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In the alveoli, oxygen from the air is absorbed into the blood. Carbon dioxide, a waste product of metabolism, travels from the blood to the alveoli, where it can be exhaled. Between the alveoli is a thin layer of cells called the interstitium, which contains blood vessels and cells that help support the alveoli.
They're called Alveoli; they are wrapped in capillaries, tiny blood vessels. Both the alveoli and capillaries are only one cell thick which allows for easy diffusion of â¦gases.