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.

Discover the warning signs of circulatory problems, from buttock pain to slow-healing wounds, plus the foods and activities ...

Very low blood pressure. The structure of the blood vessels can be easily compared when they are seen in this cross-section (not to scale).

However, these so-called static models fail to reproduce what occurs in vivo since they lack a key component of the circulatory system: the physical forces exerted by blood flowing through the blood ...

A bioreactor that mimics a circulatory system can deliver nutrients ... "We're using semipermeable hollow fibers, which mimic blood vessels in their ability to deliver nutrients to the tissues ...

lungs and blood vessels and back to the heart. Nearly half the population is blood type O, and can donate blood to people of all other blood groups but can receive only Type O themselves.