ANATOMY

Detailed explanation-1: -The descending limb of the loop of Henle is permeable to water but impermeable to electrolytes and this concentrates the filtrate as water moves out from the limb as the filtrate moves down. Whereas the ascending limb is impermeable to water but permeable to electrolytes, this dilutes the filtrate as it moves upward.

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.

Detailed explanation-3: -Overall the loop of Henle reabsorbs around 25% of filtered ions and 20% of the filtered water in a normal kidney.

Detailed explanation-4: -Loop of Henle Passive potassium transport plays a role in medullary potassium recycling (Jamison 1987). The latter allows some of the reabsorbed potassium from medullary collecting ducts to enter descending thin limbs of juxtamedullary nephrons by passive secretion.

Detailed explanation-5: -The descending limb of the loop of Henle is permeable to water. Water diffuses into the hyperosmolar medullary interstitium. The osmolarity can reach a maximum of 1200 mOsm/L at the tip of the medullary interstitium in antidiuresis. The ascending limb (where loop diuretics work) is impermeable to water.