How do the structures of alveoli and capillaries support the function of gas exchange?

Exchange of gases in alveoli takes place through diffusion.

This diffusion takes place to partial pressure differences among the gases O2 and CO2.

The partial pressure of O2in alveolar sac = 103 mm Hg

The partial pressure of O2 in blood = 50mm Hg

The partial pressure of CO2 in alveolar sac = 28 mm Hg

The partial pressure of CO2 in blood = 45 mm Hg

As a result, the O2 from alveolar sacs diffuses into blood.

the CO2 diffuses from blood into lungs.