The thick ascending limb of the loop of Henle
Which nephron segment actively reabsorbs NaCl but is impermeable to water, diluting the tubular fluid?
Answer D: explanation for every choice
A
The descending limb is permeable to water but not very permeable to salt.
B
The proximal tubule reabsorbs salt and water together.
C
With high ADH, the collecting duct reabsorbs water.
D
Correct. The Na⁺–K⁺–2Cl⁻ cotransporter pumps salt into the medulla, while the wall keeps water in the tubule.
TakeawayDescending limb: water out. Thick ascending limb: salt out, water stays.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb146.