During normal respiration, what occurs when lung volume decreases?

When lung volume decreases, the air pressure inside the lungs increases due to the principles of gas dynamics, specifically Boyle's law. This law states that if the volume of a gas decreases, the pressure of that gas will increase if the temperature remains constant.

In the context of normal respiration, when the diaphragm and other muscles responsible for inhalation relax, the volume of the thoracic cavity decreases. This decrease in volume leads to a rise in the pressure within the lungs compared to the atmospheric pressure outside the body. As a result, air is expelled from the lungs due to this pressure difference, allowing for exhalation.

Therefore, the correct answer reflects the physiological processes occurring in the respiratory system during a decrease in lung volume.