Which region of the nephron loop is impermeable to water but permeable to salts?

• A. Distal convoluted tubule
• B. Descending limb of the loop of Henle
• C. Ascending limb of the loop of Henle
• D. Proximal convoluted tubule

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the structure and function of the nephron loop (loop of Henle). The nephron loop is divided into two main limbs: the descending limb and the ascending limb. Each limb has distinct permeability characteristics.
2. Step 2: Recall the permeability of the descending limb of the loop of Henle. This region is permeable to water but relatively impermeable to salts, allowing water to leave the filtrate and concentrate it.
3. Step 3: Recall the permeability of the ascending limb of the loop of Henle. This region is impermeable to water but permeable to salts, allowing salts (such as Na+ and Cl-) to be reabsorbed into the surrounding interstitial fluid.
4. Step 4: Compare the ascending limb's characteristics with the other nephron regions mentioned in the problem. The proximal convoluted tubule and distal convoluted tubule are involved in reabsorption and secretion but do not exhibit the specific impermeability to water and permeability to salts seen in the ascending limb.
5. Step 5: Conclude that the ascending limb of the loop of Henle is the correct answer based on its unique permeability properties, which are essential for the countercurrent multiplication mechanism in the kidney.