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Unformatted text preview: on either the apical or basolateral membranes 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 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 Loop of Henle does nothing in regard to acid-base balance...
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- Spring '13
- Physiology, epithelial cell, peritubular fluid