Blood vessels can be categorized into arteries, veins, and capillaries, each with distinct histological features. Arteries have thick walls with three layers: the tunica intima, tunica media, and tunica adventitia. The tunica intima is the innermost layer, consisting of endothelial cells. The tunica media contains smooth muscle cells and elastic fibers, allowing arteries to withstand high pressure. The outermost layer, the tunica adventitia, is made of connective tissue.
Veins, in contrast, have thinner walls and less smooth muscle in the tunica media. They often contain valves to prevent backflow of blood. Capillaries are the smallest blood vessels and consist of a single layer of endothelial cells, allowing for efficient exchange of gases, nutrients, and waste products between blood and tissues.
