The
Reproductive System of a woman
The
Menstrual Cycle
The
Hormones
The
Reproductive System of a Man
The
Role of Testosterone
The
Sperm's Odyssey in the Female Reproductive Tract
The
Process of Fertilisation
The Reproductive
System of a Man
The male reproductive system begins
in the scrotum, the sack behind the penis. This contains two testicles,
which make men's sex cells, called sperm; and the male sex hormone, called
testosterone. The testicles feel solid, but a little spongy, like hard
boiled eggs without the shell. They hang from a cord called the spermatic
cord. It's normal for one testicle to hang lower than the other; and for
one testicle to feel slightly larger than the other.
The testicles make sperm best at
a temperature a few degrees cooler than normal body temperature. This is
why nature designed a scrotum - so that the testes can hang outside the
body to keep them cool.
The testicles start making sperm
when a young man reaches puberty. This is in response to the male sex hormone,
testosterone, which starts being produced at this time. The testes keep
making sperm for the rest of the man's life.
The sperms are produced inside several
hundred coiled microscopic tubules called seminiferous tubules in the testes.
These tubules converge and collect into a delta (like the mouth of a river)
near the upper part of the testis called the rete testis which then empties
through a series of very small ducts out of the testis towards the epididymis.
The epididymis is an amazing structure - it is a very long tiny tubule,
which runs back and forth in convolutions and loops to form a tiny compact
structure with a head, body and tail that sits like a cap on the top of
and behind the testis. The tail of the epididymis then leads to the vas
deferens - a thin cord like muscular tube, which is part of the spermatic
cord and which ends at the ejaculatory duct in the prostate. Here is joined
by the seminal vesicle ducts and they all open into the prostatic part
of the urethra - which in turn leads to the urethra in the penis.
Mature sperm take about 75 days to
develop in a process called spermatogenesis. Sperm production takes place
as though it were on an assembly line - with the more mature sperms being
passed along toward the center of the tubule from where they swim towards
the efferent ducts of the testis towards the epididymis. This can be a
very "temperamental" assembly line - things often go wrong, causing low
sperm counts.
When the sperm leave the testis,
they are not yet able to swim on their own. They acquire the capacity to
do so in their passage through the epididymis - which is like a swimming
school for the sperm. They spend between 2 to 15 days here during which
they attain maturity and fertilising potential. Sperm are propelled along
this tunnel by frequent contractions of its thin muscular wall. Most of
the mature sperm are then stored at the end of the epididymis - where they
wait to be rushed through the vas deferens and ejaculated at the time of
orgasm.
During ejaculation, the epididymis
and vas deferens muscles contract to propel the sperm into the ejaculatory
duct. Here the sperm is joined with the secretions of the seminal vesicles
and prostate gland (which contribute the bulk of the seminal fluid) to
form the semen. The powerful muscles surrounding the base of the urethra
then cause the semen to squirt out of the penis at the time of orgasm.
Semen and urine never mix in a healthy male ( even though the final passage
for both is common) because the bladder sphincter muscle contracts during
sexual stimulation, thus closing down the exit from the bladder to the
urethra during ejaculation - preventing urine from leaking forward out
of the bladder during sex and also preventing semen from accidentally going
backward into the bladder.
What about the penis and fertility?
Most men equate their fertility potential with their virility - and therefore
the size of their penis. However, the size of the penis has little to do
either with fertility potential or with sexual ability. (In any case, if
you worry that your penis is too small, you're not alone - most men think
their penises are too small !)
During ejaculation, about one teaspoon
of semen spurts out of the penis. Semen is a milky white color, the consistency
of egg white. Sperm account for only about 2 to 3% of semen. Most of it
consists of seminal fluid - the secretion of the seminal versicles and
the prostate gland, which provide a vehicle for the sperm into the vagina.
A normal ejaculation contains 200
to 500 million sperm. How can so many sperm fit into only a teaspoon of
semen? Simple - sperm are very tiny. If one average ejaculation filled
an Olympic size swimming pool, each sperm cell would still be smaller than
a goldfish. Sperms are the smallest living cells in the human body - and
the egg the largest. Basically, sperms are designed so that they can deliver
their contents - the male genetic material - to the egg. This is why they
are designed like projectiles - the male DNA is in the chromosomes in the
sperm head nucleus, and the tail propels the sperm up towards the egg.
Sperm are also very fragile. Men
make so many because very few survive the swim through the female reproductive
system to fertilize an egg. Perhaps the reason for this is an evolutionary
hangover. Female fish deposit eggs on the sea-bed. This is why male fish
need to produce millions of sperm which are sprayed into the sea water
where millions will be wasted in order to ensure that some reach the eggs.
What happens to the sperms if you
don't have sex for many days? Unfortunately, you cannot "store up" sperms.
If ejaculation does not occur for many days, the sperms in the reproductive
ducts simply die. This is why a sperm count done after many days of abstinence
shows a high number of dead or immotile sperms. But just like you cannot
store your sperm, you cannot run out of sperm either - masturbation and
sex cannot use sperm up. The body keeps making sperm as long as a man has
even one normal testicle.
