Antidiuresis (high vasopressin): concentrated, hyperosmotic urine up to ~1400 mOsmol/L.","src":"quizlet"},{"t":"What mass of solute (osmoles) must be excreted in the urine per day?","d":"About 600 mOsmol/day — the typical daily obligatory excretion of urea, sulfate, phosphate, other waste products, and ions.","src":"quizlet"},{"t":"How much urine is produced per day in extreme water diuresis vs. extreme water restriction?","d":"Extreme water diuresis: up to ~25 L/day. Extreme water restriction: as low as ~0.4 L/day (the obligatory minimum). Urinary water excretion ranges from ~0.4 to ~25 L/day.","src":"quizlet"},{"t":"Where does K+ recycling occur in the nephron, and what is the mechanism?","d":"K+ recycling occurs in the ascending limb of the loop of Henle. K+ absorbed through NKCC2 (Na-K-2Cl cotransporter) is recycled back to the tubular lumen through an apical ROMK potassium channel. Without this recycling, the tubular lumen would run out of the K+ needed to drive NKCC2.","src":"quizlet"},{"t":"How does countercurrent exchange in the vasa recta preserve the hypertonic medullary gradient?","d":"The vasa recta is permeable to salt, urea, and water. As blood flows down the descending limb, NaCl diffuses into the vessel from the interstitium and water diffuses out; in the ascending limb both processes are reversed (NaCl exits, water re-enters). This hairpin-loop mechanism minimizes washout of the hypertonic medullary interstitium — it preserves rather than creates the gradient established by the loops of Henle — thereby maintaining the high osmolarity of the renal medullary interstitial space.","src":"quizlet"},{"t":"What is the common range for renal clearance in mL/min?","d":"0 mL/min (substances completely reabsorbed, e.g., glucose) to approximately 600–720 mL/min (substances completely removed in one pass, e.g., PAH, which approximates renal plasma flow).","src":"quizlet"},{"t":"Rank the following from most to least filterable: inulin, Na+/K+/Cl−/glucose, serum albumin, hemoglobin.","d":"Most to least filterable:\n1. Na+/K+/Cl−/glucose — small ions and organic solutes; freely filtered.\n2. Inulin — small neutral polysaccharide (~5 kDa); freely filtered.\n3. Hemoglobin (~65 kDa) — large but smaller and less negatively charged than albumin.\n4. Serum albumin (~69 kDa, highly negatively charged) — barely crosses the glomerular barrier.","src":"quizlet"},{"t":"How is the transepithelial membrane potential created in the early proximal tubule?","d":"In the early proximal tubule the lumen is lumen-negative (~−1 to −2 mV). Electrogenic Na+ entry across the apical membrane (via Na+-glucose cotransport and Na+-H+ exchange) moves net positive charge into the cell, leaving the lumen relatively negative. Na+ is then extruded across the basolateral membrane by Na+/K+-ATPase into the interstitial space, producing this small lumen-negative transepithelial potential difference.","src":"quizlet"},{"t":"What is unique about the transepithelial membrane potential in the thick ascending limb (TAL)?","d":"The TAL has a lumen-positive transepithelial potential (lumen positive relative to the interstitium), opposite to most nephron segments. It is generated by K+ recycling back into the lumen via apical ROMK channels (after entry via NKCC2) combined with Cl− exit across the basolateral membrane, creating net positive charge in the lumen. This potential drives paracellular reabsorption of Na+, Ca2+, and Mg2+.","src":"quizlet"},{"t":"How is excess K+ removed from the body?","d":"Excess K+ is first buffered acutely by shifting into cells (especially skeletal muscle), mediated by insulin and catecholamines activating Na+/K+-ATPase. This temporary intracellular storage prevents dangerous hyperkalemia until the kidney slowly excretes the K+ load over hours.","src":"quizlet"},{"t":"What types of stimuli and receptors on muscle cells increase Na+/K+-ATPase activity for K+ uptake?","d":"Epinephrine (via β2-adrenergic receptors), insulin (via insulin receptors), and aldosterone all stimulate Na+/K+-ATPase activity in muscle cells, promoting intracellular K+ uptake. Note: GLUT4 is a glucose transporter activated by insulin signaling but is not itself a receptor that increases Na+/K+-ATPase for K+ handling.","src":"quizlet"},{"t":"How are the receptors on muscle cells that increase Na+/K+-ATPase activity signaled/activated?","d":"They are activated by an acute increase in plasma K+ concentration (e.g., after a meal). Elevated K+ stimulates insulin secretion from the pancreas, which then binds insulin receptors on muscle cells, increasing Na+/K+-ATPase activity to drive K+ into cells.","src":"quizlet"},{"t":"What is the purpose of the receptors on muscle cells that increase Na+/K+-ATPase activity?","d":"To detect an acute increase in plasma K+ concentration and respond by driving K+ from the extracellular space into cells via Na+/K+-ATPase, thereby preventing dangerous hyperkalemia while renal excretion slowly clears the K+ load.","src":"quizlet"},{"t":"What are the acid-base disturbances and K+ kinetics in cells during acidosis?","d":"In acidosis (elevated H+): H+ entering cells inhibits Na+-H+ exchange (NHE1), reducing intracellular Na+, which in turn reduces Na+/K+-ATPase activity. H+ also inhibits the NKCC cotransporter. The net result is K+ moves out of cells into the extracellular space (hyperkalemia). Alkalosis has the opposite effect: K+ moves into cells (hypokalemia).","src":"quizlet"},{"t":"What is unique about the transepithelial membrane potential in the proximal tubule?","d":"The proximal tubule has a biphasic transepithelial potential. The early proximal tubule (S1 segment) is lumen-negative (~−1 to −2 mV), driven by electrogenic Na+-glucose cotransport. The late proximal tubule (S2/S3) becomes lumen-positive (~+1 to +4 mV), driven by passive Cl− diffusion down its concentration gradient, which creates a favorable electrical gradient for paracellular Na+ and cation reabsorption.","src":"quizlet"},{"t":"Which region of the proximal tubule is most responsible for K+ movement?","d":"The late (paracellular) proximal tubule — the S2 and S3 segments. In these segments, passive Cl− reabsorption via the paracellular route creates a lumen-positive potential (~+4 mV), which provides an electrochemical driving force for paracellular K+ reabsorption. Solvent drag (bulk fluid flow) also contributes.","src":"quizlet"},{"t":"How can the gut signal how much K+ was ingested?","d":"The gut contains sensors (likely in the hepatoportal region) that detect dietary K+ intake and trigger a feedforward signal to the kidneys — independent of plasma K+ or aldosterone changes — that increases K+ secretion in the distal nephron via ENaC and ROMK channels, promoting kaliuresis before plasma K+ rises.","src":"quizlet"},{"t":"How do SGLT1 and SGLT2 differ?","d":"SGLT2 (S1 segment, high capacity, low affinity): cotransports 1 Na+ per 1 glucose (1:1 ratio); reabsorbs ~90% of filtered glucose. SGLT1 (S3 segment, low capacity, high affinity): cotransports 2 Na+ per 1 glucose (2:1 ratio); rescues residual glucose at low concentrations.","src":"quizlet"},{"t":"What does aquaporin-1 (AQP1) facilitate?","d":"AQP1 facilitates passive, osmotically driven water reabsorption across the apical and basolateral membranes of the thin descending limb of the loop of Henle (and the proximal tubule and descending vasa recta), enabling the high water permeability required for countercurrent multiplication.","src":"quizlet"},{"t":"What class of amino acids produces sulfuric acid as a metabolic byproduct, and why is this significant?","d":"Metabolism of sulfur-containing amino acids (cysteine and methionine) produces sulfuric acid, a major nonvolatile (fixed) acid that must be excreted by the kidneys.","src":"quizlet"},{"t":"What is nephrin and what is its role in the glomerular filtration barrier?","d":"Nephrin is a transmembrane protein of the immunoglobulin superfamily that forms the structural backbone of the slit diaphragm between podocyte foot processes. Nephrin molecules from adjacent foot processes interact head-to-head in a zipper-like arrangement, creating the size-selective filtration barrier.","src":"quizlet"},{"t":"What is podocin and what is its role in the glomerular filtration barrier?","d":"Podocin is a nephrin-associated scaffolding protein in podocyte lipid rafts. It interacts directly with nephrin (and CD2AP) to organize and stabilize the slit diaphragm complex, and is crucial for maintaining the selective permeability of the glomerular filtration barrier.","src":"quizlet"},{"t":"What are the two mechanisms of renal autoregulation, and how do they work together?","d":"Renal autoregulation is mediated by (1) the myogenic response and (2) tubuloglomerular feedback (paracrine actions via the juxtaglomerular apparatus). Both act by changing afferent arteriole resistance to compensate for changes in perfusion pressure. For example, increased NaCl flow past the macula densa causes paracrine constriction of the afferent arteriole to reduce GFR.","src":"quizlet"},{"t":"Over what range of mean arterial pressure does renal autoregulation maintain a nearly constant GFR?","d":"Renal autoregulation maintains a nearly constant GFR when mean arterial blood pressure is between 80 and 180 mmHg; outside this range the myogenic and tubuloglomerular feedback mechanisms fail.","src":"quizlet"},{"t":"What is the myogenic response in renal autoregulation?","d":"A mechanism of renal GFR autoregulation in which increased perfusion pressure stretches vascular smooth muscle cells in the afferent arteriole, triggering membrane depolarization and calcium influx that causes the arteriole to contract, reducing glomerular capillary pressure and GFR back toward normal.","src":"quizlet"},{"t":"What is tubuloglomerular feedback?","d":"A GFR autoregulatory mechanism mediated by the juxtaglomerular apparatus (JGA): macula densa cells in the thick ascending limb sense increased NaCl delivery (increased GFR) and release paracrine mediators (ATP/adenosine) that constrict the afferent arteriole, raising its resistance and reducing GFR back to normal.","src":"quizlet"},{"t":"What is the step-by-step sequence of tubuloglomerular feedback when GFR increases?","d":"1. GFR increases → 2. flow through tubule increases → 3. NaCl delivery past the macula densa increases → 4. macula densa releases paracrine mediators (ATP/adenosine) → 5. afferent arteriole constricts → 6. resistance in afferent arteriole increases → 7. hydrostatic pressure in glomerulus decreases → 8. GFR decreases.","src":"quizlet"}],"endo":[{"t":"What are the two types of cell-to-cell communication?","d":"1) Direct (via gap junctions, which physically link the cytosol of adjacent cells without secretion)\n2) Indirect (via secreted chemical messengers released into the extracellular fluid)","src":"quizlet"},{"t":"What are the four categories of intercellular chemical messengers?","d":"1) Hormones\n2) Neurotransmitters\n3) Paracrine substances\n4) Autocrine substances","src":"quizlet"},{"t":"What are the two systems responsible for communication and coordination (long-distance signaling) in the body?","d":"1) Nervous system (uses neurotransmitters)\n2) Endocrine system (uses hormones)","src":"quizlet"},{"t":"What are the chemical messengers of the nervous system, where do they travel, and what are their targets?","d":"Messengers: neurotransmitters. They travel across synapses (the synaptic cleft / extracellular space between a neuron and its target cell). Targets: other neurons, muscle cells, and gland cells.","src":"quizlet"},{"t":"What are the chemical messengers of the endocrine system, where do they travel, and what are their targets?","d":"Messengers: hormones. They travel through the bloodstream. Targets: their target cells, which can be essentially any cell type bearing the appropriate receptor (broad reach via the blood).","src":"quizlet"},{"t":"What does the endocrine system consist of?","d":"Endocrine cells that secrete hormones, and target cells that bear hormone receptors and produce the cellular response.","src":"quizlet"},{"t":"Where are hormone-secreting cells found?","d":"1) Grouped together into endocrine glands (e.g., gonads, pancreas, thyroid)\n2) As scattered cells distributed throughout an organ","src":"quizlet"},{"t":"List the primary (dedicated) endocrine organs.","d":"Pineal gland, hypothalamus, thyroid gland, parathyroid glands, thymus, adrenal glands, pancreas, ovaries, testes, and placenta.","src":"quizlet"},{"t":"List the secondary endocrine organs (organs with a non-endocrine primary function that also secrete hormones).","d":"Heart, stomach, liver, kidney, small intestine, and skin.","src":"quizlet"},{"t":"What regulates (controls) hormone secretion?","d":"Three main types of input to endocrine cells:\n1) Neurotransmitters from neurons ending on the endocrine cell\n2) Changes in plasma concentrations of mineral ions or organic nutrients/metabolites (e.g., glucose, amino acids)\n3) Other hormones (or, in some cases, a paracrine substance)","src":"quizlet"},{"t":"What are the functions of the endocrine system?","d":"Metabolism, growth and development, reproduction, response to stress, and water and electrolyte (mineral) balance.","src":"quizlet"},{"t":"Steroid and thyroid hormones are which type of hormone (hydrophobic or hydrophilic)?","d":"Hydrophobic (lipophilic / poorly water-soluble). Because they are poorly soluble, they circulate in the blood largely bound to plasma (carrier) proteins.","src":"quizlet"},{"t":"Which type of hormone can cross the lipid bilayer by diffusion?","d":"Hydrophobic (lipophilic) hormones, such as steroids; their lipophilic nature lets them diffuse freely across the plasma membrane and nuclear envelope.","src":"quizlet"},{"t":"Where are the receptors for hydrophobic hormones located?","d":"Inside the target cell: in the cytosol and/or the nucleus (intracellular receptors).","src":"quizlet"},{"t":"Peptide and catecholamine hormones are which type of hormone (hydrophobic or hydrophilic)?","d":"Hydrophilic (water-soluble). They are transported simply dissolved in the plasma (travel freely/unbound), with the exception of a few peptides.","src":"quizlet"},{"t":"Where are the receptors for hydrophilic hormones located?","d":"On the plasma membrane (the extracellular portion of receptor proteins embedded in the membrane), because water-soluble messengers cannot readily diffuse into the cell.","src":"quizlet"},{"t":"How are hydrophobic (steroid) hormones synthesized?","d":"Steroid hormones are derived from cholesterol, which is taken up from the extracellular fluid or synthesized by intracellular enzymes. (Note: thyroid hormones, also hydrophobic, are made instead from tyrosine plus iodine.)","src":"quizlet"},{"t":"How are hydrophilic (peptide) hormones synthesized?","d":"Peptide hormones are synthesized on ribosomes as large preprohormones, which are cleaved to prohormones in the rough endoplasmic reticulum and then processed to the active hormone. (Catecholamines, the other hydrophilic class, are made differently from tyrosine.)","src":"quizlet"},{"t":"Outline the pathway of hydrophobic (lipophilic) hormone signaling, and put these steps in order: (1) complex binds the HRE on DNA, (2) hormone binds receptor, (3) protein is made, (4) mRNA is made, (5) hormone diffuses into the cell.","d":"Order: 5 → 2 → 1 → 4 → 3.\nThe lipophilic hormone diffuses across the plasma membrane and binds a cytosolic or nuclear receptor. The hormone-receptor complex acts in the nucleus as a transcription factor, binding DNA at a regulatory region (HRE) and increasing transcription of a gene into mRNA. The mRNA leaves the nucleus and directs synthesis of a specific protein on ribosomes, producing the hormone response.","src":"quizlet"},{"t":"The cAMP second-messenger system is an example of which type of hormone signaling?","d":"Hydrophilic (water-soluble) hormone signaling, since cAMP is generated after a first messenger binds a plasma-membrane receptor.","src":"quizlet"},{"t":"Outline the signal-transduction steps of the cAMP second-messenger pathway, and put these steps in order: (1) G protein activated, (2) hormone binds receptor, (3) cellular proteins phosphorylated, (4) protein kinase A activated, (5) cAMP synthesized, (6) adenylyl cyclase activity increases.","d":"Order: 2 → 1 → 6 → 5 → 4 → 3.\nA G protein is bound to the inactive G-protein-coupled receptor. The first messenger binds the receptor, causing a conformational change that increases the G-protein alpha subunit's affinity for GTP (GDP is exchanged for GTP). The GTP-bound alpha subunit dissociates and activates its effector enzyme, adenylyl cyclase, which converts ATP to cAMP. cAMP activates protein kinase A (PKA), which phosphorylates cellular proteins to produce the response.","src":"quizlet"},{"t":"What does adenylyl cyclase produce, and what does that product (cAMP) do?","d":"Adenylyl cyclase converts ATP to cyclic AMP (cAMP). cAMP activates protein kinase A (PKA) and initiates an amplification cascade that brings about specific cellular responses.","src":"quizlet"},{"t":"What does protein kinase A (PKA) do?","d":"It phosphorylates specific proteins (adds a phosphate group from ATP), which can either activate or inactivate each target protein.","src":"quizlet"},{"t":"How does caffeine affect cAMP and neural activity?","d":"Caffeine raises cAMP and promotes neural activity by two mechanisms: (1) it inhibits cAMP phosphodiesterase, the enzyme that breaks down cAMP, thereby prolonging cAMP's actions within cells; and (2) it blocks (antagonizes) adenosine receptors — because adenosine normally reduces neuronal firing, blocking these receptors removes that inhibition and increases neural activity (disinhibition).","src":"quizlet"},{"t":"What are the possible causes of chronic extreme thirst and frequent urination, and what disorder must be ruled out first?","d":"Diabetes insipidus, which may be central (failure to synthesize or release vasopressin/ADH) or nephrogenic (kidneys unable to respond to vasopressin). In either case collecting-duct water permeability stays low, causing a large-volume water diuresis with extreme thirst. Diabetes mellitus must be ruled out first, since uncontrolled hyperglycemia causes a glucose-driven osmotic diuresis with the same symptoms.","src":"quizlet"},{"t":"Besides the hypothalamus, where else can neural tissue secrete hormones directly into the blood?","d":"The adrenal medulla, which is a modified sympathetic ganglion. When activated by preganglionic sympathetic axons, its cells release catecholamines (about 80% epinephrine, 20% norepinephrine) into the blood as hormones.","src":"quizlet"},{"t":"What is the infundibulum?","d":"The pituitary stalk — the tissue that connects the hypothalamus to the pituitary gland; it contains axons from hypothalamic neurons and small blood vessels.","src":"quizlet"},{"t":"From which pituitary lobe are the posterior pituitary hormones (oxytocin and vasopressin) released into the general circulation?","d":"The posterior pituitary. Its hormones are released from axon terminals directly into capillaries that drain into the general circulation.","src":"quizlet"},{"t":"Which two clusters of specialized hypothalamic neurons synthesize the posterior pituitary hormones (ADH/vasopressin and oxytocin)?","d":"The supraoptic nuclei and the paraventricular nuclei. Both nuclei contribute to the synthesis of both ADH and oxytocin (the classic simplification pairs supraoptic→ADH and paraventricular→oxytocin, but Vander's groups both as the shared source).","src":"quizlet"},{"t":"What are the hypothalamo-hypophyseal portal vessels?","d":"Portal vessels (veins connecting two capillary beds) that originate from capillaries in the median eminence of the hypothalamus and drain into the anterior pituitary capillaries. They deliver blood directly from the median eminence to the anterior pituitary, allowing hypophysiotropic hormones to regulate anterior pituitary cells while bypassing the general circulation.","src":"quizlet"},{"t":"What is the median eminence?","d":"The junction of the hypothalamus and infundibulum, where hypophysiotropic (regulatory) hormones are released into capillaries. It is the origin of the hypothalamo-hypophyseal portal vessels.","src":"quizlet"},{"t":"What is the purpose of the anterior pituitary capillaries, and how is anterior pituitary hormone secretion regulated?","d":"The anterior pituitary capillaries receive portal blood carrying hypothalamic (hypophysiotropic) hormones. These hormones regulate the anterior pituitary cells, which in turn release their own hormones into the blood to travel to the rest of the body.","src":"quizlet"},{"t":"What are the functions/effects of ADH (vasopressin) in the body?","d":"1) Conserves body water and blood volume by increasing water reabsorption at the kidneys (antidiuresis)\n2) Raises blood pressure by constricting arterioles/blood vessels (vasoconstriction)","src":"quizlet"},{"t":"How does ADH (vasopressin) cause water reabsorption at the kidneys?","d":"ADH binds its receptor on the basolateral membrane of collecting-duct (principal) cells → increases cAMP → activates protein kinase A (PKA) → PKA promotes insertion of aquaporin-2 (AQP2) water channels into the apical membrane → water is reabsorbed from the tubular lumen back into the body.","src":"quizlet"},{"t":"What type of hormone are ADH (vasopressin) and oxytocin, and where are their receptors located?","d":"Both are peptide hormones and therefore hydrophilic (water-soluble). Their receptors are located on the plasma membrane, consistent with hydrophilic hormones that cannot diffuse across the lipid bilayer.","src":"quizlet"},{"t":"How is ADH (vasopressin) release regulated / what stimulates it?","d":"ADH secretion is increased by:\n1) Increased plasma osmolality / high blood osmotic pressure (dehydration), detected by osmoreceptors\n2) Decreased blood pressure or blood volume, detected by cardiovascular baroreceptors (in the atria and the aortic/carotid arteries)","src":"quizlet"},{"t":"Where is ADH (vasopressin) synthesized and stored?","d":"Synthesized in the cell bodies of the supraoptic and paraventricular nuclei of the hypothalamus; transported down axons through the infundibulum and stored at axon terminals in the posterior pituitary.","src":"quizlet"},{"t":"Where is oxytocin synthesized?","d":"In the cell bodies of the supraoptic and paraventricular nuclei of the hypothalamus.","src":"quizlet"},{"t":"What stimulates oxytocin release?","d":"Suckling/nipple stimulation during nursing (the milk-ejection reflex); the sight, sound (e.g., a baby's cry), or thought of nursing; and cervical/uterine stretch during labor (parturition).","src":"quizlet"},{"t":"What are the effects of oxytocin?","d":"In females: stimulates uterine smooth muscle contraction during labor (childbirth) and milk ejection from the mammary glands during lactation. In males, its systemic endocrine functions are uncertain; research suggests it may be involved in memory and behavior, including pair bonding, maternal behavior, and emotions such as love.","src":"quizlet"},{"t":"What are the ADH-related disorders?","d":"1) Diabetes insipidus (deficient or ineffective ADH)\n2) Syndrome of inappropriate ADH secretion (SIADH; excess ADH)","src":"quizlet"},{"t":"What is the negative-feedback structure of a typical hypothalamic-pituitary-target-gland axis?","d":"Hormone 1: a hypothalamic releasing hormone → Hormone 2: an anterior pituitary stimulating hormone → Hormone 3: the target-gland hormone. The third (target-gland) hormone exerts long-loop negative feedback that inhibits release of both Hormone 1 (hypothalamus) and Hormone 2 (anterior pituitary).","src":"quizlet"},{"t":"In the CRH–ACTH–cortisol axis, which hormone provides feedback inhibition and where?","d":"Cortisol. It exerts long-loop negative feedback by inhibiting both ACTH secretion at the anterior pituitary and CRH secretion at the hypothalamus (acting via glucocorticoid receptors).","src":"quizlet"},{"t":"Compared with body height and reproductive organs, how fast does the brain grow?","d":"The brain grows the fastest and earliest — brain growth is nearly complete by about age 5, whereas maximal height and reproductive-organ size are not reached until the late teens.","src":"quizlet"},{"t":"Why is the total-body height curve S-shaped on a cumulative-growth-vs-age graph?","d":"Because humans go through two periods of rapid height increase (growth spurts): the first during the first ~2 years of life and the second during puberty.","src":"quizlet"},{"t":"Where is growth hormone (GH) released from, and what hormones regulate its secretion?","d":"GH is released by the anterior pituitary gland. Its secretion is stimulated by growth hormone-releasing hormone (GHRH) and inhibited by somatostatin (SST, also called GHIH).","src":"quizlet"},{"t":"What tissues does growth hormone (GH) act on?","d":"The liver (where GH induces IGF-1 release) and many target cells/tissues throughout the body, including bone, where GH stimulates cell division.","src":"quizlet"},{"t":"Identify the basic anatomy of a long bone: the ball-like ends and the shaft.","d":"The ball-like ends are the epiphyses (singular: epiphysis); the shaft is the diaphysis. Bone is a living, metabolically active tissue and has a rich blood supply (vasculature) that feeds it.","src":"quizlet"},{"t":"What is the epiphyseal (growth) plate, and what is its significance for growth hormone?","d":"A plate of actively proliferating cartilage between the epiphysis and the shaft (diaphysis); it is the site of linear bone growth. It contains GH-responsive (receptor-bearing) chondrocytes/prechondrocytes, so it is the bone site that responds to growth hormone.","src":"quizlet"},{"t":"What are the three bone cell types, and what does each do?","d":"Osteoblasts ('bone makers') — secrete collagen/proteoglycan matrix (osteoid) that becomes mineralized; they deposit new bone and add Ca2+.\nOsteoclasts ('bone breakers') — large multinucleated cells that resorb bone by secreting hydrogen ions (acid) to dissolve mineral and hydrolytic enzymes to digest osteoid, releasing Ca2+ into the blood.\nOsteocytes ('bone maintainers') — osteoblasts that have become surrounded by calcified matrix; they maintain bone and participate in remodeling. Together with the calcified (collagen + mineral) matrix, these make up bone.","src":"quizlet"},{"t":"What is the composition of bone (organic vs. inorganic fractions)?","d":"About two-thirds (by weight) is inorganic mineral — calcium-phosphate crystals (hydroxyapatite). About one-third is organic osteoid — mainly collagen (with proteoglycans).","src":"quizlet"},{"t":"What happens to bone if the inorganic mineral (calcium-phosphate) versus the organic collagen matrix is lost?","d":"Without the inorganic mineral, only the soft collagen matrix remains, so bone becomes soft, bendy, and floppy (as in rickets/osteomalacia from deficient mineralization). Without the organic collagen matrix, only the brittle mineral phase remains, so bone becomes extremely brittle.","src":"quizlet"},{"t":"What is the function of growth hormone (GH)?","d":"Stimulates protein synthesis and cell division (growth) throughout the body in its many target tissues.","src":"quizlet"},{"t":"What cell produces new cartilage in the epiphyseal plate, and what must happen to that cartilage for long-bone growth?","d":"Chondrocytes produce (lay down) new cartilage in the epiphyseal plate. For bone growth, the cartilage must proliferate/expand, mature and become calcified, and then die off so it can be replaced by bone.","src":"quizlet"},{"t":"Outline the mechanism of long-bone (linear) growth at the epiphyseal plate.","d":"1) Chondrocytes lay down new cartilage in the interior of the epiphyseal plate.\n2) The plate widens and the shaft lengthens (the plate is pushed away from the shaft center).\n3) Chondrocytes mature, calcify, and die.\n4) Osteoblasts at the shaft edge convert the cartilage to bone.\n5) Growth ends when the plates are fully converted to bone (epiphyseal closure).","src":"quizlet"},{"t":"How is bone growth affected during puberty, and what factors influence growth overall?","d":"Bone growth (the pubertal growth spurt of long bones and vertebrae) requires increased sex hormones (sex steroids). Overall growth is influenced by genetics, adequate nutrition (lack of amino acids, protein, fatty acids, vitamins, or minerals impairs growth), lack of severe/prolonged stress, growth hormone, peptide growth factors, insulin, androgens and estrogens, thyroid hormones, and cortisol.","src":"quizlet"},{"t":"Outline the growth hormone (GH) feedback system.","d":"The hypothalamus secretes GHRH (stimulates GH) and somatostatin/SST (inhibits GH) to the anterior pituitary. The anterior pituitary secretes GH, which acts on the liver (and other cells), and the liver secretes IGF-1 in response.\nNegative-feedback control:\n- IGF-1 and GH inhibit GHRH secretion at the hypothalamus.\n- IGF-1 and GH stimulate somatostatin (SST) secretion at the hypothalamus (raising the inhibitory SST suppresses GH — this is part of net negative feedback, not positive feedback).\n- IGF-1 inhibits GH secretion at the anterior pituitary.\n(Note: GH short-loop inhibition of GHRH is not fully established in humans.)","src":"quizlet"},{"t":"What stimulates growth hormone (GH) release, and how does acute versus chronic stress differ?","d":"Stimulators: sleep, exercise, (acute) stress, fasting, and low plasma glucose. Short, acute stress stimulates GH release; prolonged/chronic stress raises cortisol, which inhibits GH and IGF-1.","src":"quizlet"},{"t":"What are the actions of growth hormone (GH) and the insulin-like growth factors (IGFs)?","d":"1) Promote growth: increase cell number (hyperplasia, the major mitogenic effect) and cell/organ size (hypertrophy).\n2) Metabolic actions that provide fuel for growth (anti-insulin effects): stimulate lipolysis in adipose tissue, stimulate gluconeogenesis in the liver, stimulate protein synthesis (especially in muscle), increase amino-acid uptake into cells, and inhibit glucose uptake by adipose and skeletal muscle.","src":"quizlet"},{"t":"What is the difference between gigantism and acromegaly?","d":"Both result from chronic excess GH. In gigantism, excess GH is secreted before the epiphyseal growth plates close, so long bones still lengthen and the person becomes abnormally tall. In acromegaly, excess GH is secreted after the plates close, so linear growth is no longer possible; instead existing bones thicken — most noticeably the hands, feet, and head/jaw.","src":"quizlet"},{"t":"What results from too little growth hormone (GH)?","d":"Reduced growth/short stature — classically pituitary dwarfism due to anterior-pituitary GH deficiency.","src":"quizlet"},{"t":"In a person with gigantism or acromegaly (a GH-secreting tumor), what would the hypothalamic-pituitary-portal GHRH and SST levels be?","d":"Low GHRH and high SST (somatostatin), because the excess GH/IGF-1 exerts negative feedback that inhibits GHRH and stimulates SST. (The tumor itself escapes this feedback.)","src":"quizlet"},{"t":"What are the functions of calcium in the body?","d":"Structure (bone and teeth), muscle contraction, increased contractility of the heart, vesicle release (triggers exocytosis), and blood clotting (a clotting cofactor).","src":"quizlet"},{"t":"Where is most body calcium stored, and in what form?","d":"About 99% of total-body calcium is stored in bone, in the form of hydroxyapatite — crystals of calcium, phosphate, and hydroxyl ions [Ca10(PO4)6(OH)2].","src":"quizlet"},{"t":"Why is bone considered a dynamic tissue, and which cells carry out bone remodeling?","d":"Because it is constantly being remodeled throughout life. Osteoclasts resorb old bone (releasing Ca2+ into the blood), and then osteoblasts move in and lay down new matrix that becomes mineralized (depositing Ca2+). (Osteocytes also participate.)","src":"quizlet"},{"t":"What three hormones control plasma Ca2+, and what three target sites do they act on?","d":"Hormones: 1) Parathyroid hormone (PTH), 2) calcitriol (1,25-dihydroxyvitamin D), and 3) calcitonin (very limited role in humans). The major regulators are PTH and calcitriol. Target sites: bone, kidneys, and the gastrointestinal/digestive tract.","src":"quizlet"},{"t":"What stimulates parathyroid hormone (PTH) secretion?","d":"A decreased (low) plasma calcium concentration. An increased plasma Ca2+ does the opposite (suppresses PTH).","src":"quizlet"},{"t":"What are the actions of parathyroid hormone (PTH) at the bone, kidney, and intestine, and its overall effect?","d":"Bone: stimulates bone resorption by osteoclasts (moves Ca2+ and phosphate into the extracellular fluid).\nKidney: increases Ca2+ reabsorption, decreases phosphate reabsorption, and stimulates synthesis of calcitriol (which increases intestinal Ca2+ absorption).\nOverall effect: increases plasma Ca2+ concentration.","src":"quizlet"},{"t":"Name and define the two main parathyroid hormone (PTH) disorders.","d":"1) Hyperparathyroidism — excess PTH secretion (causes hypercalcemia).\n2) Hypoparathyroidism — inadequate PTH secretion or action (causes hypocalcemia).","src":"quizlet"},{"t":"What are the causes of hyperparathyroidism?","d":"Primary: a tumor (benign adenoma) or hyperfunction of the parathyroid glands. Secondary: vitamin D deficiency or chronic kidney disease, which reflexively raise PTH secretion.","src":"quizlet"},{"t":"When plasma calcium is high, is there increased activity of osteoblasts or osteoclasts?","d":"Osteoblasts. High plasma Ca2+ suppresses PTH (less osteoclast-driven resorption) and can stimulate calcitonin (which inhibits osteoclasts), favoring net bone deposition by osteoblasts.","src":"quizlet"},{"t":"What are the causes of hypoparathyroidism?","d":"Loss of parathyroid gland function — e.g., surgical removal or trauma, autoimmune damage, or congenital malformation. Also PTH resistance (pseudohypoparathyroidism), in which Ca2+ is low despite elevated PTH because target tissues do not respond.","src":"quizlet"},{"t":"What are the symptoms of hyperparathyroidism (hypercalcemia)?","d":"Hypercalcemia produces symptoms mainly through effects on excitable tissues: tiredness/lethargy with muscle weakness, nausea and vomiting (GI effects), and deposition of calcium salts (e.g., kidney stones).","src":"quizlet"},{"t":"What are the symptoms of hypoparathyroidism (hypocalcemia)?","d":"Hypocalcemia increases the excitability of nerves and muscles, leading to neuromuscular hyperexcitability — CNS effects (seizures), muscle spasms (hypocalcemic tetany), and increased neuronal excitability.","src":"quizlet"},{"t":"What are the actions and overall effect of calcitriol (1,25-(OH)2D)?","d":"The major action of calcitriol is to stimulate intestinal absorption of Ca2+ (and phosphate). Its overall effect is to increase plasma Ca2+ concentration. (Increased renal Ca2+ reabsorption is an action of PTH, not the documented major action of calcitriol.)","src":"quizlet"},{"t":"What are the characteristics/consequences of vitamin D deficiency?","d":"Deficient bone mineralization causing soft, easily fractured bones — rickets in children and osteomalacia in adults — because decreased intestinal Ca2+ absorption lowers plasma Ca2+.","src":"quizlet"},{"t":"What is the difference between rickets and osteomalacia?","d":"Both are deficient bone mineralization causing soft bones. Rickets occurs in children; osteomalacia occurs in adults.","src":"quizlet"},{"t":"What would you observe in a person with elevated plasma calcium?","d":"Increased excretion of calcium in the urine (because high plasma Ca2+ decreases renal Ca2+ reabsorption). PTH and calcitriol are suppressed, and bone resorption decreases.","src":"quizlet"},{"t":"Which is a correct step in the synthesis of calcitriol (vitamin D activation)?","d":"UV light from sunlight converts 7-dehydrocholesterol (a cholesterol derivative) in the skin to cholecalciferol (vitamin D3). This is then hydroxylated in the liver (to 25-OH D) and in the kidney (to 1,25-(OH)2D = calcitriol).","src":"quizlet"},{"t":"Is calcitriol a hydrophilic or hydrophobic hormone?","d":"Hydrophobic. Calcitriol is the active steroid-hormone form of vitamin D, and steroid hormones are lipophilic (poorly water-soluble).","src":"quizlet"},{"t":"What cells secrete calcitonin, what type of hormone is it, and what triggers its release?","d":"Calcitonin is a peptide hormone secreted by the parafollicular cells (C cells) of the thyroid gland. Its release is triggered by high plasma Ca2+ concentration (the opposite of the stimulus for PTH).","src":"quizlet"},{"t":"What are the actions and overall effect of calcitonin?","d":"Calcitonin decreases plasma Ca2+, mainly by inhibiting osteoclasts and thereby reducing bone resorption. In humans it has no role in normal day-to-day Ca2+ regulation but may help reduce bone resorption when plasma Ca2+ is very high.","src":"quizlet"},{"t":"What is osteoporosis?","d":"Porous bone resulting from loss of both matrix and mineral (an imbalance between bone resorption and formation). The decreased bone mass and strength lead to bone fragility and increased fracture risk.","src":"quizlet"},{"t":"What are the risk factors for osteoporosis?","d":"Aging (the most common setting), menopause/estrogen deficiency (loss of estrogen's antiresorptive effect, making it more common in elderly women), immobilization/lack of weight-bearing activity, and inadequate dietary calcium and vitamin D.","src":"quizlet"},{"t":"How is osteoporosis prevented and treated?","d":"Prevention: adequate dietary calcium and vitamin D throughout life plus regular weight-bearing exercise (e.g., brisk walking, stair climbing) to build and maintain bone mass.\nTreatment: adequate calcium and vitamin D; estrogen or synthetic estrogen analogs to slow bone loss; bisphosphonates (interfere with osteoclast bone resorption); and other antiresorptive agents including calcitonin and selective estrogen receptor modulators (SERMs).","src":"quizlet"},{"t":"Which drug is used to treat osteoporosis because it directly increases intestinal calcium absorption?","d":"Calcitriol (1,25-(OH)2D, the active form of vitamin D), which directly stimulates intestinal Ca2+ absorption. (PTH acts on the intestine only indirectly, via calcitriol.)","src":"quizlet"},{"t":"Outline the pathway of thyroid hormone (T3/T4) secretion starting at the hypothalamus.","d":"Hypothalamus secretes thyrotropin-releasing hormone (TRH) → anterior pituitary secretes thyroid-stimulating hormone (TSH) → thyroid gland secretes thyroid hormones T3 and T4.","src":"quizlet"},{"t":"What are thyroid follicles made of, and what are the components of the colloid?","d":"A thyroid follicle is a sphere of follicular (epithelial) cells surrounding a core of colloid. The colloid contains thyroglobulin (a protein with tyrosine residues), the enzyme thyroid peroxidase, and iodine.","src":"quizlet"},{"t":"What is the function and structure of thyroglobulin?","d":"Thyroglobulin is a large protein synthesized by thyroid follicular epithelial cells and secreted into the colloid. It acts as the scaffold/precursor for thyroid hormones: its tyrosine residues carry phenolic (aromatic) rings that are iodinated to build T3 and T4.","src":"quizlet"},{"t":"Outline the synthesis and secretion of thyroid hormones. Put these steps in the correct order: (A) T3/T4 cleaved from thyroglobulin, (B) phagosome fuses with lysosome, (C) tyrosine residues iodinated, (D) T3/T4 diffuse into blood, (E) coupling of MIT and DIT.","d":"Correct order: C → E → B → A → D.\n1) Thyroglobulin is synthesized by follicular cells and secreted into the colloid. 2) Iodide is actively cotransported with Na+ into the follicular cell (iodide trapping) and moves into the colloid. 3) [Step C] Thyroid peroxidase oxidizes iodide to iodine and attaches it to tyrosine residues of thyroglobulin (organification), forming monoiodotyrosine (MIT, one iodine) and diiodotyrosine (DIT, two iodines). 4) [Step E] Two DIT couple → thyroxine (T4); one MIT + one DIT → triiodothyronine (T3). 5) TSH stimulates endocytosis of iodinated thyroglobulin back into the cell. 6) [Step B] The endosome (phagosome) fuses with a lysosome. 7) [Step A] Lysosomal proteolysis releases T3 and T4. 8) [Step D] T3 and T4 diffuse into the blood.","src":"quizlet"},{"t":"How many tyrosines and iodines make up thyroxine (T4) versus triiodothyronine (T3)?","d":"T4 (thyroxine): formed from two coupled DIT (two tyrosine derivatives) and contains four iodines — '2 tyrosine + 4 I.'\nT3 (triiodothyronine): formed from one MIT + one DIT (two tyrosine derivatives) and contains three iodines — '2 tyrosine + 3 I.'","src":"quizlet"},{"t":"Which thyroid hormone is most abundant in the blood, which is more active, and how are they interconverted?","d":"T4 is the more abundant hormone (higher blood concentration). T3 is the more active/major hormone. A considerable amount of T4 is converted to T3 in target tissues by enzymes called deiodinases (T4 acts as a reservoir for T3).","src":"quizlet"},{"t":"Which thyroid hormone provides long-loop negative feedback on the axis?","d":"T4, the principal hormone secreted into the blood by the thyroid (T3 is largely generated in tissues from T4). It exerts negative feedback on TRH (hypothalamus) and TSH (anterior pituitary).","src":"quizlet"},{"t":"What are the actions of thyroid hormones T3 and T4?","d":"1) Regulate basal metabolic rate (calorigenic effect / energy expenditure at rest).\n2) Necessary for normal growth.\n3) Essential for normal brain development and for normal cognition in adults.\n4) Promote increased energy metabolism when in excess.\n5) Up-regulate (increase numbers of) beta-adrenergic receptors.","src":"quizlet"},{"t":"What is hyperthyroidism, what causes it, and what are its symptoms?","d":"Hyperthyroidism (thyrotoxicosis) is chronic excess of thyroid hormone. Causes: hormone-secreting thyroid tumors (rare) and, most commonly, Graves' disease (thyroid-stimulating immunoglobulins). Symptoms: nervousness/anxiety, insomnia, increased heart rate, weight loss (with increased appetite), heat intolerance, tremors; eye disease (exophthalmos) is specific to Graves' disease.","src":"quizlet"},{"t":"What is Graves' disease, and what is its relationship to hyperthyroidism and goiter?","d":"Graves' disease is an autoimmune disease in which antibodies (thyroid-stimulating immunoglobulins) bind to and activate the TSH receptors on thyroid cells, causing excess thyroid hormone production and chronic overstimulation/growth of the gland (goiter). It is the most common cause of hyperthyroidism in the world and a common cause of goiter.","src":"quizlet"},{"t":"What is hypothyroidism, what causes it, and what are its symptoms?","d":"Hypothyroidism is chronically below-normal plasma thyroid hormone (thyroid hormone deficiency). Causes: damage to/loss of functional thyroid tissue ('underactive thyroid') or inadequate dietary iodine. Symptoms: lethargy, fatigue, cold intolerance, weakness, hair changes/loss, and weight gain.","src":"quizlet"},{"t":"What happens in iodine deficiency, including effects on the thyroid axis?","d":"Iodine deficiency compromises T3/T4 synthesis. Low thyroid hormone removes negative feedback, so TRH and TSH rise. Excess TSH overstimulates the thyroid, causing follicular cell hypertrophy and division and producing a goiter (enlarged thyroid). Predicted levels: TRH high, TSH high, T3 low, T4 low.","src":"quizlet"},{"t":"Iodine deficiency is the leading cause of preventable intellectual disability — why is it uncommon in the developed world?","d":"Because iodized salt is widely used (a small fraction of NaCl is replaced with NaI). Maternal iodine deficiency is the most common cause of congenital hypothyroidism worldwide, which impairs intellectual development unless corrected early.","src":"quizlet"},{"t":"A man has an anterior pituitary tumor secreting excess TSH. Predict his TRH, T3, and T4 levels versus normal.","d":"TRH: decreased (low). T3: increased. T4: increased. Excess TSH drives more T3/T4 secretion; the elevated thyroid hormone exerts long-loop negative feedback suppressing hypothalamic TRH. (The tumor, not feedback, keeps TSH high.)","src":"quizlet"},{"t":"A woman has Graves' disease. Predict her TRH, TSH, and T3/T4 levels versus normal.","d":"TRH: decreased. TSH: decreased (suppressed). T3/T4: increased. Thyroid-stimulating immunoglobulins drive excess T3/T4, which exert long-loop negative feedback suppressing both TSH and TRH.","src":"quizlet"},{"t":"What is the basic anatomy of the adrenal gland, and what does each region secrete?","d":"The adrenal gland has an inner adrenal medulla and a surrounding adrenal cortex. The medulla secretes catecholamines (epinephrine and norepinephrine). The cortex has three layers: zona glomerulosa (secretes aldosterone), zona fasciculata (primarily cortisol, plus small amounts of androgens), and zona reticularis (primarily androgens, plus small amounts of cortisol).","src":"quizlet"},{"t":"How are adrenal cortex hormones synthesized (first step)?","d":"All adrenal cortical steroid hormones are derived from cholesterol; the first step is conversion of cholesterol to pregnenolone. Synthesis is initiated when an anterior-pituitary hormone (e.g., ACTH) binds a plasma-membrane Gs-coupled receptor that raises cAMP and activates protein kinase A.","src":"quizlet"},{"t":"List the three functional classes of adrenal cortex hormones and the function of each.","d":"1) Mineralocorticoids (aldosterone) — secreted by the zona glomerulosa; regulate salt balance (sodium, potassium).\n2) Glucocorticoids (cortisol) — secreted mainly by the zona fasciculata; regulate the body's stress response and organic metabolism.\n3) Sex hormones (androgens, e.g., DHEA) — secreted by the zonae fasciculata and reticularis; contribute to reproductive/sexual function.","src":"quizlet"},{"t":"What are aldosterone's actions at the kidney, and its overall effect?","d":"Aldosterone increases Na+ reabsorption (water follows passively by osmosis) and increases K+ secretion. Overall effect: increases blood volume/blood pressure and lowers blood K+. Because Na+ and water are reabsorbed together, plasma osmolarity stays approximately constant (it is regulated separately by vasopressin/thirst).","src":"quizlet"},{"t":"What is aldosterone's mechanism of action in collecting-duct cells?","d":"Aldosterone (a steroid) binds a cytosolic receptor and induces gene expression/protein synthesis of: apical Na+ and K+ channels, basolateral Na+/K+-ATPase pumps, and proteins that enhance opening of the apical Na+ channels. This is slow (gene-mediated). Low plasma Na+ leads to high aldosterone production.","src":"quizlet"},{"t":"What stimulates aldosterone secretion?","d":"1) High plasma potassium (hyperkalemia).\n2) Angiotensin II (generated when blood pressure/volume falls, e.g., hypotension).","src":"quizlet"},{"t":"Outline the renin-angiotensin-aldosterone system (RAAS).","d":"A hormonal system regulating blood pressure and Na+/water balance. Angiotensinogen (precursor) is produced by the liver. Renin, secreted by the juxtaglomerular cells of the kidney, cleaves angiotensinogen to angiotensin I. Angiotensin-converting enzyme (ACE), on capillary endothelial cells, converts angiotensin I to angiotensin II. Angiotensin II acts on the adrenal cortex to stimulate aldosterone secretion.","src":"quizlet"},{"t":"What is the function of juxtaglomerular (JG) cells, and what stimulates them?","d":"JG cells are afferent-arteriole wall cells that secrete the enzyme renin into the blood, initiating the RAAS. Renin secretion is stimulated by decreased arterial/renal perfusion pressure, increased renal sympathetic nerve activity, and decreased NaCl delivery to the macula densa.","src":"quizlet"},{"t":"What would be an effect of removing the adrenal glands from an individual?","d":"An increase in plasma K+ concentration. Loss of aldosterone reduces K+ secretion (so plasma K+ rises) and reduces Na+/water retention (so blood volume and blood pressure fall, and plasma Na+ falls).","src":"quizlet"},{"t":"Outline the regulation of cortisol release (the CRH–ACTH–cortisol axis).","d":"Hypothalamus secretes corticotropin-releasing hormone (CRH) → anterior pituitary secretes adrenocorticotropic hormone (ACTH) → adrenal cortex secretes cortisol. Cortisol exerts long-loop negative feedback, inhibiting both CRH at the hypothalamus and ACTH at the anterior pituitary.","src":"quizlet"},{"t":"What are the actions of glucocorticoids (cortisol)?","d":"1) Promote energy mobilization (metabolic effects).\n2) Permissive for/required in GH secretion (in synergism with thyroid hormone).\n3) Maintain vascular responsiveness to catecholamines (epinephrine/norepinephrine).\n4) Facilitate the adaptive response to stress.\n5) Clinical use: anti-inflammatory and anti-allergic at lower doses, immune suppression at high doses.","src":"quizlet"},{"t":"What are the metabolic effects of cortisol?","d":"Gluconeogenesis (in the liver), protein catabolism (in muscle and elsewhere), and lipolysis/triglyceride catabolism (in adipose tissue).","src":"quizlet"},{"t":"What is Cushing's syndrome, and what symptoms would hypersecretion of glucocorticoids produce?","d":"Cushing's syndrome is excessive cortisol (endogenous or from exogenous glucocorticoid). Symptoms of glucocorticoid excess include hyperglycemia/glucose intolerance, hypertension, weight gain with truncal obesity, 'buffalo hump' and 'moon face,' muscle wasting (protein depletion) and weakness, thin skin, osteoporosis, immunosuppression (risk of infection), mental status changes, and sodium and water retention.","src":"quizlet"},{"t":"What is Addison's disease (primary adrenal insufficiency)?","d":"Loss/destruction of adrenocortical function, resulting in chronically below-normal plasma cortisol (and aldosterone and adrenal androgens). The general term for chronically low cortisol is adrenal insufficiency.","src":"quizlet"},{"t":"What are the symptoms of adrenal insufficiency?","d":"Weakness, lethargy/fatigue, loss of appetite, hypotension (low blood pressure), hypoglycemia (especially after fasting), and poor tolerance for stress. Aldosterone deficiency leads to excess sodium loss and potassium retention (hyperkalemia → cardiac arrhythmias).","src":"quizlet"},{"t":"What percentage of adrenal medulla output is epinephrine versus norepinephrine?","d":"About 80% epinephrine and 20% norepinephrine (the medulla secretes roughly four times more epinephrine than norepinephrine).","src":"quizlet"},{"t":"How are catecholamines (epinephrine/norepinephrine) synthesized in the adrenal medulla?","d":"From the amino acid tyrosine: tyrosine → L-dopa (by tyrosine hydroxylase, the rate-limiting enzyme) → dopamine → norepinephrine. In the adrenal medulla, the enzyme PNMT (phenylethanolamine-N-methyltransferase) then converts norepinephrine to epinephrine.","src":"quizlet"},{"t":"What are the actions of epinephrine?","d":"1) Promotes energy mobilization (glycogen → glucose; fat → fatty acids).\n2) Cardiovascular changes (increased heart rate, force of contraction, and cardiac output).\n3) Shunts blood from viscera/gut and skin to skeletal muscle.\n4) Causes bronchodilation (dilates airways).","src":"quizlet"},{"t":"What is the difference between anabolism and catabolism?","d":"Anabolism is the energy-requiring synthesis of complex molecules from smaller ones. Catabolism is the energy-releasing breakdown of complex molecules into smaller ones.","src":"quizlet"},{"t":"In what forms are the macronutrients absorbed across the GI tract?","d":"Carbohydrates → glucose (monosaccharides); proteins → amino acids and small peptides (di-/tripeptides); lipids → monoglycerides and fatty acids.","src":"quizlet"},{"t":"In what forms do energy substrates (fuels) circulate in the blood?","d":"Glucose, amino acids, and free fatty acids plus lipoproteins (e.g., chylomicrons, VLDL).","src":"quizlet"},{"t":"In what forms is energy stored in the body, and where?","d":"Glycogen (stored in the liver and skeletal muscle), protein (stored in skeletal muscle), and triglycerides (stored in adipose tissue).","src":"quizlet"},{"t":"What characterizes the absorptive state versus the postabsorptive state?","d":"Absorptive state: the ~4 hours following a meal, when ingested nutrients are plentiful in the blood and glucose is the primary fuel; energy is stored. Postabsorptive state: between meals when the GI tract is empty, energy stores must be mobilized, and fatty acids become the primary fuel.","src":"quizlet"},{"t":"What drives the transition between the absorptive and postabsorptive states?","d":"The shift is governed largely by the ratio of insulin to glucagon. During the absorptive state, a high insulin/glucagon ratio promotes nutrient uptake and storage (anabolism). As the GI tract empties, falling plasma glucose lowers insulin and raises glucagon (low insulin/glucagon ratio), switching metabolism toward mobilizing stored fuels (glycogenolysis, gluconeogenesis, lipolysis).","src":"quizlet"},{"t":"What are the roles of carbohydrate (glucose) in the absorptive versus postabsorptive state?","d":"Absorptive: glucose is the primary fuel; excess is stored as glycogen (glycogenesis) and converted to triglycerides for fat storage. Postabsorptive: glycogen is broken down (glycogenolysis) and glucose is synthesized from non-carbohydrate precursors (gluconeogenesis) to maintain blood glucose.","src":"quizlet"},{"t":"What are the pathways of glucose from the blood?","d":"Glucose → liver, stored as glycogen; and glucose → body cells (all tissues), where it is oxidized to CO₂ + H₂O + energy.","src":"quizlet"},{"t":"What is the function of protein in the absorptive versus postabsorptive state?","d":"Absorptive: net protein synthesis; excess amino acids are converted to triglycerides (fat) for storage. Postabsorptive: net protein breakdown; amino acids are taken up by the liver and used for gluconeogenesis.","src":"quizlet"},{"t":"What are the pathways of amino acids/protein from the blood?","d":"Amino acids → liver (used to synthesize proteins, and deaminated). Amino acids → body cells (used for protein synthesis; their breakdown yields NH₃ + CO₂ + H₂O + energy). NH₃ from body cells travels in the blood to the liver, where amino groups are converted to urea for excretion.","src":"quizlet"},{"t":"What is the function of lipids in the absorptive versus postabsorptive state?","d":"Absorptive: triglyceride synthesis and storage in adipose tissue. Postabsorptive: triglyceride breakdown (lipolysis); fatty acids become the primary fuel; glycerol can be converted to glucose; and fatty acids can be converted to ketones in the liver.","src":"quizlet"},{"t":"What are the pathways of lipids from the blood?","d":"Blood lipoproteins are hydrolyzed by lipoprotein lipase to fatty acids and monoglycerides. The fatty acids are taken up by body cells (e.g., adipocytes, where they re-form triglycerides) and by the liver; in body cells they are oxidized to CO₂ + H₂O + energy. Glycerol released from triglycerides re-enters the blood.","src":"quizlet"},{"t":"One hour after a meal (absorptive state), which process would you expect: gluconeogenesis, lipolysis, protein synthesis, or glycogenolysis?","d":"Protein synthesis (in muscle cells). One hour after a meal is the absorptive state, characterized by net protein synthesis; gluconeogenesis, lipolysis, and glycogenolysis are postabsorptive events.","src":"quizlet"},{"t":"What are the cells of the pancreatic islets and their secretions?","d":"Beta (B) cells → insulin; alpha (A) cells → glucagon; delta cells → somatostatin; F cells → pancreatic polypeptide. (Acinar and duct cells of the exocrine pancreas produce exocrine secretions.)","src":"quizlet"},{"t":"What are the actions, stimuli, and inhibitors of insulin?","d":"Insulin is a peptide (polypeptide) hormone; secretion increases during the absorptive state. It promotes synthesis of energy-storage molecules (anabolism) and glucose uptake by muscle and adipose cells.\nStimuli: increased plasma glucose, increased plasma amino acids, increased parasympathetic activity, and incretins (e.g., GLP-1, GIP).\nInhibited during the postabsorptive state, especially by sympathetic activity/epinephrine.","src":"quizlet"},{"t":"Outline the regulation of blood glucose by insulin (negative-feedback loop).","d":"1) Receptors sense increased plasma glucose. 2) Pancreatic islet beta cells secrete insulin into the blood. 3) Increased plasma insulin causes muscle and adipose cells to take up glucose and the liver to stop glucose output (net glucose uptake). 4) Plasma glucose is restored to normal.","src":"quizlet"},{"t":"Insulin-stimulated GLUT-4 translocation leads to uptake of what, and by which cells? What happens if insulin action is defective?","d":"GLUT-4 translocation increases glucose uptake by muscle and adipose cells. If insulin action is defective, GLUT-4 translocation does not occur, so glucose is not taken up by muscle/adipose cells and accumulates in the blood (hyperglycemia, as in diabetes). (Brain glucose uptake is insulin-independent.)","src":"quizlet"},{"t":"Outline the regulation of blood glucose by glucagon, and its actions.","d":"1) Receptors sense decreased plasma glucose. 2) Pancreatic islet alpha cells increase glucagon secretion. 3) Increased plasma glucagon stimulates the liver to perform glycogenolysis, gluconeogenesis, and ketone synthesis. 4) This raises plasma glucose (and ketones). Stimuli: decreased plasma glucose, increased plasma amino acids, increased sympathetic activity/epinephrine. Inhibitors: increased plasma glucose and insulin.","src":"quizlet"},{"t":"Glucagon increases all of the following EXCEPT: gluconeogenesis in the liver, protein breakdown in muscle, glycogenolysis in the liver, lipolysis in adipose tissue?","d":"Protein breakdown in muscle. Glucagon's documented effects are hepatic (glycogenolysis, gluconeogenesis, ketone synthesis); it does not stimulate muscle protein breakdown.","src":"quizlet"},{"t":"How are triglycerides transported in the blood?","d":"Within carrier lipoproteins (e.g., chylomicrons and VLDL).","src":"quizlet"},{"t":"What is diabetic ketoacidosis?","d":"An acute, life-threatening emergency from severe (untreated) insulin deficiency, primarily in type 1 diabetes. Marked insulin deficiency drives pronounced lipolysis and hepatic conversion of fatty acids into ketones; the defining abnormality is increased plasma H+ (metabolic acidosis) from accumulation of acidic ketones (hydroxybutyric and acetoacetic acid), together with severe hyperglycemia.","src":"quizlet"},{"t":"What are the key characteristics and symptoms of diabetic ketoacidosis?","d":"1) Urinary excretion of glucose and ketones\n2) Osmotic diuresis (from the unreabsorbed solutes)\n3) Plasma acidosis (increased plasma H+)","src":"quizlet"},{"t":"What is diabetes mellitus?","d":"A group of metabolic diseases characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both.","src":"quizlet"},{"t":"Compare type 1 and type 2 diabetes mellitus.","d":"Type 1 (T1DM): formerly 'insulin-dependent'/'juvenile'; ~5% of patients; insulin completely or almost completely absent (autoimmune destruction of beta cells); treated by insulin injections or pumps.\nType 2 (T2DM): formerly 'non-insulin-dependent'/'adult-onset'; >90% of patients; reduced target-cell responsiveness to insulin (insulin resistance) plus a beta-cell secretion defect; treated by weight reduction, exercise, diet, and oral glucose-lowering drugs (insulin in some cases).","src":"quizlet"},{"t":"What are some oral/medical treatments for type 2 diabetes?","d":"Metformin (decreases hepatic gluconeogenesis), sulfonylureas (stimulate beta-cell insulin secretion), thiazolidinediones/TZDs (increase insulin sensitivity), GLP-1 agonists (incretins), and sometimes insulin injections.","src":"quizlet"},{"t":"What plasma substance signals the brain toward satiety when its concentration rises, and how?","d":"Leptin. It is secreted by adipocytes in proportion to fat stores and acts on the hypothalamus to decrease food intake (in part by inhibiting neuropeptide Y), functioning in a negative-feedback system.","src":"quizlet"},{"t":"Outline the mechanism of leptin in controlling energy stores.","d":"1) Energy intake exceeds energy expenditure. 2) Fat deposition and leptin secretion increase in adipose tissue. 3) Plasma leptin concentration rises. 4) This alters the activity of integrating centers in the hypothalamus. 5) Energy intake decreases and metabolic rate increases (negative feedback).","src":"quizlet"},{"t":"What is hypoglycemia, and how does it affect insulin, glucagon, epinephrine, and cortisol?","d":"Hypoglycemia is an abnormally low plasma glucose concentration. It reflexively decreases insulin and increases the glucose counter-regulatory hormones — glucagon (increased), epinephrine (increased), cortisol (increased), and growth hormone — which oppose insulin's actions and raise plasma glucose back toward normal.","src":"quizlet"},{"t":"Outline the sympathetic/adrenal response to low plasma glucose.","d":"Decreased plasma glucose triggers a reflex via glucose receptors in the CNS. (1) Increased sympathetic nerve activity to the liver and adipose tissue increases hepatic glycogenolysis and gluconeogenesis and adipose lipolysis. (2) Increased epinephrine secretion from the adrenal medulla increases glycogenolysis in skeletal muscle, glycogenolysis and gluconeogenesis in the liver, and lipolysis in adipose tissue. The result is increased plasma glucose, fatty acids, and glycerol.","src":"quizlet"},{"t":"What are the long-term complications of diabetes mellitus?","d":"1) Large-vessel (macrovascular) disease: stroke, heart attack, heart failure (atherosclerosis, hypertension).\n2) Small-vessel (microvascular) disease: nephropathy (kidney disease/failure), retinopathy (retinal damage → blindness), and neuropathy (peripheral nerve degeneration). Also increased susceptibility to infection.","src":"quizlet"},{"t":"A 24-year-old man has glucosuria, incessant thirst, polyphagia with 15 lb weight loss over a month, and blood glucose 23 mmol/L. Does he have diabetes, and which type? What is the cause, and how should it be treated?","d":"Yes — type 1 diabetes (a young, lean patient with marked weight loss, polyphagia/polydipsia, glucosuria, and very high glucose is classic). Cause: autoimmune destruction of insulin-producing pancreatic beta cells, causing near-total insulin deficiency. Treatment: insulin injections or an insulin pump (essential), plus lifestyle measures (blood-sugar monitoring, exercise, healthy weight) to aid glycemic control.","src":"quizlet"},{"t":"In a person with excess fat, why is satiety still decreased even though leptin is increased?","d":"Because they are leptin-resistant: leptin secretion is normal (indeed leptin concentrations are increased, not decreased), but the brain's response to leptin is blunted, so the appetite-suppressing signal is ineffective — analogous to the insulin resistance of type 2 diabetes.","src":"quizlet"},{"t":"Where are the hypothalamus and pituitary gland located?","d":"The pituitary gland (hypophysis) lies in the sella turcica of the sphenoid bone at the base of the brain, just below the hypothalamus. It is connected to the hypothalamus by the infundibulum (pituitary stalk), which contains axons from hypothalamic neurons and small blood vessels.","src":"quizlet"},{"t":"Describe the anatomy of the pituitary gland.","d":"In humans, the pituitary gland is primarily composed of two adjacent lobes: the anterior lobe (anterior pituitary gland or adenohypophysis), which arises embryologically from an invagination of the pharynx (Rathke's pouch), and the posterior lobe (posterior pituitary or neurohypophysis), which is an extension of the neural components of the hypothalamus, not a true gland. Axons of hypothalamic neurons (supraoptic and paraventricular nuclei) pass down the infundibulum and end within the posterior pituitary near capillaries.","src":"quizlet"},{"t":"Describe the anatomy of the thyroid and parathyroid glands.","d":"The thyroid gland sits within the neck in front of and straddling the trachea. Within the gland are numerous follicles, each composed of an enclosed sphere of epithelial cells surrounding a core of protein-rich colloid. There are usually four parathyroid glands embedded in the posterior surface of the thyroid gland.","src":"quizlet"},{"t":"What are the actions of parathyroid hormone (PTH)?","d":"PTH exerts multiple actions that increase extracellular Ca2+ concentration: (1) directly increases bone resorption by osteoclasts, releasing Ca2+ and phosphate into the extracellular fluid; (2) directly stimulates renal formation of 1,25-dihydroxyvitamin D, which then increases intestinal Ca2+ absorption (indirect intestinal effect); (3) directly increases Ca2+ reabsorption in the kidneys, decreasing urinary Ca2+ excretion; (4) directly decreases renal reabsorption of phosphate, increasing its urinary excretion.","src":"quizlet"},{"t":"How is calcitriol (1,25-dihydroxyvitamin D) synthesized?","d":"Vitamin D3 (cholecalciferol) is formed by the action of ultraviolet radiation from sunlight on the cholesterol derivative 7-dehydrocholesterol in skin. Regardless of source (sunlight-derived D3 or dietary D2/D3), vitamin D is metabolized by the addition of hydroxyl groups — first in the liver by 25-hydroxylase (producing 25-OH D) and then in certain kidney cells by 1-hydroxylase — to produce 1,25-dihydroxyvitamin D [1,25-(OH)₂D], the active hormonal form (calcitriol). PTH stimulates the activity of renal 1-hydroxylase. The major action of 1,25-(OH)₂D is to stimulate intestinal absorption of Ca2+.","src":"quizlet"},{"t":"How is plasma calcium regulated?","d":"Plasma Ca2+ is regulated primarily by PTH and 1,25-dihydroxyvitamin D. A decrease in plasma Ca2+ stimulates parathyroid glands to secrete PTH, which: (1) increases bone resorption by osteoclasts (releases Ca2+ into blood); (2) stimulates renal 1-hydroxylase to produce 1,25-(OH)₂D, which increases intestinal Ca2+ absorption; (3) increases renal Ca2+ reabsorption. Calcitonin (from the thyroid) inhibits osteoclasts to reduce bone resorption and is stimulated by increased plasma Ca2+, but plays no significant role in day-to-day regulation in humans.","src":"quizlet"},{"t":"Describe the anatomy of the thyroid gland.","d":"The thyroid gland sits within the neck in front of and straddling the trachea. It is a bilobed gland. Within the gland are numerous follicles, each composed of an enclosed sphere of epithelial cells surrounding a core containing a protein-rich material called the colloid. The follicular epithelial cells participate in almost all phases of thyroid hormone synthesis and secretion.","src":"quizlet"},{"t":"What is the structure and synthesis of thyroid hormones (T3 and T4)?","d":"The thyroid hormones thyroxine (T4) and triiodothyronine (T3) are amine hormones derived from the amino acid tyrosine. T4 contains four iodine atoms; T3 contains three. They are synthesized by iodination of tyrosine residues within thyroglobulin in the follicular colloid: a tyrosine with one iodine is monoiodotyrosine (MIT); with two iodines it is diiodotyrosine (DIT). Coupling of these iodotyrosines yields T3 and T4.","src":"quizlet"},{"t":"How does a bone repair itself after a fracture?","d":"1) Blood escapes from ruptured blood vessels, forming a fracture hematoma at the break site.\n2) Within ~48 hours, chondrocytes and osteoblasts form a fibrocartilaginous callus (internal and external) bridging the broken ends.\n3) Osteoblasts replace the cartilaginous callus with trabecular (spongy) bone, producing a bony callus that joins the broken ends.\n4) Osteoblasts deposit new compact bone at the periphery while osteoclasts resorb the interior spongy bone, restoring the medullary cavity and remodeling the bone to its original shape.","src":"quizlet"},{"t":"What is nocturnal enuresis?","d":"Bedwetting; the involuntary release of urine during sleep.","src":"quizlet"},{"t":"Why is nocturnal enuresis also a physiological disorder in addition to a psychological disorder?","d":"In most children, ADH (vasopressin) levels normally rise overnight, causing urine to become concentrated in a smaller volume so the bladder does not overfill during sleep. In some children with nocturnal enuresis, this nocturnal rise in ADH fails to occur, resulting in continued production of large volumes of dilute urine overnight, rapid bladder filling, and involuntary voiding (bedwetting).","src":"quizlet"},{"t":"How can physiological nocturnal enuresis be treated?","d":"Desmopressin, a synthetic analogue of ADH (vasopressin), reduces nocturnal urine production and is an established pharmacological treatment for nocturnal enuresis. It is now given orally (tablet or melt); the intranasal spray formulation was withdrawn in 2007 due to an increased risk of symptomatic hyponatraemia.","src":"quizlet"},{"t":"What are the disorders associated with oxytocin dysregulation?","d":"Dysregulation of the oxytocinergic system has been implicated in the pathophysiology of autism spectrum disorder, schizophrenia, and anxiety disorders, among other neuropsychiatric conditions.","src":"quizlet"},{"t":"What laboratory tests would be helpful in diagnosing a 38-year-old woman with chronic extreme thirst and frequent urination (possible diabetes insipidus)?","d":"Key diagnostic tests include: serum sodium and plasma osmolality, urine osmolality, plasma AVP (ADH) or copeptin measurement, and the water deprivation test (indirect dehydration test). MRI of the pituitary/hypothalamus is used to identify structural causes.","src":"quizlet"},{"t":"Who coined the term \"stress\"?","d":"Hans Selye, an Austrian-born scientist who became a Canadian citizen and worked at the Université de Montréal, coined the biological concept of stress in 1936, defining it as \"the non-specific response given by the body to any request made to it.\"","src":"quizlet"},{"t":"What is the clinical use of epinephrine?","d":"Epinephrine is the first-line, cornerstone treatment for anaphylaxis (severe allergic reaction). In anaphylaxis, it counteracts life-threatening bronchoconstriction, upper airway edema, and cardiovascular collapse by stimulating alpha- and beta-adrenergic receptors, thereby dilating bronchioles and constricting blood vessels. It is delivered via autoinjector (e.g., EpiPen) in the community setting.","src":"quizlet"},{"t":"What is StAR and what does it do?","d":"StAR (steroidogenic acute regulatory protein) regulates the transport of cholesterol from the outer to the inner mitochondrial membrane in steroidogenic cells (including adrenal cortex cells), enabling the rate-limiting conversion of cholesterol to pregnenolone by the enzyme CYP11A1, the first step in adrenal cortex steroid hormone synthesis.","src":"quizlet"},{"t":"How does distance from the equator affect cutaneous vitamin D synthesis?","d":"The further from the equator, the less vitamin D you can synthesize. At higher latitudes, the sun's UVB radiation must pass through more of the ozone layer, reducing the amount of UVB reaching the skin and thereby decreasing cutaneous vitamin D3 synthesis.","src":"quizlet"},{"t":"What are the factors affecting cutaneous vitamin D synthesis?","d":"Key factors include: (1) solar zenith angle (angle of the sun) — a higher angle/more direct sunlight increases UVB and vitamin D synthesis; (2) altitude/elevation — higher altitude reduces atmospheric UVB filtration, increasing synthesis; (3) skin melanin content — melanin competes for UVB photons and reduces conversion of 7-dehydrocholesterol to previtamin D3, so higher melanin means less synthesis. Additional factors include latitude, season, time of day, cloud cover, and clothing.","src":"quizlet"},{"t":"What stimulates and inhibits thyroid hormone secretion?","d":"Stimulation: Cold exposure, exercise, and (acutely) stress all increase TRH release from the hypothalamus, stimulating the TRH-TSH axis and thyroid hormone secretion. Cold is particularly notable in neonates, where a TSH surge occurs at birth in response to cold air. Inhibition: Elevated circulating T3/T4 exert negative feedback on the hypothalamus and anterior pituitary (reducing TRH and TSH). Warmth (by reducing the thermogenic need) reduces TRH/TSH drive. Glucocorticoids (elevated in chronic stress) also inhibit TSH at the pituitary level.","src":"quizlet"}],"repro":[{"t":"What are the gonads in females and males, and what gametes do they produce?","d":"Female gonads = ovaries (produce the female gamete, the oocyte/ovum). Male gonads = testes (produce the male gamete, sperm). The gonads serve a dual function: gametogenesis and secretion of sex (steroid) hormones.","src":"quizlet"},{"t":"Define reproduction. Is it essential for individual survival?","d":"Reproduction is the process by which a species is perpetuated. It is essential for survival of the species (and for healthy offspring), but it is NOT necessary for survival of an individual organism.","src":"quizlet"},{"t":"Why is sexual reproduction and the merging of parental chromosomes important?","d":"Combining male and female gametes produces a unique combination of genes (genetically unique offspring). This biological variation is essential for adaptation of the species to a changing environment.","src":"quizlet"},{"t":"What is the purpose of internal fetal development and amniotic fluid?","d":"The fetus floats in amniotic fluid, which buffers mechanical disturbances and temperature variations (a protective fluid cushion).","src":"quizlet"},{"t":"Define sexual dimorphism.","d":"Sex-linked differences in appearance, form, or function within a species (physical distinctions between males and females).","src":"quizlet"},{"t":"What multiple regulatory systems control reproduction, and how do they coordinate?","d":"The gonads, the hypothalamus and anterior pituitary (brain), the nervous system, and hormones/endocrine system all regulate reproduction. Successful reproduction requires efficient intercommunication and feedback between these systems (information flow between cells, tissues, and organs).","src":"quizlet"},{"t":"Outline the developmental stages from egg and sperm to fetus.","d":"Egg (ovum) + sperm → fertilization → zygote (46 chromosomes, 23 pairs) → zygote divides into an embryo (~0–8 weeks / first 2 months) → embryo continues developing into a fetus (~8 weeks to birth).","src":"quizlet"},{"t":"What are the three sets of structures of the male and female sex organs, and the function of each?","d":"1) Gonads — produce gametes (testes make sperm, ovaries make ova) and secrete sex hormones. 2) Internal genitalia — accessory ducts and glands that transport gametes (connecting gonads with the exterior). 3) External genitalia.","src":"quizlet"},{"t":"What are the gonadal steroid hormones, and which predominate in each sex?","d":"The major sex hormones (gonadal steroids) are androgens (masculinizing; e.g., testosterone, DHT), estrogens (feminizing; primarily estradiol), and progesterone (feminizing). All three are present in both sexes, but androgens predominate in males and estrogens/progesterone predominate in females.","src":"quizlet"},{"t":"Outline the mechanism of gametogenesis.","d":"The development of primordial germ cells into gametes (spermatozoa and ova) occurs in two stages: (1) mitosis — proliferation of primordial germ cells into primary spermatocytes/oocytes; (2) meiosis — two divisions yielding gametes with 23 chromosomes.","src":"quizlet"},{"t":"How many chromosomes are in a typical human body cell vs. a gamete?","d":"Each nucleated human body cell has 23 pairs of chromosomes (46 total). Gametes are haploid with only 23 single chromosomes (not 23 pairs).","src":"quizlet"},{"t":"How does the timing of germ-cell mitosis differ between males and females?","d":"Males: some mitosis occurs in the embryonic testes (generating primary spermatocytes present at birth), but germ-cell mitosis begins in earnest at puberty and continues throughout life. Females: germ-cell mitosis in the ovary occurs primarily during fetal development, generating primary oocytes.","src":"quizlet"},{"t":"How is genetic sex determined?","d":"Sex is determined by the presence or absence of a Y chromosome. The ovum always contributes an X; the sperm contributes either an X or a Y. For a male (XY), the sperm contributes the smaller Y chromosome. The complete genetic composition is the genotype: male = XY, female = XX.","src":"quizlet"},{"t":"Are both X chromosomes in a female functional?","d":"No. Only one X is functional; the nonfunctional X condenses to form a nuclear mass called the sex chromatin (Barr body), which can be seen in cheek mucosa cells or white blood cells.","src":"quizlet"},{"t":"What is karyotyping?","d":"Microscopic visualization (via tissue culture) of all the chromosomes in a nucleus, assessing their number and appearance to identify genetic sex abnormalities.","src":"quizlet"},{"t":"Give examples of chromosomal sex abnormalities and what they cause.","d":"Examples: XXX, XXY, and XO (O = absence of a second sex chromosome). These unusual chromosomal combinations usually result in failure of normal anatomical and functional sexual development.","src":"quizlet"},{"t":"What are examples of a mismatch between sexual genotype and phenotype?","d":"Intersex conditions/ambiguous genitalia — e.g., androgen insensitivity syndrome (XY genotype with testes but female phenotype) and congenital adrenal hyperplasia (XX with masculinized/ambiguous genitalia).","src":"quizlet"},{"t":"What determines whether testes or ovaries develop?","d":"Genes directly determine the gonad type: the SRY gene on the Y chromosome triggers testis development; in the absence of the Y chromosome/SRY gene, ovaries develop instead. The gonads' subsequent secretions then determine the rest of sex differentiation.","src":"quizlet"},{"t":"When do gonads remain undifferentiated in uterine life, and when do testes develop?","d":"Primordial gonads remain undifferentiated until the 6th week of uterine life. In genetic males, the testes begin to develop during the 7th week.","src":"quizlet"},{"t":"What chromosome and gene trigger testis development, and what does the gene product do?","d":"The Y chromosome's SRY gene (sex-determining region of Y) is expressed in urogenital ridge cells. It codes for the SRY protein, a DNA-binding transcription factor that sets in motion a cascade of gene activations leading to formation of the testes.","src":"quizlet"},{"t":"From what common embryonic structure do the male and female gonads derive?","d":"Both derive from the same site — the urogenital (gonadal) ridge.","src":"quizlet"},{"t":"What are the undifferentiated fetal reproductive tracts, and which persists in each sex?","d":"Before differentiation there is a double duct system — the Wolffian ducts and the Müllerian ducts — plus a common opening for the genital ducts and urinary system. In males the Wolffian ducts persist and the Müllerian ducts regress; in females the opposite occurs.","src":"quizlet"},{"t":"Do the Wolffian and Müllerian duct systems give rise to internal or external genitalia?","d":"Internal genital structures. The external genitalia and outer vagina develop from separate body-surface structures, not from the duct systems.","src":"quizlet"},{"t":"What two hormones do the fetal testes secrete, and what does each do?","d":"Testosterone (causes Wolffian ducts to differentiate into epididymis, vas deferens, ejaculatory duct, and seminal vesicles) and anti-Müllerian hormone (AMH, formerly Müllerian-inhibiting substance/MIS), which causes degeneration of the Müllerian duct system.","src":"quizlet"},{"t":"What does DHT (dihydrotestosterone) do in development, and what happens if it is absent?","d":"DHT — a potent androgen formed from testosterone by 5-alpha-reductase in target tissue — drives development of the male external genitalia (penis, scrotum) and the prostate. If DHT is absent or cannot act, male external genitalia fail to form and female-type external genitalia and a vagina develop instead. Formation of male external genitalia thus depends on functional testes acting via DHT.","src":"quizlet"},{"t":"What stimulates testicular descent, and what is cryptorchidism?","d":"Testosterone stimulates the testes to descend into the scrotum (usually in the 7th month of gestation). Cryptorchidism is failure of the testes to descend, commonly due to decreased androgen secretion; because optimal sperm formation requires a cooler temperature, sperm production is usually decreased.","src":"quizlet"},{"t":"What occurs in the female fetus in the absence of testes?","d":"Without testes (because the SRY gene is absent), the fetus secretes neither testosterone nor AMH. The Wolffian ducts degenerate, the Müllerian ducts persist and develop into fallopian tubes and uterus, and a vagina and female external genitalia develop from body-surface structures. This proceeds by default and is NOT under ovarian control.","src":"quizlet"},{"t":"Describe androgen insensitivity syndrome (testicular feminization).","d":"Genotype is XY and testes are present, but the phenotype (external genitalia and vagina) is female, caused by a mutation in the androgen-receptor gene that prevents normal testosterone binding. Typically detected when menstrual cycles fail to begin at puberty.","src":"quizlet"},{"t":"Describe congenital adrenal hyperplasia and its treatment.","d":"Caused by overproduction of androgen in the fetus: a mutation in an enzyme of the cortisol-synthesis pathway raises ACTH, increasing adrenal androgen production. This virilizes an XX fetus, causing masculinized/ambiguous genitalia. Treatment is cortisol replacement.","src":"quizlet"},{"t":"How does the brain show sexual differentiation?","d":"Certain hypothalamic nuclei are significantly larger in men. There is also an increase in gonadal steroid secretion in the first year of postnatal life that contributes to sexual differentiation of the brain (masculinization in males, feminization in females).","src":"quizlet"},{"t":"From what structures are androgens synthesized, and are adrenal androgens potent?","d":"Androgens are steroid hormones synthesized from cholesterol, mostly in the testes (males), with smaller amounts from the adrenal cortex (and, in females, small amounts from the ovaries). Adrenal androgens are much less potent than testosterone. Note: DHT, also an androgen, is more potent than testosterone.","src":"quizlet"},{"t":"What is the more potent metabolite of testosterone, and how is it formed?","d":"Dihydrotestosterone (DHT), formed from testosterone in target tissue by the enzyme 5-alpha-reductase.","src":"quizlet"},{"t":"What are the three major estrogens in humans, and where is each produced?","d":"Estradiol (predominant estrogen in plasma; produced by the ovary and placenta), estrone (produced by the ovary and placenta), and estriol (found primarily in pregnant women; produced by the placenta). Estrogens are secreted in large amounts by the ovaries and placenta.","src":"quizlet"},{"t":"How are estrogens produced from androgens?","d":"By aromatization — conversion of androgens to estrogens by the enzyme aromatase (e.g., testosterone → estradiol).","src":"quizlet"},{"t":"Where does estrogen in the blood of males come from?","d":"From small amounts released directly by the testes AND from conversion of androgens to estrogen by aromatase in nongonadal tissues (notably adipose tissue); most male estrogen arises from this peripheral aromatization.","src":"quizlet"},{"t":"What are the roles of progesterone as a hormone and as a biosynthetic intermediate?","d":"Progesterone is a major secretory product of the ovary at specific times of the menstrual cycle and of the placenta during pregnancy. It is also an intermediate in the synthetic pathways for adrenal steroids, estrogens, and androgens.","src":"quizlet"},{"t":"How do gonadal (steroid) hormones act on cells?","d":"They enter cells and bind intracellular receptors, forming a hormone-receptor complex that binds DNA in the nucleus, altering the rate of mRNA formation and thereby changing protein synthesis.","src":"quizlet"},{"t":"What are the effects of gonadal steroids? Define accessory reproductive organs and secondary sexual characteristics.","d":"Gonadal steroids control development of the accessory reproductive organs (the duct systems and glands that transport gametes, plus the breasts) and the secondary sexual characteristics (external differences between the sexes such as hair distribution, body shape, and average height; not directly involved in reproduction).","src":"quizlet"},{"t":"What male secondary sex characteristics develop with testosterone?","d":"Virtually all male secondary sex characteristics depend on testosterone and its metabolite DHT — e.g., body/facial/axillary/pubic hair growth, deepening of the voice (laryngeal growth), and increased muscle mass.","src":"quizlet"},{"t":"What gland is the primary regulator of reproduction?","d":"The brain — it is the primary regulator of reproduction.","src":"quizlet"},{"t":"What are the functions of gonadotropin-releasing hormone (GnRH)?","d":"GnRH is a hypophysiotropic hormone secreted by neuroendocrine cells in the hypothalamus. It controls anterior pituitary function by stimulating release of the gonadotropins FSH and LH.","src":"quizlet"},{"t":"What two pituitary gonadotropins does GnRH trigger the release of, and what do they do?","d":"Follicle-stimulating hormone (FSH) and luteinizing hormone (LH). They act on the gonads to cause gamete maturation (sperm or ova) and to stimulate sex-hormone secretion, which in turn affects all portions of the reproductive system.","src":"quizlet"},{"t":"What happens if hypothalamic or anterior pituitary function is impaired?","d":"Failure of gonadal steroid secretion and of gametogenesis, just as if the gonads themselves were diseased.","src":"quizlet"},{"t":"How does estrogen feedback change with its concentration?","d":"At low-to-moderate concentrations estrogen exerts negative feedback on GnRH/gonadotropin secretion; at high (rapidly rising) concentrations — as at the preovulatory peak — estrogen exerts positive feedback, leading to the LH surge.","src":"quizlet"},{"t":"Why is pulsatile (rather than constant) GnRH release essential?","d":"Constant, nonpulsatile GnRH causes the gonadotropin-secreting pituitary cells to lose sensitivity (downregulation of GnRH receptors), which decreases FSH and LH and thus decreases gonadal steroid secretion. Pulsatile release maintains pituitary responsiveness.","src":"quizlet"},{"t":"Why can stressors, emotions, and trauma inhibit reproductive function?","d":"GnRH neuron cell bodies receive input from throughout the brain and from circulating hormones, so these inputs can suppress GnRH (and thus reproductive function).","src":"quizlet"},{"t":"What is kisspeptin and what is its role?","d":"Kisspeptin is a peptide released by hypothalamic neurons that synapse on (and activate) GnRH neurons to drive pulsatile GnRH release. It is essential for coordinated regulation of reproduction, mediates the negative feedback of gonadal steroids and the positive feedback of estrogen onto GnRH neurons, and helps initiate the timing of puberty (kisspeptin neurons receive peripheral inputs that signal the brain to increase GnRH pulses at puberty).","src":"quizlet"},{"t":"What feedback effect do the sex hormones (gonadal steroids) exert on LH and FSH secretion?","d":"They exert (mainly) negative feedback on the secretion of GnRH and the gonadotropins LH and FSH — i.e., they inhibit their own controlling signals. (Estrogen exerts positive feedback only at specific times in the female menstrual cycle.)","src":"quizlet"},{"t":"What are the main structures of the male reproductive anatomy?","d":"Paired testes; accessory reproductive organs/internal genitalia (ducts that store and transport sperm, plus associated glands — prostate, seminal vesicles, bulbourethral glands); and external genitalia (penis and scrotum).","src":"quizlet"},{"t":"Why does enlargement of the prostate make urination difficult?","d":"The prostate is a walnut-sized gland that surrounds the upper urethra, so when it swells it compresses/obstructs the urethra, impeding urine flow.","src":"quizlet"},{"t":"What is the function of the male urethra?","d":"It is the common passage for both urine and semen — once the ejaculatory ducts join the urethra within the prostate, the urinary and reproductive tracts have merged.","src":"quizlet"},{"t":"Why must the testes be suspended outside the abdomen (in the scrotum)?","d":"Optimal sperm formation requires a temperature about 2°C lower than core body temperature; the scrotum keeps the testes cooler so sperm production is not impaired.","src":"quizlet"},{"t":"What is the purpose of the heat-exchange (countercurrent) blood flow in the testes?","d":"It cools arterial blood before it enters the testes — heat is transferred from warm incoming arterial blood to cooler outgoing venous blood — helping maintain the lower temperature needed for sperm formation.","src":"quizlet"},{"t":"Trace the path of sperm from production to the urethra (the male duct system).","d":"Seminiferous tubules (sperm production) → rete testis → efferent ductules → epididymis (storage) → vas deferens (carries sperm toward the urethra; extends behind the bladder) → joins the seminal vesicle ducts to form the ejaculatory ducts → ejaculatory ducts enter the prostate and join the urethra.","src":"quizlet"},{"t":"What is found in the interstitial tissue between the seminiferous tubules?","d":"Connective-tissue spaces containing blood vessels and Leydig (interstitial) cells, which synthesize and release testosterone.","src":"quizlet"},{"t":"What does the prostate gland secrete, and what is the function of the bulbourethral glands?","d":"The prostate secretes fluid into the urethra through tiny openings. The bulbourethral glands (below the prostate, draining into the urethra just after it leaves the prostate) secrete a small volume of lubricating mucoid fluid.","src":"quizlet"},{"t":"What is the combined function of the prostate and seminal vesicles, and what is semen?","d":"Together the prostate and seminal vesicles secrete most of the fluid in which ejaculated sperm are suspended. Semen = this fluid (mostly from prostate and seminal vesicles) + sperm (from the testes).","src":"quizlet"},{"t":"What are the functions/components of seminal fluid (the glandular secretions of semen)?","d":"Provides nutrients (energy) for sperm; provides buffers that protect sperm from acidic vaginal secretions and residual acidic urine in the male urethra; contains chemicals (particularly from the seminal vesicles) that increase sperm motility; and contains prostaglandins that aid sperm function and movement in the female tract.","src":"quizlet"},{"t":"What is a vasectomy and its effects?","d":"Surgical tying-off and removal of a segment of each vas deferens. It does not cause much fluid accumulation; sperm build up, break down, and are reabsorbed into the bloodstream. It does not affect testosterone secretion because Leydig cell function is unaltered.","src":"quizlet"},{"t":"What is spermatogenesis and what are its steps?","d":"Formation of sperm in the seminiferous tubules of the testes. Steps: spermatogonium divides by mitosis → primary spermatocyte undergoes meiosis I → two secondary spermatocytes → each undergoes meiosis II → four spermatids → spermatids differentiate into spermatozoa (sperm). The whole process takes ~64 days.","src":"quizlet"},{"t":"How is the supply of undifferentiated spermatogonia maintained?","d":"Type A spermatogonia serve as a self-renewing reservoir: at an early point one cell of each clone drops out of the mitosis-differentiation cycle to remain a stem-cell spermatogonium that later re-enters its own division sequence, so the original pool is maintained.","src":"quizlet"},{"t":"Before the first meiotic division of spermatogenesis, what happens to the primary spermatocytes?","d":"They increase markedly in size, then undergo the first meiotic division.","src":"quizlet"},{"t":"What is spermiogenesis (the final phase of spermatogenesis)?","d":"The morphological transformation/differentiation of spermatids into motile spermatozoa, involving extensive cell remodeling (including elongation and tail formation) but no further cell divisions.","src":"quizlet"},{"t":"What are the parts of a sperm cell and the function of each?","d":"Head: almost entirely nucleus (carries DNA), tipped by the acrosome (a vesicle of enzymes important for fertilization). Midpiece: packed with mitochondria that provide energy for movement. Tail: mostly a flagellum that propels the sperm (1–4 mm/min).","src":"quizlet"},{"t":"What cell types are in the testis (Leydig, Sertoli, smooth muscle) and their functions?","d":"Leydig (interstitial) cells — synthesize/release testosterone (have LH receptors). Sertoli cells — support and nourish developing sperm; secrete luminal fluid with androgen-binding protein (ABP); have FSH receptors; secrete inhibin (inhibits FSH) and anti-Müllerian hormone (AMH); form the blood-testes barrier; phagocytose defective sperm; secrete paracrine agents for spermatogenesis. Smooth (myoid) muscle — peristaltic contractions propel sperm.","src":"quizlet"},{"t":"By what structures are the sperm-producing vs. testosterone-producing functions of the testes carried out?","d":"Sperm production is carried out by the seminiferous tubules; testosterone production is carried out by the Leydig cells.","src":"quizlet"},{"t":"What surrounds each seminiferous tubule, and what cells make up its wall?","d":"Each seminiferous tubule is bounded by a basement membrane. Its wall is composed of developing germ cells and their supporting Sertoli cells; mature sperm (spermatozoa) lie in the fluid-filled central lumen.","src":"quizlet"},{"t":"What is the Sertoli (sustentacular) cell, and how do these cells form the blood-testes barrier?","d":"Sertoli cells (also called sustentacular cells) each extend from the basement membrane to the lumen and are joined to adjacent Sertoli cells by tight junctions, forming an unbroken ring around the seminiferous tubule. This ring is the blood-testes (Sertoli cell) barrier, which prevents many chemicals and antibodies from passing into the lumen and divides the tubule into a basal and a central compartment.","src":"quizlet"},{"t":"Besides structural support, what do Sertoli cells provide/secrete?","d":"Nourishment for developing germ cells, plus secretion of androgen-binding protein (ABP) in luminal fluid, inhibin, and paracrine agents/growth factors that drive germ-cell proliferation and differentiation and modulate Leydig cell function.","src":"quizlet"},{"t":"When are Leydig cells active vs. inactive?","d":"Active in the fetus and from puberty onward; relatively inactive (quiescent) from after birth until puberty.","src":"quizlet"},{"t":"What does androgen-binding protein (ABP) do?","d":"Secreted by Sertoli cells, ABP binds the testosterone made by Leydig cells and crosses the blood-testes barrier into the tubule, maintaining a high concentration of total testosterone in the seminiferous tubule lumen.","src":"quizlet"},{"t":"Outline the hormonal control of sperm production (FSH and LH actions in the testes).","d":"GnRH triggers pituitary release of LH and FSH. LH acts on Leydig cells to stimulate testosterone secretion; testosterone diffuses into the seminiferous tubules and enters Sertoli cells to facilitate spermatogenesis. FSH acts on Sertoli cells to stimulate secretion of the paracrine agents (and inhibin) required for spermatogenesis.","src":"quizlet"},{"t":"How do testosterone and inhibin provide negative feedback in the male?","d":"Testosterone inhibits LH secretion by acting on the hypothalamus (decreasing GnRH burst amplitude) and on the anterior pituitary (decreasing LH response to GnRH). Inhibin (from Sertoli cells) acts directly on the anterior pituitary to decrease FSH secretion.","src":"quizlet"},{"t":"How do GnRH-secreting cells fire, and how does GnRH reach the pituitary?","d":"GnRH-secreting neuroendocrine cells in the hypothalamus fire a brief burst of action potentials about every 90 minutes. The released GnRH travels to the anterior pituitary via the hypothalamo-hypophyseal portal vessels, triggering release of LH and FSH (which then act on the testes).","src":"quizlet"},{"t":"What does testosterone get converted into in the prostate vs. in the brain/liver/adipose tissue?","d":"In the prostate, testosterone is converted to the more potent DHT by 5-alpha-reductase. In the brain, liver, and adipose tissue, testosterone is converted to estradiol by aromatase (estradiol being the active hormone there).","src":"quizlet"},{"t":"What happens when aromatase is absent in a male?","d":"A 46,XY male lacking aromatase cannot convert testosterone to estradiol in tissues such as the brain, so he shows certain signs of (effective) estrogen deficiency in those tissues but not others.","src":"quizlet"},{"t":"What does 5-alpha-reductase deficiency cause in a 46,XY individual?","d":"Normal differentiation of male reproductive duct structures (a testosterone effect) but abnormal development of the external male genitalia, which requires DHT.","src":"quizlet"},{"t":"What hormone mediates male libido?","d":"Androgens (testosterone) — they are required for sex drive (libido) in the adult male.","src":"quizlet"},{"t":"What promotes male pattern baldness and how is it treated?","d":"Locally produced DHT (hair follicles express 5-alpha-reductase) promotes scalp hair loss; it can be treated with 5-alpha-reductase inhibitors.","src":"quizlet"},{"t":"What male reproductive functions depend on testosterone, and what are the effects of decreased testosterone?","d":"Testosterone permits fetal differentiation and later growth and function of the entire male duct system, glands, and penis. With decreased testicular function/testosterone: accessory organs shrink, glands reduce secretion, duct smooth-muscle activity falls, and libido, erection, and ejaculation are impaired.","src":"quizlet"},{"t":"Outline the mechanism of penile erection.","d":"At rest, the three cylindrical vascular compartments of the penis are flaccid because dominant sympathetic input releases norepinephrine, contracting arterial smooth muscle. During sexual excitation, sympathetic input is inhibited and nonadrenergic, noncholinergic autonomic neurons (and endothelial cells) release nitric oxide, relaxing the arterial smooth muscle. The small arteries dilate, the compartments engorge with blood, adjacent veins are passively compressed, and erection results.","src":"quizlet"},{"t":"What are the primary stimuli for an erection, and is physical stimulation required?","d":"The primary stimulus is from mechanoreceptors in the genital region (especially the head of the penis); afferent fibers synapse in the lower spinal cord on interneurons that control efferent outflow. Physical stimulation is NOT required — thoughts, emotions, sights, and odors can induce erection alone.","src":"quizlet"},{"t":"What is the role of PDE5, and how do PDE5 inhibitors treat erectile dysfunction?","d":"PDE5 (cGMP-phosphodiesterase type 5) breaks down cGMP, ending erection. PDE5 inhibitors (e.g., sildenafil/Viagra, vardenafil/Levitra, tadalafil/Cialis) block this enzyme, raising cGMP and improving the ability to achieve and maintain an erection.","src":"quizlet"},{"t":"What is erectile dysfunction (impotence)?","d":"The consistent inability to achieve or sustain an erection rigid enough for intercourse; affects up to ~10% of men aged 40–70. Causes include damage to efferent nerves/descending pathways, endocrine disorders, therapeutic and recreational drugs (e.g., alcohol), various diseases, and psychological factors.","src":"quizlet"},{"t":"What are the phases of the male sexual response and the nervous control of each?","d":"Erection — inhibition of sympathetic input plus activation of nonadrenergic, noncholinergic autonomic neurons (classic parasympathetic-type pathway), causing vasodilation. Emission — sympathetic; smooth muscle of the epididymis, vas deferens, ejaculatory ducts, prostate, and seminal vesicles contracts, emptying sperm and secretions into the urethra. Ejaculation — somatic/skeletal; semen is expelled by rapid contractions of urethral smooth muscle and skeletal muscle at the base of the penis (with the bladder sphincter closed).","src":"quizlet"},{"t":"What constitutes a male orgasm?","d":"Rhythmic muscular contractions during ejaculation associated with intense pleasure and systemic physiological changes (transient increase in heart rate and blood pressure), followed by a latent period during which a second erection is not possible.","src":"quizlet"},{"t":"How is sperm transported and concentrated in the male tract before ejaculation?","d":"Sertoli-cell fluid secretion raises pressure in the seminiferous tubules, moving the still-nonmotile sperm to the epididymis. The vas deferens and adjacent epididymis store sperm; fluid is absorbed from the epididymal lumen, concentrating the sperm. Peristaltic smooth-muscle contractions of the epididymis and vas deferens propel sperm at ejaculation.","src":"quizlet"},{"t":"What is the overall effect of anabolic steroids, and what are their negative effects?","d":"Anabolic steroids (synthetic androgens) directly stimulate protein synthesis in muscle; androgens also stimulate kidney erythropoietin secretion (higher hematocrit in men). Negative effects: overstimulation of the prostate, increased aggression, and negative feedback that decreases GnRH/LH/FSH — reducing endogenous testosterone and spermatogenesis, shrinking the testes, and causing low sperm count (infertility). Low doses are being tested as a potential male birth control pill.","src":"quizlet"},{"t":"What triggers the first signs of puberty in males, and what are they?","d":"The first signs are driven not by gonadal steroids but by increased adrenal androgen secretion (probably stimulated by ACTH), causing early development of pubic and axillary hair and the early stages of the pubertal growth spurt (with GH and IGF-1).","src":"quizlet"},{"t":"Outline the hormonal sequence that initiates puberty.","d":"Increased input from hypothalamic kisspeptin neurons raises the amplitude and pulse frequency of GnRH → increased pituitary gonadotropin (LH/FSH) secretion → stimulation of the gonads (in males, seminiferous tubules and testosterone secretion) → pubertal changes in accessory reproductive organs, secondary sex characteristics, and sex drive. (Other puberty events reflect increased activity of the hypothalamo-pituitary-gonadal axis.)","src":"quizlet"},{"t":"What are the primary and secondary sex characteristics of male puberty?","d":"Primary: development/enlargement of the penis, scrotum, and testes. Secondary (dependent on testosterone and DHT): deepening of the voice, pubic/facial/axillary/body hair, and a masculine redistribution of muscle and fat.","src":"quizlet"},{"t":"What is hypogonadism, and what distinguishes primary from secondary hypogonadism?","d":"Hypogonadism is a decrease in testosterone release from the testes. Primary hypogonadism = testicular failure. Secondary hypogonadism = failure to supply the testes with gonadotropic stimulus (decreased LH/FSH), e.g., from hyperprolactinemia, hypopituitarism, or GnRH deficiency.","src":"quizlet"},{"t":"What is the effect of hypogonadism before puberty?","d":"Failure to develop secondary sex characteristics (voice deepening, pubic/axillary hair, libido) and failure to develop normal sperm production.","src":"quizlet"},{"t":"What is Klinefelter's syndrome and its treatment?","d":"A common genetic cause of primary hypogonadism with an extra X chromosome (47,XXY). Patients appear normal before puberty; afterward the testes stay small and poorly developed with insufficient Leydig and Sertoli cell function → low testosterone → abnormal seminiferous tubule development and decreased sperm production. Secondary sex characteristics fail to appear, breast size increases (gynecomastia), and LH/FSH are high. Treated with androgen-replacement therapy.","src":"quizlet"},{"t":"What is hyperprolactinemia?","d":"Increased blood prolactin, commonly from a prolactin-secreting pituitary tumor; the excess prolactin inhibits LH and FSH secretion from the anterior pituitary (a cause of secondary hypogonadism).","src":"quizlet"},{"t":"What is hypopituitarism and how is it treated?","d":"A significant decrease in (or absence of) anterior pituitary function, caused by head trauma, infection, or inflammation of the pituitary. Treatment replaces the missing downstream hormones: testosterone, cortisol (for low ACTH), and thyroid hormone (for low TSH); GH is added for children/some adults.","src":"quizlet"},{"t":"What is andropause?","d":"The age-related decrease (rarely complete cessation) in testosterone in men (the male climacteric), less drastic than menopause. It reflects slow deterioration of testicular function and failure of the gonads to respond to pituitary gonadotropins; testosterone declines from about age 40, with decreased libido, less motile sperm, and sometimes emotional problems such as depression.","src":"quizlet"},{"t":"What are the components of the female reproductive system?","d":"Two ovaries plus the female reproductive tract: two fallopian tubes (oviducts), the uterus, the cervix, and the vagina.","src":"quizlet"},{"t":"What structures make up the vulva (female external genitalia)?","d":"Mons pubis, labia majora (female homologue of the scrotum), labia minora, clitoris (female homologue of the penis), vestibule of the vagina, and vestibular glands — collectively called the vulva.","src":"quizlet"},{"t":"What is the hymen?","d":"A thin fold of mucous membrane that partially overlies the vaginal opening.","src":"quizlet"},{"t":"What are the functions of the ovaries before vs. after ovulation?","d":"Before ovulation: oocyte maturation and the ovary's endocrine functions occur within a single structure, the follicle. After ovulation: the now egg-less follicle differentiates into the corpus luteum.","src":"quizlet"},{"t":"Describe the follicle growth cycle (primordial to mature antral follicle).","d":"A primordial follicle is one primary oocyte surrounded by a single layer of granulosa cells. As it grows: granulosa cells multiply into multiple layers and secrete estrogen, inhibin (and a little progesterone); the oocyte enlarges and is separated from inner granulosa cells by the zona pellucida (glycoproteins that bind sperm); inner granulosa cells form gap junctions with the oocyte for nutrient/messenger exchange; surrounding connective tissue forms the theca layers (which help synthesize estrogen); and a fluid-filled antrum forms once the oocyte reaches full size.","src":"quizlet"},{"t":"What is the zona pellucida?","d":"The thick glycoprotein layer secreted by follicular cells that directly surrounds the oocyte; its glycoproteins serve as receptors that bind sperm at fertilization.","src":"quizlet"},{"t":"When does follicle development begin, and how many follicles begin developing each cycle?","d":"Progression of primordial follicles to the preantral/early antral stages is continuous throughout infancy, childhood, and the entire menstrual cycle. At the start of each cycle, 10–25 preantral/early antral follicles begin developing into larger antral follicles.","src":"quizlet"},{"t":"What happens during week 1 of the menstrual cycle (dominant follicle selection)?","d":"About one week into the cycle, a selection process leaves only one larger antral follicle — the dominant follicle — to continue developing. Selection is directed by local estrogen secretion within the follicle; the nondominant follicles undergo atresia (degeneration/programmed cell death).","src":"quizlet"},{"t":"What is atresia?","d":"Degeneration (programmed cell death/apoptosis) of ovarian follicles — i.e., degeneration of the nondominant follicles.","src":"quizlet"},{"t":"What happens to the dominant follicle approaching ovulation?","d":"It enlarges as antral fluid increases; the granulosa cells around the egg form the cumulus oophorus projecting into the antrum. As ovulation nears, the primary oocyte emerges from meiotic arrest and completes its first meiotic division to become a secondary oocyte. The cumulus separates so it and the oocyte float free in antral fluid, and the mature (graafian) follicle balloons out on the ovarian surface.","src":"quizlet"},{"t":"When and how does ovulation occur?","d":"On about day 14 of the menstrual cycle, the thin walls of the follicle and ovary rupture at their junction (by enzymatic digestion). The secondary oocyte — surrounded by its zona pellucida, granulosa cells, and cumulus oophorus — is carried out of the ovary onto the ovarian surface by the antral fluid.","src":"quizlet"},{"t":"What hormone surge triggers ovulation, and what does the LH surge do?","d":"The midcycle surge of LH is the primary event that induces ovulation. The LH surge — caused by extremely elevated/rapidly rising estrogen (positive feedback) — also stimulates the oocyte to complete its first meiotic division, releases the oocyte from the follicle, and stimulates formation of the corpus luteum.","src":"quizlet"},{"t":"When is the first vs. second meiotic division of the oocyte completed?","d":"The first meiotic division is completed just before ovulation (primary oocyte → secondary oocyte). The second meiotic division is completed only after fertilization (penetration by a sperm), in the fallopian tube.","src":"quizlet"},{"t":"How are fraternal (dizygotic) twins formed?","d":"Two or more follicles reach maturity and more than one egg is ovulated; the separate eggs (carrying different genes) are fertilized by different sperm.","src":"quizlet"},{"t":"How does the corpus luteum form, and what is its function?","d":"After the mature follicle discharges its antral fluid and egg, it collapses and rapidly transforms — the remaining granulosa and theca cells enlarge into the gland-like corpus luteum. This transient endocrine gland secretes progesterone, estrogen (estradiol), and inhibin, preparing and supporting the endometrium for early pregnancy.","src":"quizlet"},{"t":"Does the corpus luteum reach maximum development after ovulation, and what happens to it if there is no fertilization?","d":"Yes — in the nonpregnant cycle (egg not fertilized) the corpus luteum reaches maximum development within about 10 days, then rapidly degenerates by apoptosis. Loss of corpus luteum function leads to menstruation and the start of the next cycle. (If fertilization occurs, hCG rescues and maintains it.)","src":"quizlet"},{"t":"What are the two phases of the ovarian cycle and what separates them?","d":"The follicular phase (before ovulation; a mature follicle and secondary oocyte develop) and the luteal phase (after ovulation; the corpus luteum forms and persists until it dies). The two roughly equal phases are separated by ovulation.","src":"quizlet"},{"t":"Describe the follicular phase of the ovarian cycle.","d":"The first phase (about days 1–14), during which a follicle (oocyte plus surrounding cells) enlarges and matures under the control of FSH and secretes estrogen. The ovarian follicular phase corresponds to the uterine menstrual and proliferative phases.","src":"quizlet"},{"t":"Describe the luteal phase of the ovarian cycle.","d":"The second phase (about days 15–28), during which a corpus luteum forms from the ovulated follicle and secretes progesterone and estrogen. Its formation is triggered by the LH surge; as LH declines after the surge, the corpus luteum degenerates. The ovarian luteal phase corresponds to the uterine secretory phase.","src":"quizlet"},{"t":"How do FSH and LH levels change across the menstrual cycle?","d":"FSH rises in the early follicular phase, then steadily decreases through the rest of the cycle except for a small midcycle peak. LH stays fairly constant through most of the follicular phase, then shows a large midcycle surge (peaking ~18 h before ovulation), followed by a rapid drop and slow decline during the luteal phase.","src":"quizlet"},{"t":"What are the follicular actions of FSH and LH on the follicle cells?","d":"FSH acts on granulosa cells, stimulating them to multiply, produce estrogen, and enlarge the antrum. LH acts on theca cells, stimulating them to proliferate and synthesize androgens.","src":"quizlet"},{"t":"How do theca and granulosa cells cooperate to produce estrogen?","d":"LH-stimulated theca cells synthesize androgens (granulosa cells lack the enzymes for this). The androgens diffuse into the granulosa cells, where FSH-stimulated aromatase converts them to estrogen.","src":"quizlet"},{"t":"What is the effect of estrogen on granulosa cells (within the follicle)?","d":"Estrogen acts as a paracrine/autocrine agent (with FSH) to stimulate further proliferation and gonadotropin sensitivity of granulosa cells (increasing the number of FSH receptors), which further increases estrogen production.","src":"quizlet"},{"t":"Why do nondominant follicles degenerate while the dominant follicle survives?","d":"Falling FSH (FSH is needed for follicle-cell survival) leaves too little FSH to prevent atresia in nondominant follicles. The dominant follicle survives because its granulosa cells have more FSH receptors (greater FSH sensitivity) and it secretes enough estrogen to raise plasma estrogen.","src":"quizlet"},{"t":"What feedback effects does estrogen have on gonadotropin secretion at low (early/mid follicular) concentrations?","d":"Negative feedback: estrogen acts on the anterior pituitary to decrease FSH and LH secreted in response to GnRH, and on the hypothalamus to decrease the amplitude of GnRH pulses (and total GnRH). FSH falls more than LH because granulosa-cell inhibin preferentially inhibits FSH.","src":"quizlet"},{"t":"When does estrogen peak, and how does this peak trigger the LH surge (positive feedback)?","d":"Estrogen peaks in the late follicular phase (sustained ~1-2 days) when the dominant follicle secretes large amounts. This high, rising estrogen exerts positive feedback — acting on the pituitary and hypothalamus (the increase in GnRH release may be mediated by kisspeptin neurons) — to cause the LH surge. This positive feedback is essential for normal cycles and ovulation.","src":"quizlet"},{"t":"What stimulates and what maintains the corpus luteum (role of LH)?","d":"The LH surge (high LH) stimulates transformation of the remaining granulosa and theca cells into the corpus luteum; afterward, a low but adequate LH concentration maintains the corpus luteum for about 14 days.","src":"quizlet"},{"t":"How do progesterone and inhibin suppress gonadotropins during the luteal phase?","d":"In the presence of estrogen, the high progesterone of the luteal phase decreases pituitary gonadotropin secretion and prevents LH surges during the first half of the luteal phase. Increased luteal inhibin further suppresses FSH. Consequently, plasma gonadotropin levels are very low in the luteal phase.","src":"quizlet"},{"t":"What three hormones does the corpus luteum secrete in large quantities?","d":"Progesterone, estrogen, and inhibin.","src":"quizlet"},{"t":"What drives the uterine changes during the menstrual cycle, and which uterine phases match the ovarian phases?","d":"Uterine changes are driven by changing plasma concentrations of estrogen and progesterone secreted by the ovaries. The ovarian follicular phase includes the uterine menstrual and proliferative phases; the ovarian luteal phase is the same as the uterine secretory phase.","src":"quizlet"},{"t":"Describe the menstrual (uterine) phase.","d":"Days ~1-5 (day 1 = first day of flow). The endometrium degenerates and is shed: vasoconstriction, then dilation of endometrial arterioles causing hemorrhage through weakened capillaries, plus rhythmic uterine smooth-muscle contractions — all mediated by prostaglandins released as estrogen and progesterone fall.","src":"quizlet"},{"t":"Describe the proliferative (uterine) phase.","d":"Roughly days 6-14, after menstruation ends and before ovulation. Rising estrogen (from the developing follicle) stimulates regrowth/thickening of the endometrium and underlying myometrium and induces progesterone receptors in endometrial cells. Lasts ~10 days.","src":"quizlet"},{"t":"Describe the secretory (uterine) phase.","d":"Roughly days 15-28, after ovulation and formation of the corpus luteum. Progesterone (with estrogen) converts the estrogen-primed endometrium into actively secreting tissue: glands coil and fill with glycogen, blood vessels increase, and enzymes/glycoproteins/mucopolysaccharides accumulate — making the endometrium hospitable for implantation and nourishment of the embryo.","src":"quizlet"},{"t":"What are the roles of progesterone in the uterus during pregnancy?","d":"Progesterone inhibits myometrial contractions (largely by opposing the stimulatory actions of estrogen and locally generated prostaglandins), ensuring a fertilized egg can safely implant and maintaining uterine quiescence throughout pregnancy. A drastic fall in progesterone can lead to premature delivery.","src":"quizlet"},{"t":"How do estrogen and progesterone change cervical mucus across the cycle?","d":"Estrogen and progesterone modulate cervical mucus. Under high estrogen (around ovulation) the mucus is abundant, clear, and watery, facilitating sperm passage into the uterus and tubes. Under high progesterone (after ovulation) the mucus becomes thick and sticky, forming an antibacterial plug that protects the uterus/embryo.","src":"quizlet"},{"t":"When do estrogen and progesterone peak relative to ovulation?","d":"Estrogen is highest at/just before ovulation (late follicular phase). Progesterone is highest after ovulation (luteal/secretory phase).","src":"quizlet"},{"t":"What does involution (degeneration) of the corpus luteum cause?","d":"A decrease in plasma progesterone and estrogen, which deprives the developed endometrium of hormonal support and causes menstruation.","src":"quizlet"},{"t":"Outline the events of menstruation and the typical blood loss.","d":"1) Constriction of uterine blood vessels (mediated by prostaglandins as estrogen/progesterone fall); 2) disintegration of the endometrial lining; 3) rhythmic uterine smooth-muscle contractions (prostaglandins); 4) dilation of endometrial arterioles causing hemorrhage through weakened capillary walls. Typical blood loss is about 50-150 mL.","src":"quizlet"},{"t":"What are the typical effects of estrogen on the female reproductive system?","d":"Beyond its paracrine action within the ovaries and its feedback on the anterior pituitary/hypothalamus, estrogen acts on the uterus (increasing myometrial contractions and responsiveness to oxytocin) and primes the endometrium for progesterone by inducing progesterone receptors.","src":"quizlet"},{"t":"What are some effects of progesterone on the female reproductive system?","d":"After ovulation, progesterone inhibits proliferation of the vaginal lining cells, raises basal body temperature (~0.5°C after ovulation), and exerts an antiestrogen effect (probably by decreasing the number of estrogen receptors).","src":"quizlet"},{"t":"What is the layered structure of the uterine wall, and which layer does what?","d":"From outer to inner: perimetrium (outer serosa), myometrium (middle smooth-muscle layer — richest in actin and myosin for contraction), and endometrium (inner glandular lining). Estrogen stimulates growth of both the endometrium and the underlying myometrium.","src":"quizlet"},{"t":"What is menarche?","d":"The first menstruation — a late event of puberty (averaging about 12.5 years of age in the U.S.).","src":"quizlet"},{"t":"When is puberty usually initiated in girls, and what hormone levels are low during childhood?","d":"Female puberty usually begins at 8-13 years old (earlier than in boys); menarche, a late event, averages ~12.5 years. During childhood, GnRH, gonadotropins, and estrogen are all secreted at very low rates.","src":"quizlet"},{"t":"What does leptin do in relation to reproduction?","d":"Leptin, an adipose-tissue hormone, stimulates GnRH secretion and may contribute to the onset of puberty.","src":"quizlet"},{"t":"What is amenorrhea, and how do primary and secondary amenorrhea differ?","d":"Amenorrhea is the failure to have menstrual flow. Primary amenorrhea = failure to begin normal menstrual cycles at puberty (menarche). Secondary amenorrhea = loss of previously normal cycles (most common causes: pregnancy and menopause; also excessive exercise and anorexia nervosa).","src":"quizlet"},{"t":"What is the fertile window, and how long are sperm and the egg viable?","d":"Fertilization requires sperm in the female tract between 5 days before and 1-2 days after ovulation. After ejaculation, sperm remain capable of fertilizing for up to 4-6 days; an ovulated egg remains viable for only 24-48 hours.","src":"quizlet"},{"t":"What is capacitation and what does it cause?","d":"Capacitation is the functional maturation sperm must undergo after residing several hours in the female tract, acted on by tract secretions, before they can fertilize the egg. It causes: (1) the regular wavelike beats of the tail to become a stronger whiplike action that propels the sperm forward; and (2) alteration of the sperm plasma membrane so it can fuse with the egg's surface membrane.","src":"quizlet"},{"t":"Where and when does fertilization occur, and how does a sperm reach the egg?","d":"Fertilization (fusion of a sperm and egg) occurs in the uterine (fallopian) tube, usually within a few hours after ovulation (within the 24-48 h egg-viability window). Sperm move between the granulosa cells (corona radiata) surrounding the egg and bind to the zona pellucida, whose glycoproteins act as receptors for sperm surface proteins.","src":"quizlet"},{"t":"What is the acrosome reaction — what triggers it, where does it occur, and what does it do?","d":"Triggered by a sperm binding to the zona pellucida, it occurs in the bound sperm: the sperm head's plasma membrane is altered, exposing acrosomal enzymes that digest a path through the zona pellucida so the sperm can advance (using its tail) toward the egg.","src":"quizlet"},{"t":"Which sperm fertilizes the egg, and what is the block to polyspermy?","d":"The first (fastest) sperm to fully penetrate the zona pellucida and reach the egg's plasma membrane fuses with it. Normally only one sperm fertilizes the egg: the cortical reaction (egg peripheral secretory vesicles release enzymes by exocytosis) inactivates sperm-binding sites and hardens the zona pellucida, preventing additional sperm from entering (the block to polyspermy).","src":"quizlet"},{"t":"What is a zygote, and what happens immediately after fertilization?","d":"A zygote forms when an ovum and sperm fuse (sperm's 23 chromosomes + ovum's 23 = 46-chromosome cell). After fertilization the egg completes its second meiotic division (within a few hours); the two pronuclei (23 chromosomes each) migrate to the cell center, their DNA replicates, and the cell prepares for mitosis — completing fertilization.","src":"quizlet"},{"t":"What is cleavage, and what is the blastocyst?","d":"Cleavage is the series of cell divisions in the early conceptus (e.g., the morula) that increases cell number without increasing overall size (no cell growth between divisions). About 5-6 days after fertilization the conceptus becomes a blastocyst — a fluid-filled sphere of an outer trophoblast layer, an inner cell mass, and a central cavity — the structure that implants in the endometrium.","src":"quizlet"},{"t":"What do the trophoblast (outer layer) and inner cell mass of the blastocyst become?","d":"The outer trophoblast becomes the (embryonic/fetal portion of the) placenta and is involved in nutrition and hormone secretion (including hCG, which maintains the corpus luteum). The inner cell mass becomes the developing human — an embryo (first 2 months) and then a fetus (after 2 months).","src":"quizlet"},{"t":"When does the blastocyst stage occur in the cycle, what prepares the uterus, and when does implantation begin?","d":"The zygote develops into a blastocyst on days ~14-21 of the cycle, while progesterone (from the corpus luteum) prepares the uterine lining. Implantation — the embedding of the blastocyst in the endometrium — begins about day 21 (7 days after ovulation). The trophoblast cells (especially over the inner cell mass) are sticky, allowing them to adhere to the endometrium and initiate implantation.","src":"quizlet"},{"t":"What is placentation, and what are the embryonic and maternal portions of the placenta?","d":"Placentation is formation of the disc-shaped placenta, an organ of exchange made of interlocking fetal and maternal tissues, attached to the uterine wall and to the fetus via the umbilical cord. Embryonic portion = the chorion (outermost trophoblast cells); maternal portion = the endometrium underlying the chorion.","src":"quizlet"},{"t":"What are chorionic villi?","d":"Fingerlike, capillary-rich projections of trophoblast (chorion) that extend into the endometrium and become surrounded by pools of maternal blood. Substances (gases, nutrients, wastes, hormones) are exchanged between fetal and maternal blood across them, but the two bloodstreams do not mix.","src":"quizlet"},{"t":"What do the umbilical arteries and umbilical vein carry, and what does the umbilical cord contain?","d":"The umbilical cord contains (typically) two umbilical arteries that carry deoxygenated, waste-laden blood from the fetus to the placenta, and one umbilical vein that carries oxygenated, nutrient-rich blood from the placenta to the fetus.","src":"quizlet"},{"t":"What is the amniotic sac, and what are the functions of amniotic fluid?","d":"The amnion (amniotic sac) is a fluid-filled, baglike membrane (derived from the inner cell mass) in which the fetus develops; it fuses with the inner surface of the chorion. Amniotic fluid buffers mechanical disturbances and temperature variations and cushions/protects the fetus and umbilical cord, allowing buoyancy and fetal movement. The fetus floats in amniotic fluid, attached to the placenta by the umbilical cord.","src":"quizlet"},{"t":"Roughly five weeks after implantation, what is the state of the placenta and fetal heart?","d":"The placenta is well established and functioning, and the fetal heart has begun to pump blood through the fetal (and placental) circulation. (This is ~6 weeks after fertilization.)","src":"quizlet"},{"t":"What happens to plasma estrogen and progesterone during pregnancy, and what does each do?","d":"Both continually increase throughout pregnancy. Estrogen stimulates growth of the uterine muscle mass that later supplies the contractile force for delivery. Progesterone inhibits uterine contractility to prevent premature delivery.","src":"quizlet"},{"t":"What maintains the corpus luteum during pregnancy, and why is hCG used in pregnancy tests?","d":"Human chorionic gonadotropin (hCG) — an LH-like hormone secreted by trophoblast cells starting around the time of endometrial invasion — prevents corpus luteum degeneration and strongly stimulates its steroid (estrogen/progesterone) secretion. Because the conceptus's trophoblast secretes hCG into the maternal circulation (and it appears in urine), detecting hCG is used as a pregnancy test.","src":"quizlet"},{"t":"How does the placenta produce estrogen if it lacks the enzymes to make androgens?","d":"The placenta has the enzymes to synthesize progesterone but not those to form androgens (the precursors of estrogen). Androgens are supplied by the maternal ovaries and the maternal and fetal adrenal glands; the placenta then converts these androgens to estrogen using aromatase.","src":"quizlet"},{"t":"How long is a full-term pregnancy, and what is parturition?","d":"A normal pregnancy lasts ~40 weeks from the first day of the last menstrual period (~38 weeks from ovulation/conception). Parturition is the collective events in the uterus and fetoplacental unit culminating in birth of the infant followed by delivery of the placenta.","src":"quizlet"},{"t":"What maternal changes (driven by estrogen) occur in preparation for parturition?","d":"Rising estrogen causes: softening of the cervix; synthesis of connexins forming gap junctions between myometrial cells (enabling strong, coordinated/rhythmic contractions); and increased myometrial expression of oxytocin receptors.","src":"quizlet"},{"t":"When do uterine contractions begin, and what happens during the last month of pregnancy?","d":"Weak, infrequent uterine contractions begin around 30 weeks and gradually increase in strength and frequency. In the final month, the uterine contents shift downward, bringing the near-term fetus into contact with the cervix.","src":"quizlet"},{"t":"Outline the events of labor and delivery.","d":"1) The amniotic sac ruptures and amniotic fluid flows out (water breaks); 2) strong uterine contractions occur (~10–15 min intervals); 3) the cervix is progressively dilated to ~10 cm; 4) contractions move the fetus through the cervix and vagina; 5) the baby is delivered and the umbilical and placental vessels constrict; 6) the placenta is delivered.","src":"quizlet"},{"t":"Why is the mother instructed to push during delivery, and in what position is the fetus normally delivered?","d":"Bearing down increases abdominal pressure, adding to the uterine contractions to help deliver the baby. In over 90% of births the baby is delivered head first (vertex presentation), the head acting as a wedge to dilate the cervix.","src":"quizlet"},{"t":"What are the controllers of parturition?","d":"1) Myometrial smooth-muscle cells have inherent rhythmicity and autonomous contractions; 2) uterine (placental) prostaglandins stimulate smooth-muscle contraction; 3) oxytocin (synthesized in the hypothalamus, reflexively released from the posterior pituitary) directly stimulates uterine muscle and stimulates prostaglandin synthesis; 4) progesterone inhibits uterine contractions during pregnancy by decreasing myometrial sensitivity to estrogen, oxytocin, and prostaglandins.","src":"quizlet"},{"t":"What is lactogenesis, and how do the mammary glands prepare for lactation?","d":"Lactogenesis is the production and secretion of milk by the mammary glands (within the breasts). The mammary glands increase in size and cell number during late pregnancy.","src":"quizlet"},{"t":"What is the structure of the mammary glands, and where does milk secretion occur?","d":"Each breast has numerous mammary glands whose ducts branch through the tissue and converge at the nipple. The ducts begin in saclike alveoli, which are the sites of milk secretion; the alveoli and adjacent ducts are surrounded by contractile myoepithelial cells.","src":"quizlet"},{"t":"What is the major milk-production hormone, and why is no milk secreted before delivery despite high prolactin?","d":"Prolactin is the major hormone stimulating milk production. During pregnancy, high estrogen and progesterone inhibit prolactin's action on the breasts, so no milk is secreted. Delivery removes the placenta (the source of estrogen/progesterone), releasing milk production from this inhibition.","src":"quizlet"},{"t":"After estrogen falls postpartum, what happens to prolactin secretion during breastfeeding?","d":"Basal prolactin decreases from its late-pregnancy peak and over months returns toward prepregnancy levels, but each bout of nursing triggers large secretory bursts of prolactin (a neural response).","src":"quizlet"},{"t":"What is the milk ejection (let-down) reflex?","d":"Suckling stimulation of the nipple reflexively releases oxytocin (synthesized in the hypothalamus) from posterior pituitary neurons. Oxytocin makes the myoepithelial cells surrounding the alveoli contract, moving milk forward through the ducts to the nipple.","src":"quizlet"},{"t":"What is colostrum?","d":"The watery, protein-rich \"early breast milk\" secreted after delivery; it contains secretory IgA antibodies, leukocytes and other immune mediators, growth factors and hormones, neuropeptides and endogenous opioids, and minerals.","src":"quizlet"},{"t":"What distinguishes contraceptives from abortifacients, and what are the main contraceptive types?","d":"Contraceptives work prior to implantation; procedures causing death of the embryo/fetus after implantation are abortions. Main contraceptive types: vasectomy, tubal ligation, vaginal diaphragm/cap/sponge, spermicides, condoms, and oral contraceptives.","src":"quizlet"},{"t":"How do oral contraceptives work, what types exist, and what other effects do they have?","d":"Exogenous estrogen and/or progesterone inhibit anterior pituitary gonadotropin release, preventing the estrogen-driven LH surge so ovulation does not occur. Types: a combined estrogen + progestin pill, and the progesterone-only \"minipill.\" Other effects: thickening cervical mucus (hampering sperm passage) and inhibiting estrogen-induced endometrial proliferation (making it inhospitable to implantation).","src":"quizlet"},{"t":"How does emergency (postcoital) contraception work, and how does mifepristone act?","d":"Within 72 hours of intercourse, a high dose of estrogen/progestin (or an antiprogesterone) interferes with ovulation, transport of the conceptus, or implantation. Mifepristone binds competitively to uterine progesterone receptors without activating them; antagonizing progesterone erodes the endometrium and increases contractions of the fallopian tubes and myometrium.","src":"quizlet"},{"t":"What is menopause, when does it occur, and what is perimenopause?","d":"Menopause is the permanent cessation of menstrual cycles due to ovarian failure, with declining estrogen; it occurs around 48–55 years and is defined once cycles have been absent for more than 12 months. Perimenopause is the preceding phase of menstrual irregularity, marked by a decreasing number of ovarian follicles and hyporesponsiveness of the remaining follicles to gonadotropins.","src":"quizlet"},{"t":"What occurs during menopausal ovarian failure (hormonally)?","d":"The ovaries lose responsiveness to gonadotropins (most follicles lost via atresia). Falling estrogen and inhibin release the hypothalamus/pituitary from negative feedback, so GnRH and gonadotropin (LH/FSH) secretion rise.","src":"quizlet"},{"t":"What is the source of the small amount of estrogen that persists after menopause?","d":"Peripheral conversion of adrenal androgens to estrogen by aromatase.","src":"quizlet"},{"t":"What are the signs/symptoms of menopause, and a possible treatment?","d":"Hot flashes, atrophy of the breasts and genital organs (with vaginal thinning/dryness), osteoporosis (decreased bone mass), and an increased risk of cardiovascular disease. Many symptoms and osteoporosis can be reduced by estrogen administration (hormone replacement therapy), though its use is controversial.","src":"quizlet"},{"t":"What are folliculogenesis and oogenesis?","d":"Folliculogenesis is the maturation of the ovarian follicle; oogenesis is the development of the female gamete (production of mature ova by two meiotic divisions).","src":"quizlet"},{"t":"What kind of hormone is testosterone and from what is it synthesized?","d":"Testosterone is a steroid hormone (an androgen), synthesized from the precursor cholesterol.","src":"quizlet"},{"t":"What are gonadotropes (gonadotrophs)?","d":"Cells in the anterior pituitary gland that produce the gonadotropins LH and FSH.","src":"quizlet"},{"t":"What is the precursor of all steroid hormones?","d":"Cholesterol — steroid hormone synthesis (as in the adrenal cortex) starts with cholesterol.","src":"quizlet"},{"t":"Which structure does NOT contribute fluid to semen: bulbourethral glands, prostate, vas deferens, or seminal vesicles?","d":"The vas deferens. The prostate, seminal vesicles, and bulbourethral glands secrete the fluid of semen; the vas deferens is a transport duct/storage reservoir for sperm and does not contribute glandular fluid.","src":"quizlet"},{"t":"What happens to chromosomes during interphase (before meiosis/mitosis)?","d":"Chromosomal DNA is replicated, so each chromosome then consists of two identical sister chromatids joined by a centromere.","src":"quizlet"},{"t":"What does inhibin do?","d":"Inhibin (secreted by Sertoli cells in males and granulosa/luteal cells in females) inhibits FSH secretion from the anterior pituitary as a negative-feedback controller.","src":"quizlet"},{"t":"What are some effects of aging on reproductive function in males and females?","d":"In males (andropause): a steady decrease in testosterone secretion beginning around age 40, decreased libido, and less motile sperm (reduced fertility), but rarely complete cessation of function. In females (menopause): ovarian failure with loss of estrogen and progesterone, cessation of menstrual cycles and fertility, atrophy of the breasts and genital organs, thinning/dryness of the vaginal epithelium, and decreased bone mass (osteoporosis).","src":"quizlet"},{"t":"About how many sperm are produced per day, and how many are in a single ejaculation?","d":"About 30 million sperm are produced per day; about 300 million sperm are expelled in a single ejaculation (average semen volume ~3 mL).","src":"quizlet"},{"t":"What is perimenopause?","d":"The phase of life during which menstrual cycles become less regular (begin to occur irregularly), preceding the ultimate cessation of menstrual cycles (menopause).","src":"quizlet"},{"t":"At what gestational age does the developing conceptus transition from embryo to fetus?","d":"At approximately 2 months (8 weeks) of gestation. The placenta has been well established since five weeks after implantation.","src":"quizlet"},{"t":"Which ovaries secrete hormones — embryonic or post-natal?","d":"Post-natal ovaries. The female fetus does not have testes and therefore does not secrete testosterone or AMH; female differentiation of both internal and external genitalia proceeds in the absence of gonadal hormones. Post-natal ovaries begin hormone secretion at puberty.","src":"quizlet"},{"t":"By what week of fetal life does sexual differentiation of external genitalia become apparent, and by what week is it unmistakable?","d":"Sexual differentiation of the external genitalia becomes apparent at 10 weeks of fetal life and is unmistakable by 12 weeks, driven by the presence of testosterone and its local conversion to DHT in target tissue.","src":"quizlet"},{"t":"What secondary sex characteristics are stimulated by estrogen in females at puberty?","d":"Estrogen stimulates breast growth (particularly ducts and fat deposition), female body configuration (narrow shoulders, broad hips, female fat distribution on hips and breasts), and growth of external genitalia. Note: pubic and axillary hair in females is stimulated by androgens (from adrenal glands and ovaries), not estrogen.","src":"quizlet"},{"t":"Where does aromatization (conversion of testosterone to estradiol) occur?","d":"Aromatization of testosterone to estradiol occurs in certain non-gonadal target tissues (e.g., the brain), not as a primary function of Leydig cells. Leydig cells synthesize and secrete testosterone; it is in specific target cells that the enzyme aromatase converts testosterone to estradiol, which then acts as the active hormone in those cells.","src":"quizlet"},{"t":"What temperature condition impairs spermatogenesis?","d":"Optimal sperm formation requires a temperature approximately 2°C (3.8°F) lower than normal internal body temperature; this is why the testes descend into the scrotum, where cooling is achieved by air circulating around the scrotum and by a heat-exchange mechanism in the blood vessels supplying the testes.","src":"quizlet"},{"t":"What is the glans of the male reproductive system?","d":"The conical-shaped, bulbous structure at the distal end of the penis (the head of the penis); in uncircumcised males it is covered by the prepuce (foreskin), a retractable double layer of skin and fascia.","src":"quizlet"},{"t":"What is removed in a circumcision?","d":"The prepuce (foreskin) — the retractable skin covering the glans of the penis — is surgically removed.","src":"quizlet"},{"t":"Other than for reproductive purposes, what do secretions of the male accessory glands achieve?","d":"Accessory sex gland secretions are bacteriostatic and can protect the male genital tract from bacterial infection (e.g., zinc in seminal plasma has antibacterial properties).","src":"quizlet"},{"t":"Which gonadotropin is preferentially secreted by the anterior pituitary during high-frequency GnRH pulses?","d":"LH (luteinizing hormone) — high-frequency GnRH pulses (>1 pulse per hour) favor preferential LH synthesis and secretion from anterior pituitary gonadotropes.","src":"quizlet"},{"t":"Which gonadotropin is preferentially secreted by the anterior pituitary during low-frequency GnRH pulses?","d":"FSH (follicle-stimulating hormone) — low-frequency GnRH pulses (<1 pulse per 2–3 hours) favor preferential FSH synthesis and secretion from anterior pituitary gonadotropes.","src":"quizlet"},{"t":"What else can hCG stimulate in the developing embryo, beyond supporting the corpus luteum?","d":"Testosterone production. Placental hCG binds LH/CG receptors on fetal Leydig cells and stimulates testosterone secretion during the critical period of male sex differentiation.","src":"quizlet"},{"t":"alleles","d":"Alternative forms of a gene at a given locus that code for the same trait but may differ from one another (e.g., one allele may encode dimples, another smooth skin).","src":"quizlet"},{"t":"climacteric","d":"The broad transitional period encompassing perimenopause and extending into postmenopause, during which ovarian function declines. Signs include irregular or missed periods, hot flashes, and mood changes such as irritability.","src":"quizlet"},{"t":"When does the placenta begin to form, and what structures develop during weeks 2 and 3 after fertilization?","d":"The placenta begins forming at weeks 2–3. During week 2, primary chorionic villi develop (cytotrophoblast projections surrounded by syncytiotrophoblast); during week 3, secondary villi with a mesodermal core form.","src":"quizlet"},{"t":"What is different about reproduction between humans and other animals?","d":"Humans differ from most other mammals in that females are sexually receptive outside their fertile periods (continuous sexuality, no strict estrus), and humans engage in mating for both pleasure and procreation.","src":"quizlet"},{"t":"What is the same about reproduction between humans and other animals?","d":"Humans share with other mammals: internal fertilization, internal fetal development (viviparity), and mating/courtship behaviors.","src":"quizlet"},{"t":"What environmental factors commonly affect female reproductive function?","d":"Stress, nutritional status, and the daylight (photoperiod) cycle via melatonin. Stress and energy deficit can suppress GnRH/LH/FSH, and melatonin secreted during darkness regulates seasonal reproductive cycles.","src":"quizlet"},{"t":"What types of environmental substances can bind to hormone receptors?","d":"Phytoestrogens (plant-derived compounds such as isoflavones) and synthetic chemicals (including plasticizers and pesticides) that act as endocrine disruptors by binding to estrogen receptors.","src":"quizlet"},{"t":"How do phytoestrogens and synthetic endocrine disruptors affect hormones and reproduction?","d":"They bind to estrogen receptors and can act as weak estrogen agonists or as anti-estrogens (antagonists) by competing with endogenous estrogens for receptor binding sites, thereby inhibiting estrogenic effects.","src":"quizlet"},{"t":"What can result from high-level exposure to phytoestrogens or synthetic endocrine disruptors in a male embryo?","d":"Decreased capacity to produce sperm (reduced sperm counts and impaired spermatogenesis) in adult male offspring.","src":"quizlet"},{"t":"What is the corpus spongiosum?","d":"A cylindrical mass of erectile (spongy) tissue on the ventral surface of the penis that surrounds and protects the urethra and participates in the erectile mechanism. It has a thinner, more elastic tunica albuginea than the corpora cavernosa.","src":"quizlet"}]};

const CLASS_QUESTIONS = {"cell":[],"blood":[{"q":"Here are three statements about diapedesis. Which statement(s) is/are correct?\n  Statement 1: Diapedesis is a crucial feature of innate immunity.\n  Statement 2: Impairment of diapedesis would lead to persistent bacterial infections.\n  Statement 3: Diapedesis is preceded by margination, rolling and adhesion; and followed by chemotaxis and phagocytosis.","options":["Statement 1 only","Statements 1 and 2","Statements 1 and 3","Statements 2 and 3","All statements are correct"],"a":4,"e":"Diapedesis (WBCs squeezing through the endothelium) is a key step in innate immunity; its impairment leaves bacteria unchallenged. The full sequence of cellular events is: margination → rolling → adhesion → diapedesis → chemotaxis → phagocytosis, making all three statements correct.","src":"course","cite":"PHYSL 210 sample questions — blood"},{"q":"Here are 3 statements about plasma proteins. Which of these are correct?\n  Statement 1: Plasma proteins are mainly produced by the liver.\n  Statement 2: Transport of oxygen is a major function of plasma proteins.\n  Statement 3: Removal of fibrinogen and other clotting factors from plasma results in the formation of serum.","options":["Statement 1: Correct, Statement 2: Correct, Statement 3: Correct","Statement 1: Correct, Statement 2: Not correct, Statement 3: Correct","Statement 1: Correct, Statement 2: Correct, Statement 3: Not correct","Statement 1: Not correct, Statement 2: Not correct, Statement 3: Correct","Statement 1: Not correct, Statement 2: Not correct, Statement 3: Not correct"],"a":1,"e":"The liver is the major site of plasma protein synthesis. Oxygen is transported by hemoglobin inside red blood cells, not by plasma proteins, so Statement 2 is false. Serum is plasma with fibrinogen and other clotting factors removed, making Statement 3 correct.","src":"course","cite":"PHYSL 210 sample questions — blood"}],"nms":[{"q":"Place the following events in the correct sequence describing synaptic transmission:\n1. Calcium influx causes synaptic vesicles to move to and fuse with the presynaptic membrane.\n2. Ions flow across the membrane to depolarize or hyperpolarize the postsynaptic cell.\n3. Voltage-gated calcium channels open following depolarization of the terminal.\n4. An action potential arrives in the presynaptic terminal.\n5. Transmitter is released by exocytosis and diffuses across synaptic cleft to bind to receptors.","options":["3, 4, 1, 2, 5","4, 3, 1, 2, 5","4, 3, 1, 5, 2","2, 4, 1, 5, 2","2, 4, 2, 5, 1"],"a":2,"e":"The correct order is: action potential arrives (4) → voltage-gated Ca²⁺ channels open (3) → Ca²⁺ influx causes vesicle fusion with presynaptic membrane (1) → neurotransmitter is released by exocytosis and diffuses to bind receptors (5) → ions flow to depolarize or hyperpolarize the postsynaptic cell (2).","src":"course","cite":"PHYSL 210 sample questions — nms"}],"cns":[{"q":"Which one of the following represents the correct sequence from innermost to outermost layers of the meninges?","options":["dura mater, arachnoid mater, pia mater","pia mater, dura mater, arachnoid mater","arachnoid mater, dura mater, pia mater","dura mater, pia mater, arachnoid mater","pia mater, arachnoid mater, dura mater"],"a":4,"e":"The meninges from innermost to outermost are: pia mater (delicate, directly on brain), arachnoid mater (spidery, with subarachnoid space below it), and dura mater (tough, outermost layer).","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which of the following cells produce cerebrospinal fluid?","options":["Interneurons","Astrocytes","Ependymal cells","Oligodendrocytes","Microglia"],"a":2,"e":"Ependymal cells line the ventricles and produce cerebrospinal fluid (CSF) at a fairly steady rate; the CSF then flows through the interconnected ventricular system and into the subarachnoid space.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"An impairment of language comprehension is consistent with a lesion in:","options":["Wernicke's area","Broca's area","Occipital cortex","Forebrain","Cerebellum"],"a":0,"e":"Wernicke's area (temporal lobe) is responsible for language comprehension; a lesion there impairs the ability to understand spoken or written language, while Broca's area (frontal lobe) governs language production.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which of the following will promote sleep?","options":["Increased adenosine levels in the blood","Activation of orexin producing neurons by the suprachiasmatic nucleus","A negative energy balance causing hunger","Release of monoamines which inhibit the sleep center","Activation of orexin producing neurons by the limbic system"],"a":0,"e":"A gradual increase in adenosine concentration due to metabolic activity inhibits the orexin-producing neurons and monoaminergic RAS neurons, allowing the GABAergic sleep center to become active and promote sleep.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"The hypothalamus is involved in:","options":["Memory","Language production","Balance","Emotions","None of the above"],"a":3,"e":"The hypothalamus is a key component of the limbic system and is involved in regulating emotions, as well as homeostasis, feeding, and hormone release; language and balance are functions of other brain regions.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which one of the following statements is correct?","options":["The spinal cord is primarily involved in language.","The brainstem is primarily involved in control of cognitive functions.","The spinal cord is primarily involved in control of sleep/wakefulness.","The cerebellum controls the respiratory and cardiovascular system.","The hypothalamus is involved in homeostasis."],"a":4,"e":"The hypothalamus is the primary homeostatic centre, regulating body temperature, fluid balance, feeding, and autonomic function; language, cognition, and sleep/wake control reside in the cerebral cortex and brainstem, not the spinal cord.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which of the following sensory receptors responds to vibration and deep pressure?","options":["Golgi tendon organ","Pacinian corpuscle","Meissner's corpuscle","Muscle spindle","Free nerve endings"],"a":1,"e":"Pacinian (lamellated) corpuscles are rapidly adapting mechanoreceptors specialized to detect vibration and deep pressure; Meissner's corpuscles detect light touch, while Golgi tendon organs and muscle spindles are proprioceptors.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which statement about memory is true?","options":["Consolidation converts long term memory into short term memory.","In retrograde amnesia, there is a loss of memory after the injury.","In anterograde amnesia there is a loss of memory prior to the injury.","Working memory can be divided into declarative and procedural classes.","Damage to the hippocampus results in complete anterograde amnesia."],"a":4,"e":"The hippocampus is essential for consolidating new declarative (explicit) memories; bilateral hippocampal damage prevents the formation of any new long-term declarative memories, producing profound anterograde amnesia.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"The midbrain, pons, and medulla oblongata are housed in the:","options":["Diencephalon","Brainstem","Corpus callosum","Hypothalamus","Cerebellum"],"a":1,"e":"The brainstem consists of three subdivisions — midbrain, pons, and medulla oblongata — and is distinct from the diencephalon (thalamus and hypothalamus) and the cerebellum.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which one of the following statements regarding sensory stimulus processing is correct?","options":["Different modalities are processed in the same region of the brain.","A rapidly adapting receptor responds the entire time a stimulus is applied.","A larger receptive field provides greater spatial acuity.","Overlapping stimulation between neighboring receptive fields provides information about the location of a stimulus.","Two-point discrimination is best on the abdomen and proximal parts of the limbs."],"a":3,"e":"When two neighbouring receptive fields are both stimulated, their overlap helps the brain triangulate the precise location of the stimulus; smaller receptive fields (not larger ones) provide greater spatial acuity, and two-point discrimination is best on the hands and face.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which of the following is involved in the transmission of pain to the central nervous system?","options":["Endogenous opiate neurotransmitters","Acetylcholine","Substance P","Norepinephrine","Glycine"],"a":2,"e":"Substance P is the primary neuropeptide released by nociceptors (C fibres and Aδ fibres) at the dorsal horn synapse to transmit pain signals to the CNS; endogenous opiates suppress pain rather than transmit it.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"The hemispheres of the cerebrum are connected by a nerve tract called the:","options":["Pons","Corpus callosum","Neural network","Thalamus","Medulla"],"a":1,"e":"The corpus callosum is a large bundle of myelinated axons that connects the left and right cerebral hemispheres, allowing them to share information and coordinate activity.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which of the following regarding muscle receptors is true?","options":["Gamma motoneurons activate extrafusal muscle fibers to contract.","Muscle spindles respond to changes in muscle force.","Alpha motoneurons activate intrafusal muscle fibers to contract.","Alpha-gamma coactivation ensures the muscle spindle remains sensitive to changes in muscle length.","Golgi tendon organs respond to changes in muscle length."],"a":3,"e":"Alpha-gamma coactivation means that when alpha motoneurons drive extrafusal fibre contraction, gamma motoneurons simultaneously shorten intrafusal fibres, keeping the muscle spindle taut so it can continue to detect changes in muscle length.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Which of these receptors detects an increase in tension in a muscle?","options":["Meissner's corpuscle","Nociceptors","Muscle spindle","Merkel's corpuscle","Golgi tendon organ"],"a":4,"e":"Golgi tendon organs are located at the musculotendinous junction and are sensitive to increases in muscle tension (force); muscle spindles, in contrast, monitor changes in muscle length.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"Corticospinal neurons make _________________ connections with spinal _____________ motoneurons whose axons activate muscles.","options":["Monosynaptic; alpha","Disynaptic; alpha","Monosynaptic; gamma","Disynaptic; gamma","Monosynaptic; delta"],"a":0,"e":"Corticospinal tract (CST) neurons make direct monosynaptic connections onto alpha motoneurons in the ventral horn of the spinal cord; alpha motoneurons then send their axons to extrafusal (force-generating) muscle fibres.","src":"course","cite":"PHYSL 210 sample questions — cns"},{"q":"The basal ganglia are responsible for:","options":["Initiating movement","Regulation of homeostasis, including temperature regulation","Suppressing activity of muscles that would resist the intended movement","Control of the sleep/wake cycle","More than one of the above"],"a":4,"e":"The basal ganglia contain circuits that both facilitate and suppress movement, ensuring smooth execution; some circuits initiate movement while others suppress activity in muscles opposing the intended movement, making both A and C correct.","src":"course","cite":"PHYSL 210 sample questions — cns"}],"ans":[{"q":"A postganglionic neuron:","options":["Has a myelinated axon","Releases neurotransmitter at the effector cell","Is the first part of an autonomic pathway","Has its cell body in the brain or spinal cord","Has its axon exiting the CNS through spinal nerves"],"a":1,"e":"Postganglionic neurons are the second neuron in a two-neuron autonomic pathway; their unmyelinated axons terminate on effector cells (smooth muscle, cardiac muscle, or glands) where they release neurotransmitter. The cell body of a postganglionic neuron resides in an autonomic ganglion, not the CNS.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"In the ANS, preganglionic neurons synapse with postganglionic neurons in the:","options":["Autonomic ganglia","Dorsal root ganglia","Brain stem","Ventral root","Spinal cord"],"a":0,"e":"The defining structural feature of the ANS is that preganglionic axons leaving the CNS synapse onto postganglionic neurons within autonomic ganglia (sympathetic chain/collateral ganglia or parasympathetic terminal ganglia) before reaching the target organ.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"Which of the following characteristics apply to the ANS? 1) Consciously controlled  2) Two neurons between the CNS and effector organs  3) Preganglionic and postganglionic neurons are myelinated  4) Neurotransmitters can be acetylcholine or norepinephrine","options":["1, 2","1, 3","1, 4","2, 3","2, 4"],"a":4,"e":"The ANS is involuntary (not consciously controlled) and uses two neurons — a myelinated preganglionic and an unmyelinated postganglionic — between the CNS and effector. Neurotransmitters are acetylcholine (at ganglia and parasympathetic endings) and norepinephrine (at most sympathetic postganglionic endings).","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"Which of these characteristics describes the parasympathetic division of the ANS?","options":["Preganglionic cell bodies are found in the brainstem and lateral parts of spinal cord gray matter (S2–S4).","Chain ganglia and collateral ganglia are present.","Norepinephrine is released by the postganglionic neurons.","Short preganglionic neurons, long postganglionic neurons.","All of these are correct."],"a":0,"e":"The parasympathetic division has a craniosacral origin: preganglionic cell bodies lie in brainstem nuclei (CN III, VII, IX, X) and in spinal cord segments S2–S4. Chain and collateral ganglia belong to the sympathetic division; parasympathetic postganglionic neurons release ACh, not NE, and are short (terminal ganglia are near or within target organs).","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"The separate effects of sympathetic and parasympathetic innervation of the pacemaker region of the heart can best be described as:","options":["Antagonistic","Complementary","Cooperative","Synergistic","None of the above; the pacemaker receives only sympathetic innervation"],"a":0,"e":"Sympathetic stimulation increases heart rate while parasympathetic (vagal) stimulation decreases heart rate at the SA node — opposing actions that are antagonistic. Both divisions innervate the pacemaker, so the last option is incorrect.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"Which of the following target tissues is innervated by only neurons from the sympathetic nervous system?","options":["Bronchioles","Adrenal medulla","Pacemaker of the heart","Pupil of the eye","None of the above"],"a":1,"e":"The adrenal medulla is innervated exclusively by sympathetic preganglionic neurons; it is itself a modified sympathetic ganglion that secretes epinephrine and norepinephrine directly into the blood. Bronchioles, the cardiac pacemaker, and the pupil all receive dual (sympathetic and parasympathetic) innervation.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"Regarding the sympathetic division of the autonomic nervous system:","options":["Acetylcholine is secreted by some sympathetic postganglionic fibres.","Most sympathetic preganglionic fibres secrete norepinephrine (noradrenaline).","The cell bodies of sympathetic postganglionic neurons are found in spinal segments from T1 to L2.","The sympathetic division acts to conserve and store energy, regulate basic body functions.","Convergence leads to mass sympathetic discharge."],"a":0,"e":"Although most sympathetic postganglionic fibres release norepinephrine, those innervating sweat glands and blood vessels of skeletal muscle release acetylcholine instead. Preganglionic fibres always release ACh, not NE, and the cell bodies of postganglionic (not preganglionic) neurons are in the sympathetic ganglia.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"Regarding synaptic transmission in the autonomic nervous system:","options":["The acetylcholine receptors in both parasympathetic and sympathetic ganglia are predominantly muscarinic.","Norepinephrine secreted by sympathetic postganglionic fibres acts preferentially on muscarinic receptors.","The adrenal medulla secretes epinephrine in response to the activation of muscarinic receptors.","Acetylcholine secreted by parasympathetic postganglionic fibres acts on muscarinic receptors.","Parasympathetic ganglia lie in a chain running parallel to the spinal cord."],"a":3,"e":"Parasympathetic postganglionic fibres release ACh onto muscarinic receptors on effector cells (smooth muscle, cardiac muscle, and glands), mediating their effects via G-protein coupled mechanisms. Ganglionic receptors in both divisions are nicotinic (NN), not muscarinic, and the chain ganglia belong to the sympathetic system.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"Which of these is NOT a feature of postganglionic neurons in the sympathetic nervous system?","options":["Pass through chain ganglia","Unmyelinated","Short","Most release norepinephrine","May produce excitatory or inhibitory responses"],"a":2,"e":"Sympathetic postganglionic neurons are long, not short — they travel from the sympathetic chain or collateral ganglia (located near the spinal cord) out to distant target organs. In contrast, parasympathetic postganglionic neurons are short because their terminal ganglia are located near or within the target organ.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"The targets of the autonomic nervous system include all except the following:","options":["Smooth muscle of the bladder","Ventricular myocardium","Smooth muscle of blood vessels","Salivary glands","Skeletal muscle"],"a":4,"e":"The ANS innervates smooth muscle, cardiac muscle, and glands — it does not innervate skeletal muscle, which is under somatic (voluntary) motor control. Bladder smooth muscle, cardiac muscle, blood vessel walls, and salivary glands are all classic ANS targets.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"Which statement about autonomic neurotransmitters and their receptors is correct?","options":["Muscarinic receptors (acted on by acetylcholine, ACh) are present in smooth muscle.","Nicotinic receptors (acted on by norepinephrine) are present in autonomic ganglia.","Adrenergic receptors act as ligand-gated ion channels.","No more than one type of transmitter is ever released at a given time from any autonomic nerve terminal.","Both c and d are correct."],"a":0,"e":"Muscarinic receptors, which are G-protein coupled (metabotropic) and activated by ACh, are found on effector cell membranes including smooth muscle. Nicotinic receptors at autonomic ganglia are activated by ACh (not NE), and adrenergic receptors also signal through G-proteins, not ligand-gated ion channels.","src":"course","cite":"PHYSL 210 sample questions — ans"},{"q":"When a transmitter binds to a metabotropic receptor it may trigger a cascade reaction (signal transduction). What is the correct physiological order in which the following play a role? [G = G-protein; E = membrane-bound enzyme; P = protein kinase; S = second messenger]","options":["G, P, E, S","S, G, E, P","P, E, G, S","S, P, G, E","G, E, S, P"],"a":4,"e":"In G-protein coupled (metabotropic) signalling, the receptor activates a G-protein (G), which activates a membrane-bound enzyme (E) such as adenylate cyclase, producing a second messenger (S) such as cAMP, which in turn activates a protein kinase (P) to phosphorylate target proteins.","src":"course","cite":"PHYSL 210 sample questions — ans"}],"ss":[{"q":"Which of the following is a rapidly adapting receptor?","options":["Meissner's corpuscle","Merkel's corpuscle","Free neuron ending","Ruffini corpuscle","None are rapidly adapting mechanoreceptors"],"a":0,"e":"Meissner's corpuscles are rapidly adapting mechanoreceptors that respond to touch and pressure; they fire at the onset (and offset) of a stimulus but not during sustained stimulation. Merkel's and Ruffini corpuscles are slowly adapting.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"In the human eye, the structure primarily responsible for refraction is the:","options":["aqueous humor","iris","cornea","lens","vitreous humor"],"a":2,"e":"The cornea is responsible for most of the eye's refracting power; the lens fine-tunes focus by changing shape (accommodation) but contributes less overall refraction than the cornea.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"The sensory hair cells of the organ of Corti are anchored at their base to the:","options":["incus","basilar membrane","tectorial membrane","tympanic membrane","malleus"],"a":1,"e":"Hair cells of the organ of Corti sit on the basilar membrane; their stereocilia project upward and contact the tectorial membrane. Displacement of the basilar membrane bends the stereocilia and transduces sound into electrical signals.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"Hyperopia (farsightedness) is caused by:","options":["an eyeball that is too short.","increased intraocular pressure.","clouding of the lens.","an eyeball that is too long.","loss of elasticity of the lens."],"a":0,"e":"In hyperopia the eyeball is too short relative to the focusing power of the cornea/lens, so parallel rays converge behind the retina. Convex lenses are used to correct this by adding converging power.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"Rods and cones are:","options":["nociceptors","thermoreceptors","mechanoreceptors","photoreceptors","chemoreceptors"],"a":3,"e":"Rods and cones are photoreceptors — they transduce light energy into graded receptor potentials using the photopigment molecules rhodopsin (rods) and opsins (cones).","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"In the absence of light, which event occurs in a cone cell?","options":["Retinal changes conformation.","cGMP is broken down.","Cyclic GMP phosphodiesterase is activated.","cGMP opens a cation channel.","The cation channel closes."],"a":3,"e":"In darkness, cGMP levels are high and cGMP binds directly to cation channels, keeping them open and allowing Na+ (and Ca2+) to flow in — the so-called 'dark current' that maintains the cell in a slightly depolarized state.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"In vision, a nerve impulse travels from:","options":["rods and cones to bipolar cells to retinal ganglion cells","retinal ganglion cells to bipolar cells to rods and cones","bipolar cells to retinal ganglion cells to rods and cones","rods and cones to retinal ganglion cells to bipolar cells","retinal ganglion cells to rods and cones to bipolar cells"],"a":0,"e":"The retinal circuit flows outward: photoreceptors (rods/cones) → bipolar cells → retinal ganglion cells, whose axons form the optic nerve and carry signals to the brain.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"The axons of which cell make up the optic nerve?","options":["Rods and cones","Amacrine cells","Horizontal cells","Retinal ganglion cells","Bipolar cells"],"a":3,"e":"Retinal ganglion cells are the output neurons of the retina; their axons converge at the optic disc and form the optic nerve, transmitting visual information to the lateral geniculate nucleus and visual cortex.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"In the visual pathway, which cells generate action potentials?","options":["Retinal ganglion cells","Bipolar cells","Rods","Cones","More than one of the above"],"a":0,"e":"Photoreceptors and bipolar cells only generate graded (non-propagating) potentials. Retinal ganglion cells are the first cells in the visual pathway to fire true action potentials, which they propagate along the optic nerve.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"When the stereocilia bend in response to displacement of the basilar membrane,","options":["mechanically-gated K+ channels open and K+ leaves the cell.","the hair cell depolarizes due to the inward movement of K+.","the hair cell depolarizes due to the inward movement of Na+.","action potentials are generated in the hair cell.","the neurotransmitter glycine is released from the hair cells."],"a":1,"e":"The endolymph surrounding stereocilia is unusually high in K+; when mechanically-gated channels open upon stereocilia deflection, K+ flows down its concentration gradient into the hair cell, depolarizing it.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"A person with an eye that is 'too long' is said to have __________ and would wear __________ lenses to correct their vision.","options":["hyperopia/concave","myopia/concave","hyperopia/convex","myopia/convex","cataracts/convex"],"a":1,"e":"An eye that is too long causes light rays to focus in front of the retina — this is myopia (nearsightedness). Concave (diverging) lenses spread the rays so they focus correctly on the retina.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"In a slowly adapting receptor,","options":["a persistent or slowly decaying response is generated in the receptor during a constant stimulus.","action potentials are generated during the entire duration of the stimulus.","a response is only generated in the receptor when the stimulus is turned on or off.","Both A and B.","Both B and C."],"a":3,"e":"Slowly adapting receptors (e.g., Merkel's corpuscles) produce a sustained generator potential throughout the stimulus, which continuously drives action potentials in the afferent nerve for as long as the stimulus is applied.","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"Light results in the __________ of Na⁺/Ca²⁺ channels in the membrane of the photoreceptor cells, resulting in __________ of the rod or cone cell.","options":["opening; depolarization","opening; hyperpolarization","closing; depolarization","closing; hyperpolarization","closing; no change in the membrane potential"],"a":3,"e":"Light activates cGMP phosphodiesterase, which breaks down cGMP; without cGMP to hold them open, the cation channels close, preventing Na⁺ and Ca²⁺ from entering the cell, and the photoreceptor hyperpolarizes (from about −35 mV to −75 mV).","src":"course","cite":"PHYSL 210 sample questions — ss"},{"q":"Information from the lateral field of view of the eye goes to the __________ region of the retina. Information from the medial field of view goes to the __________ region of the retina. The information from the __________ field(s) of view crosses to the contralateral side at the optic chiasm.","options":["temporal; nasal; lateral","temporal; nasal; medial","nasal; temporal; lateral","nasal; temporal; medial","nasal; temporal; lateral and medial"],"a":2,"e":"Due to the optics of the eye, light from the lateral visual field strikes the nasal retina, and light from the medial field strikes the temporal retina. Only nasal retinal fibers cross at the optic chiasm, carrying lateral visual field information to the contralateral cortex.","src":"course","cite":"PHYSL 210 sample questions — ss"}],"cardio":[{"q":"Which of the following is not normally apparent on the ECG?","options":["Atrial depolarization","Atrial repolarization","Ventricular depolarization","Ventricular repolarization","None of the above"],"a":1,"e":"Atrial repolarization occurs during the same time as ventricular depolarization (QRS complex) and is therefore masked by the much larger QRS signal; it does not produce a distinct visible wave on the ECG.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"As the wave of action potentials travels from the atria to the ventricles, it is delayed by about 0.1 second as a result of slow conduction through:","options":["The SA node","The cardiac skeleton","The AV node","Purkinje fibers","The atrioventricular bundle"],"a":2,"e":"The AV node has slow-type action potentials and conducts impulses much more slowly than other cardiac tissues, imposing a ~0.1 s delay that allows the atria to finish contracting before the ventricles are excited.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Pressure in the left ventricle:","options":["Is less than pressure in the right ventricle","Remains unchanged during isovolumetric contraction","Is equal to pressure in the right ventricle","Increases during isovolumetric relaxation","Increases during isovolumetric contraction"],"a":4,"e":"During isovolumetric contraction all valves are closed and the ventricle generates force without changing volume, so ventricular pressure rises steeply until it exceeds aortic pressure and the semilunar valve opens.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Which of the following components of the electrocardiogram (ECG) is correctly matched with the corresponding event in the heart?","options":["QRS complex - depolarization of the atria","P wave - repolarization of the atria","T wave - repolarization of the ventricles","QRS complex - repolarization of the atria","P wave - depolarization of the SA node"],"a":2,"e":"The T wave reflects ventricular repolarization; the P wave represents atrial depolarization and the QRS complex represents ventricular depolarization.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"The amount of blood pumped out of each ventricle during a single beat is the:","options":["Cardiac output","End diastolic volume","Stroke volume","Ejection fraction","End systolic volume"],"a":2,"e":"Stroke volume is defined as the volume of blood ejected by one ventricle per heartbeat; cardiac output equals stroke volume multiplied by heart rate.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Each of the following statements about sinusoidal capillaries is correct except:","options":["They have very wide lumens","They are the least permeable capillary type","They have abundant fenestrations","They are not found in skeletal muscle","They often have phagocytic cells inserted between the endothelial cells of their lining"],"a":1,"e":"Sinusoids are the most permeable capillary type, not the least — they have large gaps between endothelial cells and allow red blood cells and large proteins to pass through freely; continuous capillaries are the least permeable.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"An individual with a blood pressure of 140/90:","options":["Has a systolic pressure of 90 mmHg","Has a diastolic pressure of 140 mmHg","Has an undetermined systolic pressure","Has a heart rate of 70 beats/min","Has a diastolic pressure of 90 mmHg"],"a":4,"e":"Blood pressure is recorded as systolic/diastolic; the numerator (140 mmHg) is the peak systolic pressure and the denominator (90 mmHg) is the diastolic pressure.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"During ventricular filling:","options":["The ventricles contract.","The semilunar valves are closed.","The atrioventricular (AV) valves are closed.","Blood flows from the ventricles to the atria through the AV valve.","The pressure in the ventricles decreases."],"a":1,"e":"During ventricular filling (diastole), the ventricles are relaxed and the AV valves are open so blood can flow from the atria into the ventricles; the semilunar valves remain closed because aortic and pulmonary pressures exceed ventricular pressure.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"During ventricular ejection:","options":["The AV valves are open; the semilunar valves are closed","The AV valves are open; the semilunar valves are open","The AV valves are closed; the semilunar valves are open","Blood flows from the atria to the ventricles","The ventricle empties its entire volume of blood"],"a":2,"e":"When ventricular pressure exceeds arterial pressure the semilunar valves open; simultaneously the AV valves are held shut by the pressure gradient, preventing backflow into the atria.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"The cardiac skeleton:","options":["Is composed of smooth muscle and blood vessels.","Separates the left and right ventricles.","Provides attachment for the heart valves and cardiac muscle","Is a wall of muscle that separates the left and right atria.","Conducts action potentials from the atria to the ventricles."],"a":2,"e":"The cardiac skeleton is a ring of dense fibrous connective tissue that anchors the four heart valves and provides attachment points for the atrial and ventricular cardiac muscle; it also electrically insulates the atria from the ventricles.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Which of the following contains deoxygenated blood in an adult human?","options":["Left atrium","Pulmonary artery","Pulmonary vein","Left ventricle","Aorta"],"a":1,"e":"The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs for oxygenation; all structures on the left side of the heart and the aorta carry oxygenated blood.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Which statement regarding the heart is correct?","options":["The right side of the heart contains fully oxygenated blood.","The right ventricle develops greater pressures than the left ventricle during contraction.","The arteries return blood to the heart.","All veins contain deoxygenated blood.","The left ventricle has a thicker myocardium than the right ventricle."],"a":4,"e":"The left ventricle must pump blood through the high-resistance systemic circulation, so it develops much higher pressures and has a substantially thicker myocardium than the right ventricle, which pumps to the low-resistance pulmonary circuit.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"In the normal myocardium, the correct sequence of excitation is:","options":["AV node → SA node → Bundle branches → AV bundle → Purkinje fibers","SA node → AV node → Bundle branches → AV bundle → Purkinje fibers","SA node → AV node → AV bundle → Bundle branches → Purkinje fibers","AV node → SA node → AV bundle → Purkinje fibers → Bundle branches","SA node → AV bundle → AV node → Purkinje fibers → Bundle branches"],"a":2,"e":"The SA node fires first and conducts to the AV node; after the AV nodal delay the impulse passes through the Bundle of His (AV bundle), then divides into the left and right bundle branches, and finally travels through the Purkinje fibers to excite the ventricular myocardium.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Which of the following statements regarding cardiac action potentials is correct?","options":["Parasympathetic stimulation of the SA node increases the slope of the pacemaker potential.","Between action potentials, cells of the SA node have a stable resting potential.","The repolarization phase of the SA node action potential is due to the opening of potassium channels.","During the absolute refractory period, action potentials may be generated with a stronger stimulus.","Sympathetic stimulation to the SA node decreases the slope of the pacemaker potential."],"a":2,"e":"Repolarization of the SA node action potential occurs when voltage-gated K+ channels open and K+ exits the cell; between beats the SA node undergoes the gradual pacemaker depolarization rather than a stable resting potential.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Which of the following is correctly matched?","options":["Bicuspid valve — permits the flow of oxygenated blood from the left atrium to the left ventricle","Pulmonary valve — prevents the backflow of blood into the right atrium when the right ventricle contracts","Bicuspid valve — found on the right side of the heart","Tricuspid valve — opens and closes as a result of contraction of papillary muscles","Pulmonary valve — permits the flow of oxygenated blood from the ventricle into the pulmonary trunk"],"a":0,"e":"The bicuspid (mitral) valve is the AV valve on the left side of the heart; it opens to allow oxygenated blood from the left atrium to fill the left ventricle during diastole.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"The source of nutrients for the heart is the:","options":["The coronary circulation","Blood in the atria and ventricles","Pulmonary veins","Pulmonary arteries","The aorta"],"a":0,"e":"The coronary arteries, which originate at the base of the aorta just beyond the aortic valve, supply oxygenated blood and nutrients directly to the myocardium; blood inside the cardiac chambers cannot diffuse far enough to nourish the thick wall.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Which of the following statements regarding the conduction system of the heart is true?","options":["Between action potentials, the cells of the sinoatrial node have a steady resting potential.","The atrioventricular node is the dominant pacemaker and fires at the fastest rate.","The spread of cardiac excitation speeds up at the atrioventricular node.","The Purkinje fibers are the only electrical connection between the atria and the ventricles.","The Purkinje fibers transmit action potentials to the ventricular myocardium by gap junctions."],"a":4,"e":"Purkinje fibers are electrically coupled to ventricular myocardial cells via gap junctions (intercalated discs), allowing the action potential to spread rapidly throughout the ventricular myocardium for coordinated contraction.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"In the coronary circulation:","options":["Myocardial blood flow is maximal during ventricular systole.","The cardiac veins empty into the left atrium.","Myocardial blood flow is minimal during ventricular diastole.","The coronary sinus is an artery that supplies the heart muscle.","Myocardial blood flow is maximal during ventricular diastole."],"a":4,"e":"During ventricular systole the contracting myocardium compresses the intramural coronary vessels, reducing flow; during diastole the muscle relaxes, compression is released, and blood flow through the coronary arteries is maximal.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Here are three statements about capillaries — are they correct or not correct? (1) Fenestrated capillaries allow blood cells to cross the endothelial cells. (2) Sinusoids are found in liver, bone marrow and spleen. (3) Capillaries contain a layer of smooth muscle lined by endothelial cells to control blood flow.","options":["1 Correct, 2 Correct, 3 Not correct","1 Correct, 2 Correct, 3 Correct","1 Not correct, 2 Correct, 3 Not correct","1 Not correct, 2 Correct, 3 Correct","1 Correct, 2 Not correct, 3 Correct"],"a":2,"e":"Fenestrated capillaries allow rapid exchange of water and small solutes but not blood cells — only sinusoids (discontinuous capillaries) permit RBC passage. Sinusoids are indeed found in liver, bone marrow and spleen. True capillaries lack smooth muscle; only arterioles and metarterioles have smooth muscle.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"Which of the following regarding the pericardial sac is correct?","options":["It allows the heart to contract and expand within the chest cavity with minimal friction.","It insulates the chest wall from the electrical impulses generated by the heart.","It helps conduct the electrical activity throughout the heart.","The fibrous pericardium is also part of the heart wall.","It is a doubled layered sac."],"a":0,"e":"The pericardium secretes pericardial fluid between its two serous layers, creating a frictionless environment that allows the heart to contract and expand freely within the thoracic cavity.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"__________ is the ability of certain myocardial cells to produce an electrical impulse without the need for outside nerve stimulation.","options":["Excitability","Conductivity","Automaticity","Contractility","Electricity"],"a":2,"e":"Automaticity (autorhythmicity) is the property by which cardiac pacemaker cells — such as those in the SA node — generate spontaneous action potentials driven entirely by intrinsic ion channel activity rather than external nervous or hormonal input.","src":"course","cite":"PHYSL 210 sample questions — cardio"},{"q":"In the sinoatrial (SA) node, the pacemaker potential is attributable to which of the following?","options":["An increase in K+ conductance","A decrease in Cl- conductance","An increase in Na+ conductance","A decrease in Ca2+ conductance","Simultaneous increases in K+ and Cl- conductances"],"a":2,"e":"The SA node pacemaker potential results from the progressive closure of K+ channels (reducing outward K+ current), opening of F-type channels (allowing Na+ influx), and opening of T-type Ca2+ channels; the net effect is a gradual depolarization driven importantly by increased Na+ conductance through funny (If) channels.","src":"course","cite":"PHYSL 210 sample questions — cardio"}],"gi":[],"resp":[],"renal":[],"endo":[],"repro":[]};

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