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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.
An alveolus is a tiny air sac formed at the tip of the lungs' smallest airways, the bronchioles. The primary function of the alveoli is the exchange of carbon dioxide for oxygen.Tissues within the alveoli also carry out secondary functions, such as the production of hormones, enzymes, and pulmonary surfactant.he exchange of carbon dioxide for oxygen is the primary function of the alveoli. The capillaries of the alveolus branch from both the pulmonary artery and the pulmonary vein.