What happens to the pressure in the thoracic cavity during exhalation?

• A. It decreases
• B. It increases
• C. It remains constant
• D. It fluctuates randomly

Answer: (B)

During exhalation, the pressure in the thoracic cavity increases. This process begins with the contraction of the diaphragm and the intercostal muscles, which leads to the reduction in volume of the thoracic cavity. According to Boyle's Law, when the volume of a container decreases, the pressure inside that container increases, provided the temperature remains constant.

As the volume of the thoracic cavity decreases, the air pressure inside the cavity rises above atmospheric pressure. This pressure difference drives air out of the lungs and into the atmosphere. Therefore, the increase in thoracic cavity pressure during exhalation is a key part of the mechanics of breathing, facilitating the expulsion of air from the lungs.

While some options suggest alternative outcomes like a decrease, constant pressure, or random fluctuations, these do not accurately describe the physiological process occurring in the thoracic cavity during exhalation.