Where does external respiration take place?

External respiration refers to the process of gas exchange that takes place in the lungs, specifically within the alveoli. These tiny air sacs are crucial because they provide a large surface area for the exchange of oxygen and carbon dioxide between the air in the lungs and the blood in the capillaries that surround them.

When you inhale, oxygen-rich air fills the alveoli, and oxygen diffuses across the thin walls of the alveoli into the blood in the nearby capillaries. At the same time, carbon dioxide, a waste product of metabolism, moves from the blood into the alveoli to be exhaled. This exchange of gases is what characterizes external respiration and is essential for supplying oxygen to the body while removing carbon dioxide.

While the bronchi and trachea are parts of the respiratory tract involved in conducting air to and from the lungs, they do not facilitate the actual exchange of gases. Instead, they serve as pathways. Capillaries do play a role in the gas exchange process, but they cannot be considered the site of external respiration since the actual exchange occurs in the alveoli. Thus, the alveoli are recognized as the key site for external respiration.