Blood vessels consist of three primary layers or tunics: - Tunica intima: The innermost layer composed of a single layer of endothelial cells supported by a thin subendothelial layer of connective tissue. The endothelium plays a critical role in regulating vascular tone and permeability. - Tunica media: The middle layer containing smooth muscle cells and elastic fibers. This layer is responsible for regulating vascular diameter and blood pressure. - Tunica adventitia: The outermost layer comprised of connective tissue, containing nerves and vasa vasorum (small blood vessels that supply the vessel wall).
