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

Ithyphallic redirects here. You may be looking for the album by the American death metal band Nile.

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.

The ability to maintain the erectile state is key to the reproductive system and life itself could not reproduce in a natural way with out this ability.

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. ^{[citation needed]}

Slang

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

Penis erection

thumb|right|An uncircumcised penis flaccid (left) and erect (right)

A penis 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. After a man has ejaculated during sexual encounter or masturbation, his erection usually ends, but this may take time depending on the length and thickness of the penis.

By actively contracting the Ischiocavernosus muscle at the base of the penis, a man can prolong his erection. Erection stays on because the sexual arousal is toned down by the pressure of this muscle on the surrounding tissue. The ejaculation is delayed by this. The author Gianni Venice proposes this method as best alternative to the stop-start technique, most often prescribed by sex therapists, to prevent premature ejaculation. According to Venice, the method to train the Ischiocavernosus is escpecially suited for younger men who do not have a spouse or partner to help them train the stop-start technique.

Penis erection usually results from sexual stimulation and/or sexual 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.

thumb|right|A circumcised penis flaccid (left) and erect (right). 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.

Shape and Size

An erect penis can take on a number of different shapes and angles, ranging from a straight tube angled at a 45-90 degree angle, to a curvature to the left or right, up or down. A tightly curved penis, known as Peyronie's disease, is identified by a severe curve in the erect penis. This may cause physical and psychological effects for the affected individual, which could include erectile dysfunction or pain during erection. Treatments include oral medication (such as Vitamin E) or surgery, which is most often reserved as a last resort.

Generally the size of an erect penis is fixed throughout post-pubescent life and little can be done to increase the size without modifying these tissues directly through surgery on the penis.

Clitoral erection

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

Swelling and enlargement also occur during a clitoral erection but because a large proportion of the clitoris is within the body, it may not be obvious.

Nipple erection

Human female nipple in erect state.

Nipple erection may result from 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. It is more akin to a hair follicle standing on end than to a sexual erection.

Bibliography

• Drake, Richard, Wayne Vogl and Adam Mitchell, Grey's Anatomy for Students. Philadelphia, 2004. (ISBN 0-443-06612-4)
• Harris, Robie H. (et al.), It's Perfectly Normal: Changing Bodies, Growing Up, Sex And Sexual Health. Boston, 1994. (ISBN 1-56402-199-8)
• Milsten, Richard (et al.), The Sexual Male. Problems And Solutions. London, 2000. (ISBN 0-393-32127-4)
• Tanagho, Emil A. (et al.), Smith's General Urology. London, 2000. (ISBN 0-8385-8607-4)
• Williams, Warwick, It's Up To You: Overcoming Erection Problems. London, 1989. (ISBN 0-7225-1915-X)

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See also

• Priapism
• Sexual function
• Death erection

zh-yue:扯旗

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