What physiological process is described as the transfer of gases between the alveoli and the pulmonary capillaries?

The correct answer is diffusion, which refers to the process by which gases move across a membrane from an area of higher concentration to one of lower concentration. In the context of the lungs, diffusion is the mechanism by which oxygen (O2) from the alveoli transfers into the blood within the pulmonary capillaries, and carbon dioxide (CO2) moves from the blood into the alveoli, where it can be exhaled. This gas exchange is facilitated by the thin walls of the alveoli and capillaries, allowing for rapid and efficient transfer of gases.

Ventilation involves the movement of air in and out of the lungs, which is essential for bringing fresh oxygen into the alveoli but is not the process of gas exchange itself. Perfusion describes the flow of blood through the pulmonary capillaries and is a critical component of gas exchange, but it does not describe the actual transfer of gases. Elastic recoil refers to the ability of the lungs to return to their resting state after being stretched during inhalation, which is related to lung mechanics rather than the exchange of gases.