PENIS
ANATOMY
Although the penis is a rather ordinary, everyday
organ (at least for about 50% of the population), it is surprising how
little some people know about this part of the body. In some
animals, the penis is equipped with a small bone, not so in humans. In
the adult male, the penis is about 2 to 3 inches long, although this
can differ from day to day. When it is cold, the penis can withdraw
into the fatty tissue overlying the pubic bone, which makes it seem
shorter, especially in men with a lot of fat there. There is generally
little variation in the 'real' length of the penis between different
men; in some races it's somewhat longer, in others a bit shorter.
During erection, the penile length varies between 6 and 8 inches.
Three major structures can be found in the penis:
the urethra and two long cylinders, the erectile bodies.
The urethra, with a thick, spongy cylinder
around it, is located below. The urethra is designed to conduct urine
to the outside world, but can only be considered a tube when it does;
after the urine is expelled, the elastic fibers in its wall make sure
it collapses. The tube ends at the glans of the penis. The skin
on the glans is very sensitive and is normally protected by the
foreskin, which acts as a cover. The foreskin should be able to slide
back and forth over the glans easily, although this is not always the
case yet in children. To ease the sliding, small glands produce a kind
of grease. When this area of the body is not cleaned regularly, the
grease may become noticeable as smegma. In the middle of the
lower part of the foreskin a small skin-slip can be found (Latin: phrenulum),
running from the foreskin towards the opening of the urethra; the
function of this slip of foreskin is unknown, but sometimes it can be
painful during erections when it is too short.
The erectile bodies, long cylinders, that are
located next to each other at the 'back' of the penis. They contain
blood. During erection, the amount of blood inside the cylinders
increases, because the inflow increases and the outflow of blood
decreases; the cylinders are filled to the limit with blood and will
stand upright, causing erection of the penis; it works just like those
cylindric balloons. To ensure a good blood supply, several blood
vessels run towards the erectile bodies and a dense web of small nerve
fibers ensure the opening and closing of the right vessels during
erection. Since there are no stiff structures, like bones or something
similar, in the penis to give it rigidity, the penis is connected to
the pubic bone by strong connective tissue; because of this, the erect
penis is still rather stabile and pointing slightly upwards.
FUNCTION
As you will undoubtedly know, the penis has three
functions:
Urinating. This is a rather plain and simple
function, where the penis serves as a extension of the urethra, thus
enabling males to urinate easy anywhere they want without spilling any
urine. In women this is more difficult and they will have to find a
place to squat.
Sexuality. Simply put: an erect penis, i.e. a
stiff one, can give pleasure. Having an erection is, however, a
complicated procedure. In order to have an adequate erection three
conditions must be fulfilled:
- a certain amount of lust is required
(Latin: libido)
- a good inflow and outflow of blood is
necessary
- the management, i.e. the nerve supply,
must be functioning properly
Getting and maintaining an erection is an automated
process. It is mainly run from the nerve cells in the spinal chord. Of
course, the owner of the penis does have some say in it, but only up
to a limit, for instance by thinking or not thinking about
someone/something (porn movies). The effects will generally be limited
to erection or no erection; it is pretty hard to want to have only
a bit of an erection. To show that the erection is governed by the
spinal chord one can use a vibrator. The vibrations of the machine
will excite the nerve endings in the glans of the penis and will
elicit an erection via a reflex mechanism in the spinal chord (just
like the knee-jerk reflex causes automatic contraction of the muscles
in the leg). The 'erectile nerves' that run from the spinal chord to
the penis will cause the inflow of blood to the erectile bodies to
increase and the outflow to decrease, thus filling these bodies with
blood and causing erection of the penis. If there is no sense of
lust, the inflow of blood is too low or the nerves to the penis are
damaged, then the erection will be limited or even non-existing.
Reproduction. In terms of evolution, erection
has proven to be a good method to put male sperm into a womans womb.
In ejaculation (coming) an amount of semen (prostatic fluid +
sperm cells) is ejected into the urethra at the level of the
prostate. The semen is propelled through the urethra by rapid
muscular movements in its wall and ejected through the penis, on its
way to the female egg-cell; to prevent the semen going the wrong way
(to the bladder, which is closer by) the entry to the bladder is
closed by a tiny sphincter at that very moment - that is the reason
that ejaculation and urinating at the same time is impossible.
Ejaculation is not called 'coming' for nothing: according to mother
nature the goal is reached the very moment the semen came and erection
is not needed any further.
