Explain how estrogen and progesterone control each phase of the uterine cycle

Answer 1

At the beginning of the 28 day cycle, both estrogen and progesterone levels are very low. The low levels of these hormones causes the menstrual phase because not enough progesterone is available to maintain the functional layer of the endometrium so it is sloughed off. As the ovarian follicle grows the granulosa cells produce increasing amounts of estrogen. The rising estrogen concentration causes the proliferative phase of the uterine cycle to begin and continue through ovulation. When the oocyte is ovulated the corpus luteum forms from the follicle and begins producing progesterone. The rising progesterone stimulates the secretory phase of the uterine cycle. This phase continues until the oocyte is fertilized or if it is not fertilized then the levels of progesterone fall and the menstrual phase begins again.