The Circulatory System

The heart and blood vessels form the circulatory system. Blood flows around the body constantly, pumped by rhythmic contractions and relaxation of the heart muscle. Blood flows through the body via three types of blood vessel: arteries, veins and capillaries.

The force that is exerted on the blood flow by the hearts contractions through arteries is known as blood pressure. This force varies with the strength of the heartbeat, the elasticity of the arterial walls, and the volume and thickness of the blood. The circulating blood carries oxygen and nutrients to the body cells and carries away waste products of respiration, such as carbon dioxide.