One of the following is impermeable to water

Options

A. PCT
B. DCT
C. Descending limb of Renie's loop
D. Ascending limb of Henle's loop

Answer

To determine which part of the nephron is impermeable to water, let's analyze each option provided in the question step by step:

1. **Understanding the Nephron**: The nephron is the structural and functional unit of the kidney, responsible for urine formation. It consists of several parts: Proximal Convoluted Tubule (PCT), Distal Convoluted Tubule (DCT), Loop of Henle (which includes the descending and ascending limbs), and the collecting duct.

2. **Analyzing the PCT**: The Proximal Convoluted Tubule (PCT) is known for reabsorbing a significant amount of water along with glucose, amino acids, and ions. Therefore, the PCT is permeable to water.

3. **Analyzing the DCT**: The Distal Convoluted Tubule (DCT) also allows for the reabsorption of water, although to a lesser extent compared to the PCT. It is permeable to water, especially under the influence of hormones like aldosterone.

4. **Analyzing the Descending Limb of Henle's Loop**: The descending limb of the Loop of Henle is permeable to water. It allows water to be reabsorbed into the surrounding medullary interstitium, concentrating the filtrate as it descends.

5. **Analyzing the Ascending Limb of Henle's Loop**: The ascending limb of the Loop of Henle is impermeable to water. This part of the nephron actively transports electrolytes (such as sodium and chloride) out of the filtrate but does not allow water to follow, making the filtrate dilute as it ascends.

6. **Conclusion**: Based on the analysis of each part of the nephron, the correct answer to the question "One of the following is impermeable to water" is the **ascending limb of Henle's loop**.

### Summary of the Solution:
- PCT: Permeable to water
- DCT: Permeable to water
- Descending limb of Henle's loop: Permeable to water
- **Ascending limb of Henle's loop: Impermeable to water** (Correct answer)