In mammals, what happens to the thoracic cavity when the diaphragm contracts?

When the diaphragm contracts in mammals, it moves downward, increasing the volume of the thoracic cavity. This action reduces the pressure in the thoracic cavity relative to the atmospheric pressure, allowing air to flow into the lungs, facilitating inhalation. The horizontal movement of the diaphragm creates a larger space in the thoracic region, and as a direct consequence, the lungs expand to fill this increased volume.

This mechanism is fundamental to the process of breathing, as an increase in the thoracic cavity volume is essential for drawing air in and ensuring that oxygen is available for exchange in the alveoli of the lungs. Therefore, the option indicating that the thoracic cavity increases in volume due to diaphragm contraction is clearly aligned with the physiological processes of respiration in mammals.