The
male sex hormones, or androgens, are
essential for normal physical development,
fertility, sex drive and normal sexual
functioning in men. The two main androgens
are testosterone and dihydrotestosterone,
which is a more powerful variation of
testosterone.
Even
though testosterone is produced in your
testicles (also known as your testes),
its production is under the control of the
brain, via a complex cascade of messenger
proteins: this is fairly similar in both
sexes, though in women the control system
works on the ovaries, not the testicles.
The
first signal for testosterone production
comes from the hypothalamus, a structure
deep inside the brain which regulates many
body functions and keeps our homeostatic
balance. The hypothalamus releases a hormone
called gonadotropin releasing hormone (GnRH).
This affects another structure close by in
the brain, called the pituitary gland, which
is the main hormone producing gland in the
brain; its secretions help to coordinate
reproduction and body growth. In response to
GnRH the pituitary releases two hormones
called luteinizing hormone (LH) and
follicle-stimulating hormone (FSH). Both
hormones are released into the blood stream
from where they reach all parts of the body,
including the testicles.
LH
stimulates cells called Leydig cells in
the testicles to produce testosterone, a
fat-based hormone synthesized from
cholesterol. Testosterone is released from
the Leydig cells and finds its way into the
blood stream, which transports it around the
body. The cells of tissues which are
influenced by testosterone have receptors on
their cell walls for the hormone. (An
example of this is your muscles, which grow
under the influence of the hormone to give
you more bulk and strength as a man.) These
receptors trigger the activation or
deactivation of various genes which then
stimulate the production of specific
proteins. This means testosterone has a
direct influence on anabolism, or protein
production, and it's this aspect of their
operation which is artificially triggered
when men use anabolic steroids to bulk up
their muscle mass. Some tissues are able to
convert testosterone into its more potent
derivative dihydrotestosterone.
The
second hormone from the pituitary (FSH) also
stimulates cells in the testicles, however
this time it's the Sertoli cells in
the seminiferous tubules. These cells
produce sperm. The last step of sperm
production is also aided by testosterone
produced by the nearby Leydig cells.
The
androgens have a major impact on the body of
a man, an influence which begins before his
birth by promoting the development of male
reproductive organs and the growth of
external male genitalia. During puberty, the
production of a boy's testosterone
increases, causing the development of male
characteristics: growth of his penis and
testicles, more muscle tissue, deeper voice,
more hair. A higher testosterone level also
facilitates a higher sex drive, sperm
production, and ejaculation. Additionally,
testosterone stimulates the productions of
protein all over the body; it is an anabolic
hormones - one that stimulates protein
production.
Before
I say a bit more about artificial anabolic
hormones, it's important to describe the
regulation of testosterone levels in the
blood stream to really understand the
consequences of increasing your anabolic
hormone levels. Testosterone is regulated by
a negative feedback loop in the brain which
works like this: high levels of testosterone
in the blood directly impact on receptors in
the hypothalamus. This results in the
hypothalamus releasing less GnRH, which in
turn results in less stimulation of the
pituitary gland and less production of LH.
And less LH results in less production of
testosterone by the Leydig cells in your
testicles.
Most
of you will probably have heard of the
illegal use of anabolic steroids by athletes
and the wider male population. These
anabolic steroids are similar to
testosterone and have the same effect of
boosting protein production, which means
more muscle and more power. However, very
large doses need to be introduced into the
body from the outside to produce these
effects. Such high doses can have damaging
effects on various body systems and may
produce side effects including liver cancer,
kidney damage, wide mood swings and higher
levels of aggressiveness, stunted growth,
and a higher risk of heart disease. Also,
having high levels of testosterone-like
hormones in the blood means that the body's
own negative feedback loop is activated. The
body starts to produce less and less of its
own testosterone, which can result in the
testicles shrinking, infertility and
baldness.
Testosterone
is the most important protein in the male
reproductive system. Putting it simply,
testosterone is what makes you a man
physiologically. And not surprisingly, a
fall in testosterone production, for example
due to age (andropause), illness or
lifestyle choices (such as drinking too much
alcohol), has widespread consequences for
men. In some men the uptake of testosterone
may be inhibited by problems in the
testosterone receptors. If you are
experiencing sexual problems, loss of sex
drive and generally a lack of energy you may
want to go to your doctor to get your
testosterone levels checked. Replacement
therapies are now available, but are
expensive and sometimes difficult to get.
See the page on low sex drive for men for
more information.
Source
for the facts cited in this page:
ABC
of Sexual Health (2005) Second edition
edited by John M Tomlinson, British Medical
Journal Books and Blackwell Publishing.
Principles
of anatomy and physiology (2000) Ninth
edition by Gerard J. Tortora and Sandra
Reynolds Grabowski. Publishers: John Wiley
and Sons
