Why is the lumen of an artery smaller than vein?

Answer 1

The lumen size in an artery is smaller as it has a thicker Tunica Media to compensate for the greater arterial pressure; owing to the smaller lumen.

As to opposed to veins which has a larger lumen and a reduced venous pressure.

Answer 2

The walls of blood vessels consist of different tissues. There is a lining of endothelium which helps the blood flow smoothly inside the lumen (hole), and some smooth muscle layers which allow the vessel to expand as the blood flows along it, and contract again behind the blood once it has surged passed. The walls have to give a bit to withstand the pressure of the blood flow, otherwise they would burst. Blood vessels also expand and contract to help maintain the total blood pressure in your body.

Arteries carry blood at high pressure because it has just been pumped by the heart, and so they need extra muscle thickness in the wall to cope with the expansion and contraction as the blood flows along them. The blood pressure in veins is lower and so the walls do not need to be as thick, but they contain tiny valves to ensure the blood can only flow one way i.e. back to the heart.

Veins are not darker in colour than arteries. They appear blue due to the colour of the tissues in the walls, NOT due to the colour of blood in them. Veins are closer to the surface of the body than veins which might lead to the belief that they are darker because you can see them more easily.

Answer 3

The lumen is the hollow portion where blood is found.

Answer 4

Because capillaries have to be small to be able to exchange co2 (carbon dioxide) and oxygen.

Answer 5

Because their walls are so thick.