b'ChapterThe heart is a muscular pump situated behind the breastbone (sternum).It continuously pumps blood around the body through arteries and veins.Arteries are large blood vessels that carry oxygen-rich blood from the heart to therest of the body. The arteries gradually become smaller and eventually subdivide into even smaller blood vessels called capillaries.Capillaries transfer the blood to all of the cells, nourishing them with oxygen. The heart then pumps blood low in oxygen through veins back to the lungs in order to collect more oxygen for another return trip.The pumping action of the heart is called a contraction. The beat you can feel with each contraction is called a pulse. You can feel for the carotid pulse in the neck or the radial pulse in the wrist.Contractions are controlled by the hearts own electrical pace making system. It generates an electrical impulse which is conducted along a pathway, resulting in a smooth muscular contraction with blood pumping through the heart regularly. The heart muscle cells are working continuously and need a constant supply of oxygen. Blood is supplied to the heart muscle (myocardium) by coronary arteries that branch around the surface of the heart.FactIf all the blood vessels in your body, including the ones that are so small that you can hardly see them, were placed end to end, they would stretch around the world twice. Your blood travels every kilometre of that distance!24 How Your Body Works'