What happens to the expiratory reserve volume when the diaphragm is displaced by the uterus?

When the diaphragm is displaced by the uterus, such as during pregnancy, it restricts the downward movement of the diaphragm during inhalation. This mechanical displacement can lead to a reduction in the available space within the thoracic cavity for lung expansion, subsequently affecting various lung volumes. Expiratory reserve volume, which is the amount of air that can be forcibly exhaled after a normal exhalation, decreases in this scenario because the diaphragm's limited movement results in less overall lung capacity.

The presence of the uterus in the abdominal cavity pushes upward on the diaphragm, leading to decreased lung volumes, and specifically impacts the ability to fully expel air from the lungs. As a result, the ability to take a deep breath and then exhale fully is compromised, leading to a decrease in expiratory reserve volume. Thus, the correct answer reflects this physiological change.