Penile erection
An uncircumcised penis flaccid (left) and erect (right)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.
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.
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An uncircumcised penis flaccid (left)
and erect (right) |
A circumcised penis flaccid (left) and
erect (right) |
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.
| Typical human female nipple in erect state |
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Nipple erection
Typical human female nipple in erect stateNipple 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
both in women and in men. Nipple erection can also be caused by
cold temperature in both male and female. This is merely due to
tactile response to cold temperature than anything linked to sexual
drive.
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
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