The hypothalamic-pituitary-gonadal axis controls the development of germ cells and the secretion of steroid hormones. Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the gonadotropic cells in the pituitary to release follicle stimulating hormone (FSH) and luteinizing hormone (LH). In women, LH stimulates androgen production in the thecal cells and initiates the ovulation process in the follicle ending in a fertilizable oocyte. FSH stimulates estrogen synthesis in the granulosa cells. After ovulation, the corpus luteum starts to produce progesterone. The steroid hormones have a feedback control at the level of the GnRH secretion in the hypothalamus and gonadotropin secretion in the pituitary.
It depends on the phase of the ovulatory cycle whether this feedback is positive or negative. The steroid hormones have also effects on other body cells, like mucous membranes, muscle cells, adipose tissue cells, mammary gland cells, endothelial and bone cells.
The graphic above shows an overview of the biochemistry of all gonadal steroids. Cholesterol is the overall precursor belonging to the C27-group. The main female steroid hormones are the progestagens (C21-steroids) and the estrogens (C18).
Progesterone is produced by: