from
the book How to Have a Baby: Overcoming Infertility
by Dr. Aniruddha Malpani, MD and Dr. Anjali Malpani,
MD.
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What
happens during ejaculation ?
What happens during ejaculation
?
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 vesicles
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.
Figure 3. The male reproductive system - front view
Figure 4. The male reproductive system - side view
Figure 5. A section
through the testis and epididymis
As already mentioned, the main male sex hormone is testosterone
and this is made by the testicles, starting at puberty.
Testosterone is produced by specialized cells in the
testis called the Leydig cells. These are stimulated
to release testosterone in response to the LH signal
from the pituitary . LH is luteinizing hormone - the
same hormone found in women.
In addition to testosterone, the production
and maturation of sperm in the seminiferous tubules
of the testis is stimulated by FSH produced by the pituitary
gland - and this FSH is identical to that found in women.
FSH acts on the Sertoli cells to cause them to secrete
androgen-binding protein, which binds testosterone and
facilitates its action on sperm production. The Sertoli
cells also produce growth factors such as SGF ( seminiferous
growth factor) which help to regulate spermatogenesis.
Note that there are two separate components
in the testis - and that the Leydig cells are outside
the seminiferous tubules where the sperms are manufactured.
This explains why there is no relation between virility
(which depends upon testosterone production) and fertility
(which depends upon sperm production).
continued . .
.
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