Where does the diffusion of oxygen and carbon dioxide occur?

In the lungs, the diffusion of oxygen occurs from the alveoli (air sacs) into the blood capillaries, while the diffusion of carbon dioxide occurs from the blood capillaries into the alveoli for exhalation. This exchange process is facilitated by differences in partial pressures of oxygen and carbon dioxide between the air in the alveoli and the blood in the capillaries.