Oogenesis - Human Oogenesis

Human Oogenesis

At the start of the menstrual cycle, some 12-20 primary follicles begin to develop under the influence of elevated FSH to form secondary follicles. The primary follicles have formed from primordial follicles, which developed in the ovary at around 10–30 weeks after conception. By around day 9 of the cycle, only one healthy secondary follicle remains, with the rest having undergone cellular atresia. The remaining follicle is called the dominant follicle and is responsible for producing large amounts of estradiol during the late follicular phase. Estradiol production depends upon co-operation between the theca and granulosa cells. On day 14 of the cycle, an LH surge occurs, which itself is triggered by the positive feedback of estradiol. This causes the secondary follicle to develop into a tertiary follicle, which then ovulates some 24–36 hours later. An important event in the development of the tertiary follicle occurs when the primary oocyte completes the first meiotic division, resulting in the formation of a polar body and a secondary oocyte. The empty follicle then forms a corpus luteum which later releases progesterone hormone