Structural differences
To begin with, arteries are thicker and muscular. The thickness of the walls helps the arteries to withstand high pressure. The masculine walls help in vasoconstriction and vasodilation as well as ineffective regulation of blood pressure. Veins have thin and non-muscular walls. They are structurally thin blood vessels to allow the surrounding muscles to press against them and aid in pushing blood towards the heart. They lack masculine walls as blood in them flows in low pressure. On the other hand, capillaries have a one-cell layer thick wall, which enables easy diffusion of substances in and out of the capillaries. They are the smallest blood vessels.
Additionally, veins have valves that prevent the backflow of blood as blood flows under low pressure. Arteries do not have valves as blood flows under high pressure; hence there is no chance of back flow of blood. Capillaries are also valve-less.
Arteries have thick outer layers made up of collagen and elastic fibers, which aid in preventing bulges and leakages, while capillaries have pores within their wall, which allow for the leakage of plasma fluid which is essential in transporting body substances. On the other hand, veins have thin layers made up of a few elastic fibers for easy transportation of blood.
Functional differences
Arteries move oxygenated blood away from the heart to other body organs, while Veins carry deoxygenated blood back to the heart. On the other hand, capillaries transport blood away from the body and also allow the exchange of carbon dioxide, oxygen, nutrients, and waste products in the body. They also serve as a link between veins and arteries.
Similarities
Arteries, veins, and capillaries all carry blood. All blood vessels generally transport blood. Like veins, arteries comprise three layers, an inner layer made up of epithelial cells, an outer layer of tissue, and a layer of muscles between them. In distributing blood and nutrients, all three vessels supplement each other. Capillaries connect arteries to veins hence allowing the exchange of products between them.
