Lung alveoli. Coloured scanning electron microgr- aph (SEM) of healthy human lung alveoli around a bronchiole. The bronchiole (lower left) is one of the tiny tubes which lead to air passages deep within the lung. The air passages end in alveoli (spaces around the bronchiole), air sacs through which gas exchange with the blood takes place. Magnification: x82 at 35mm size.
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