The circulatory system is made up of vessels and muscles that help and control the flow of the blood around the body. This process is called circulation. The main parts of the system are the heart, arteries, capillaries and veins. The circulatory system does a very important job in your body. It carries oxygen and essential nutrients to all cells around the body in arteries and carries the waste products and carbon dioxide in veins. The average human body contains over 60,000 miles of blood vessels.