What are the structural differences between arteries and veins?

Arteries have thicker, more elastic walls than veins, which have thinner walls and contain valves.

Arteries and veins are both types of blood vessels that form part of the circulatory system, but they have different structures to fulfil their specific functions. Arteries are responsible for carrying oxygenated blood from the heart to the rest of the body. To withstand the high pressure of blood pumped directly from the heart, arteries have thick, muscular walls. These walls are made up of three layers: the innermost tunica intima, the middle tunica media, and the outermost tunica adventitia. The tunica media is particularly thick in arteries and contains smooth muscle and elastic fibres, allowing the arteries to expand and contract with each heartbeat, maintaining the pressure and flow of blood.

Veins, on the other hand, carry deoxygenated blood from the body back to the heart. The pressure in veins is much lower than in arteries, so their walls are thinner and less muscular. However, veins have a feature that arteries do not: valves. These valves prevent the backflow of blood, ensuring it moves in one direction towards the heart. Like arteries, veins also have three layers, but the tunica media is much thinner.

Another structural difference between arteries and veins is their lumen size. The lumen is the hollow part of the blood vessel where blood flows. Arteries have a smaller lumen than veins, which is another adaptation to withstand high pressure. In contrast, veins have a larger lumen, which facilitates the flow of blood at lower pressure.

In summary, the structural differences between arteries and veins - the thickness and elasticity of their walls, the presence of valves in veins, and the size of their lumens - are adaptations to their different roles in the circulatory system.