BLOCK III - Blood that leaves vasa recta is constant in...

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12/11/10 BLOCK III Blood that leaves vasa recta is constant in osmolarity – makes sure Amplification of absorptive capacity of the loop Works because of asymmetric permeability in two loops of Henle Start with 300 mOsmol solution; because of absorption and NaCl, osmotic difference is set up between the two limbs
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12/11/10 This works by interaction with Vasa Recta In a shallow nephron, it might only see 600 at the tip Water that leaves the loop of Henle in descending part which is pulled by osmolarity in the interstitium is pulled by ascending limb As NaCl is being reabsorbed to decrease osmolarity, it contributes to maintaining the osmolarity of the interstitium by moving to Vasa recta
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12/11/10 Counter current exchange – two tubes needed; to make sure that there is absorption, osmolarity not washed away and making sure that there is no marked change in osmolarity ° contributes to maintaining the loop of Henle’s function There is a countercurrent exchange in all nephrons but in cortical nephrons, peritubular capillaries are loosely defined so not well organized as medullary nephrons
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12/11/10 BLOCK III START Anything you take in is absorbed with regards to NaCl, only less than 5-10% is excreted 120 – 5mmol enters the plasma, that partitions into the fluid compartments Sodium is higher in ECF, low in ICF ICF has the highest water Small losses via sweat glands; most goes to kidney 110mmol dealt in kidney, absorb 110,
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12/11/10 Majority of it is reabsorbed, minor excretion of 100mmol Thus, high flow rates and reabsorb majority of what is being filtered and then in latter segments, dilute it Take a human give sodium bolus continuously, in order to prevent continuous volume expansion, first restrict sodium and then increase sodium by 10 folds What you see is that your sodium output increases to mere increase in
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12/11/10 This happens because of the ability of nephron to compensate water and salt – from regulation of hormone and collecting duct If you take two nephrons – one in water balance, uvolemia; pair with increased volume – hypervolemia similar to hypernatremia In one case, you want to conserve water, in other you want to excrete sodium or water In the case of Uvolemia, what leaves
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12/11/10 HYPERVOLEMIC: GFR goes up; in the PT, start saturating some machinery, it will absorb more which is not a perfect compensation; increase amount that is reabsorbing but it is less since there is no perfect balance Example PT absorbs 50%, loop absorbs more, DT absorbs more, the fluid that is left going to the collecting duct is 80% of the initial filtrate; no ADH, no aldosterone thus majority of it is excreted
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12/11/10 MAJOR DETERMINANTS OF SODIUM EXCRETION GFR : if GFR goes up, the tendency is absorption to go up, there
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