Expiration takes place when

Answer

### Step-by-Step Solution:

1. **Understanding Breathing**: Breathing consists of two main processes: inspiration (inhaling) and expiration (exhaling). Both processes are essential for gas exchange in the lungs.

2. **Inspiration Process**: During inspiration, the diaphragm contracts and flattens, which increases the volume of the thoracic cavity. This increase in volume leads to a decrease in intrapulmonary pressure (the pressure within the lungs) compared to atmospheric pressure, causing air to flow into the lungs.

3. **Expiration Process**: In contrast, expiration is primarily a passive process. It occurs when the diaphragm relaxes, returning to its dome-shaped position. This relaxation decreases the volume of the thoracic cavity, which increases intrapulmonary pressure.

4. **Pressure Changes**: When the intrapulmonary pressure becomes greater than atmospheric pressure, air is pushed out of the lungs. Therefore, expiration occurs when the intrapulmonary pressure is higher than the atmospheric pressure.

5. **Conclusion**: Thus, expiration takes place when the intrapulmonary pressure is greater than atmospheric pressure, leading to the expulsion of air from the lungs.

### Final Answer:
Expiration takes place when the intrapulmonary pressure is greater than atmospheric pressure.

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