BSIP, GILLES / SCIENCE PHOTO LIBRARY BSIP, GILLES / SCIENCE PHOTO LIBRARY
Respiratory system. Artwork showing the lungs and upper respiratory tract. At upper left, the facial sinuses (pink, rounded) are seen behind the nose, with the airways from the nose joining the trachea behind the mouth. The trachea travels down until it divides into two bronchi, which each lead to a lung (pink, lower left and right). In the lungs the bronchi branch into many bronchioles (small red tubes), which terminate in air sacs called alveoli (grape-like cluster, lower right). Capillaries between the alveoli carry red blood cells, which take oxygen from the air and release carbon dioxide to be exhaled.
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