Bicarbonate reabsorption requires\"suhle Figs 17.29 HCO-cannot be directly reabs
ID: 3505662 • Letter: B
Question
Bicarbonate reabsorption requires"suhle Figs 17.29 HCO-cannot be directly reabsorbed oo polar H' and HCO, combine to form compounds (CO2 and H2O) that can- - . catalyzed by the enzyme carbonic attached to the luminal side of tubule cell membrane (outside of cell) HCO, and H' then regenerated within the tubule cell byenzyme reaction is reversible e H and combines with more HCO3 -That is, H+shuttles between lumen and IEF to cause reabsorption of bicarbonate Net effect: retention of all bicarb; excretion of H+ Shuttles important in physiology .Explanation / Answer
explaination: HCO3- is reabsorbed in kidney at two places ( proximal convulated tubule and distal convulated tubule) when the pH of the urine is high. In PCT reabsorption requires Na+ and in DCT reabsorption requires Cl-.
when the HCO3- cocentration rises the pH value also rises making the urine more basic. thus, H+ enters the lumen and combines with HCO3- to form H2CO3 in the presence of carbonic anhydrase (because, HCO3- cannot directly pass through the tubule cell membranes).
This H2CO3 then dissociates to form CO2 and H2O; CO2 then pass easily from the lumen into the tubular cells. There the CO2 again combines with H2O and forms H2CO3 (a weak acid) which then by simple dissociation form H+ and HCO3-.
This HCO3- then pass from the tubular cells to the blood vessels through Na+ and HCO3-sympoter in PCT and through Cl- and HCO3- antiporter in DCT.
Thus the HCO3- is reabsorbed into the blood by this mechanism.
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