Name how the structure of the three main blood vessels are adapted to their function.

A) Arteries - Arteries carry blood away from the heart at high blood pressure. Therefore they have a thick muscle layer and elastic tissue in their walls to cope with and maintain the high blood pressure produced by the heart contracting. The endothelium is also folded, which allows the lumen to expand under high blood pressure. B) Veins - Veins carry blood back to the heart at low pressure. Therefore, they have a large wide lumen with little elastic or muscle tissue to keep blood pressure low. They also have valves to stop the backflow of blood and keep it travelling in the right direction. C) Capillaries - These are the smallest of all three blood vessels. Capillaries are responsible for exchanging substances such as glucose, oxygen and CO2. Therefore, they have very thin walls just one cell thick for efficient diffusion.