Lecture 31 – Renal Physiology VI

This depends on the ph of the ecf basolateral

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This depends on the pH of the ECF Basolateral transporters NaKATPase pumps that transport Na out and K into the epithelial cell Na/bicarbonate cotransporters that transport both Na and bicarbonate out of the  epithelial cell Bicarbonate/Cl antiporters that transport Cl into the cell and bicarbonate out of the  epithelial cell The chloride ion diffuses into the peritubular fluid, just goes around and around so long  as the [] gradients are favorable for it Apical transporters Na/H antiporters that transport Na into the cell and H out of the cell Sodium concentration is low inside the cell because of ATPase pump so this transport is  always favorable
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H pumps that use ATP to transport H into the tubular fluid (out of the cell) Role of carbonic anhydrase Located in the cytosol and on the microvilli of the apical membrane The membrane bound CA catalyzes the conversion of carbonic acid (which comes from  filtered bicarbonate) to CO2 and water in the lumen of the PT The CO2 then diffuses in to the epithelial cell where it is converted back into carbonic  acid by cytosolic CA The carbonic acid the dissociates into H and bicarbonate The H formed inside the epithelial cell by this reaction is then transported into the  tubular filtrate either by counter transport with Na or by active transport by the H pumps The intracellular Na is kept low by the NaKATPase pumps in the basolateral membrane  In the lumen of the renal tubule, the H combines with filtered bicarbonate to form  carbonic acid under the influence of carbonic anhydrase, will split to form water and CO2 again this process repeats again The carbonic acid formed inside the cell by CA rxn is transported by cotransport with  sodium or antiport with Cl into the peritubular fluid This results in bicarbonate reabsorption Under normal conditions, 80=90% of filtered bicarbonate is reabsorbed by very indirect  method (back to CO2, then to carbonic acid, then bicarbonate, then secreted out) When protons are secreted (and therefore excreted)  Na is reabsorbed through this mechanism In exchange for proton secretion Distal part of DT and collecting ducts
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  • Spring '13
  • ArthurDunham
  • Physiology, epithelial cell, peritubular fluid

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