BSIP / SCIENCE PHOTO LIBRARY BSIP / SCIENCE PHOTO LIBRARY
Lung alveoli. Coloured scanning electron micrograph (SEM) of healthy human lung alveoli. The alveoli are air sacs through which gaseous exchange takes place. Capillaries (not seen) around the alveoli allow red blood cells to 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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