Which layer of a blood vessel wall contains smooth muscle cells responsible for vasoconstriction and vasodilation

Which layer of a blood vessel wall contains smooth muscle cells responsible for vasoconstriction and vasodilation? Tunica externa/adventitia Tunica media Tunica interna/intima

The correct answer and explanation is:

Correct Answer: Tunica media

Explanation:

Blood vessels have three main layers in their walls, each with distinct structures and functions:

1. Tunica intima (or interna): This is the innermost layer of a blood vessel. It is composed primarily of a thin layer of endothelial cells that line the lumen (the inside space) of the vessel. These cells provide a smooth surface to reduce friction for blood flow and play roles in regulating blood clotting and immune responses.
2. Tunica media: This is the middle layer and is the thickest layer in arteries. It contains smooth muscle cells and elastic fibers, which allow the blood vessel to expand and contract. The smooth muscle in the tunica media is responsible for two vital functions:
   • Vasoconstriction: The contraction of the smooth muscle causes the vessel diameter to decrease, reducing blood flow.
   • Vasodilation: The relaxation of the smooth muscle causes the vessel diameter to increase, allowing more blood to flow through.
   These processes help regulate blood pressure and blood flow to different parts of the body depending on the body’s needs. For example, during exercise, blood vessels dilate to deliver more oxygen-rich blood to muscles.
3. Tunica externa (or adventitia): This is the outermost layer and consists mainly of connective tissue. It provides structural support and anchors the blood vessel to nearby tissues. In larger vessels, it contains small blood vessels (vasa vasorum) that supply nutrients to the vessel wall itself.

Because the tunica media contains smooth muscle cells, it is the layer responsible for controlling the diameter of blood vessels through vasoconstriction and vasodilation.

Summary:

The correct answer is Tunica media because it contains smooth muscle cells that regulate blood vessel diameter and blood pressure through vasoconstriction and vasodilation.