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PCT Sodium Reabsorption — FRCA Primary MCQ

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HardPhysiology - RenalPCT Sodium ReabsorptionFRCA Primary

Which nephron segment reabsorbs the largest fraction of filtered sodium under normal conditions?

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Correct answer: B — The proximal convoluted tubule through high-capacity isosmotic reabsorption

The best answer is “The proximal convoluted tubule through high-capacity isosmotic reabsorption”. The proximal convoluted tubule reabsorbs about 65–70% of filtered sodium and water isosmotically, the largest fraction in the nephron. The thick ascending limb reabsorbs a substantial smaller fraction and the distal nephron fine-tunes sodium balance. The thin descending limb is chiefly permeable to water rather than sodium.

Reference: Royal College of Anaesthetists, Primary FRCA Syllabus 2021: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf