53) .BICARBONATE REABSORPTION IN THE KIDNEY

[Editor]

a) occurs in the proximal tubules
b) is accompanied by the excretion of hydrogen ions
c) is facilitated by carbonic anhydrase
d) is accompanied by sodium reabsoption
e) is independent of arterial pco2

[Editor]

tttff
90% of the filtered HCO3 is reabsorbed in the proximal tubule.HCO3 reabsorption in the proximal and distal tubule is dependant on the filtered HCO3,Hydrogen ion secretion since HCO3 is reabsorbed in exchange of Hydrogen ion.Carbonic anhydrase catalyses the formation of Carbonic acid and its breakdown to bicarbonate in the proximal and distal tubular cells.Sodium reabsorption is in exchange of Hydrogen at the luminal surface and by active transport in exchange for Potassium facilitated by Na-K ATPase at the basolateral and the interstitial side in the proximal tubular cells.Bicarbonate reabsorption is dependent on the arterial Pco2 because more CO2 is available to form carbonic acid,more hydrogen ions can be excreted and more bicarbonate can be absorbed in the process.

[Tonic]

D) is an interesting question. For each HCO3 absorbed a Na ion will have been reabsorbed in exchange for a hydrogen ion, so you could argue it being true. I guess it's how you interpret the wording of the question.