Lungs. Artwork of the lungs and respiratory system superimposed on a man's torso. Air is breathed in through the mouth or nose (upper left). It travels down the trachea (windpipe, blue). The trachea divides into two bronchi, each of which leads to a lung (blue, lower left and right). The bronchi divide further into bronchioles (not seen), each of which ends with air sacs called alveoli (not seen). Capillaries in the lungs allow red blood cells to take up oxygen and release carbon dioxide into the alveoli. The oxygenated blood is then pumped around the body by the heart, while the carbon dioxide is exhaled.
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