The wall of a blood vessel contains three layers ( inner-side
to outer side):
Tunica intima - this layer contains endothelial cells, basement
membrane and subendothelial layer of connective tissue.
Tunica media - this layer contains smooth muscle cells, elastic
and connective tissue. This layer is thicker in arteries and
thinner in veins.
Tunica externa - this layer contains only connective tissue. It
also contain elastic lamina. The elastic lamina helps the blood
vessel to attach to the surrounding tissue. It provides structural
integrity to veins.