How do the lungs swap oxygen for carbon dioxide?
Quick Answer
In the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses out into exhaled air. The lungs contain hundreds of millions of alveoli to make this exchange efficient.
The Full Story
The smallest air sacs in the lungs are called alveoli, and they have very thin walls surrounded by capillaries. Oxygen moves from the air in the alveoli into the blood because its concentration is higher there, while carbon dioxide moves in the opposite direction to be exhaled. This exchange happens by diffusion and depends on a huge surface area created by the many tiny sacs. Breathing movements and the flow of blood keep the gradients moving efficiently. Without this gas exchange, body cells could not make enough energy.
Key Facts
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Suggested video title for this topic:
"The microscopic exchange that keeps you alive"