Gaseous Exchange
The alveoli are the tiny air sacs at the ends of the bronchioles and the site of gaseous exchange. It is here that oxygen is absorbed into the blood while carbon dioxide is put into the air.
Deoxygenated blood arrives at the alveoli in tiny blood capillaries. These have very thin walls, as does the alveoli itself. This makes it easier for the gases to pass from the air into the blood or vice versa. The deoxygenated blood has red blood cells low in oxygen and blood plasma high in carbon dioxide. The carbon dioxide diffuses from the blood plasma into the air. The oxygen diffuses from the air into the red blood cells. Blood constantly moves through the capillaries picking up O2 and giving up its CO2.
