Final answer:
The tunica media is the blood vessel layer comprised of elastic fibers and muscle, responsible for providing strength and contractility to vessels such as arteries.
Step-by-step explanation:
Tunica Media and Blood Vessel Contractility
The part of the blood vessel that is made of elastic fibers and muscle, providing strength and contractility, is the tunica media. The tunica media is considerably the thickest layer in arteries and contains smooth muscle tissues, which control the diameter of the vessels through vasoconstriction and vasodilation. This layer is supported by connective tissue rich in elastic fibers arranged mainly in circular sheets for flexibility and contraction, as well as collagenous fibers for added strength. The tunica media's well-developed muscle and elastic fiber content allow it to play a crucial role in regulating blood pressure and vessel diameter.