Exchange of gases
The exchange of carbon dioxide and oxygen occurs in the alveoli. Each alveolus is surrounded by a network of small blood vessels. Like the alveoli, these small blood vessels have extremely thin walls. Blood that enters the vessels has a high level of carbon dioxide, which it picked up from the body tissues. It contains little oxygen. The carbon dioxide leaves the blood and moves through the walls of the blood vessels and alveoli into the lungs. Oxygen from the air in the lungs then passes through the walls of the alveoli and blood vessels and into the blood. The blood, now rich in oxygen, leaves the lungs and travels to the heart. The heart then pumps it to cells throughout the body. The carbon dioxide is finally expelled from the lungs when we exhale.
Exchange of gases (3,173 KB)
