Question

how is alveoli designed and why​

Answer 1

Alveoli provide a surface for the exchange of gases. An extensive network of blood vessels is present in the wall of the alveoli. ... Air is sucked into the lungs and alveoli. The oxygen from the breath, diffuses into the blood and CO2 from the blood brought from the body, diffuses out into the air.

Answer 2

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The alveoli are thin-walled and richly supplied with a network of blood vessels to facilitate the exchange of gases between blood and the air-filled in alveoli. They have a balloon-like structure that provides maximum surface area for exchange of gases.