STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Lung alveoli. Coloured scanning electron micrograph (SEM) of healthy human lung alveoli (numerous holes) and a bronchiole (top left). The bronchiole is a tube leading to these air passages deep within the lung. The air passages end in alveoli, air sacs through which gas exchange with the blood takes place. Red blood cells take up oxygen from the alveoli, releasing carbon dioxide at the same time. The carbon dioxide is exhaled, while the oxygenated blood is pumped around the body. Magnification: x40 at 6x7cm size.
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