What is the difference in structure between arteries and veins?

Arteries carry blood away from the heart to the rest of the body and veins then take blood back to the heart. Because the heart directly pumps blood into the arteries by its forceful contractions, arteries carry blood at a much higher pressure relative to veins and therefore are structurally adapted very differently to veins.

Arteries have a much thicker, more muscular and elastic tissue wall with the inner lining (endothelium) being folded. These properties allow the artery to expand and recoil as blood passes through it without being damaged enabling it to cope with the high pressure. Veins, on the other hand, contain little muscular or elastic tissue so have a much thinner wall and relatively larger lumen. Because the the blood in veins is flowing under very low pressure, veins have valves to prevent the backflow of blood to ensure blood travels in the correct direction towards the heart.