Which type of blood vessel contains valves to prevent backflow?

Veins contain valves to prevent backflow of blood. This is especially important because veins carry deoxygenated blood back to the heart from the tissues, and without valves, gravity could cause blood to flow backward, particularly in the legs and arms where it must work against gravitational forces.

The structure of veins includes these one-way valves, which ensure that blood flows in the correct direction toward the heart and helps maintain efficient circulation. In addition to the presence of valves, veins have thinner walls and a larger lumen compared to arteries, which allows them to accommodate varying volumes of blood as they transport it back to the heart.

In contrast, arteries have thick muscular walls to withstand high pressure as they carry oxygenated blood away from the heart, capillaries are the smallest blood vessels with walls that are only one cell thick for nutrient and gas exchange, and arterioles are small branches of arteries that lead into capillaries, also lacking valves. The unique presence of valves in veins is a critical adaptation to support venous return and prevents the backflow of blood.