What is the three major parts of the blood vessels?

The three major parts of blood vessels are the tunica intima, tunica media, and tunica externa. The tunica intima is the innermost layer, consisting of a smooth endothelial lining that reduces friction for blood flow. The tunica media is the middle layer, composed of smooth muscle and elastic tissue, which regulates the diameter of the vessel and controls blood pressure. The tunica externa, or adventitia, is the outer layer made of connective tissue that provides structural support and protection to the blood vessel.