Write one structural difference between the composition of arteries and veins.

Hint: Arteries are the blood vessels that carry blood away from the heart to other parts of the body and veins are the blood vessels that carry blood to the heart from different parts of the body. The blood in arteries flows at a higher pressure than in the veins since the heart pumps the blood at higher pressure for it to reach all the organs.

Complete answer:
Since the blood flows at a higher pressure in the arteries the walls of the arteries should be thick enough to withstand the pressure. For that very reason, the walls of the arteries are thicker and the lumen is smaller. This is one of the striking differences between arteries and veins. The walls of veins are thin and the lumen is much bigger. Because of this, the veins have a collapsed look and arteries maintain a rigid cylindrical shape.

Since the pressure is low in veins, there is a risk of backflow of blood. This is prevented by flaps (valves) that are present in valves. These valves resemble the valves in the heart which perform the same function.

Note: Blood loss from the arteries is much severe when compared to the blood loss from the veins. This is again attributed to the pressure of the blood in the artery. When an artery is cut the blood flows out at a greater speed and the clotting time is lesser. On the other hand, in the veins when a cut is present the blood flows out really slowly when compared to the arteries and the time for clotting is more.