a Layers - the blood vessels have three layers:
• tunica adventitia (outer connective tissue);
• tunica media (middle, muscle a n d elastic fiber); and
•tunica intima (inner, endothelial cell).
b Lumen - space inside the blood vessel where the blood flows.
c. Valves - found in the veins, these are thin membranous leaflets that
prevent the backflow of blood.