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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.
Alveoli. The epithelium of the alveoli, contains two main types of cells: 1. type I pneumocytes: large flattened cells - (95% of the total alveolar area) which present a very thin diffusion barrier for gases.They are connected to each other by tight junctions.2. type II pneumocytes (making up 5% of the total alveolar area, but 60% of total number of cells).lveoli. The epithelium of the alveoli, contains two main types of cells: 1. type I pneumocytes: large flattened cells - (95% of the total alveolar area) which present a very thin diffusion barrier for gases.