Inspiration occurs when

Options

A. the volume of the lung increase while the pressure in the lung decreases
B. the volume of the lung decreases while the pressure in the lung increases
C. the volume of the lung increases while the pressure in the lung increases
D. the volume of the lung decreases while the pressure in the lung decreases

Answer

To answer the question "Inspiration occurs when," we need to analyze the relationship between lung volume and pressure during the process of inspiration.

### Step-by-Step Solution:

1. **Understanding Inspiration**:
- Inspiration is the process of taking air into the lungs. It occurs when the pressure inside the lungs (pulmonary pressure) is lower than the atmospheric pressure.

2. **Pressure-Volume Relationship**:
- According to Boyle's Law, pressure and volume have an inverse relationship. This means that if the volume of a gas increases, the pressure decreases, and vice versa.

3. **Mechanism of Inspiration**:
- During inspiration, the diaphragm and intercostal muscles contract, which increases the volume of the thoracic cavity.
- As the volume of the thoracic cavity increases, the pressure inside the lungs decreases.

4. **Air Movement**:
- When the pressure inside the lungs is lower than the atmospheric pressure, air flows into the lungs. This is the essence of inspiration.

5. **Evaluating the Options**:
- **Option A**: The volume of lungs increases while the pressure in the lung decreases.
- This is correct because an increase in volume leads to a decrease in pressure, allowing air to flow into the lungs.
- **Option B**: The volume of the lung decreases while the pressure in the lung increases.
- This is incorrect because a decrease in volume would increase pressure, leading to expiration, not inspiration.
- **Option C**: The volume of the lung increases while the pressure in the lung increases.
- This is incorrect as it contradicts the inverse relationship between volume and pressure.
- **Option D**: The volume of lung decreases while the pressure in the lung decreases.
- This is also incorrect because a decrease in volume would not lead to a decrease in pressure.

6. **Conclusion**:
- The correct answer is **Option A**: "The volume of lungs increases while the pressure in the lung decreases."