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Final Exam Lecture 11

Final Exam Lecture 11 - Lecture 11 April 7 2005 RENAL...

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Lecture 11 April 7, 2005 RENAL PHYSIOLOGY II Today Lecturer: Tyler Rork [email protected] Room: B 219 Nelson Labs Read in text: pg. 590-595, 597-601, 617-623 Test questions come from LECTURES ONLY Basic Renal Principles Review Filtration, reabsorption, secretion, excretion Clearance : the rate at which a substance is excreted Table 19.1 Note that the reabsorption rate almost equals the filtration rate, i.e. reabsorption rates are very high Reabsorption is thus the major process in the renal tubules REABSORPTION Fig 19.13 : For reabsorption to occur, the substance must pass through 2 significant barriers Must cross epithelial cells of the renal tubules Must cross capillary endothelium of the peritubular capillaries Tubular epithelial cells have 2 barriers on either side of the cell Apical membrane : faces tubule lumen Basolateral membrane : faces peritubular capillaries Renal tubule epithelial cells have specialized tight junctions no solutes generally pass between cells in large quantities Passive vs. Active Reabsorption Fig 19.14 Passive reabsorption : occurs via diffusion of a solute down its concentration gradient; requires no energy Active reabsorption : occurs via ATP-mediated pathways on either the apical or basolateral membranes Example from the figure: Y crosses the apical membrane into the cell by passive facilitated diffusion since there is not a great concentration gradient between the luminal and cellular [Y]. Y crosses the basolateral membrane by active transport since [Y] is greater in the interstitial fluid than in the cell The reabsorption of water is passive because it follows the osmotic gradient created by the active reabsorption of solutes Reabsorption example: glucose Glucose is freely filtered at the glomerulus
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Reabsorption of glucose is by secondary active transport via a sodium co transporter across the apical membrane followed by facilitated diffusion across the basolateral membrane Under normal conditions no glucose is excreted in urine since all tubular glucose is reabsorbed Fig 19.15 Secondary active transport doesn’t directly require ATP to transport substances against their concentration gradients The Na-glucose symporter (a cotransporter) brings both Na and glucose into the cell Na is going down its concentration gradient and glucose goes along for the ride Yet, it does require energy to set up the Na gradient that drives the Na-glucose symporter: the Na-K ATP-ase on the basolateral membrane uses ATP to set up
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Final Exam Lecture 11 - Lecture 11 April 7 2005 RENAL...

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