PATHOLOGY

Detailed explanation-1: -The loop of Henle contributes 20–30% of sodium reabsorption. The thin descending limb is water permeable due to the presence of aquaporin-1, but impermeable to solutes. The ascending limb on the contrary is impermeable to water and the main site of Na+ reabsorption, especially in the thick ascending limb (TAL).

Detailed explanation-2: -Water is readily reabsorbed from the descending limb by osmosis. Also, the medullary interstitium is highly concentrated (because of the activity of the ascending limb), leading to a strong osmotic gradient from the descending limb to the medulla.