During expiration, what occurs to the thoracic diaphragm?

During expiration, the thoracic diaphragm plays a central role in the mechanics of breathing. This process typically involves the abdominal muscles contracting, which increases intra-abdominal pressure and pushes the diaphragm upwards into its dome-shaped position. As the diaphragm moves upwards, it decreases the volume of the thoracic cavity, leading to an increase in pressure within the lungs compared to atmospheric pressure. This pressure differential causes air to flow out of the lungs, facilitating expiration.

Choosing the option that states the abdominal muscles contract and the diaphragm is pushed up accurately reflects the physiological process that occurs during expiration. It emphasizes the importance of the diaphragm's movement, as it aids in forcing air out of the lungs when the abdominal muscles activate.