Sexual function of the man
Male hormones
Sperm production
In order to understand which factors can effect male infertility, it is necessary to know how a mans' body functions hormonally and how the male reproductive system in constructed. This area of medical science is known as Andrology.
Male hormones
Sperm production and maturation is controlled by the gonadotrophins LH and FSH. The latter being follicle stimulating hormone, so named because it is identical to the hormone which stimulates the maturation of follicles in the female ovary. In the male, it indirectly stimulates the production of sperm cells. LH (luteinising hormone) is indirectly responsible for the ripening of sperm cells.
Where do gonadotrophins come from? They are secreted by the hypofyse, a small gland in the brain which is controlled by the hypothalamus. The hypothalamus regularly secretes a hormone called GnRH or Gonadotrophin releasing hormone, which stimulates the release of LH and FSH. In short, FSH an LH stimulate the reproductive organs to function and in turn, to produce sex hormones. in the male, this is primarily testosterone.
TESTOSTERONE
This is the hormone which turns a boy into a man. Production of this hormone begins at puberty and starts the development of secondary sexual characteristics (beard growth, deepening of voice, muscle development etc). From puberty, testosterone controls the sexual function and libido of the man and is responsible for the maturation of sperm cells. Production of testosterone peaks around the age of 30-35, then gradually begins to decline.
In the male 'cycle', testosterone levels are monitored in the brain and if sufficient levels are present, the secretion of GnRH reduces, resulting in a lower of gonadotrophins produced. Similarly, if testosterone levels are low, the secretion of GnRH increases, and the testis are stimulated to produce more testosterone.
The CENTRAL HEATING PRINCIPLE This hormonal regulation can be likened to a central heating system, with the testis compared to the water boiler and the hypofyse compared to the thermostat. If its cold in the room (i.e. too little testosterone present) the thermostat activates the heating system (production of gonadotrophin). As soon as the room reaches the desired temperature (sufficient testosterone levels), the heating shuts off. The male 'pill' was developed with this principle in mind. It also explains why taking testosterone (e.g. bodybuilders) can lead to infertility. Men who take testosterone in order to increase their muscle mass are in principle adding additional heating to the room where the thermostat is located. This gives an incorrect signal to the hypofyse, i.e. that sufficient male hormone is present in the body, which in turn leads to a halt in gonadotrophin production. But gonadotrophins are necessary for the production and maturation of sperm cells. In other words, the unnatural presence of testosterone causes a drop in the natural impulse to produce gonadotrophins, leading to a significant reduction in sperm production. |
Sperm production
Sperm cells are produced in very tiny canals (tubules) in the testicles. (See also examination of testicular tissue under anatomy). The production itself is a complicated process of cell division and cell differentiation which takes about three months in total. But of course the process occurs in thousands of tubules and at different stages constantly, so that there is always a constant supply of mature sperm available. After its production in the testicle, the sperm travels to the epididymis, which contains a fewer number of tightly coiled tubules. The sperm remains here for about a week, during which it continues to mature and become more motile. The epididymis also serves as a reservoir. During an orgasm, sperm cells are expelled from the epididymis and begin their journey to the outside world via the vas deferens, through the prostate and seminal vesicles, where they are mixed with a nutrient-rich plasma and out through the urethra.
A fertile man usually ejaculates 1.5-4ml of semen containing 20-200 million sperms per ml. Any less than 2 million sperms per ml would indicate a significant fertility problem.
This production and ejaculation process forms crucial examination grounds in the treatment of infertile couples. Ejaculation problems can sometimes be bypassed using surgical techniques, for example for reversal of vasectomy or sperm extraction.