✍ Posted by: Rapahel Siniora
How does a man get an
erection? What is the process behind a penis going from flaccid to erect? Why is a penis normally in the flaccid state? And what is it that causes the
erection to end? This page will answer all those questions, and also explain how the penis is built up and which parts of the penis are most important in this
erection process.
A Brief Anatomy Of The Penis
The two
corpora cavernosa are chambers consisting of networks of open spaces,
sinusoids,
smooth muscle,
nerves and small
arteries. Together, these are called the spongy
erectile tissue.
During an
erection, these two chambers fill with blood and provide the stiffness of the
erection. Another key part that supports the
erection is the layer around the
corpora cavernosa called the
tunica albuginea. This layer or
membrane is of limited flexibility. Therefore, when blood flows into the penis, the
tunica albuginea ensures pressure builds up inside the
corpora cavernosa. As a result, the
corpora cavernosa become firm and the penis as a whole becomes erect.
This can simplistically be compared to filling a bike tire with air: as the inner tube becomes filled with air, pressure increases, the outer rubber provides resistance and the tire becomes firm and hard. Also, the wall between the two units of
corpora cavernosa has a number of openings that let blood flow freely between the two sides so that the pressure is similar in both of these chambers. As the
tunica albuginea expands outward, it also squeezes off the drainage veins at the bottom of the
corpora cavernosa, which traps the blood and increases the blood pressure inside the penis.
There are three main
arteries that supply blood to the penis: the cavernosal
artery, the
dorsal artery, and the
bulbourethral artery. All three arise from an internal
artery called the
penile artery.
The
corpus spongiosum, the two
corpora cavernosa, and the
tunica albuginea are surrounded by something called the
Buck’s fascia. The
Buck’s fascia is a strong, deep, fascial layer that sits on top of the
tunica albuginea, and this is in turn surrounded by the penile skin which we see externally.
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Leonardo Da Vinci |
Leonardo Da Vinci, through his dissection of human bodies, was the first scientist to realize that during an
erection, the penis fills with blood. During his investigation,
Da Vinci wrote, “The penis does not obey the order of its master, who tries to erect or shrink it at will, whereas instead the penis erects freely while its master is asleep. The penis must be said to have its own mind, by any stretch of the imagination.”
The reason a penis is normally kept in a flaccid state, is because the
smooth muscles inside the erectile structures of the penis are contracted. These contracted muscles keep the tiny
arteries inside the
erectile tissue squeezed shut, allowing only tiny amounts of blood to flow into the penis to keep up penis maintenance and to provide nutrients and other essential components.
This minimal bloodflow keeps blood pressure inside the
corpora cavernosa space low – lower than the average blood pressure in
arteries throughout the rest of the body. And as long as this blood pressure is adequately low, blood will not flow into the penis and the penis will remain flaccid.
This changes when a man gets ‘turned on’.
Dopamine then sets off a chain reaction that starts the process of making the penis erect. Levels of
calcium, the chemical whose job it is to keep the
smooth muscles contracted, are decreased. The
smooth muscles then relax and open up, and blood is allowed to flood into the penis. As blood enters the
corpora cavernosa, these chambers starts getting filled up, blood is pushing on the
tunica albuginea, and firmness and pressure is building.

This was the easy explanation of how an
erection works. The more complicated and detailed process behind a penis
erection is described below.
The process of a penis to become
erect is normally started when a man has a sexual thoughtor experiences some form of sexual stimulation. This stimulation could for instance be a kiss or a touch. This in turn, releases
dopamine in the brain and sets off signals that are sent from the brain through special
autonomic nerves to the
spinal cord and the
cavernous nerves that run along the
prostate gland to reach the
corpora cavernosa, the
corpus spongiosum and the
arteries that supply them with blood.
This in turn converts a
molecule in the blood called
guanosine trisphosphate to a chemical called
cyclic guanosine monophosphate (‘cGMP’).
cGMP is a key component in the
erectionprocess as it decreases free
calcium concentrations.
cGMP also helps deactivate the
calciumsensitizing mechanism in the penis as receptors connected to
proteins that help drive the contraction of
smooth muscle cells decrease sensitivity to free
calcium.
This reduction of free
calcium induces relaxation of the cavernosal
smooth muscle cells. As these
smooth muscles relax, blood starts to freely flow into the
corpora cavernosa and the
corpus spongiosum, and the
erection is starting to build.
The increased bloodflow expands the
corpora cavernosa which then stretches the
tunica albuginea (the
membrane of limited elasticity on the outside of the
corpora cavernosa). As the
tunica albuginea stretches, it builds up pressure and firmness. This pressure also compresses the veins at the bottom of the penis where blood would normally flow out of the penis. Or put differently, the pressure makes the
tunica albuginea block off the veins that take blood away from the
corpora cavernosa. This traps blood within the penis, the pressure increases and the penis becomes erect.
The continuation of the
erection is made possible by the
tunica albuginea which acts as a gatekeeper by keeping up the pressure and pressing down on the veins that hold blood off from flowing out of the penis.
Testosterone is another key ingredient in the
erection process.
Nitric oxide synthase is highly dependent on
testosterone to function properly, and if there is an inadequate level of
testosterone, this will normally cause these
enzymes to produce less than optimal amounts of
nitric oxide. The reason for this is that lower than normal levels of
testosterone will normally cause a decrease in the number of
nitric oxide synthase neurons in the brain.
Additionally, a certain level of
testosterone needs to be present in order for
dopamine to be released (or synthesized) as
testosterone is one of the ingredients needed for this
dopaminecreation. And also, increased
nitric oxide production in turn causes further
dopamine release. To learn more about
dopamine on Truelibido, please go
here.
When a man has had an orgasm, or sexual stimulation is ceased, the
erection will normally fade. The mechanism behind the end of an
erection is the reverse of the process of the
erection taking place. The amounts of
cGMP in the penis are decreased and therefore, levels of free
calcium are allowed to increase. When free
calcium levels are increased, the
smooth muscles in the penis will again contract. Blood is then forced out of the penis by the contracting tissues, and the
erection ends.
In short, both contraction and relaxation of the
smooth muscles in the erectile structures of the penis are regulated by free
calcium, therefore free
calcium also regulates the onset and end of a man’s
erections.
There are
pharmaceutical drugs that target this free
calcium level in order to help a man both get an
erection and also maintain the
erection for longer than would otherwise be possible.
Viagra,
Cialis and
Levitra all do this. These drugs act on an
enzyme called
phosphodiesterase type 5 (‘PDE5’). This
enzyme is part of the
erection process as it helps control the level of
cGMP, or rather, it breaks down
cGMP. When
cGMP is broken down, the free
calcium levels are allowed to rise,
smooth muscles start to contract and blood will flow out of the penis. What these drugs do is to inhibit this
PDE5 so that it does not break down
cGMP (or breaks it down much slower). When there is more
cGMP present, this will decrease free
calcium levels and the
erection builds and is allowed to remain
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