Excretion and Osmoregulation

  1. Define Excretion
    The removal from the body of waste products of metabolic pathways
  2. Draw and label a diagram of the kidney
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  3. Annotate a diagram of a glomerulus and associated nephron to show the function of each part
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    • 3) Afferent arteriole: brings blood from renal arteriole to the glomerulus
    • 2) Glomerulus: ultrafiltration; a ball of fenestrated capillaries that produces the initial filtrate
    • 4) efferent arteriole: connects the glomerulus to the peritubular capillaries; blood more concentrated
    • 9) Vasa recta: capillaries that serve the loop of Henle and exchange water with it by countercurrent exchange
    • 1) Bowman's capsule: collects filtrate expelled from the glomerulus
    • 5) Proximal convoluted tubule- reabsorbs glucose, water, HCO3- and salt from the filtrate; secretes H+ and ammonia for pH balance
    • 8) Loop of Henle: (descending) water is reabsorbed, (ascending) salt is reabsorbed (both passively and actively
    • 6) Distal convoluted tubule: reabsorbs Na+, Cl-, Ca2+ HCO3- and water; secretes H+ K+ and NH3
    • 7) Collecting duct: concentrates the urine by absorbing water
    • Blood vessels in sequene (3,2,4,9), followed by nephron components in sequence (1,5,8,6,7)
  4. Explain the process of ultrafiltration, including blood pressure, fenestrated blood capillaries and basement membrane
    • Ultrafiltration occurs as high blood pressure (hydrostatic) forces fluid from the glomerulus into the lumen of the Bowman's capsule. Blood pressure is high due to proximity to aorta
    • Proteins and blood cells are too large to fit through the fenestrations (pores/openings) in the blood capillaries
    • Basement membrane: semi permeable tissue with podocytes that is permeable to water/small molecules but no proteins
    • Initial filtrate identical to blood plasm except it lacks proteins and red blood cells.
  5. Define osmoregulation
    control of water balance of the blood, tissue, or cytoplasm of a living organism
  6. Explain the reabsorption of glucose, water, and salts in the proximal convoluted tubule, including the role of microvilli, osmosis, and active transport
    • Active: salt and nutrients, such as glucose, are actively transported into the endothelial cells lining the proximal tubule
    • Microvilli of the endothelium increase surface area for transport
    • Water and bicarbonate passively follow the salts and nutrients (by diffusion and osmosis)
  7. Explain the roles of the loop of Henle, medulla, collecting duct, and ADH in maintaining the water balance of the blood
    • the medulla is hyperosmotic to the filtrate (has a higher solute concentration by comparison)
    • the water moves out of the descending loop Henle by osmosis
    • the thin segment of the ascending loop of Henle is permeable to salt, which diffuses out
    • the thick limb actively transports salt out to maintain the high solute concentration of the medulla
    • the loop of Henle passes through the very hyperosmotic inner medulla, allowing water to be removed from the filtrate by osmosis
    • Water leaves the collecting duct by osmosis, concentrating the urine as it passes through the medulla
  8. Explain the differences in the concentration of proteins, glucose, and urea between blood, plasma, glomerular filtrate, and urine.
    • Protein: Proteins are unable to fit through the pores of the glomerular capillaries and are absent from the filtrate (remain in blood)
    • Glucose: present in the filtrate, but reabsorbed in the proximal convoluted tubule
    • Urea: not reabsorbed, leading the high concentration of urea in the urine (some diffuses out into medulla)
    • Glucose: concentration is equal in blood plasma and initial filtrate and should be absent from the urine
    • Proteins: found in blood plasma only (do not pass through the basement membrane)
    • Urea: concentration is greatest in urine, initially present in filtrate and blood plasma where it is equal
  9. Explain the presence of glucose in the urine of untreated diabetic patients
    • Insulin signals body cells to remove glucose from blood plasma. So in the absence of insulin, glucose is not removed by cells and builds up in the plasma
    • High plasma levels of glucose in diabetic patients prevent complete reabsorption of glucose in the proximal tubules
Card Set
Excretion and Osmoregulation
Excretion and Osmoregulation