Which layer of the arterial wall is the thickest and made up largely of elastic type of smooth muscle and connective tissue?

The tunica media is the correct answer as it is the middle layer of the arterial wall and is known for being the thickest layer, primarily composed of smooth muscle and elastic fibers. This composition is crucial because it allows the arteries to maintain blood pressure and regulate blood flow through vasoconstriction and vasodilation. The smooth muscle fibers enable the artery to contract and relax, while the elastic fibers provide the necessary elasticity to accommodate the pulsatile nature of blood flow caused by the heart's contractions.

The other layers, while important, do not have the same structural characteristics. The tunica externa, also known as the adventitia, primarily consists of connective tissue and serves to anchor the artery to surrounding tissues. The tunica intima is the innermost layer, made up of a thin layer of endothelial cells that provide a smooth surface for blood flow, but it lacks the thickness and the muscular and elastic composition that defines the tunica media. Understanding these distinctions is key in vascular physiology and pathology.