In order to withstand the high pressure as the heart beats, arteries need to be relatively thick and muscular. They resist stretching, helping to maintain enough pressure to push blood around the body without bursting under the strain. However, by the time the blood has travelled through the capillaries and into the veins, the pressure is much lower.
Veins are wider in internal diameter than arteries are, and their walls are much thinner, allowing them to store up to 70 per cent of the blood in the body as it makes its way back to the heart. One-way valves help to keep the low-pressure blood travelling in the right direction.