In the countercurrent mechanism, the high osmolarity in the medullary interstitial fluid is primarily maintained by:
- ATransport of NaCl from the ascending limb of Henle's loop together with urea movement into the medullary interstitium.
- BPassive diffusion of water from the descending limb of Henle's loop and active transport of K⁺ from the ascending limb.
- CActive transport of Na⁺ from the descending limb of Henle's loop and urea secretion into the collecting duct.
- DDiffusion of water into the vasa recta and active transport of H⁺ into the collecting duct.
✓ Correct answer: A
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