ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Alveoli. Computer graphic illustration showing the alveoli (round light blue structures), the microscopic air sacs of the lungs. They are seen wrapped by an intricate network of capillaries; it is in this network that gases, such as carbon dioxide and oxygen, are exchanged during respiration. Alveoli are found at the end of a bronchiole, one of the many small air passages in the lungs, and are arranged in groups that resemble bunches of grapes. About 300 million alveoli are found in each lung.
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