Bicarbonate is maximally absorbed in which pa of the nephron?

80-90% of bicarbonate reabsorption occurs in the PCT. The secreted H+ ion combines with filtered HCO3- to form H2CO3 and the presence of carbonic anhydrase on the apical membrane of the proximal tubule catalyzes the formation of H2O and CO2 from H2CO3. The apical membrane of epithelial cells lining the proximal tubule is permeable to CO2 and H2O, and they enter the tubule rapidly. Eighty per cent of the filtered load of HCO3- is reabsorbed in the proximal tubule. The cells of the proximal tubule are also involved in vitamin D hydroxylation. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 39. Acidification of the Urine & Bicarbonate Excretion. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.