The Circulatory System—the Body's Moving company The circulatory system is an organ system that includes the heart, the blood vessels, and the blood itself. It has three functions: • to transport materials (i.e., nutrients and oxygen) and cells from one place to another • to defend the body against invasion by harmful organisms by taking white blood cells to an area of injury or infection • to maintain a constant body temperature Your body has a closed network of blood vessels—hollow tubes—that move blood and nutrients. A pumping organ—the heart—pushes blood through this network of vessels.
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