Question

which of the following occurs during expiration?
multiple choice
increased alveolar volume causes increased alveolar pressure.
increased alveolar volume causes decreased alveolar pressure.
decreased alveolar volume causes increased alveolar pressure.
decreased alveolar volume causes decreased alveolar pressure.
decreased alveolar pressure causes increased alveolar volume.

Explanation:

During expiration, the diaphragm relaxes and moves upward, and the intercostal muscles relax, causing the rib cage to move downward and inward. This reduces the volume of the thoracic cavity. According to Boyle's law ($P_1V_1 = P_2V_2$, where pressure and volume are inversely related when temperature is constant), a decrease in alveolar volume (due to the reduction in thoracic cavity volume) leads to an increase in alveolar pressure. When alveolar pressure is greater than atmospheric pressure, air is forced out of the lungs (expiration).

Answer:

Decreased alveolar volume causes increased alveolar pressure.