The wall of the aorta is thicker than that of the inferior venacava; this is because the aorta is the artery that carries blood from the heart from the left ventricle to the whole body (except the lungs), while the superior and inferior venacava are the veins that carry blood from the body to the right atrium. Therefore, like the other arteries the aorta has walls that are thicker than those of veins.
