1. What is the function of the immune system and its two components (general)?
    • Protects body from disease-causing agents (pathogens)
    • Innate (nonspecific) immunity: provides general defenses to pathogens
    • Adaptive (specific immunity: respond to presence of specific substances (antigens)
    • Innate and adaptive immunity occur simultaneously
  2. What are the components of innate immunity and a general description of their functions?
    • Epithelial membranes (body surfaces): block entrance of pathogens into body
    • Stomach acid (pH 1-2): kills various microorganisms ingested
    • Phagocytic cells: neutrophils, monocytes, macrophages, other phagocytes
    • Complement proteins (in plasma): proteins that kill pathogens when activated by antibodies
    • Natural killer cells: kill tumor cells and pathogens by cell-cell contact (similar to killer T-cells)
  3. What is a pathogen?
    A disease-causing agent
  4. Generally describe adaptive immunity.
    Lymphocytes “learn” to respond to specific antigens (hundreds of thousands of receptor proteins specific for different antigens vs. around 10 for innate immunity)
  5. Describe the local inflammation response.
    • Bacteria enter a break in the skin to reach CT
    • Phagocytosis by local macrophages and neutrophils
    • Chemical signals can summon more neutrophils and monocytes (which will differentiate into macrophages) from the blood
    • These cells leave the blood by squeezing between endothelial cells of capillaries (extravasation / diapedesis)
    • Neutrophils accumulate quickly, engulf bacteria and/or release proteases (protein-digesting enzymes) that liquefy surrounding tissue (creating pus)
    • Neutrophils die, engulfed by macrophages
    • Mast cells secrete histamine (induces vasodilation, increases permeability of capillaries to bring in defensive proteins and antibodies, leads to local edema, redness, pain, and warmth) and cytokines (proteins that regulate immune cells)
    • Specific immune response may be triggered (antibodies produced)
  6. What causes a fever? Describe the process of a fever.
    • A fever is generated in reponse to continued inflammation
    • Monocytes and macrophages release endogenous pyrogen in response to bacterial molecules
    • Endogenous pyrogen causes the hypothalamus to raise the body temperature set point (increasing body temperature)
    • This response is thought to help fight infections
  7. What is an antigen?
    Molecules or parts of molecules that stimulate adaptive immune response by lymphocytes (chemicals that lymphocytes recognize as being foreign)
  8. Describe lymphocyte “creation” and types / where they are produced for the adaptive immune system.
    • Lymphocytes produced in bone marrow
    • Undergo several developmental stages
    • Colonize the thymus, lymph nodes, and spleen (multiplication of lymphocytes)
    • B-Lymphocytes “produced” in bone marrow
    • T-Lymphocytes “produced” in the thymus
  9. What are the primary lymph organs?
    Thymus and bone marrow
  10. What is an antibody? Describe it and its functions (detailed).
    • Proteins that bind to specific antigens
    • Agglutination (stick antigen-bearing cells together)
    • “Tag” pathogenic cells to induce phagocytosis
    • Stimulate B-lymphocyte multiplication / differentiation
  11. What is the general function of B Lymphocytes what type of immunity is provided?
    • Produce antibodies (aka immunoglobulins)
    • Provide “humoral immunity” (B-Lymphocytes secreted into blood and interstitial fluid)
  12. What causes B-Lymphocyte differentiation, describe it.
    • Antigens bind to antibody receptors on B-lymphocytes, triggering clonal division of lymphocytes (exact copies)
    • Copies are further differentiated into…
    • Plasma cells – produce antibodies in response to one specific antigen
    • Memory cells – enlarged population of reserve cells that can produce specific antibodies
  13. Describe Active immunity
    • Clonal selection theory
    • Body is exposed to pathogen (antigen) [eg. Vaccination]
    • [primary response] B-Lymphocytes respond and attack specific pathogen (antibody production ~1 week)
    • Large population of memory cells formed that can respond to that specific pathogen (clonal selection) on second exposure
    • [secondary response] If pathogen enters body again memory cells provide a larger and more rapid response (antibody production ~2 hours)
  14. Describe Passive Immunity
    • Injection of exogenous antibodies (produced by another human or animal, retrieved from serum) to the body
    • Used to protect people exposed to virulent infections or toxins (hepatitis, rabies, snake venom)
    • Examples include antisera, antitoxin
    • Subject does not develop memory cells and will not have a secondary response if exposed to the substance again
    • Also occurs in newborns where antibodies cross the placenta and continued through breastmilk (immunological competence doesn’t develop until ~1 month post birth)
  15. What is another name for allergy? A brief description? The two types (w/o details)
    • Hypersensitivity
    • Abnormal immune response to an antigen (allergen)
    • Immediate hypersensitivity and delayed hypersensitivity
  16. Describe immediate hypersensitivity
    • An abnormal B cell response
    • Symptoms develop in seconds/minutes (rhinitis [runny/stuffy nose], asthma, dermatitis [hives])
    • Triggered by the release of IgE class antibodies (rather than IgG class) which…
    • Bind to mast cells and basophils (rather than circulate in blood)
    • Binding of allergen induces secretion of histamines, leuoktrienes, etc which induce allergic symptoms (from mast cells/basophils)
  17. Describe anaphylactic shock and its treatment
    • Sever allergic hypersensitivity that results in bronchiole constriction, blood vessel dilation, and increased capillary permeability
    • Treated with epinephrine (which gives the opposite effects)
  18. Describe delayed hypersensitivity
    • An abnormal T cell response (no antibodies involved)
    • Sysmptoms develop 24-72 hours after exposure
    • Examples include poison oak contact dermatitis, and the TB test
    • Treated with hydrocortisone which suppresses the immune system
  19. What is an autoimmune disease? Describe both B and T responses.
    • Diseases caused by the failure of the immune system to recognize and tolerate self-antigens
    • Stimulation of B cells that produce antibodies that bind to self-antigens (autoantibodies)
    • Killer T cells activated which target self antigens (autoreactive T cells)
  20. Give examples of autoimmune disorders and the immune response that causes them.
    • Multiple sclerosis: antibodies to oligodendrocytes
    • Grave’s disease: antibodies stimulate TSH receptors
    • Type 1 diabetes: antibodies to beta cells in pancreas
    • Systemic lupus erythematosus: antibodies to connective tissue and more (systemic)
  21. Explain how T lymphocytes vary from B Lymphocytes regarding antigens.
    • T lymphocytes do not bind to free antigens
    • Antigen presenting cells (macrophages, dendritic cells) engulf an antigen, then bind to the antigen receptor on a T lymphocyte – activating the T cell
  22. Describe the function of Helper T Lymphocytes
    • Stimulate B-cell proliferation / differentiation (plasma cells, antibodies)
    • Activates killer T lymphocytes by secreting lymphokines (a type of cytokine)
  23. Describe the function of Cytotoxic (killer) T lymphocytes
    • Destroy cancerous / virus-infected cells
    • Once activated, killer T cells migrate throughout the body
    • When the cell physically contacts a cell with its specific antigen present perforins are secreted, which destroy the target’s plasma membrane
    • This induces lysis of the target cell (allows contents of cell to escape)
  24. What are the two general functions of the respiratory system?
    • Exchange of O2 and CO2 between atmosphere and blood
    • Regulation of blood and tissue pH (important to protein conformation)
  25. What are the components of the conducting zone and its purpose?
    • Trachea
    • Primary Bronchi
    • Respiratory/bronchial tree (in lungs) – secondary bronchi, tertiary bronchi, …, bronchioles, terminal bronchioles
    • Conducts air atmospheric air to respiratory zone and vice versa
  26. What are the components of the respiratory zone and its purpose?
    • Respiratory bronchioles (branch from terminal bronchioles, contain alveoli)
    • Alveoli (very small, thin -walled, inflatable sacs)
    • Location of gas exchange between air and blood
  27. Alveoli in depth
    • The location of respiration (diffusion of O2 and CO2)
    • ~300 million / lung in human adults
    • Diffusion promoted by increased surface area from alveoli (~100’ x 76’) and the short distance for diffusion (alveolar squamous cell, basement membrane, capillary squamous cell [~2 μm])
    • Intra-alveolar air pressure varies based on the size of the thoracic cavity
  28. What are the thoracic cavity, diaphragm, and mediastinum?
    • Diaphragm – dome shaped muscle that separates the thoracic cavity (upper) from the abdominal cavity (lower)
    • Thoracic cavity – the upper area of the peritoneal cavity
    • Mediastinum – The central area of the peritoneal cavity containing the heart and trachea
  29. What is the pleural membrane? Name its substructures.
    • The two-layered membrane that surrounds the lungs.
    • The parietal pleura lines the interior of the thoracic wall
    • The visceral pleura lines the surface of the lungs
    • The intrapleural space (pleural cavity) exists between the layers
  30. Describe the intrapleural space in detail
    • The region between the parietal and visceral pleura
    • Filled with intrapleural fluid
    • Intrapleural pressure kept below atmospheric pressure, creating a slight vacuum
    • This vacuum adheres the lung surface to the surface of the thoracic cavity
  31. Describe the intrapleural space vacuum in detail. How does it relate to lung expansion? Lung tissue has elastic recoil and tends to shrink
    • Thoracic wall recoil tends to expand
    • This generates a vacuum in the intrapleural space (pressure in intrapleural space < atmosphere)
    • This causes the lung to adhere to the thoracic wall
    • Changing the volume of the thoracic cavity changes lung volume
    • The vacuum also prevents lung collapse
  32. What is pneumothorax? Why does it occur?
    • a collapsed lung which does not subsequently inflate
    • It is caused when the chest wall is opened (eg punctured), preventing the intrapleural space vacuum. As such the punctured lung no longer adheres to the thoracic wall, and the intra-alveolar air pressure equilibrates with atmospheric pressure.
  33. What drives the movement of air in the lungs?
    • Pressure differences between atmospheric pressure and intra-alveolar pressure
    • Changing the size of the thoracic cavity (thus lung volume) changes intra-alveolar pressure. Atmospheric pressure remains constant.
  34. What is atmospheric pressure? Its typical units? Physiological value?
    • The pressure exerted by the weight of air in the atmosphere
    • ~760 mmHg (1 atm)
    • Physiologically considered “0” for comparison to intra-alveolar and intra-pleural pressure (negative creates a vacuum (inhalation) and positive creates a pressure (exhalation))
  35. Describe intra-alveolar pressure, physiological value during normal breathing, and what occurs.
    • The pressure inside the alveoli
    • Changes from -3 (inhalation) to +3 (exhalation) during normal breathing
  36. Summarize Boyle’s Law. How does this relate to breathing?
    • The pressure of gas is inversely proportional to its volume
    • Increased lung volume = decreased intra-alveolar pressure = air flows in
    • Decreased lung volume = increased intra-alveolar pressure = air flows out
  37. Describe the influence of surface tension on ventilation.
    • Surface tension is created by the formation of H-bonds between water molecules
    • Surface tension within alveoli should be so that they collapse, however they have surfactant which lowers the surface tension
  38. Describe surfactant in detail
    • protein + phospholipid – nonpolar
    • Secreted by Type II alveolar cells late in fetal life [no need for inflated lungs in the watery womb]
    • Premature infants may suffer from Respiratory distress syndrome (a lack of surfactant) which causes increased surface tension and thus an increased force is needed to inflate the lungs.
  39. Describe the mechanics of lung ventilation (inspiration).
    • Contraction of the diaphragm (flattening) increases thoracic volume
    • Enlarged thoracic cavity results in expanded lung volume (intrapleural vacuum)
    • Expanded lung volume results in decreased intra-alveolar pressure (-3)
    • Air moves into the lungs (pressure gradient)
  40. Describe the mechanics of lung ventilation (expiration).
    • Relaxation (convexing) of the diaphragm decreases thoracic volume
    • Smaller thoracic cavity results in decreased lung volume (elasticity/intrapleural vacuum)
    • Decreased lung volume results in increased intra-alveolar pressure (+3)
    • Air moves out of the lungs (pressure gradient)
  41. What is spirometry? Difference between “volume” and “capacity?”
    • Measurements of breathing
    • Volume: a single measurement
    • Capacity: the sum of multiple volumes
  42. What are the 4 primary lung volumes? (spirometry)
    • Tidal volume (TV): volume of air entering and leaving lungs in a single unforced breath
    • Inspiratory reserve volume (IRV): additional volume of air that can be maximally inspired beyond the tidal volume by forced inspiration
    • Expiratory reserve volume (ERV): additional volume of air that can be maximally expired beyond tidal volume by forced expiration
    • Residual volume (RV): volume of air still in lungs following forced maximum expiration
  43. What are the 2 primary lung capacities?
    • Total lung capacity: Amount of air in lungs at the end of a maximal inspiration (sum of all 4 lung volumes)
    • Vital capacity: Maximum amount of air that can move out of lungs after a person inhales as deeply as possible (sum of TV, IRV, and ERV)
  44. What are the three air-flow disorders (no descriptions)?
    Restrictive disorders, obstructive disorders, and Chronic Obstructive Pulmonary Diseases (COPD)
  45. Describe restrictive disorders (air-flow disorders).
    • Condition where vital capacity is low
    • Pulmonary fibrosis – reduced compliance (stretching ability)
    • Emphysema – walls of alveoli are destroyed
  46. Describe Obstructive disorders (air flow disorders).
    • Obstruction of the pulmonary air passages (decreased radius)
    • Bronchitis (inflammation and edema)
    • asthma (bronchiolar constriction – increases resistance, lowers flow)
    • Abnormally low Forced Expiratory Volume (FEV1) (% of vital capacity exhaled in one second – normal ~80%)
    • Vital capacity may be normal
  47. Describe COPD (air-flow disorders)
    • Conditions that are both obstructive and restrictive (low FEV1 and low vital capacity)
    • Emphysema
  48. What are the O2 and CO2 %’s of air content and partial pressures in the atmosphere?
    • O2: 21%, PO2 = 160mmHg
    • CO2: .04%, PCO2 = .3mmHg
  49. How does partial pressure affect gas diffusion in the body?
    Gases diffuse down partial pressure gradients between alveolar air and blood, and between blood and body tissues (automatic exchange)
  50. What factors affect the amount of gas that can dissolve in a solution? Which is the “major factor,” and why?
    • Temperature: body temperature – relatively constant
    • Gas solubility: constant for each gas
    • Partial pressure of gas in air with which the solution is at equilibrium – major factor, can easily be altered
    • The concentration of a gas in solution (blood) is directly proportional to the partial pressure of the gas (alveolar air)
  51. What are the PO2 and PCO2 values for atmospheric and alveolar air? Why do they differ?
    • Atmospheric: PO2 = 160mmHg, PCO2 = .3mmHg
    • Alveolar: PO2 = 105mmHg, PCO2 = 40mmHg
    • Difference is due to immediate diffusion of gases between alveolar air and blood, and the residual volume in alveoli (new air and old air are mixed)
  52. How is breathing controlled? What triggers an increase in breathing rate?
    • Peripheral chemoreceptors (carotid bodies and aortic bodies) monitor PO2, PCO2, and pH in blood
    • This information is relayed to the breathing center in the medulla via cranial nerves IX and X
    • The medulla influences an efferent path to breathing muscles which influences breathing.
    • Breathing rate increases with: increased PCO2, increased H+ (decreased pH), and decreased PO2 [very insensitive]
  53. What is different about PO2 regulation of respiration from PCO2 and pH?
    The set point for PO2 has a wide range before respiration is altered (60-120+ mmHg)
  54. What is hypoventilation and hyperventilation? How are they defined?
    • Both are defined in terms of CO2
    • Hypoventilation: more CO2 produced than exhaled, resulting in an increase to PCO2 levels
    • Hyperventilation: more CO2 exhaled than produced, resulting in a decrease to PCO2 levels
  55. How do PCO2 levels influence ph?
    • CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
    • pH/CO2 is the primary short-term influence on respiration (blood pH = 7.35-7.45)
  56. Describe the respiratory basis of acid-base balance. Also, how breathing affects PCO2, H+, and pH.
    • CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
    • An increase in CO2 results in an increase in H+ (lowered pH)
    • An increase in H+ results in an increase of CO2 (higher PCO2)
    • Hypoventilation results in increased PCO2, increased H+, and decreased pH (respiratory acidosis, pH < 7.35)
    • Hyperventilation results in decreased PCO2, decreased H+, and increased pH (respiratory alkalosis, pH > 7.45)
  57. How does the respiratory system respond to changes in blood pH (increase/decrease)? Why? What is the set point for blood pH? What else can cause a change in pH?
    • Normal blood pH = 7.35 – 7.45
    • If pH decreases respiration increases (CO2 exhaled faster, causing pH to increase)
    • If pH increases respiration decreases (CO2 exhaled slower, causing pH to decrease)
    • Decreased pH can be caused by increased lactic acid (anaerobic respiration in muscles)
  58. Describe the carbonic acid-bicarbonate buffer system
    • CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
    • The most important buffer for blood pH
    • Maintains blood pH ~7.4 with lungs and kidneys
    • Lungs remove CO2, kidneys remove HCO3-
  59. How is oxygen transported through the blood?
    • Most (~98.5%) O2 is bound to hemoglobin
    • O2 is poorly soluble in blood plasma (nonpolar)
    • Hemoglobin, therefore, enhances the oxygen carrying capacity of blood
  60. Describe the structure of hemoglobin
    • Protein made of four polypeptide subunits with four heme molecules
    • Can reversibly bind up to four O2 molecules to its heme units
    • Oxyhemoglobin vs. Deoxyhemoglobin
  61. Describe hemoglobin’s oxygen loading and unloading. [alveolar air ->
    • Loading: hemoglobin picks up oxygen in the lungs (oxyhemoglobin)
    • Unloading: hemoglobin releases oxygen to the tissues (deoxyhemoglobin) [hemoglobin -> plasma -> interstitial fluid -> cytoplasm of cell]
    • Hemoglobin converts between oxyhemoglobin and deoxyhemoglobin
  62. What are the factors affecting hemoglobin’s O2 loading and unloading to?
    • In the lungs PO2 is ~100mmHg – hemoglobin bonds oxygen (~97% oxyhemoglobin saturation in systemic arteries)
    • In tissues PO2 <40mmHg – hemoglobin releases oxygen to tissues (~75% oxyhemoglobin saturation in systemic veins)
  63. How is Carbon dioxide transported through the blood?
    • ~10% dissolved gas in plasma
    • ~20% bound to hemoglobin (not to heme unit, hemoglobin can bind O2 and CO2 simultaneously)
    • ~70% dissolved in plasma as bicarbonate ion (HCO3-) – results from CO2 + H2O <-> H2CO3 <-> HCO3- + H+
    • CO2 diffuses from tissues into blood, trends toward becoming HCO3- and H+ (decreasing pH)
    • CO2 diffuses from blood to alveolar space in lungs, decreasing HCO3- and H+ levels (increasing pH)
  64. 4 macroscopic structures of the urinary system and functions (general).
    • Kidneys – Produce urine
    • Ureters – transport urine to urinary bladder
    • Urinary Bladder – stores urine and releases urine
    • Urethra – transports urine from bladder to outside of body
    • Ureteres, Urinary bladder, and Urethra are just pathways (no urine formation)
  65. Basic anatomy of the kidney
    • Cortex (outer)
    • Medulla (inner) – renal pyramids, renal columns
    • Renal Pelives (central cavity) – urine collecting cavity that leads to ureter at renal hilus
  66. General description/function of nephrons.
    • Microscopic
    • Urine forming units of the kidney
    • Over one million per kidney
    • Simultaneously located in both cortex and medulla
    • Consist of nephron tubules and associated blood tubules
  67. List the components of a nephron and their location in the kidney in order of filtrate flow.
    • Renal corpuscle [cortex] – Glomerulus (capillaries), Renal (Bowman’s) capsule
    • Proximal Convoluted tubule [cortex]
    • Loop of Henle [medulla] – descending limb (to medulla), ascending limb (from medulla)
    • Distal Convoluted tubule [cortex]
    • Collecting duct [begins in cortex, ends in medulla]– receives fluid from several different nephrons in the cortex, empties into the renal pelvis
  68. Give a brief description of all the renal / nephron blood vessels
    • Renal arteries: enter kidney, branch several times, and deliver blood to each glomerulus
    • Afferent arteriole: brings blood to glomerulus
    • Efferent arteriole: takes blood away from glomerulus
    • Cortical and medullary capillaries: supply kidney tissues
    • Renal veins: drains blood out of kidneys
  69. General overview of urine formation
    • Filtration: glomerular filtrate is formed (similar composition to plasma without proteins or cells)
    • Reabsorption: remove valuable materials from filtrate and transport to interstitial fluid, then blood
    • Secretion: transfer wastes (specific items) from interstitial fluid (blood) to filtrate
  70. Describe the components and layers in the renal corpuscle
    • Glomerulus: capillary bed supplied by afferent arterioles and drained into efferent arterioles, located within glomerular (Bowman’s) capsule
    • Glomerular (Bownman’s) capsule: Parietal layer (external, simple squamous epithelium), Capsular Space (glomerular filtrate, between layers, opens to proximal tubule), Visceral layer (internal, covers glomerulus, podocytes)
  71. Describe the structures regarding filtration within the glomerulus.
    • Filtration membrane: endothelial cells (fenestrae – small pores – in endothelial cells), basement membrane, podocytes cover outside of basement membrane (visceral layer of capsule).
    • Slits between podocyte foot processes retain plasma proteins (limiting factor for size of molecule that will not be filtered), all other plasma proteins are filtered into capsular space
  72. Describe the mechanism behind filtration in the golmerulus.
    • Hydrostatic pressure (BP) pushes plasma out from glomerular capillaries.
    • Plasma proteins and cells do not pass filtration membrane
    • All other plasma components are filtered into the glomerular capsule (not selective)
    • Glomerular filtrate = plasma without proteins and cells
  73. Describe glomerular filtration rate and its influences
    • Rate at which fluid is filtered out of the glomerulus and into the nephron tubules (both kidneys, vol/time)
    • Averages 180L / day
    • Blood pressure: increased pressure filters more fluid out of the glomerulus
    • Colloid osmotic pressure: increased protein concentration drives osmosis of water back into the capillaries
  74. Describe reabsorption
    • Of the 180L fluid filtered each day, only ~1.5L of urine is extracted (99% H2O reabsorption), can be as low as 400mL
    • Reabsorption occurs in proximal and distal tubules, the loop of Henle, and collecting ducts
    • Selective movement of substances from glomerular filtrate to interstitial fluid to blood in the peritubular capillaries
    • Active or passive transport mechanisms used to drive reabsoprtion
    • Reapsorption affects BP (long term)
  75. Describe secretion
    • Occurs in tubules (proximal and distal tubules + collecting ducts)
    • Addition of material to glomerular filtrate from interstitial fluid (peritubular capillaries) – excess K+, Ca2+, H+, uric acid, foreign and compounds (eg penicillin)
    • Typically driven by active carrier transport
    • Least important of the 3 urine-forming processes
  76. Describe the reabsorption of the proximal tubules (specific substances, details)
    • 65% of the filtrate is reabsorbed in the proximal tubule, it is a constant process that does not adjust for blood pressure or dehydration
    • Na+: Na+/K+ ATPase pumps Na+ out of the tubule cells into the interstitial fluid, creates a gradient from Na+ to flow into cells from the glomerular filtrate
    • Cl-: Moves passively out of filtrate, through cells, and into blood by following the Na+ gradient (secondary transport)
    • Water: Flow from filtrate to blood because of osmotic gradient created by Na+ and Cl- (secondary transport)
  77. How does the loop of Henle produce a hypertonic medulla (all details)?
    • Fluid leaving the proximal tubule is isoltonic to blood plasma (~300 mOsm)
    • Kidneys can produce a hypertonic urine (more concentrated than blood plasma, allows retaining water when dehydrated)
    • Concetrating mechanism involves the Loop of Henle (descending limb, ascending limb, located in medulla)
    • Ascending limb: impermeable to water (no aquaporins), Na+ pumped into interstitial fluid, Cl- follows due to charge
    • Descending limb: permeable to water, no active transport of solutes
    • Medullary peritubular capillaries can absorb water (not NaCl), keeping the NaCl high in medulla
    • Interactions between ascending limb and descending limb form a countercurrent multiplier system (+ feedback loop)
  78. Describe the countercurrent multiplier system in the Loop of Henle
    • Pumping ions out of the ascending limb creates osmotic pressure in the interstitial fluid of the medulla
    • Water flows out of descending limb along this osmotic gradient
    • Water subsequently absorbed by capillaries
    • Net effect: reabsorption of water and NaCl, creates hypertonic gradient in interstitial fluid (300-1400 mOsM)
    • Fluid in the tubule becomes more concentrated as it passes down descending limb (~1400 mOsM at the turn of the loop [equal to interstitial fluid])
    • Removal of ions from ascending limb while water is retained causes fluid to become less concentrated in the ascending limb
    • Fluid leaving the loop of Henle is hypotonic (~100-200 mOsM)
  79. Describe reabsorption in the distal tubule and collecting duct (specific substances, what hormone?)
    • Distal tubule: Some water and Na+ reabsorption, depends on ADH and aldosterone
    • Collecting duct: Hypertonic medulla causes osmosis, osmosis depends on ADH
  80. Describe the ADH regulation of water reabsorption
    • ADH stimulates the insertion of aquaporins in the collecting duct
    • Increased permeability to water, increased H2O reabsorption due to hyperosmotic medulla, decreased urine volume, increased urine concentration, urine range: 1400-400 mOsm
    • Secreted by posterior pituitary in response to stimulation of osmoreceptors in hypothalamus (high Osm – more ADH)
  81. Describe the most common measurement of kidney function
    • Renal plasma clearance: the ability to remove substances from the plasma (100% reabsorption -> RPC = 0) (0% reabsorption -> RPC = GFR)
    • Clearance of creatinine is used to measure GFR as an indication of kidney function
    • Creatinine is a metabolic waste product from creatine that is constantly produced, filtered, and excreted by the muscles (creatine phosphate)
    • Creatinine levels in urine or blood can be compared with normal values as a sign of kidney function
  82. How is glucose treated by the nephron?
    • Glucose is filtered out of the blood and into the glomerular filtrate
    • Glucose is reabsorbed by carrier proteins (Renal plasma clearance is normally 0)
    • All of the glucose is reabsorbed normally
    • If blood glucose levels rise, carriers could be saturated, glucose spills into urine, diabetes
  83. Endocrine control of renal function (aldosterone)
    • Aldosterone stimulates Na+ reabsorption and K_ secretion by the distal tubule and upper (cortical) collecting duct
    • Elevated plasma K+ directly stimulates adrenal cortex to secrete aldosterone
    • Low Na+ concentrations indirectly stimulate aldosterone secretion via the renin-angiotensin-aldosterone sytem
    • Kidney detects low BP and secretes renin
  84. Describe the Renin-Angiotensin-Aldosterone System with emphasis on the kidney/urinary system.
    • Juxtaglomerular apparatus releases renin in response to sensory receptors in the afferent arteriole
    • Renin (enzyme) secreted into blood in response to decreased blood pressure (low Na+ levels)
    • Renin converts angiotensinogen (plasma protein) to angiotensin I
    • Angiotensin I converted to angiotensin II by angiotensin converting enzyme (ACE) in lungs
    • Angiotensin II stimulates aldosterone release from adrenal cortex and causes vasoconstriction
  85. Describe what elements of the plasma are controlled/regulated by the kidney
    • Homeostasis of (filtration and reabsorption): H2O, Na+, K+, Ca2+, H+, HCO3-
    • Excretion of (filtration and secretion): Penicillin, urea, creatinine, waste products
  86. Name the structures involved in the digestive system (GI tract) and accessory organs
    • GI tract: oral cavity, pharynx, esophagus, stomach, small intestine, large intestine
    • Accessory: teeth, salivary glands, pancreas, liver, gall bladder
  87. What are the functions of the digestive tract (with descriptions)?
    • Motility: Movement of food through the digestive system
    • Secretion: Release of substances to enhance breakdown of food
    • Digestion: Physical and chemical breakdown of food
    • Absorption: Transfer of materials to internal environment
    • Excretion: Temporary storage of undigested material followed by expulsion from the body
  88. Describe the general Gastrointestinal Tract Structure (the tube)
    • Mucosa: (Lumen side) – epithelial tissue and lamina propria (loose CT)
    • Submucosa: Connective tissue, contains lymph vessels and blood vessels
    • Muscularis (externa): Smooth muscle layers (allow peristalsis, etc)
    • Adventitia/Serosa: Epithelium/serous membrane (peritoneum), secretes serous fluid
  89. Esophagus functions.
    • Transport food and water to stomach, secretes mucus
    • Movement of food bolus in esophagus (and rest of GI tract) via peristalsis
    • Empties into stomach through the lower esophageal sphincter
  90. Generally describe the stomach
    • Muscular, sac-like organ
    • Chemcial and physical digestion forms chyme (food + gastic juices)
    • Stores food, releases small amounts to small intestine (takes 2-6 hours for stomach to empty)
    • Inner surface lined with gastric rugae (folds) to increase surface area
  91. Describe stomach mucosal cells (with general functions).
    • Gastric glands (large indentations in mucosa) contain specialized secretory cells including…
    • Goblet cells: secrete mucus
    • Parietal cells: secrete hydrochloric acid, intrinsic factor (necessary for B12 absorption, B12 needed for erythropoesis)
    • Chief cells: secrete pepsinogen (a precursor to pepsin)
    • Enteroendocrine and secretory cells: Histamine and Gastrin (stimulate parietal cells), Ghrelin-secreting cells (hunger related)
  92. Describe stomach acid secretion in detail
    • Parietal cells secrete H+ into the gastric lumen using active transport (H+ / K+ ATPase)
    • Cl- follows H+ from cells into the lumen
    • HCl used to denature ingested proteins, activate pepsinogen, create acidic pH for pepsin action, and destroy bacteria
    • HCl secretion stimulated by Histamine and Gastrin
  93. Describe the activation of pepsinogen
    • Pepsinogen secreted by chief cells into the lumen
    • Low pH of gastric juice activates pepsinogen (-> pepsin)
    • Pepsin digests pepsinogen into pepsin (+ feedback)
    • Pepsin function: digest proteins into shorter polypeptides
  94. Describe the three phases regarding gastric function
    • Cephalic phase: regulation of stomach by the brain via CN X, stimulates gastrin and histamine secretion in response to stimuli associated with food and anticipation of food
    • Gastric phase: arrival of food in stomach, amino acids and short polypeptides (not full proteins) stimulate pepsinogen, gastric, histamine, and HCl secretion
    • Intestinal phase: Arrival of chyme in small intestine stimulates neural reflex that inhibits gastric motility and secretion, fats in chyme stimulate secretion of hormones from the intestine that slow stomach function (allows more time for fat digestion in intestine)
  95. Describe the small intestine
    • ~3m long in living adults
    • Duodenum: receives chyme (stomach), bile (liver), pancreatic juice (pancreas)
    • Jejunem:
    • Ileum:
    • Large surface area due to Plicae circularis (macroscopic circular folds in mucosa, similar to rugae), villi (microscopic fingerlike projections, contain capillaries and central lacteal for absorption), and microvilli (electron-microscopic “brush border” on surface of mucosal cells)
  96. What are brush-border enzymes? Describe them and give examples?
    • Enzymes bound to epithelial cell membranes (microvilli)
    • Digest disaccharides, small peptides, etc (finish digestion started in stomach)
    • Include sucrase and lactase
  97. Describe small intestine motility and its regulation
    • Peristalsis: propels chyme through the small intestine
    • Segmentation: mixes chyme with digestive secretions (major form of motility)
    • Intestinal contractions occur due to pacemaker potentials in smooth muscles
    • Parasympathetic innervation stimulates motility (ACh)
    • Enteric nervous system
  98. Describe the enteric nervous system
    • Neurons within the walls of the digestive tract
    • ~100 million neurons, including association neurons, sensory neurons, and autonomic motor neurons
    • Control digestive function independent of the CNS
  99. Describe the large intestine
    • ~5m long in adults
    • Regions: cecum, appendix, ascendning colon, transverse colon, descending colon, rectum
    • Absorption of: salt water, and vitamins
    • Main function: storage of undigested material (feces)
    • Enormous number of symbiotic bacteria in colon (probiotics will increase this number)
  100. Functions of symbiotic bacteria in large intestine
    • Synthesize vitamins
    • Synthesize short chain fatty acids (fuel, aid in absorption)
    • Inhibit pathogenic bacteria
  101. Describe the organization of the liver and delivery of blood (general)
    • Consists of hepatocytes organized into hepatic plates/cords (2 cells thick) separated by sinusoids (fenestrated capillaries)
    • Grouped into liver lobules
    • Blood delivered to liver lobules from the hepatic artery (oxygenated) and hepatic portal vein (deoxygenated, nutrient rich)
  102. Describe blood flow through the liver. (How does the liver perform its tasks)
    • Blood enters periphery of liver lobules, flows through sinusoids
    • Sinusoids are fenestrated, leaky, and lack basement membrane
    • Allow passage of proteins and fats (into and out of hepatocytes)
    • Kupffer cells (macrophages) phagocytize, cleanse blood, remove old rbc’s
    • Blood drains out of the lobule via central vein that empties into the hepatic vein
  103. Describe bile secretion from the liver.
    • Bile secreted into bile caniliculi from hepatocytes (flows from center toward periphery of liver lobules)
    • Bile caniliculi drain into bile ducts
    • Bile ducts drain into gall bladder, where bile is stored
    • Gall bladder transports to bile small intestine when needed
  104. Describe the liver functions
    • Bile production: Converted from cholesterol for excretion, Bile salts emulsify fats, smaller droplets allow lipase to digest fats into fatty acids,
    • Bilirubin secreted into bile, derived from heme of the hemoglobin of destroyed RBCs, broken down bilirubin colors feces brown. A small amount is taken up by the small intestine and filtered by the kidney colorin urine yellow.
    • Detoxification of blood: Degradation of waste, hormones, drugs, etc by hepatocytes, phagocytosis by kupferr cells
    • Regulation of blood glucose: remove excess glucose from blood and convert it to glycogen (insulin), can secrete glucose into the blood when needed (glucagon)
    • Metabolism of lipids: converts cholesterol into bile salts and excretes it from the body, produces ketone bodies from fatty acids (provides fuel).
    • Excess ketone bodies can cause ketacidosis (associated with uncontrolled type I diabetes) hyperventilation to compensate
    • Synthesizes plasma proteins: albumin, clotting factors, and carrier proteins from nonpolar materials
  105. Describe Jaundice
    • High blood concentration of bilirubin leading to a “yellow” appearance
    • Caused by blockage of bilirubin excretion from gallstones, excessive RBC breakdown, liver damage
    • In a newborn can be caused by the slow breakdown of fetal hemoglobin (HbF), exposure to blue light expedites breakdown
  106. Describe Ascites
    • Associated with liver disease or cirrhosis
    • Decreased blood osmolarity leads to buildup of fluid in the peritoneum (“beer belly”)
  107. Describe the functions of the pancreas (re: digestion) + enzymes
    • Produces pancreatic juice (consists of bicarbonate to neutralize stomach acidity, and various enzymes…)
    • Pancreatic amylase – breaks down starch, Trypsin and other proteases (not pepsin) – break down polypeptides, Pancreatic lipase – digests triglycerides, phospholipases, nucleases, etc
    • Pancreatic juice travels through the pancreatic duct and enters the duodenum through the duodenal papilla, along with bile
  108. How are enzymes secreted by the pancreas? Describe the specifics.
    • Pancreatic juice secreted by exocrine tissue in the pancreatic acini (not islets)
    • Cells secrete enzymes principally in the form of zymogens (inactive enzymes)
    • Zymogens are activated in the small intestine
    • Enterokinase (a brush border enzyme) converts trypsinogen into trypsin
    • Trypsin converts other zymogens into active enzymes
  109. Describe the hormone regulation of Pancreatic Juice and bile secretion.
    • All are released FROM the small intestine
    • Hormones that inhibit the stomach are released when chyme enters the duodenum through the pyloric sphincter, this slows the flow of chyme to allow time for digestion
    • Secretin: stimulated by drop in pH below 4.5 (from acidic chyme), stimulates secretion of bicarbonate into the pancreatic juice, stimulates secretion of bile from the liver (alkaline)
    • Cholecystokinin (CCK): Stimulated by fat and protein content in chyme, stimulates digestive enzyme secretion into pancreatic juice, stimulates bile secretion from the liver and contraction of the gall bladder (more bile release)
    • CCK receptors in the hypothalamus (arcuate nucleus) give a feeling of satiety (negative feedback)
  110. Describe carbohydrate digestion and absorption in detail
    • Amylase secreted in saliva AND pancreatic juice break starch into smaller carbohydrates (NOT monosaccharides)
    • Small carbohydrates are digested into monosaccharides by brush border enzymes (small intestine)
    • Monosaccharides are absorbed into the mucosa
    • Transported into blood, enter hepatic portal system
    • Used for metabolism OR stored as glycogen
  111. Protein digestion and absorption in detail
    • Pepsin in the stomach cleaves proteins into smaller polypeptides
    • Pancreatic enzymes (trypsin) and brush border enzymes digest polypeptides into amino acids or small peptides (small intestine)
    • Small peptides and amino acids are transported into the mucosa
    • Small peptides broken into amino acids inside mucosal cells
    • Transferred into blood, enter hepatic portal system
    • AA taken up by cells and used for protein synthesis
  112. Lipid Digestion and absorption in detail
    • Chyme mixed with bile in duodenum – lipids in chyme interact with bile salts, form emulsification droplets which prevent the lipids from aggregated into large droplets
    • Pancreatic lipases break emulsified fat into free fatty acids and monoglycerides
    • Fatty acids and monoglycerides are absorbed by the epithelium
    • Triglycerides are reformed in epithelial cells
    • Newly reformed triglycerides are combine with protein to form chylomicrons
    • Chylomicrons released via exocytosis, enter central lacteal of villus (lymph vessels have large pores)
    • Transported through the lymphatic system
    • Enters blood through thoracic duct at left subclavian vein
    • Fatty acids used as fuel or stored as triglycerides
  113. What are the major factors for caloric expenditure of the body?
    • Basal metabolic rate (BMR): ~60% of calories used
    • Adaptive Thermogenesis: Energy expended to maintain body temperature and digest/absorb food
    • Physical activity:
  114. What happens to BMR when dieting? Why?
    • Body mass homeostasis (set point) achieved when caloric intake balances caloric expenditure
    • Homeostasis will slow BMR when dieting to maintain
  115. Describe the arcuate nucleus and all of its influences
    • Regulates hunger and feeding behavior (hunger inhibiting neurons AND hunger stimulating neurons)
    • Arcuate nucleus influenced by….
    • Other brain areas: smell, vision, suggestion, emotions, nucleus accumbans etc
    • Ghrelin: secreted when stomach is empty (from stomach), stimulates hunger
    • CCK: reduces appetite (released when small intestine is filled with chyme)
    • Satiety factors (eg Leptin): suppresses hunger and elevates metabolic rate (released in response to increasing storage of fat in adipocytes, from adipose tissue)
    • Insulin: acts as a satiety factor (released from beta cells of Pancreas in response to increased blood glucose)
    • nucleus accumbans: Pleasure center of the brain
  116. Describe the two phases of sexual reproduction (overview)
    • 1. Production of gametes (sperm and ova)
    • produced by gonads (testes or ovaries)
    • Haploid (n, 23 chromosomes) – unique to gametes
    • 2. Fertilization- Sperm and egg fuse to form a zygote
    • Zygote is diploid (2n, 46 chromosomes) – 22 pair autosomal chromosomes, one pair of sex chromosomes
  117. Reproductive differences between males and females (gamete production, sex steroid release, and duration of reproductive life)
    • Gamete production: Ova released intermittently and in small numbers (1/month). Mature sperm are produced continuously and in massive numbers (~30 million/day)
    • Sex steroid release (endocrine): female hormones have cyclical release. Testosterone released continuously.
    • Duration of reproductive life: Both sexes begin at puberty, female ends during middle age (menopause). Male potential continues throughout life.
  118. General function of the testis including specific compartments (and their functions)
    • General functions: produce sperm, produce testosterone
    • Seminferous tubules: site of spermatogenesis (sperm production)
    • Interstitial tissue: contains Leydig cells (produce androgens [testosterone])
  119. Describe the endocrine regulation of the testes (and from the testes) in detail. Including negative feedback.
    • Testes function influenced by secretion of gonadotropins (FSH and LH) from the anterior pituitary [stimulated by GnRH from hypothalamus]
    • FSH: stimulates spermatogenesis in the seminferous tubules and inhibin secretion. Inhibin inhibits FSH secretion.
    • LH: stimulates the Leydig cells to secrete testosterone. Testosterone inhibits LH and GnRH.
  120. What are the various functions of testosterone?
    • Spermatogenesis (seminiferous tubules produce sperm)
    • Secondary sex characteristics: growth of reproductive organs, facial and body hair
    • Body growth: musculoskeletal system, bone, larynx, erythropoeisis
  121. Describe the various spermatogenic cells and give information if available
    • Spermatogonia: stem cells, can reproduce via mitosis to produce primary spermatocytes
    • Primary spermatocytes: diploid cells that undergo meiosis to produce secondary spermatocytes
    • Secondary spermatocytes: 2 haploid cells produced from the first meiotic division
    • Spermatids: 4 haploid cells produced from the second meiotic division
    • Spermatozoa: 4 “sperm” with flagellae and reduced cytoplasm produced from spermiogenesis
  122. Describe spermatogensis in terms of location within the testes
    • As spermatogenic cells mature, they migrate toward the interior of the seminiferous tubule
    • Mature spermatozoa released into tubule lumen (no motility)
    • Conducted to the epididymis where sperm mature and develop motility
    • Spermatogenesis is supported by Sertoli (nurse) cells throughout the seminiferous tubules
  123. Describe the various Structures in the male reproductive tract with descriptions (beginning with Epididymis)
    • Epididymis: storage and maturation of sperm (don’t leave unless ejaculation occurs)
    • Vas Deferens: Transport sperm out of scrotum into the pelvic cavity
    • Ejaculatory Duct: Vas deferens + seminal vesicle duct.
    • The seminal vesicle secretion forms 60% of semen volume; rich in fructose
    • Urethra: conducts semen to exterior, receives prostate gland secretions
  124. Describe the structure of the penis and how blood flow is directed to or from the penis
    • Urethra runs along the ventral surface, surrounded by corpus spongiosum
    • Corpora cavernosa: paired dorsal column
    • Sympathetic NS constricts arterioles when penis is flaccid
    • Parasympathetic NS stimulates nitric oxide release which dilates the arterioles, causing erection
    • Ejaculation by peristaltic contraction (sympathetic NS)
  125. Describe the various structures of the female reproductive system (including the layers of the uterus)
    • Ovaries: Oogenesis, hormone secretion (endocrine)
    • Fallopian Tubes: Receives and transports ovulated eggs, site of fertilization
    • Uterus:
    • Perimetrium: outer layer of tissue in the uterus
    • Myometrium: middle smooth muscle layer of the uterus
    • Endometrium: inner lining of the uterus with epithelium, many blood vessels, glands. Site of implantation/gestation, placenta, menstrual cycle
    • Cervix: Narrowed distal end of the uterus
    • Vagina: copulation, birth canal
  126. General functions of ovaries
    • Oogenesis: storage and development of ova, ovulation
    • Secretion of estradiol and progesterone
  127. Describe oogenesis throughout the lifespan (general)
    • Ovaries contain primary oocytes at birth (formed from stem cells (oogonia) during fetal development. 400,000 remain at puberty)
    • Primary oocytes are surrounded by a layer of follicular cells (support cells) to form a primary follicle
    • One primary oocyte matures and is released from its follicle each ovarian cycle (ovulation)
    • ~400 ovulated in lifetime, remainder degenerate
    • By age 50 very few eggs are left, menopause
  128. Describe the ovarian cycle in terms of follicle growth
    • Under stimulation of FSH, some primary follicles (more than one) in one ovary begin to grow and develop
    • Follicle cells differentiate into granulosa cells and proliferate (secrete estradiol)
    • Primary oocyte grows
    • Secondary follicle: (fluid filled spaces form between granulosa cells) contains primary oocyte
    • A single secondary follicle becomes the dominant follicle (usually 1 / cycle)
    • All others undergo follicular atresia (degeneration)
    • Secondary follicle becomes Graafian follicle (1.5-2.5 cm in diameter)
    • Oocyte becomes secondary oocyte (haploid) via first meiotic division (+1 polar body)
    • Fluid filled spaces in graffian follicle merge to form a single antrum
    • Continues to grow until walls thin and fluid pressure increases to near rupturing point (ovulation)
  129. What is ovulation and what day of the ovarian cycle does it occur?
    • Release of secondary oocyte and surrounding granulosa cells
    • ~day 14 of ovarian cycle
  130. What is the corpus luteum? What unique function does it have?
    • Follicle after ovulation
    • The granulosa cells continue to secrete estradiol, and begin to secrete progesterone
  131. Give an overview of oogenesis (in terms of the oocyte)
    • Oogonium: Germ cell, all develop into primary oocytes by birth
    • Ovarian cycles begin during puberty
    • Primary oocyte: (diploid) undergoes first meiotic division just before ovulation (one per ovarian cycle)
    • Scondary oocyte: (haploid) formed from first meiotic division of primary oocyte, which also creates the first polar body which is discarded
    • Secondary oocyte completes second meiotic division at fertilization, enables fusion of nuclei from sperm and egg to form zygote.
    • This will form the second polar body which degenerates.
  132. List (without description) the phases of the ovarian cycle and the days
    • Lasts ~28 days
    • Follicular phase (days 1-14)
    • Ovulation (day 14)
    • Luteal phase (days 14-28)
  133. Give information regarding the follicular phase of the ovarian cycle
    • Days 1-14
    • Follicles develop with FSH stimulation leading to formation of one dominant graafian follicle
    • Secondary oocyte develops (1st meotic division)
    • Estrogen levels increase – secreted by granulosa, stimulates LH secretion (+feedback)
  134. Give information regarding the ovulation phase of the ovarian cycle
    • Day 14
    • Rupture of mature follicle and release of secondary oocyte into the reproductive tract
    • Triggered by LH surge on day 13
  135. Give information regarding the luteal phase of the ovarian cycle
    • Days 15-28
    • Empty follicle becomes the corpus luteum
    • Granulosa cells secrete estrogen and progesterone
    • -Final build-up of endometrium for pregnancy
    • -Inhibits GnRH, FSH, and LH secretion
    • -Inhibits further follicular development
    • Regresses at the end of the cycle if pregnancy does not occur
  136. List (without description) the phases of the uterine (menstrual) cycle and the days. Also give general information about the uterine cycle.
    • Cyclical buildup and breakdown of inner 2/3 of endometrium
    • Driven by cyclical changes in steroid release from ovaries
    • Menstrual phase (days 1-4)
    • Proliferative phase (days 4-14)
    • Secretory phase (days 14-28)
  137. Give information regarding the Menstrual phase of the uterine (menstrual) cycle
    • Days 1-4
    • Due to decrease in estrogen and progesterone as corpus luteum degenerates
    • Discharge of blood and endometrial debris
  138. Give information regarding the Proliferative phase of the uterine (menstrual) cycle
    • Days 4-14
    • Induced by increase in estrogen as ovarian follicles develop (follicular phase in ovarian cycle)
    • Proliferation of endometrium
  139. Give information regarding the secretory phase of the uterine (menstrual) cycle
    • Days 14-28
    • Corresponds to luteal phase of ovaries
    • Induced by progesterone and estrogen
    • Endometrium becomes thick, highly vascularized, and spongy
    • Glands fill with glycogen
    • Essentially, the endometrium is prepared for embryonic implantation
  140. Describe fertilization in detail
    • Occurs in oviduct (of the 300 million sperm released only 100 reach each fallopian tube)
    • Secondary oocyte is surrounded by a layer of granulosa cells (corona radiata) and a thick layer of glycoprotein (zona pellucida)
    • Sperm have a cap on the tip of the sperm called the acrosome
    • Contact with surface of the ovum triggers acrosomal reaction (acrosome ruptures, releasing enzymes that digest through the zona pellucida)
    • Ovum completes 2nd meiotic division when sperm penetrates egg (ejecting 2nd polar body)
    • Sperm and egg nuclei fuse to form a zygote
    • Zygote begins mitotic cell divisions (cleavage) instantly, without allowing for a change in total size
  141. Describe what happens around day 3 after fertilization
    Morula (ball of cells) enters the uterus
  142. Describe what happens around day 6 after fertilization
    • Blastocyst (hollow ball of cells) is formed, and implants in endometrium
    • Inner cell mass: future fetus (stem cells)
    • Chorion (surrounding layer): consists of trophoblast cells, will form part of the placenta
  143. What happens after implantation of the blastocyst?
    • Trophoblast cells secrete hCG (human chorionic gonadtropin)
    • Sustains the corpus luteum until 5-6 weeks into the pregnancy
    • This allows the maintenance of estradiol and progesterone secretion until the placenta develops
  144. Describe placenta in full detail including development and functions
    • Develops from trophoblast cells and endometrial tissue
    • Allows exchange between maternal and fetal blood
    • Chorionic villi of embryo invade maternal blood cavities
    • Performs functions of urinary, digestive, and respiratory systems for the fetus
    • Produces estrogen and progesterone which prevent menstruation and keep FSH and LH low
    • Produces hCG early in development to sustain corpus luteum (before it is able to secrete its own estrogen and progesterone)
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