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Circulatory System What’s the Function of the Cardiovascular System? • Carries needed substances to cells • Carries waste products away from cells Blood Vessels: Arteries • Arteries: large thick walled muscular elastic vessels that carry oxygenated blood away from the heart. • Blood is under pressure pushed through by heart pumping. • Arteries branch off from heart divide into smaller vessels called arterioles. • Arterioles enter tissues where they branch in capillaries. Capillaries • Microscopic blood vessels. • Walls are one celled thick • Blood cells move through in single file line. • Capillary walls enable nutrients and gases to diffuse easily between blood cells and surrounding tissue cells. Veins • Veins: large blood vessels that carry blood from tissues back toward the heart. • Blood is not under pressure. • Veins in arms and legs have valves that prevent blood from flowing backward. Your Heart • Main function of the heart is to keep blood moving constantly throughout the body. • Large organ made of cardiac muscle that are rich with mitochondria • Mammalian hearts have four chambers. – atria – ventricles