Which uterine layer is composed of three-layer thick smooth muscle?

• A. Endometrium
• B. Myometrium
• C. Perimetrium
• D. Cervix

Answer: (B)

The uterus is made of three layers, and the one that contains thick smooth muscle arranged in three distinct orientations is the middle muscular layer. This myometrium consists of inner circular fibers, a middle longitudinal layer, and outer oblique fibers, collectively providing the powerful contractions the uterus uses during labor and menstruation. The inner lining, the endometrium, is mucosa with glands that shed cyclically; the outer covering, the perimetrium, is a thin serous layer. The cervix is a fibromuscular canal and does not have the same three-layer thick smooth-muscle arrangement. So the layer with three-layer thick smooth muscle is the myometrium.