Circulatory system is a network that carries blood throughout the body. All animals except the simplest kinds have some type of circulatory system.
In some invertebrates (animals without a backbone), the circulatory system consists of a simple network of tubes and hollow spaces. Other invertebrates have pumplike structures that send blood through a system of blood vessels. In human beings and other vertebrates (animals with a backbone), the circulatory system consists primarily of a pumping organ--the heart--and a network of blood vessels.
The human circulatory system supplies the cells of the body with the food and oxygen they need to survive. At the same time, it carries carbon dioxide and other wastes away from the cells. The circulatory system also helps regulate the temperature of the body 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.
