BSIP / SCIENCE PHOTO LIBRARY BSIP / SCIENCE PHOTO LIBRARY
Lung alveoli. Coloured scanning electron micrograph (SEM) of healthy human lung alveoli around bronchioles. The bronchioles (lower centre) are tiny tubes which lead to air passages deep within the lung. The air passages end in alveoli (spaces around the bronchioles), air sacs through which gas exchange with the blood takes place. Red blood cells release carbon dioxide into the alveoli, taking up oxygen at the same time. The carbon dioxide is exhaled, while the oxygenated blood is pumped around the body. Magnification: x200 at 35mm size.
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