What physiological change occurs upon exhalation in mammals?

Upon exhalation in mammals, the diaphragm and intercostal muscles relax, leading to a decrease in the volume of the thoracic cavity. As the volume of the thoracic cavity decreases, the pressure within the lungs increases due to Boyle's Law, which states that pressure and volume are inversely related in a closed system. Consequently, this increase in pressure drives air out of the lungs and into the environment until pressures equalize.

The choice concerning volume decrease and pressure increase accurately reflects this physiological process. The lungs themselves expel air as a result of the higher intra-thoracic pressure compared to the atmospheric pressure, which facilitates the movement of air out of the lungs.

In contrast, the option regarding volume increase and pressure decrease does not align with the mechanics of exhalation. During exhalation, the lung volume does not increase; rather, it decreases. The selection about static lung volume and constant internal pressure misrepresents the dynamic changes occurring during breathing. Lungs do not remain static during breathing cycles, as they continually fluctuate in volume and pressure in response to inhalation and exhalation.