2.1.7

Explain the process of gaseous exchange at the alveoli.

Gaseous exchange occurs in the alveoli by a process called diffusion, which occurs between the surface of alveoli and pulmonary capillary beds. Oxygen, once inhaled into the lungs, is passed from the alveoli into the bloodstream for distribution to the rest of the body. This occurs because there is a higher concentration of O₂ in the alveoli than in the blood. There, O₂ diffuses across to the capillaries where there is a lower concentration. At the same time, CO₂ goes from the high concentration in the capillaries to a low concentration in the alveoli and is breathed out during exhalation.

(Partial pressure= concentration)