: the movement of blood through the vessels of the body that is induced by the pumping action of the heart and serves to distribute nutrients and oxygen to and remove waste products from all parts of the body—see pulmonary circulation, systemic circulation
Process by which nutrients, respiratory gases, and metabolic products are transported throughout the body. In humans, blood remains within a closed cardiovascular system composed of the heart, blood vessels, and blood. Arteries carry blood away from the heart under high pressure exerted by the heart's pumping action. Arteries divide into smaller arterioles, which branch into a network of tiny capillaries with thin walls across which gases and nutrients diffuse. Capillaries rejoin into larger venules, which unite to form veins, which carry blood back to the heart. (Seeartery; capillary; vein.) The right and left heart chambers send blood into separate pulmonary and systemic circulations. In the first, blood is carried from the heart to the lungs, where it picks up oxygen and releases carbon dioxide; in the second, blood is carried between the heart and the rest of the body, where it carries oxygen, nutrients, metabolic products, and wastes.