Erection

:This article discusses physiological erection. For erection of manmade structures, see construction.

Mechanism

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Physiologically, an erection is achieved by two mechanisms that play together: increased inflow of blood into the vessels of erectile tissue, and decreased outflow. The vessel system involved is known as the corpara cavernosa and the corpus spongiosum. Muscles in the region relax, allowing more blood to enter these sponge-like tissues. Contraction of other muscles reduce the outflow. The enlarged structure then exerts pressures on the exit veins, further reducing the outflow.

Related Topics:
Blood - Vessels - Erectile tissue - Corpara cavernosa - Corpus spongiosum - Muscles - Veins

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As blood flows in, the penis stiffens, its girth and length increases, and it rises to an angle that can vary from below horizontal to almost vertical.

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Certain conditions (e.g. diabetes mellitus) result in erectile dysfunction, a problem where penile erection is insufficient to achieve normal sexual intercourse. In recent years, several drugs have been developed for treatment of this condition.

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If present, the foreskin normally retracts and exposes the glans. The skin of the scrotum tightens, pulling the testicles in towards the base of the penis.

Related Topics:
Foreskin - Glans

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Erection is caused by signals from the parasympathetic nervous system; it is countered by the sympathetic nervous system which is mainly responsible for the "fight-or-flight" response. This explains why under stressful conditions, an erection is often difficult or impossible to achieve, and sudden onset of stress can deprive one of erection. The sympathetic nervous system is also responsible for causing ejaculation, which explains why most males lose their erection after ejaculation.

Related Topics:
Parasympathetic nervous system - Sympathetic nervous system - Ejaculation

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Erections may occur even after death, if the pressure within the penis increases for some reason, for example due to sinking fluids or the formation of gases of putrefaction. See death erection.

Related Topics:
Putrefaction - Death erection

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The clitoris of females also contains erectile tissue and may become erect during sexual arousal; the erection of nipples, however, is not due to erectile tissue.

Related Topics:
Clitoris - Female - Erectile tissue - Nipple

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