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 men, LH stimulates androgen production in the testes and spermatogenesis; FSH matures spermatozoa and makes them motile. 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. The steroid hormones have a feedback control at the level of the GnRH secretion in the hypothalamus and gonadotropin secretion in the pituitary. 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.
For more specific information on reproductive physiology please check the sections on male and female reproduction in the chapter gynaecology & obstetrics.
I. GnRH, LH and FSH are released in a pulsatile manner.
II. GnRH, LH and FSH are only released during the reproductive ages of human life.
Extra info: GnRH is released in a pulsatile manner from neurons in the hypothalamus; as a result its gonadotropic target cells in the pituitary release their FSH and LH in a pulsatile way as well. GnRH, LH and FSH are released from gestation till death. During gestation, infancy and senescence high levels of these hormones are measured. However, only during the female reproductive period estrogens are released by the ovary upon stimulation by LH and FSH, in cyclic bursts.