Inspiration occurs when intra-pulmonary pressure is

Options

A. Higher than atmospheric pressure
B. Lower than atmospheric pressure
C. Equal to atmospheric pressure
D. Zero compared to atmospheric pressure

Answer

To solve the question "Inspiration occurs when intra-pulmonary pressure is:", we need to understand the relationship between intra-pulmonary pressure and atmospheric pressure during the process of breathing.

### Step-by-Step Solution:

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

2. **Pressure Gradient**:
- Air flows from an area of higher pressure to an area of lower pressure. Therefore, for air to move into the lungs, the intra-pulmonary pressure must be lower than the atmospheric pressure.

3. **Analyzing the Options**:
- **Option A**: Higher than atmospheric pressure - This would cause expiration (air moving out of the lungs), not inspiration. So, this option is incorrect.
- **Option B**: Lower than atmospheric pressure - This is correct because it allows air to flow into the lungs, facilitating inspiration.
- **Option C**: Equal to atmospheric pressure - If the intra-pulmonary pressure is equal to atmospheric pressure, there would be no pressure gradient, and no air movement would occur. Thus, this option is incorrect.
- **Option D**: Zero compared to atmospheric pressure - This is also incorrect for the same reason as option C; it does not create a pressure gradient.

4. **Conclusion**:
- The correct answer is that inspiration occurs when intra-pulmonary pressure is lower than atmospheric pressure.

### Final Answer:
Inspiration occurs when intra-pulmonary pressure is **lower than atmospheric pressure**.

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