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Male Hormones
The development of normal, mature sperm is the
key to male fertility. Sperm production is primarily regulated by
two hormones:- FSH: is responsible for
stimulating sperm production in the testicles
- LH: stimulates the
production of testosterone, the hormone that helps maintain male
sexual characteristics
Under the influence of testosterone and other
hormones, immature sperm cells develop through several stages and
eventually become mature sperm cells, called spermatozoa.
Spermatozoa then pass through the epididymis, where, after 18 to 24
hours, they gain motility, or movement. Finally, mature sperm move
through the vas deferens and are stored in the seminal vesicles
until ejaculation. The complete process takes about 72
days.
When a man ejaculates (or expels the fluid from his penis), sperm
from the seminal vesicles combine with a thick fluid from the
prostate and other glands to create semen. This fluid can be
deposited into a woman's vagina, where it travels through the
cervix and uterus to fertilize an egg.
Men produce sperm from germ cells within the testes throughout
adult life. The production is controlled by various hormones,
including FSH and LH (see illustrations 2). LH stimulates the
specialised Leydig cells in the testes to secrete the male hormone
testosterone. FSH, in conjunction with testosterone, stimulates the
seminiferous tubules in the testes to produce mature sperm (see
illustration 3). Completion of the entire process of sperm
production (spermatogenesis) takes about 72 days.
Sperm are highly specialized cells, which
comprise two essential parts: the head, formed by the acrosome, and
the tail, which enables the movement. The acrosome surrounds the
nucleus where genetic information is stored (see illustration
5).
The production of sperm is, however, an inefficient and vulnerable
process and for the daily production of several hundred million
mature sperm, more than eight times as many germ cells are
required. Furthermore, only a fraction of the sperm produced will
have fertilizing potential.
Sperm can live in the genital tract up to 48 hours or even longer.
The most motile sperm will progress through the uterus and the
fallopian tubes, where fertilization occurs. Only several hundred
sperm will succeed in reaching the egg (oocyte). After the fusion
of one sperm within the egg, cell division will begin. Six or seven
days after ovulation, the embryo will implant in the uterus (see
illustration 4).
Fertilization depends upon such a complex array
of mechanisms that it is surprising that it is ever successful.
However, failures in fertilization may not always stem from a
failed interaction between the egg and the sperm. The problems can
begin long before this.
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