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WHAT
IS AN ERECTION?
Well, you can call it what you like; from woody to hard-on, the
horn, a babies arm; whatever - they are all erections. But how
do they happen (mechanically at least)? The penis has three long
tubes of cylindrical erectile tissue which , are connected together
by fibrous tissue. Called corpora cavernosa these two identical
sections run parallel along the sides of the penis with the third
tube (corpus spongiosum) laying underneath. These three also surround
the urethra the tube which transports either sperm or urine. All
three masses are like sponges in that they contain large spaces
between loose networks of tissue. When the penis is limp (doctors
call this 'flaccid' or 'resting'), then the spaces collapse and
the tissue is reduced (that's why it's smaller). However when you
start to get an erection, blood flows into these spaces causing
the penis to enlarge. Now in theory this happens because of physical
or psychological stimulation, but try telling that to a teenage
boy who gets one while slumbering through algebra! Anyway as blood
enters there is also a temporary reduction in the rate and volume
of blood leaving the penis. So as the arteries carrying blood to
the penis dilate the veins leading away use funnel-shaped valves
to restrict the outflow of blood. Then as the erectile tissue begins
to enlarge additional pressure happens as the veins to be compressed
against the surrounding tissue, which in turn further restricts
the outflow of blood. Now during all this process the three tubes
don't swell up by the same pressure. The underneath tube (remember
it's called the corpus spongiosum) doesn't become as hard as the
two main sections (corpora cavernosa), if it did this would crush
the urethra making it impossible to ejaculate (no thanks)! When
this process is over your penis is becoming soft again as the arteries
relaxed and contract.
And that's the end of the story until the process starts again;
for teenagers this will probably be in five minutes - but for the
rest of us it takes a little longer, but that's another story!
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