The circulating blood brings oxygen and nutrients to all the organs and tissues of the body, including the heart itself. It also picks up waste products from the body's cells. These waste products are removed through the kidneys, liver and lungs. The pumping or beating action of the heart is controlled by electrical impulses from a small bundle of cells called the sinoatrial node. The system The circulatory system includes the heart and blood vessels.
Arteries carry oxygen-rich blood from the heart to all parts of the body.
Veins carry blood low in oxygen from various parts of the body back to the heart. Arteries and veins are connected by tiny capillaries. We need cholesterol because it is used to form cell membranes, some hormones, and other tissues. About 80 per cent of the cholesterol in our blood is manufactured by the liver. The remaining 20 per cent comes from the food we eat.