What is the process of external respiration primarily concerned with?

The process of external respiration is primarily concerned with the exchange of gases that occurs specifically between the air in the alveoli of the lungs and the blood in the pulmonary capillaries. This vital process involves oxygen diffusing from the alveolar air into the blood, while carbon dioxide moves in the opposite direction—from the blood into the alveoli—to be exhaled. This exchange ensures that oxygen is delivered to the body's tissues for cellular respiration and that carbon dioxide, a waste product of metabolism, is expelled from the body.

Understanding this process is crucial because it highlights the role of the alveoli as the primary sites for gas exchange, where the thin walls facilitate efficient diffusion due to the large surface area and rich capillary network. While the choice regarding the exchange of gases between the lungs and the environment does describe a fundamental function of the respiratory system, it is more inclusive of both external and internal environments and does not specifically pinpoint the critical interface between alveoli and blood. Thus, the focus on alveolar-blood gas exchange captures the essence of external respiration more accurately.