Each 2.54 square centimetre (a square inch) of human skin has six metres (20ft) of blood vessels. Veins hold about 65 per cent of the body's blood and have one-way valves tohelp blood move.

The circulatory system consists of one heart, five liters of blood, and approximately 96,000 kilometers of blood vessels, responsible for transporting nutrients and waste throughout the body.

There are three types of blood vessel: arteries, veins and capillaries. The heart is a muscular organ that pumps blood around your circulatory system. The circulatory system is the heart and all ...