Which of the following mechanism help to exhale air out of the lungs

Options

A. The relazation of diaphragm
B. Contraction of external intercostal
C. The up lifting of sterum
D. All of the above

Answer

To solve the question "Which of the following mechanisms help to exhale air out of the lungs?", we need to analyze the options provided and understand the mechanics of breathing, specifically expiration.

### Step-by-Step Solution:

1. **Understanding Breathing Mechanics**:
- Breathing consists of two main processes: **inspiration (inhaling)** and **expiration (exhaling)**.
- During inspiration, air is drawn into the lungs, while during expiration, air is expelled from the lungs.

2. **Role of Pressure in Breathing**:
- The movement of air in and out of the lungs depends on the **pressure gradient** between the atmospheric pressure and the intrapulmonary pressure (pressure inside the lungs).
- When the intrapulmonary pressure is higher than the atmospheric pressure, air is expelled from the lungs.

3. **Mechanism of Expiration**:
- To exhale air, we need to **increase the intrapulmonary pressure**. This can be achieved by decreasing the volume of the thoracic cavity.
- The volume of the thoracic cavity can be decreased by the **relaxation of the diaphragm** and the **relaxation of the intercostal muscles**.

4. **Analyzing the Options**:
- **A. The relaxation of diaphragm**: When the diaphragm relaxes, the volume of the thoracic cavity decreases, which increases the intrapulmonary pressure, allowing air to be expelled. This option is correct.
- **B. Contraction of external intercostal muscles**: This action increases the volume of the thoracic cavity, which decreases the intrapulmonary pressure, causing air to flow into the lungs, not out. This option is incorrect.
- **C. The uplifting of sternum**: Similar to the contraction of external intercostal muscles, uplifting the sternum increases the volume of the thoracic cavity, leading to decreased pressure and air intake. This option is incorrect.
- **D. All of the above**: Since options B and C are incorrect, this option is also incorrect.

5. **Conclusion**:
- The mechanism that helps to exhale air out of the lungs is **A. The relaxation of diaphragm**.

### Final Answer:
**A. The relaxation of diaphragm**