Which hormone is primarily associated with promoting growth of uterine muscles and breast ducts?

• A. Estrogen
• B. Progesterone
• C. Prostaglandins
• D. Relaxin

Answer: (C)

Estrogen is the hormone most closely linked to the growth of both the uterine muscle (the myometrium) and the breast ductal system. It stimulates proliferation of the uterine smooth muscle and drives the development and branching of ducts in the breast, which sets the stage for further breast maturation with other hormones later on. Prostaglandins, in contrast, are lipid mediators mainly involved in uterine contractions and labor, not sustained growth of uterine muscle or breast ducts. Relaxin helps loosen ligaments and soften tissues, and while progesterone supports glandular development in the breast and maintains pregnancy, it does not primarily drive ductal growth the way estrogen does.