What is a "gonadotropin-releasing hormone" or "GnRH"?
Most hormone-producing glands in the body are controlled from the pituitary gland. For example the thyroid is controlled by TSH, thyroid-stimulating hormone; and the ovary and the testicle are controlled by FSH, follicle-stimulating hormone. These are all produced by the pituitary. How does the pituitary know when to release these? We come to the releasing factors, and the gonadotropin-releasing hormone, GnRH, also which used to be called LHRH, or luteinizing hormone releasing hormone. These are releasing hormones or releasing factors that come from the brain and are stimulated and delivered directly to the pituitary gland so that the pituitary gland produces FSH and LH, luteinizing hormone, and that then stimulates the ovary in the woman and the testicle in the man. A good way to think of this is when you think of stress as affecting reproductive function, how does that happen? So, stress affects the central nervous system. The central nervous system says “I'm under stress; I better not allow reproduction to occur.” The brain stops the production of GnRH. As a consequence, the pituitary doesn't make any FSH or LH, and as a consequence, the ovary doesn't work, and the testicle doesn't work. And we have lack of reproduction so, if you will, early on in evolution, when our ancestors roamed the wild plains, if there was not enough food, and everybody was hungry and under a lot of stress, that would have been a bad time to have women become pregnant, and so nature chose to put this system into place so women would not ovulate and become pregnant at an inconvenient time. So GnRH comes from the brain, and stimulates the pituitary. The pituitary makes FSH, and that stimulates the ovary, and that makes reproduction go around.
