Bicarbonate PCT Reabsorption 85% — FRCA Primary MCQ
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Correct answer: C — Bicarbonate is freely filtered and 85% is reabsorbed in the proximal tubule
Bicarbonate is freely filtered (~4320 mmol/day). Approximately 85% is reabsorbed in the PCT / 10% in the thick ascending limb / and 5% in the collecting duct. Reabsorption is indirect: luminal carbonic anhydrase (CA-IV) converts filtered HCO3- + H+ to CO2 + H2O. CO2 diffuses into cells where intracellular CA-II regenerates HCO3- which exits basolaterally.
Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist