In the presence of vasopressin the greatest fraction of filtered water is reabsorbed in which pa of the nephron?: (A) Proximal tubule, (B) Distal tubule, (C) Loope of Henle, (D) Collecting duct
Answer is A. The proximal tubule is responsible for reabsorbing ~60% of filtered water irrespective of the presence or abscence of vassopressin. Ref: Harrisons principles of internal medicine, 18th edition, chapter: 277.