The circulatory system is composed of the following structures:

Heart – pumps blood through the system
Arteries – vessels that deliver blood to tissues
Capillaries – networks of small vessels that perfuse tissues
Veins – vessels that return blood to the heart

Arteries convey blood from the heart to systemic and pulmonary circulations. The tunica media is the thickest layer and contains prominent elastic tissue.

Veins, on the other hand, have thinner walls than arteries with less distinct layers. The tunica adventitia is the thickest of the three layers.

Vena Cava is a large vein. Its wall is thinner and has less distinct layers than the aorta.