The ovarian follicle
Gonadotropin-releasing hormone (GnRH), which is secreted from the hypothalamus, stimulates the gonadotropic cells in the anterior pituitary to release FSH and LH. In the beginning of the follicular phase a small amount of FSH stimulates the proliferation of the estradiol producing granulosa cells of the follicle (1). The local estradiol concentrations promote the number of FSH receptors and thus amplify their own production process (2). FSH now also increases the number of LH receptors in the growing follicle, which makes the granulosa and thecal cells more sensitive to LH. Meanwhile, FSH levels will drop due to the negative feedback by estradiol. The primary follicle is now maturing.
Small amounts of LH induce proliferation and androgen production in the dominant follicle. The androgens are converted into estrogens
By understanding the ovulatory cycle and its hormonal regulation, one can modify the reproductive system by inhibiting it (contraception) and by stimulating it (IVF).