Introduction to the Circulatory System Introduction to the Circulatory System The circulatory system is a network that carries blood throughout the body. All animals except the simplest kinds have some type of circulatory system. The human circulatory system supplies the cells of the body with the food and oxygen needed to survive. At the same time, it carries carbon dioxide and other wastes away from the cells. The circulatory system also helps regulate body temperature and carries substances that protect the body from disease. In addition, the system transports chemical substances called hormones, which help regulate the activities of various parts of the body. The Heart The heart is a hollow, muscular organ that pumps blood. It consists of two pumps that lie side by side. These pumps relax when taking in blood and contract as they send out blood. The left side of the heart is a stronger pump than the right side. The stronger pump receives blood from the lungs and sends it to cells t...