The circulatory system consists of the heart, blood vessels, and blood. The heart pumps blood through a network of arteries, veins, and capillaries that extend over 60,000 miles throughout the body, delivering oxygen and nutrients to tissues and removing waste. Blood flows from the heart through arteries, into smaller arterioles and capillaries, then into venules and veins before returning to the heart. The circulatory system allows for the transportation of blood, oxygen, hormones, and other substances essential for life.