Salt & Water Balance

  1. Excretory systems control __
    volume, concentration, and composition of the extracellular fluid & excrete wastes
  2. Cell volume depends on __, which depends on __
    • water movement to or from extracellular fluid;
    • differences in solute concentrations
  3. osmolarity
    number of moles of active solutes per liter of solvent

    more solutes in solution = higher osmolarity

    The osmolarity of the extracellular fluid must be maintained for cellular water balance.
  4. Excretory organs control osmolarity and volume of extracellular fluids by excretion of __ & conserving __
    • solutes that are in excess, such as NaCl;
    • valuable solutes or solutes in short supply, such as glucose & amino acids
  5. __ is the output of the excretory system
    Urine (filled with waste products)
  6. Excretory systems have 3 processes in common:
    • filtration: extracellular fluid is filtered to contain no cells or large molecules (size filter)
    • secretion: modifies the filtrate
    • reabsorption: concentrates the urine
  7. Terrestrial animals must conserve __ & freshwater animals must conserve __
    • salts & water;
    • salts but excrete excess water
  8. metabolic waste products that are easily excreted
    Carbs and fats end as water and CO2
  9. __ & __ contain nitrogen so metabolism produces __
    Proteins; nucleic acids; nitrogenous waste
  10. Mammals secrete mostly __ as their nitrogenous wastes.

    Humans are ureotelic but also excrete uric acid (from metabolism of nucleic acids and caffeine) & ammonia (regulates pH of extracellular fluid by buffering urine)
  11. The __ is the main excretory organ and the __ is the main functional unit of that organ.
    kidney; nephron

    kidneys > ureters > urinary bladder > urethra
  12. function of nephrons
    filter large volumes of blood & achieve bulk reabsorption
  13. main function of the kidney
    filter blood & produce urine
  14. From the renal artery, blood flows through the __ in the cortex then to the __ surrounded by a __. This is where __ occurs. The blood continues to the __ to the __ & down the __ in the medulla and back up and out through the renal vein.
    • afferent arteriole;
    • glomerulus (fenestrated capillaries with leaky pores);
    • Bowman's capsule;
    • filtration (size filter - large stay in blood, small enter the nephron);
    • efferent arteriole;
    • peritubular capillaries (surround the tubule)
    • vasa recta (surrounds the loop of Henle)

    The peritubular capillaries and the vasa recta serve as exchange sites.

    (page 14 on slide)
  15. Filtration:__ stay in the blood and __ enter __
    • RBCs and proteins;
    • small molecules such as ions, amino acids, water, urea, glucose, and small toxins;
    • Bowman's capsule (start of the nephron)

    Glucose, amino acids, and valuable solutes will need to be reabsorbed.
  16. __ are capsule cells that contact the glomerular capillaries.

    Podocytes have fine processes that wrap around the capillaries.
  17. Blood is filtered in the __ Tubular reabsorption occurs mainly in the __
    • glomerulus (to Bowman's capsule)
    • proximal convoluted tubule (of glucose, amino acids, and valuable solutes)
  18. The rate of filtration is high in the glomerulus due to __
    • high capillary blood pressure;
    • high permeability of glomerular capillaries and their podocytes
  19. 3 parts of the filtration membrane
    • fenestrations (pores)
    • basal lamina
    • foot processes of podocyte
  20. From the Bowman's capsule, __ enter the __ of the nephron where __ are reabsorbed into the interstitial fluid. The nephron continues down the __ and up the __ to the __ to the __.
    • small molecules;
    • proximal convoluted tubule;
    • glucose & valuable solutes;
    • descending loop of Henle;
    • ascending look of Henle;
    • distal convoluted tubule;
    • collecting duct
  21. __ are membrane proteins abundant in highly water-permeable areas.

    not found in the ascending loop of Henle
  22. The proximal convoluted tubule is responsible for the __ of water & solutes - osmolarity __
    • isosmotic reabsorption;
    • does not change
  23. The PCT cells have __ to increase surface area & have mitochondria. They actively transport __.
    • microvilli;
    • Na+, glucose, and amino acids (Water follows the transport of solutes.)
  24. Concentration of urine is due to a __ mechanism in the loops of Henle.
    countercurrent multiplier
  25. As the loop of Henle descends down the medulla, the osmolarity of the fluid inside the nephron increases due to __. In the thin ascending limb, __. In the thick ascending limb, __. In the distal convoluted tubule, __. Down the collecting duct, __, resulting in a __
    • diffusion of H2O from the descending loop to the interstitial fluid via aquaporins (transfers indirectly to the vasa recta);
    • due to no aquaporins, no H2O leaves, but NaCl leaves, decreasing osmolarity;
    • osmolarity continues to decrease as no H2O leaves and membrane proteins transport out NaCl into the interstitial fluid;
    • osmolarity has decreased greatly
    • osmolarity increases again as H2O leaves, because of the increasing solute concentration in the interstitial fluid down into the medulla;
    • concentrated urine with very high osmolarity (up to 1200 mOsm/L)
  26. Renal failure results in:
    • salt and water retention (high bp)
    • urea retention (uremic poisoning)
    • decreasing pH (acidosis)

    Dialysis treatments passes blood through membrane channels bathed in a plasma-like solution to remove wastes.
Card Set
Salt & Water Balance
Week 8