Lungs contain millions of tiny air sacs called alveoli. They are adapted for efficient gas exchange. Blood is pumped from the heart to the lungs and passes through the network of capillaries surrounding the alveoli. Carbon Dioxide diffuses from the blood into the air in the alveoli. Oxygen Diffuses from the air in the lungs into the blood. The oxygenated blood travels back to the heart to be pumped around the body. Oxygen dissolves in the layer of fluid lining the alveolus before it diffuses into the blood.
- A large surface area
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