Hormones are chemicals that are produced by endocrine glands in the body. These substances are released into the extracellular fluid, where they diffuse into the bloodstream. Hormones regulate the physiological control of various organs and tissues. In males there are three primary hormones involved in male reproduction and characteristics—testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). Testosterone is the sex hormone that signals the development of male sex organs and contributes to specific secondary sexual characteristics in males. Testosterone is derived from cholesterol, a lipid. It circulates as a prohormone that can be used to make a hormone called dihydrotestosterone. This conversion to dihydrotestosterone takes place in tissues of the testes, prostate gland, and muscles and is necessary to help develop the penis and scrotum during fetal development.
FSH and LH are both gonadotropins, hormones that stimulate activity of gonads. A gonad is a reproductive organ that produces gametes and sex hormones. Release of FSH and LH is regulated by the hypothalamus. The hypothalamus (the brain region responsible for regulating many involuntary body functions) releases gonadotropin-releasing hormone (GnRH) that stimulates the release of FSH and LH from the anterior pituitary gland. If testosterone levels exceed their normal range, testosterone has an inhibitory effect on the hypothalamus and anterior pituitary gland, reducing the release of GnRH and LH and signaling the interstitial endocrine cells to stop testosterone production.Sperm production is also controlled by a negative feedback system. When large numbers of sperm are present in the testes, the sustentocytes in the testes release the hormone inhibin. Inhibin has an inhibitory effect on the hypothalamus and anterior pituitary. Consequently GnRH, FSH, and LH secretions decline and sperm production falls.