How does gas exchange occur in the lungs?

Gas exchange in the lungs primarily occurs across the walls of the alveoli, which are tiny air sacs at the end of the bronchial tubes. The alveoli are surrounded by a network of capillaries, which are small blood vessels. The key to gas exchange lies in the thinness of the walls of both the alveoli and the capillaries, allowing for a process called diffusion.

Oxygen from the air in the alveoli diffuses through the alveolar walls into the blood in the capillaries, where it binds to hemoglobin in red blood cells. At the same time, carbon dioxide, which is a waste product of metabolism, moves from the blood into the alveoli to be exhaled. This exchange is driven by the concentration gradients of the gases; oxygen moves from an area of higher concentration (in the alveoli) to an area of lower concentration (in the blood), while carbon dioxide moves in the opposite direction.

The effectiveness of this gas exchange relies significantly on the large surface area of the alveoli, their proximity to capillaries, and the fact that both membranes (alveolar and capillary) are incredibly thin, facilitating efficient diffusion of gases.