During expiration, what happens to alveolar pressure?

During expiration, alveolar pressure increases and becomes greater than atmospheric pressure. This occurs as the diaphragm and intercostal muscles relax, leading to a decrease in lung volume. Since the lungs are elastic, they naturally recoil. As the volume decreases, the pressure inside the alveoli (the tiny air sacs in the lungs) rises above the pressure outside the body (atmospheric pressure). This pressure gradient allows air to flow out of the lungs and into the atmosphere.

The increase in alveolar pressure during expiration is essential for the process of ventilation, as it facilitates the expulsion of air from the lungs. This mechanism is crucial for the maintenance of proper gas exchange and overall respiratory function. The other options do not accurately represent the physiological changes that occur in the lungs during the expiration phase.