One of the following is impermeable to `H_(2)O` normally

Options

A. PCT
B. DCT
C. Descending limb
D. Ascending limb

Answer

To determine which part of the nephron is impermeable to water (H₂O) normally, we will analyze the four options provided: Proximal Convoluted Tubule (PCT), Distal Convoluted Tubule (DCT), Descending Limb, and Ascending Limb of the Loop of Henle.

### Step-by-Step Solution:

1. **Analyze the Proximal Convoluted Tubule (PCT)**:
- The PCT is responsible for the reabsorption of a significant amount of water from the glomerular filtrate.
- Since it allows water to pass through, it is permeable to water.
- **Conclusion**: PCT is not the correct answer.

2. **Analyze the Distal Convoluted Tubule (DCT)**:
- The DCT also reabsorbs some water, although less than the PCT.
- It is still permeable to water, allowing some reabsorption to occur.
- **Conclusion**: DCT is not the correct answer.

3. **Analyze the Descending Limb of the Loop of Henle**:
- The descending limb is permeable to water, allowing for water reabsorption.
- It is important for concentrating urine as water exits this limb.
- **Conclusion**: The descending limb is not the correct answer.

4. **Analyze the Ascending Limb of the Loop of Henle**:
- The ascending limb is impermeable to water.
- It does not allow water to be reabsorbed, which is crucial for the dilution of urine.
- **Conclusion**: The ascending limb is impermeable to water and is the correct answer.

### Final Answer:
The part of the nephron that is impermeable to H₂O normally is the **Ascending Limb of the Loop of Henle**.

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