Inspiration occurs when there is a negative pressure in the lungs with respect to atmospheric pressure. This negative pressure is achieved when

Options

A. intrapulmonary pressure is less than the atmospheric pressure
B. Intrapulmonary pressure is greater than the atmospheric pressure
C. intrapulmonary pressure is equal to the atmospheric pressure
D. intrapleural pressure becomes more than the intra-alveolar pressure.

Explanation

To understand how inspiration occurs when there is a negative pressure in the lungs with respect to atmospheric pressure, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Pressure in the Lungs**:
- The lungs contain air, and the pressure of this air is referred to as intrapulmonary pressure. This pressure is crucial for the process of breathing.

2. **Pressure Gradient**:
- For air to flow into the lungs (inspiration), there must be a pressure gradient. This means that the pressure inside the lungs (intrapulmonary pressure) must be lower than the pressure outside the lungs (atmospheric pressure).

3. **Creating Negative Pressure**:
- Negative pressure in the lungs is achieved when the intrapulmonary pressure drops below atmospheric pressure. This can occur when the diaphragm and intercostal muscles contract, expanding the thoracic cavity and decreasing the pressure inside the lungs.

4. **Intrapulmonary Pressure**:
- When the intrapulmonary pressure is less than atmospheric pressure, air from the atmosphere rushes into the lungs to equalize the pressure. This is the essence of inspiration.

5. **Conclusion**:
- Therefore, the statement that "inspiration occurs when intrapulmonary pressure is less than atmospheric pressure" is correct.

### Final Answer:
- The negative pressure in the lungs during inspiration is achieved when the intrapulmonary pressure is less than the atmospheric pressure.