Final answer:
The reduction in progesterone and estrogen stimulates follicular development through increased levels of FSH and LH, which promotes the growth of ovarian follicles leading to ovulation.
Step-by-step explanation:
The reduction in progesterone and estrogen that occurs at the beginning of the follicular phase is responsible for stimulating follicular development through the increase of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). At the start of the cycle, lower levels of estrogen and progesterone remove the inhibition on FSH and LH release from the anterior pituitary gland. Rising FSH and LH levels then promote the growth of ovarian follicles, each containing an immature egg.
The process prepares the eggs for ovulation, with one follicle becoming dominant and continuing to grow while the others undergo atresia. As the dominant follicle grows, it produces increasing amounts of estrogen, which initially exerts a negative feedback on the release of FSH, preventing the maturity of other follicles. However, when estrogen reaches a peak level, it switches to a positive feedback mechanism, triggering a surge in LH, which ultimately leads to ovulation around the 14th day of a typical 28-day menstrual cycle.