Final answer:
In the uterine cycle, the proliferative phase is encouraged by the hormone estrogen, while the secretory phase is enhanced by progesterone.
Step-by-step explanation:
In the uterine cycle, the proliferative phase is promoted by estrogen, whereas the secretory phase is promoted by progesterone. The proliferative phase is the period when estrogen secreted by the cells of the maturing ovarian follicle stimulates the growth of the uterine lining and makes fertilization more likely by causing the cervix to secrete a thinner mucus that aids sperm motility. In contrast, the secretory phase follows ovulation and is characterized by the production of progesterone by the corpus luteum, which leads to further development of the endometrium to make it receptive to a fertilized egg if implantation occurs. During this phase, progesterone increases blood flow to the uterus, promotes uterine secretions, and decreases uterine muscle contractility.