Reabsorption of water in proximal convoluted tubules and distal convoluted tubules is respectively

Options

A. Obligatory and facultative
B. Facultative and obligatory
C. Obligatory only
D. Active and passive

Answer

To solve the question regarding the reabsorption of water in the proximal convoluted tubules (PCT) and distal convoluted tubules (DCT), we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding Water Reabsorption**:
- Water reabsorption in the kidneys occurs primarily in the nephron, which includes the proximal convoluted tubule (PCT) and the distal convoluted tubule (DCT).

2. **Reabsorption in Proximal Convoluted Tubule (PCT)**:
- The PCT is responsible for the reabsorption of approximately 65% of the water filtered from the blood. This process is called obligatory reabsorption, meaning it occurs regardless of the body's hydration status.

3. **Reabsorption in Distal Convoluted Tubule (DCT)**:
- The DCT reabsorbs about 20% of the water. This reabsorption is also obligatory, meaning it occurs consistently, but is influenced by the body's needs and hormonal regulation.

4. **Total Water Reabsorption**:
- In total, about 85% of the water is reabsorbed in the nephron, with 65% occurring in the PCT and 20% in the DCT.

5. **Conclusion**:
- Therefore, the correct answer to the question is that both the PCT and DCT perform obligatory reabsorption of water.

### Final Answer:
- The reabsorption of water in the proximal convoluted tubules and distal convoluted tubules is respectively **obligatory**.