How does a man's body function hormonally and how does the male reproductive system work?Male hormonesSperm production
This is known as Andrology, the area of medical science which specialises in male (in)fertility.
Sperm production and maturation is controlled by the gonadotrophins FSH and LH.
- FSH (follicle stimulating hormone, so named because it is identical to the hormone which stimulates the maturation of follicles) indirectly stimulates the production of sperm cells.
- LH (luteinising hormone) is indirectly responsible for the ripening of sperm cells.
FSH and LH are secreted by the hypophysis, a small gland in the brain which is controlled by the hypothalamus, part of the midbrain just above it.
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 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 the production of less gonadotrophins. Similarly, if testosterone levels are low, e.g. because the testicles are not producing enough testosterone, the brains receive the message to produce more FSH en LH.
Central heating principle
This hormonal regulation can be likened to a central heating system, with the testicles as the water boiler and the hypophysis the thermostat.
- If it is cold in the room (i.e. too little male hormone present) the thermostat activates the heating system (production of gonadotrophins).
- As soon as the room reaches the desired temperature (sufficient testosterone levels), the heating shuts off (no more gonadotrophins produced).
The male pill is developed with this principle in mind.
It also explains why taking testosterone (e.g. bodybuilders) can lead to infertility. Men who take testosterone 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 hypophysis, i.e. that sufficient male hormone is present in the body, which in turn leads to a halt in gonadotrophin production.
However, 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 no (or a significant reduction in) sperm production.
Sperm cells are produced in very tiny canals (tubules) in the testicles. Production starts at puberty and continues a man's entire life.
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, i.e. a man does not have to wait 3 months for his next ejaculation.
After its production in the testicle, the sperm travels to the epididymis, which contains a single tightly coiled tubule. The sperm remains here for about a week, during which time it continues to mature and become more motile.
The epididymis also serves as a reservoir of sperm. 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 to the penis.
The vas deferens and the accompanying nerves and blood vessels constitute the spermatic cord. Before they enter the prostate there is a widening which forms the connection with the seminal vesicles. Both the seminal vesicles and the prostate secrete a liquid which forms a nutrient-rich plasma, in which the sperm are ultimately transported via the urethra of the penis into the outside world.
From less than 2 million (and less) motile sperm per ml the man has a serious fertility problem. From less than 20 million sperm per millilitre reduced fertility is possible.
A fertile man usually ejaculates 1.5 to 4ml of semen containing 20-200 million sperm per ml. Any less than 2 million (and less) motile sperm per ml would indicate a significant fertility problem (see also the sperm quality
This production and ejaculation process forms a crucial examination ground in the treatment of couples with reduced infertility. Ejaculation problems can sometimes be bypassed using surgery or techniques for sperm extraction.