Question

Blood vessels have a middle layer of what kind of muscle?

Answer 1

Smooth Muscle

Explanation:

Blood vessels (both artery and vein) have three layers (tunics) in it's wall :

1. Tunica intima
2. Tunica media
3. Tunica adventitia

Following diagram shows the layers of the wall of an artery :

Tunica Intima consists of endothelium, which is a single layer of squamous epithelium resting on a basement membrane.

Tunica media or middle layer is composed of smooth muscle and elastic fibers.

Tunica adventitia consists of fibroblasts and collagen fibers.

In case of veins, the same three tunics compose the wall, with the difference in thickness and valves. Here is a diagram for comparison between arterial and venous wall : see both of them have smooth muscle in middle layer.