How many alveoli are in the human lungs?
Quick Answer
The human lungs are thought to contain about 300 million to 500 million alveoli. These tiny air sacs provide the huge surface area needed for gas exchange.
The Full Story
A typical adult human has roughly 300 million to 500 million alveoli in the lungs, though the exact number varies. Alveoli are tiny sacs at the ends of the smallest airways, where oxygen moves into the blood and carbon dioxide moves out. Their walls are very thin, and they are wrapped in capillaries to make exchange fast and efficient. Collectively, the alveoli create a surface area often estimated at around 70 square metres in adults, about the size of a tennis court. This large surface area is one reason humans can absorb oxygen efficiently during rest and exercise.
Key Facts
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"Inside your lungs are millions of tiny air sacs doing the real work of breathing."
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