Question

the lungs contain over 300 million of alveoli surrounded by blood vessels why​

Answer 1

Answer:

Healthy lungs have about 300 million air sacs in them. Each air sac is surrounded by a network of fine blood vessels (capillaries). The oxygen in inhaled air passes across the thin lining of the air sacs and into the blood vessels. ... When oxygen passes into the bloodstream, carbon dioxide leaves it.

Answer 2

Answer:

Healthy lungs have about 300 million air sacs in them. Each air sac is surrounded by a network of fine blood vessels (capillaries). The oxygen in inhaled air passes across the thin lining of the air sacs and into the blood vessels. ... When oxygen passes into the bloodstream, carbon dioxide leaves it.