which of the following statements is/ are correct regarding normal expiration?
(A) it is a passive process (B) it is an active process (C) The vloume of thoracic cavity increases (D) The lower ends of the lungs are pulled downwords by the contraction of diaphragm

Options

A. (A),(C) only
B. (A),(B) & (C) only
C. only (A)
D. (A),(C) & (D) only

Answer

To determine which statements are correct regarding normal expiration, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Normal Expiration**:
- Normal expiration is the process of breathing out air from the lungs. It is a part of the respiratory cycle.

2. **Analyzing Statement (A)**:
- **Statement (A)**: "It is a passive process."
- **Explanation**: During normal expiration, the diaphragm relaxes, and the elastic recoil of the lungs helps push air out. This process does not require active muscle contraction, making it a passive process.
- **Conclusion**: This statement is **correct**.

3. **Analyzing Statement (B)**:
- **Statement (B)**: "It is an active process."
- **Explanation**: An active process would require muscle contraction to expel air. However, normal expiration primarily relies on the relaxation of the diaphragm and the elastic recoil of the lungs, which does not involve active muscle work.
- **Conclusion**: This statement is **incorrect**.

4. **Analyzing Statement (C)**:
- **Statement (C)**: "The volume of thoracic cavity increases."
- **Explanation**: During expiration, the diaphragm relaxes, which causes the thoracic cavity's volume to decrease, not increase. This decrease in volume helps push air out of the lungs.
- **Conclusion**: This statement is **incorrect**.

5. **Analyzing Statement (D)**:
- **Statement (D)**: "The lower ends of the lungs are pulled downwards by the contraction of the diaphragm."
- **Explanation**: During expiration, the diaphragm relaxes, causing the lungs to compress and the lower ends to move upwards, not downwards. The diaphragm's contraction occurs during inhalation, not expiration.
- **Conclusion**: This statement is **incorrect**.

### Final Conclusion:
- The only correct statement regarding normal expiration is **(A)**: "It is a passive process." Therefore, the correct answer is **A only**.