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2011-02-07 18:13:10

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  1. Na in proximal tubules
    • obeys the gradient time rule
    • the higher the concentration the more reabsorbed
    • the slower the flow the greater the time spent in the tubules the more reabsorption occurs
    • This is due to the fact that some of the Na actively transported out of the luman passively diffuses back in through the cellular junctions
  2. Na in the distal tubules
    • can reach a transport maximum
    • that maximum is controlled by aldosterone
  3. Proximal tube diffusion of water
    • follows the Na gradient and diffuses through the tight junctions of cells
    • Ca, and Mg are drug out of the luman by water
  4. Distal tubule diffusion of water
    • tiggt junctions become much tighter
    • water must diffuse through special pores
    • Dependant on ADH
  5. Movement of Cl
    • Na active transport sets up an electrochemical gradient and the negative Cl follows the positive Na. It diffuses through the paricellulaer spaces
    • also the passive diffusion of water increases the tubular conc of Cl and then Cl will flow out of the tubule down its conc gradient
    • Is secondary active transport with Na in the proximal tubules
  6. Urea reabsorption
    • coupled to osmosis of water. As water is absorbed the concentration of urea increases driving it out of the luman
    • must go though special urea channels
    • about 50% of urea is reabsorbed
    • mostly happens in the medulla
  7. Protein carriers
    mostly found in the proximal tubule brush border
  8. Na co transport
    • frost half of proximal tubule Na is transported with AA, Glucose
    • Second half of proximal tubule Na is transported with Cl. The change is due to the fact that most AA and glucose are absorbed by the late proximal and water reabsorption has increased the Cl conc
  9. TAL
    • about 25% of solutes are reabsorbed here
    • Ca, HCO3, and Mg are passively absorbed here
    • impermeable to water
  10. Na/K pump
    keeps the intercellular conc of Na low so Na can easily be transported into the cell
  11. Loop diuretics
    • furosemide
    • ethacrynic acid
    • bumetanide
  12. K in TAL
    • it is transported out of the luman along with Na and Cl
    • some of the intercellular K will diffuse into the plasma and some will diffuse back into the luman
    • The K that diffuses back into the luman sets up an electrical gradient across the luminal membrane that drives cations through the pericellular channels
    • K causes the luminal side to become more positive
  13. Site of K sparing diuretics
    • principal cells of the late distal tubule and collecting duct
    • Na channel blockers inhibit the passive diffusion of Na into the cell. Decreases the conc that activates the Na/K pump
    • ALdosterone antagonist stop the Na/K pump eliminating the gradient that causes Na to enter the cells
  14. Intercalated cells
    • actively secrete H and reabsorb K and HCO3
    • The H is from intercellular CA
    • So for each H excreted a HCO3 is available for absorption across the baasil membrane
  15. Functional characteristics of the late distal tubule and the cortical collecting duct
    • impermeable to urea. Most urea that enters this section is excreted
    • reabsorb Na under control of Aldosterone, at the same time secrete K
    • Intercallated cells secrete H actively. Differes from the proximal tubule in that it can secrete H against a large gradient. ATPase. Key role in acid base balance
    • Water absorption is controlled by ADH and aquaporin channels
  16. H transport
    • Proximal. anti transported with Na down a concentration gradient. Secondary transport
    • Distal actively transported against a gradient . ATPase
  17. Characteristics of medullary collecting ducts
    • permeability is controlled by ADH
    • unlike the cortical collecting duct it is permeable to urea. Urea helps raise the osmolarity of interstitial fluid
    • secretes H against a high conc gradient. Acid base balance
  18. Glomerulotubular balance
    • intrinsic ability of the tubules to increases there absorption in response to an increase in GFR
    • Percent of absorption still stays the same.
    • ex. increase GFR to 150 ml/min proximal reabsorption will increase from 81 ml/min to 97.5 ml/min but it is still 65% of the GFR
    • mechanism is not understood
    • helps prevent overloading of the distill tubule when GFR increases
  19. diffusion coefficient
  20. peritubular absorption
    • increases in arteriel pressure lead to less absorption
    • decreases in arterial pressure lead to more absorption
    • afferent and efferent resistance play a role in this
    • Colloid osmotic pressure changes absorption/filtration forces
  21. Filtration fraction and peritubular absorption
    • increasing the filtration fraction leads to an increase in osmotic pressure and favors reabsorption in the peritubuilar capillaries
    • filtration fraction = GFR/Plasma flow
  22. Kf and peritubular absorption
    increase in Kf means a larger GFR and larger alteration fraction which leads to a higher osmotic pressure and an increase in peritubular absorption
  23. A decrease in peritubular reabsorption
    • either due to increase in peritubular pressure or decrease in oncotic pressure
    • causes less absorption into the pertubular capillaries and an increase in interstitial fluid pressure and a decrease in interstitial fluid osmolarity
    • this leads to a decrease in fluid absorption out of the urinary tubules
  24. Capilary absortion and tubule absorption
    forces that increase peritubular capillary reabsorption also increase reabsorption form the renal tubules
  25. pressure naturesis and diuresis
    increases in arterial pressure increase water and solute excretion
  26. Agiotensin and arterial pressure
    • when pressure is increases there is more GFR and a decrease in reabsorption of Na
    • Increases in peritubular capillary pressure leads to the decrease in reabsorption
  27. ANP
    • dilates the afferent; this leads to an increase in GFR by increasing hydrostatic pressure, also an increase in peritubular pressure / washout of peritubular osmotic pressure decreases reabsorption
    • inhibits renin secretion
    • decreases the effect of aldosterone
  28. Aldosterone
    • Na/K pumps of the cortical collecting tubules
    • principle cells
    • also increases permeability of Na channel on the apical membrane
  29. Angiotensin II
    • stimulates Na/k pumps on the basil membranes of all parts of the renal tubules
    • also stimulates the Na/H pump in the apical membrane in the proximal; tubule
  30. Mechanism of action of ADH
    • binds V2 receptors that increase cAMP and thus turn on protein kinase A
    • Protein kinase A stimulates AQP-2 channels to move to the apical membrane
    • AQO-3 and 4 to move to the basal membrane
  31. PTH
    increases Ca absorption and inhibits PO4 absorption
  32. Sympathetic stimulation
    • decreases Na and water excretion by contracting the renal arterioles and decreasing GFR
    • Increase angiotensin II formation
    • increase Na reabsorption in the tubules
  33. Renal plasma flow
    • is equal to the PAH clearance
    • PAH is close to 100% cleared
  34. GFR
    • is equal to the inulin clearance rate
    • is clinically estimated using the creatinine clearance rate
  35. reabsorptive rate
    = filtered load mmol/min - excreted load mmol/min
  36. Aldosterone on distal tube
    max aldosterone stimulation will only cause less then 10% of Na to be reabsorbed in distal collecting duct