Excretory Hormones
This posterior pituitary hormone increases permeability of the collecting duct so more water is reabsorbed; explain its stimulus and feedback control.
ADH (antidiuretic hormone). Stimulus: decreased blood volume sensed by osmoreceptors in hypothalamus. Negative feedback: restored blood volume/osmolality suppress ADH.
List the three main processes of urine formation and identify where pressure filtration occurs.
Pressure (glomerular) filtration, selective (tubular) reabsorption, tubular secretion/excretion. Pressure filtration occurs in Bowman's capsule/glomerulus.
Approximately what percent of filtered water is reabsorbed?
~99% of filtered water is reabsorbed.
Which organ is the primary site for enzymatic digestion and nutrient absorption?
Small intestine (duodenum/jejunum/ileum).
Name the salivary enzyme that begins starch digestion and its primary product.
Salivary amylase — begins starch → maltose (disaccharide).
Name the adrenal-cortex-mediated hormone that causes sodium retention and the renal apparatus (structure) that secretes renin when blood volume is low.
Aldosterone; juxtaglomerular apparatus (JG cells) secrete renin.
Explain why plasma proteins and blood cells are normally absent from glomerular filtrate.
They are too large to pass the glomerular filtration barrier.
Which solute shows about 100% reabsorption (present in plasma and filtrate but absent in urine), and why is that physiologically important?
Glucose (and amino acids) — 100% reabsorbed by carrier-mediated transport in the proximal convoluted tubule. This prevents loss of valuable nutrients and maintains blood glucose/amino acid homeostasis.
List three accessory digestive organs and one primary function of each.
Liver — produces bile, detoxifies, stores glycogen/vitamins; Pancreas — secretes pancreatic juice (enzymes and bicarbonate) and hormones (insulin/glucagon); Gall bladder — stores and concentrates bile and releases it into the duodenum.
Name two pancreatic enzymes and the macromolecules they digest.
Pancreatic amylase — starch → maltose; Pancreatic lipase — triglycerides → glycerol + fatty acids. (Also: trypsin — proteins → peptides.)
Two common substances act as diuretics by different mechanisms: one inhibits ADH secretion, the other inhibits sodium reabsorption in tubules. Name each and state their mechanism.
Alcohol — inhibits ADH secretion; Caffeine — inhibits sodium reabsorption in proximal/distal tubules.
Distinguish passive (osmotic) versus active reabsorption in the PCT and give one example molecule for each.
Passive/osmotic: water follows osmotic gradient (example: H2O). Active: carrier-mediated, ATP-dependent transport (example: Na+).
If blood is too acidic, describe two renal adjustments that increase blood pH and indicate where they occur.
(1) Increase tubular H+ secretion (urine becomes more acidic) and (2) increase bicarbonate (HCO3−) reabsorption into blood; occur in proximal and distal convoluted tubules.
Name three structural adaptations of the small intestine that increase surface area and state where glucose and fatty acids enter circulation.
Folds, villi, microvilli (brush border). Glucose → capillaries → hepatic portal vein to liver; fatty acids/glycerol → lacteals → lymphatic system.
Explain why bile is not an enzyme and how it facilitates lipid digestion; include the hormone that stimulates bile release.
Bile is not an enzyme; it emulsifies fats (breaks large droplets into smaller droplets) to increase surface area for lipase action. CCK (cholecystokinin) stimulates gall bladder contraction and bile release.
Describe how atrial natriuretic hormone (ANH) counteracts the renin–angiotensin–aldosterone system and predict its net effect on sodium and water handling.
ANH inhibits renin and aldosterone secretion → promotes sodium excretion and water loss → decreases blood volume/pressure.
Explain how the Loop of Henle creates a hypertonic medulla and how that enables water reabsorption from the descending limb and collecting duct.
Ascending limb actively pumps out Na+/Cl− (impermeable to water) → raises medullary osmolarity (hypertonic) → descending limb/permeable collecting duct allow water to leave by osmosis into hypertonic medulla → water reabsorbed into peritubular capillaries.
Describe expected urine concentration and color when ADH secretion is high and explain why this happens during dehydration.
Urine is low in volume, highly concentrated, and darker yellow because ADH increases water reabsorption from collecting ducts to conserve water.
Explain why pepsin is secreted as pepsinogen and the role of HCl and mucus in stomach function.
Pepsinogen is an inactive zymogen to prevent autodigestion of stomach cells; HCl activates pepsinogen to pepsin and kills microbes; mucus protects stomach lining from HCl and pepsin.
For gastrin, secretin, and CCK: state where each is produced, the trigger for release, and the primary effect.
Gastrin: produced in stomach; triggered by protein/stretch in stomach; stimulates gastric glands to secrete gastric juice. Secretin: produced in duodenum; triggered by acidic chyme; stimulates pancreas to release bicarbonate. CCK: produced in duodenum; triggered by fats/proteins in chyme; stimulates pancreas enzyme secretion and gall bladder bile release.
Outline the cascade from low blood pressure to increased Na+ reabsorption, naming the kidney sensor, enzyme, and hormone involved, and explain how water follows.
Low BP → juxtaglomerular apparatus releases renin → stimulates adrenal cortex to release aldosterone → aldosterone increases Na+ reabsorption in distal tubule/collecting duct → water follows passively down osmotic gradient.
Name typical substances secreted into tubules from peritubular capillaries and explain why secretion is important for pH regulation and drug clearance.
H+, K+, creatinine, some drugs (e.g., penicillin). Secretion removes excess H+ to regulate blood pH and clears drugs/toxins not filtered or that require active removal.
Explain qualitatively how urea recycling raises medullary osmolarity and aids water conservation.
Urea is concentrated in the collecting duct and diffuses into the medulla, increasing interstitial osmolarity; recycled urea entering loop/distal tubule helps maintain hypertonic medulla so more water is reabsorbed from descending limb/collecting duct, conserving water.
Explain the immediate effect of rapid transit (diarrhea) through the large intestine on water absorption, stool, and one systemic consequence if prolonged.
Reduced water reabsorption → watery stool (diarrhea); prolonged leads to dehydration and electrolyte imbalances
Integrate digestion and renal physiology: after a high-protein meal, explain how digestive processing increases nitrogenous wastes in the body.
Protein digestion yields amino acids that are deaminated in the liver; amino groups form ammonia which is converted to urea (less toxic) — blood urea rises.