Which of the following factors contribute to the reduction of the pulmonary volume ?

Options

A. Relaxation of diaphragm
B. Relaxation of the intercostal muscles
C. Return of sternum to their normal positions
D. All of the above

Answer

To solve the question regarding which factors contribute to the reduction of pulmonary volume, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Pulmonary Volume**:
- Pulmonary volume refers to the amount of air that the lungs can hold. During the process of breathing, this volume changes with inhalation and exhalation.

2. **Option 1: Relaxation of the Diaphragm**:
- During expiration, the diaphragm, which is a dome-shaped muscle at the base of the thoracic cavity, relaxes. This relaxation leads to a decrease in the volume of the thoracic cavity, which in turn reduces the pulmonary volume as air is expelled from the lungs.
- **Conclusion**: This option contributes to the reduction of pulmonary volume.

3. **Option 2: Relaxation of the Intercostal Muscles**:
- The intercostal muscles are located between the ribs and assist in the expansion and contraction of the thoracic cavity. During expiration, these muscles also relax, allowing the ribs to move back to their original position, further decreasing the thoracic cavity volume and consequently the pulmonary volume.
- **Conclusion**: This option also contributes to the reduction of pulmonary volume.

4. **Option 3: Return of the Sternum to its Normal Position**:
- The sternum, or breastbone, moves upward and outward during inspiration. During expiration, it returns to its original position, which decreases the volume of the thoracic cavity and contributes to the reduction of pulmonary volume.
- **Conclusion**: This option contributes to the reduction of pulmonary volume as well.

5. **Option 4: All of the Above**:
- Since all the previous options (1, 2, and 3) contribute to the reduction of pulmonary volume, this option is correct as it encompasses all the factors mentioned.
- **Conclusion**: The correct answer is option 4, "All of the above."

### Final Answer:
The factors that contribute to the reduction of pulmonary volume are:
- Relaxation of the diaphragm
- Relaxation of the intercostal muscles
- Return of the sternum to its normal position
Thus, the correct answer is **Option 4: All of the above**.

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