The circulatory system is important because it is transports blood and other materials throughout the body. Without the circulatory system, the body does not receive oxygen, and the heart and lungs fail to work.
The main organ of the circulatory system is the heart, which is responsible for pumping oxygenated blood throughout the body. Without the heart, a human cannot live. Other parts of the circulatory system include the blood and blood vessels, such as arteries and veins. Arteries are responsible for carrying blood away from the heart, and veins are responsible for carrying blood toward the heart.
Capillaries are also blood vessels; they are the structures that connect arteries to veins throughout the body. The blood itself has many different types of cells that help the body function, such as red blood cells, white blood cells and platelets. Red blood cells are transporters of oxygen and carbon dioxide, and white blood cells serve to protect the body against harmful germs and disease. Platelets are thick blood cells that stop the body from bleeding when there is an injury, such as a cut or a wound. Plasma is the liquid part of blood that transports the blood cells throughout the body.