Men's
sexual anatomy 2: The testicles, epididymis
and other sexual glands
This
page describes the internal parts of
men's sexual organs: the testicles,
epididymis, prostate, Cowper's glands and
seminal vesicles.
Testicles
The
testicles have many names: balls
colloquially, testes, or even gonads. (When
we talk about testes, one of them is
referred to as a testis, the singular form
which goes back to the good old Latin name).
The testicles are two paired glands which
sit in the scrotum and mostly produce sperm
and testosterone.
Each
testis is about 5 cm long and 2.5 cm thick
with an oval shape. The testicles form
originally in the abdominal wall during
development and descend into their space in
the scrotum just before birth. Each testicle
sits in a dense fibrous capsule, the tunica
albuginea, the inward extensions of which
divide the testicle into lobes. Each of the
two to three hundred lobes has a few tightly
coiled tubules called the seminiferous
tubules, where the sperm are produced. In
between the tubules sit the Leydig cells,
which secrete testosterone, the most
important male sex hormone. All the tubules
eventually lead to a duct, which allows
sperm and fluid to leave the testicles via
the epididymis.
Epididymis
and Vas deferens
The
epididymis is a small, about 4 cm long,
comma-shaped organ that sits on the back of
each testicle. It consists of a long thin
tube, which is tightly wound up.
Straightened out the tube would measure more
than 6 meters in length! The epididymis
stores sperm; it's also the place where
sperm develop their motility (ability to
move around). Sperm can be stored in the
epididymis for more than a month. The end of
the epididymis leads on to the vas deferens,
the duct that carries sperm and fluid from
the scrotum into the body cavity, up and
around the bladder to the prostate. It
broadens at its end (the ampulla) to be able
to store sperm, which can survive in the vas
deferens for a few months.
Seminal
vesicles
These
are the first of three sets of accessory sex
glands in the human male. The seminal
vesicles lie just to the front of the
bladder, above the prostate, and their
outgoing tube joins the vas deference at its
very end in the prostate. Each seminal
vesicle is about 5 cm long.
The
seminal vesicles produce 60% of the fluid
volume of semen with different biological
components. They produce an alkaline,
viscous fluid, which also contains fructose
(a sugar), prostaglandins and clotting
proteins. The alkaline fluid is required to
neutralize the acidic environment of the
male urethra and the female reproductive
system as sperm would not be able to survive
these acidic environments. Fructose becomes
the energy source for sperm, which they need
to survive and move around.
Prostate
gland
The
prostate gland is the next gland through
which the sperm pass on their onward
journey. It's a small, chestnut-sized organ
at the bottom of the bladder. It's shaped
like a thick ring around the urethra, the
tube through which a man passes urine away
from the bladder. The prostate secrets a
milky, slightly acidic fluid which supports
the health and mobility of sperm. 25% of the
volume of semen is made up by the prostate's
secretions.
The
prostate gland slowly increases in size
during childhood and than expands more
quickly during puberty. Its size should
remain more or less stable during adulthood,
but it may start to enlarge again in older
men. This may lead to the prostate putting
pressure on the urethra, the tube which
allows one to pass urine from the bladder to
the tip of the penis. Obviously, the extra
pressure isn't good for peeing and may lead
to dribbling and poor stream.
Cowper's
glands
These
small, pea-sized glands are located below
the prostate and are also called
bulbourethral glands. There are two of them,
and their outgoing ducts lead into the
urethra. Cowper's glands secret a sticky,
alkaline fluid during sexual arousal, which
neutralizes the acidity of the male urethra.
Additionally, they also secret a mucus
substance (you may know this as
"pre-cum"), which acts as a
natural lubricant for the tip of the penis.
The quantity of pre-cum in any episode of
sex varies between a small droplet and 5 ml,
with some men not being aware of producing
any at all. This fluid may already contain
some live sperm, released before
ejaculation, which is why it is essential to
put on a condom for birth control prior to
penetration, not just before ejaculation.
