Erection (penis)


 * This article discusses human physiological erection. For erection of artificial structures, see construction.

The erection of the penis, clitoris or a nipple is its enlarged and firm state. It depends on a complex interaction of psychological, neural, vascular and endocrine factors. The term is also applied to the process that leads to this state.

Penile erection


The pituitary gland, the prostate and testosterone all have an important role in the process of erection of a penis.

A penile erection occurs when two tubular structures that run the length of the penis, the corpora cavernosa, become engorged with venous blood. This may result from any of various physiological stimuli. The corpus spongiosum is a single tubular structure located just below the corpora cavernosa, which contains the urethra, through which urine and semen pass during urination and ejaculation, respectively. This may also become slightly engorged with blood, but less so than the corpora cavernosa.

Penile erection usually results from sexual stimulation and/or arousal, but can also occur by such causes as a full urinary bladder or spontaneously during the course of a day or at night, often during erotic or wet dreams (see "nocturnal penile tumescence"). An erection results in swelling and enlargement of the penis. Erection enables sexual intercourse and other sexual activities (sexual functions), though it is not essential for all sexual activities.

In the presence of mechanical stimulation, erection is initiated by the parasympathetic division of the autonomic nervous system (ANS) with minimal input from the central nervous system. Parasympathetic branches extend from the sacral plexus into the arteries supplying the erectile tissue; upon stimulation, these nerve branches initiate the release of nitric oxide, a vasodilating agent, in the target arteries. The arteries dilate, filling the corpora spongiosum and cavernosa with blood. Erection subsides when parasympathetic stimulation is discontinued; baseline stimulation from the sympathetic division of the ANS causes constriction of the penile arteries, forcing blood out of the erectile tissue. The cerebral cortex can initiate erection in the absence of direct mechanical stimulation (in response to visual, auditory, olfactory, imagined, or tactile stimuli) acting through erectile centers in the lumbar and sacral regions of the spinal cord. The cortex can suppress erection even in the presence of mechanical stimulation, as can other psychological, emotional, and environmental factors.

The opposite term is detumescence.

Clitoral erection
Clitoral erection is a part of sexual arousal in women. The female clitoris is the anatomically homologous counterpart of penis, and the physiological mechanism of its erection is similar.

Nipple erection
Nipple erection may result from basically three kinds of response. It happens in females during breast feeding. It is also an early part of the sexual response in females and males. Both of these are caused by the release of oxytocin. Nipple erection can also be caused by cold temperature in both male and female. This is merely due to tactile response to cold temperature rather than anything linked to sexual drive. The erection of nipples is not due to erectile tissue, but due to the contraction of smooth muscle under the control of the autonomic nervous system.

Culture
In many countries, movies and magazines available to juveniles may not depict penile erection; such depictions are often taken as one criterion to distinguish between soft and hard pornography.

Slang
As with nearly any aspect of the human body that is involved in sex, there are many slang words for an erection; see WikiSaurus:erection &mdash; the WikiSaurus list of synonyms and slang words for erection in many languages.