When the internal intercostal muscles are contracted, the lungs are at (After forceful expiration)

Options

A. Expiratory reserve volume
B. Functional residual capacity (FRC)
C. Residual volume
D. Vital capacity

Answer

To answer the question "When the internal intercostal muscles are contracted, the lungs are at (After forceful expiration)", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Breathing Mechanics**:
- Breathing involves two main processes: inspiration (breathing in) and expiration (breathing out). The lungs change volume to create pressure differences that allow air to flow in and out.

2. **Role of Internal Intercostal Muscles**:
- The internal intercostal muscles are primarily involved in forceful expiration. When these muscles contract, they pull the ribs downward and inward, decreasing the volume of the thoracic cavity.

3. **Effect of Forceful Expiration**:
- During forceful expiration, the volume of air in the lungs decreases significantly as air is pushed out. However, it is important to note that not all air can be expelled from the lungs.

4. **Residual Volume**:
- After a forceful expiration, there remains a certain volume of air in the lungs known as the residual volume. This volume typically ranges from 1000 to 1200 ml and cannot be expelled, preventing the lungs from collapsing.

5. **Conclusion**:
- Therefore, when the internal intercostal muscles are contracted during forceful expiration, the lungs contain residual volume, which is the air that remains in the lungs even after the maximum effort to exhale.

### Final Answer:
The lungs are at **residual volume** after forceful expiration when the internal intercostal muscles are contracted.

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