The alveoli are completely covered in blood vessels (capillaries). The walls of the capillaries are extremely thin and the distance between air and blood is only 0.3μm.
This means that O2 has no distance to travel to get into the blood. The alveoli increase the surface area hugely. Humans have 300 million alveoli in both lungs giving a total surface area of 80 m2 (The skin is 2m2).
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i am pretty sure that is takes in oxygen and gives back carbon dioxide for the other organs..im am not positive