Which physiological process involves the transfer of gases in the lungs?

The process of gas transfer in the lungs is best described by diffusion. In the context of respiration, when air is inhaled into the lungs, oxygen from the air enters the bloodstream while carbon dioxide in the blood moves into the air sacs of the lungs. This transfer occurs through the process of diffusion, which is driven by the concentration gradient.

Oxygen is typically at a higher concentration in the alveoli (the air sacs) compared to the blood in the capillaries surrounding them. Therefore, oxygen diffuses into the blood. Conversely, carbon dioxide is at a higher concentration in the blood than in the alveoli, leading to its diffusion out of the blood into the air sacs for exhalation.

While respiration encompasses the entire process of gas exchange, including inhalation and exhalation, it is the diffusion of gases that specifically describes how oxygen and carbon dioxide move across the alveolar and capillary membranes. Inhalation refers specifically to the act of breathing in, and exhalation refers to the act of breathing out, but neither of those terms describes the mechanism of gas transfer itself, which is fundamentally a diffusion process.