Arteries have thicker walls than veins because they must be able to withstand the tremendous pressure from a beating heart. Veins have thinner walls because they need more room to hold blood.
Arteries have more smooth muscle in their walls than veins to accommodate the pulses of blood generated by each contraction of the heart. All arteries comprise three layers: the tunica intima, the tunica media and the tunica adventitia.
The veins also consist of three layers that contain smooth muscle and connective tissue like the arteries, but in lesser amounts than the arteries. The heart cannot hold all the blood in the body at once, so the blood needs to be stored somewhere. This extra blood is stored in the veins, which have wider diameters than the arteries.