Arteries and veins

Arteries and veins are different from one another because they have different parts to play in our blood's circulation. Arteries take blood from the heart to the rest of the body, while veins return it. Blood is pumped from the right side of the heart through the pulmonary artery to the lungs and returns through the pulmonary vein to the left side of the heart. From there it is pumped via the large artery called the aorta to the rest of the body and eventually returns to the right side of the heart again through the veins known as the inferior vena cava, from the legs and abdomen, and superior vena cava, from the head neck and arms.

Blood is forced through the arteries in spurts at high pressure, so their walls are thick and flexible and expand with every pulse of blood. In the veins, blood pressure is low and the blood flow is steadier. The walls of veins are thin and collapsible and valves prevent the blood flowing back in the wrong direction. In general, the arteries lie deep within the body, and the veins nearer the surface, which is why the blood vessels we see on our hands, for instance, appear blue in colour as they contain blood that has lost most of its oxygen and is therefore blue.