The body's circulatory system has two distinct parts; pulmonary circulation (Lungs) and systemic circulation (other organs). Blood flows in one direction through the blood vessels – arteries, veins, capillaries – forming a closed system that irrigates all of the body’s organs. The heart and its coronary circulation (not represented here) is the central organ of this system, which, via the rhythmic pumping of the heart, makes about 5 liters of blood continually travel through the body’s blood vessels.