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Photograph of an closed pulmonary valve, a semilunar valve consisting of 3 flaps (cusps) that maintains a one-way flow of blood from the right ventricle of the heart into the pulmonary artery. The pulmonary artery conducts blood to the lungs and is the only artery in the body that carries deoxygenated blood. The single artery leaving the heart divides to serve each lung, ending in the many fine capillaries that surround the air sacs (alveoli), where exchange of oxygen and carbon dioxide takes place.
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