This schematic shows how a manís hormones and organs work together to regulate sperm production. Positive feedback relationships are indicated with a plus sign; negative feedback relationships with a minus sign.
The hypothalamus is part of the brain. It produces gonadotropin releasing hormone (GnRH) in pulses, from once a day to once an hour. GnRH triggers the release of 2 hormones from the pituitary gland: luteinizing hormone (LH) and follicle stimulating hormone (FSH). LH and FSH act on different types of cells within the testes. LH induces the Leydig cells surrounding the seminiferous tubules to secrete testosterone (T). FSH, along with the T from the Leydig cells, induces the Sertoli cells lining the seminiferous tubules to make both inhibin B and immature sperm, or spermatids.
Inhibin B acts on the pituitary gland in a negative feedback loop. When enough inhibin is present, the pituitary stops producing FSH. T gives negative feedback to both the pituitary and the hypothalamus, decreasing the production of GnRH and LH directly.
The immature sperm travel through the seminiferous tubules to the epididymis. In the epididymis, the spermatids are converted to mature sperm. The process takes about 2.5 months to complete. Only once the sperm are mature do they pass into the vasa deferentia.
Male hormonal contraceptives work by attempting to block the production of sperm. Depending on the formulation, the MHC stops the secretion of one or more of the hormones and feedback loops in the diagram.
There are 3 major classes of MHCs
Blocks the production of natural T by giving a dose of synthetic T higher than normally found circulating in the blood. The synthetic T suppresses the production of GnRH and LH. Synthetic T in the blood cannot cross into the testes, keeping levels of T there too low for sperm production.
Progestin with androgen replacement
Blocks the production of the gonadotropins FSH and LH using a synthetic progestin. Lack of FSH and LH blocks the production of spermatids and T in the testes. T is given as replacement therapy to maintain male secondary sex characteristics.
GnRH antagonist with androgen replacement
Blocks the action of GnRH using a type of drug called a GnRH antagonist. Lack of GnRH stops FSH and LH production, and consequently the production of spermatids and T in the testes. T is given as replacement therapy to maintain male secondary sex characteristics.