Which hormone promotes the growth of your uterine muscles and their blood supply, encourages production of vaginal mucus and stimulates development of the blood supply and ductal system in the breasts?

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

Answer: (A)

Estrogen drives the proliferative growth of the uterus and its blood supply, promotes the production of vaginal mucus, and stimulates the development of the breast ductal system and its vascular network. In the uterus, estrogen causes the endometrium to thicken and to become more richly supplied with blood vessels, creating a receptive environment. It also increases cervical mucus production, which changes the vaginal environment in a way that supports fertilization. In the breast, estrogen stimulates the growth and branching of ducts and the accompanying blood vessels, preparing the tissue for potential milk production. Progesterone, relaxin, and prostaglandins have other primary roles—for example, progesterone supports secretory changes in the uterus and breast later in the cycle and during pregnancy, relaxin affects pelvic ligament laxity, and prostaglandins participate in labor-related processes—so they don’t match all the described effects as well as estrogen does.