As menstruation ends, estrogen levels in the blood rise rapidly. What is the source of the estrogen?
In the nonpregnant female, the only significant source of estrogen is ovarian follicles or corpus luteum. Menstruation begins when the corpus luteum degenerates. Menstruation ends when developing follicles secrete estrogen sufficiently to raise circulating concentration to a level that stimulates regrowth of the endometrium
Corpus luteum
Developing follicles
Endometrium
Stromal cells of the ovaries
Female Reproductive System