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circulation cir·cu·la·tion (sûr'kyə-lā'shən)
Movement in a circle or circuit, especially the movement of blood through bodily vessels as a result of the heart's pumping action.
The flow of fluid, especially blood, through the tissues of an organism to allow for the transport and exchange of blood gases, nutrients, and waste products. In vertebrates, the circulation of blood to the tissues and back to the heart is caused by the pumping action of the heart. Oxygen-rich blood is carried away from the heart by the arteries, and oxygen-poor blood is returned to the heart by the veins. The circulation of lymph occurs in a separate system of vessels (the lymphatic system). Lymph is pumped back to the heart by the contraction of skeletal muscles.