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There are about 300 million alveoli in each of your lungs. These tiny air sacs provide an ideal site for the diffusion of gases into and out of the blood - also known as gaseous exchange.

The alveoli have a very large surface area - in fact if all of the alveoli in your lungs were spread out flat

they would cover the area of a tennis court.

This large surface area is the result of all the alveoli being small spheres - it is another example of the

importance of the surface area- to-volume ratio.

If your lungs were simply two large balloon-like structures, the surface area wouldn't be big enough for you to get enough oxygen by diffusion to supply the needs of your cells.

But each alveolus is a very tiny sphere. The smaller the radius of a sphere, the bigger the relative surface area - halving the radius increases the relative surface area by a factor of four.

The millions of tiny alveoli in the human lungs are a very effective adaptation which provides a huge surface area for gaseous exchange into and out of the blood.

The alveoli have a good air supply from the bronchioles and a rich blood supply.

This is vital for successful gaseous exchange because it maintains a steep concentration gradient for oxygen from the air in the alveoli to the blood, and for carbon dioxide from the blood to the alveoli.

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7y ago

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