Which muscle type encircles blood vessels?

• A. Cardiac muscle
• B. Skeletal muscle
• C. Visceral smooth muscle
• D. Smooth muscle

Answer: (D)

Blood vessels are lined by a layer of smooth muscle that wraps around the tube in a circular fashion. This smooth muscle is involuntary and non-striated, and its contraction narrows the vessel (vasoconstriction) while relaxation widens it (vasodilation). This circular arrangement around the vessel wall is what lets the body regulate how much blood flows through each vessel and how much pressure it has to generate. Cardiac muscle makes up the heart walls and is striated and not arranged around vessels; skeletal muscle is attached to bones and is voluntary; visceral smooth muscle is smooth muscle found in the walls of hollow organs, not specifically arranged around blood vessels. So the muscle type that encircles blood vessels is smooth muscle.