Erection

erectpenile erectionerect peniserectile functionerectionsspontaneous erectionbonermale erectionpenile tumescenceHard
An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged.wikipedia
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Sexual arousal

sexually arousedarousalaroused
Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with sexual arousal or sexual attraction, although erections can also be spontaneous. Erection is a common indicator of sexual arousal and is required for a male to effect vaginal penetration and sexual intercourse. As an autonomic nervous system response, an erection may result from a variety of stimuli, including sexual stimulation and sexual arousal, and is therefore not entirely under conscious control.
Male arousal will lead to an erection, and in female arousal the body's response is engorged sexual tissues such as nipples, vulva, clitoris, vaginal walls and vaginal lubrication.

Nocturnal penile tumescence

morning erectionnocturnal erectionmorning erections
Erections during sleep or upon waking up are known as nocturnal penile tumescence (NPT).
Nocturnal penile tumescence is a spontaneous erection of the penis during sleep or when waking up.

Erectile dysfunction

impotenceimpotentimpotency
Absence of nocturnal erection is commonly used to distinguish between physical and psychological causes of erectile dysfunction and impotence.
Erectile dysfunction (ED), also known as impotence, is a type of sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual activity.

Corpus cavernosum penis

corpora cavernosacorpus cavernosumcorpora cavernosa penis
The arteries dilate causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum) to fill with blood; simultaneously the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa restricting the egress and circulation of this blood. Erection and protrusion take place gradually, by the increasing tumescence of the erectile vascular tissue in the corpus cavernosum penis.
A corpus cavernosum penis (singular) (literally "cave-like body" of the penis, plural corpora cavernosa) is one of a pair of sponge-like regions of erectile tissue, which contain most of the blood in the penis during an erection.

Ischiocavernosus muscle

ischiocavernosus
The arteries dilate causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum) to fill with blood; simultaneously the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa restricting the egress and circulation of this blood.
It helps (in males) stabilize the erect penis and (in females) tense the vagina during orgasm.

Blood

human bloodhematologicaloxygen consumption
The arteries dilate causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum) to fill with blood; simultaneously the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa restricting the egress and circulation of this blood.
The restriction of blood flow can also be used in specialized tissues to cause engorgement, resulting in an erection of that tissue; examples are the erectile tissue in the penis and clitoris.

Ejaculation

ejaculateejaculatedejaculates
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.
A usual precursor to ejaculation is the sexual arousal of the male, leading to the erection of the penis, though not every arousal nor erection leads to ejaculation.

Glans penis

glanscoronal sulcusglans of the penis
Generally, the foreskin automatically and gradually retracts, exposing the glans, though some men may have to manually retract their foreskin.
The foreskin can generally be retracted over and past the glans, and may automatically retract during an erection.

Sexual intercourse

sexcopulationintercourse
Erection is a common indicator of sexual arousal and is required for a male to effect vaginal penetration and sexual intercourse.

Phallophobia

An unusual aversion to the erect penis is sometimes referred to as phallophobia.
Phallophobia in its narrower sense is a fear of the erect penis and in a broader sense an excessive aversion to masculinity.

Sexual stimulation

sexual pleasuresexually stimulatederotic pleasure
As an autonomic nervous system response, an erection may result from a variety of stimuli, including sexual stimulation and sexual arousal, and is therefore not entirely under conscious control.
A subsequent study investigating male arousal showed that men were able to achieve rigid erections through visual stimulation of an erotic film alone.

Bulbospongiosus muscle

bulbospongiosusbulbocavernosusbulbocavernosus muscle
The arteries dilate causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum) to fill with blood; simultaneously the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa restricting the egress and circulation of this blood.
In males it contributes to erection, the contractions of orgasm and ejaculation.

Puberty

pubescentpubescencesexual development
After reaching puberty, erections occur much more frequently.
Erections during sleep or when waking up are medically known as nocturnal penile tumescence and colloquially referred to as morning wood.

Foreskin

prepuceforeskinspenial sheath
Generally, the foreskin automatically and gradually retracts, exposing the glans, though some men may have to manually retract their foreskin.
During erection, the degree of automatic foreskin retraction varies considerably; in some adults, the foreskin remains covering all or some of the glans until retracted manually or by sexual activity.

Priapism

prolonged erectionClitorismN 48.3
Priapism is a painful condition in which the penis does not return to its flaccid state, despite the absence of both physical and psychological stimulation.
Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended.

Penis

peniledickcock
An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged.
In many mammals, the size of a flaccid penis is smaller than its erect size.

Death erection

A death erection, angel lust, or terminal erection is a post-mortem erection, technically a priapism, observed in the corpses of men who have been executed, particularly by hanging.

Canine penis

dog's penisdog penisCoyote's Penis
At the time of penetration, the canine penis is not erect, and only able to penetrate the female because it includes a narrow bone called the baculum, a feature of most placental mammals.
At the time of penetration, the canine penis is not erect, and can only penetrate the female because it includes a narrow bone called the "baculum", a feature of most placental mammals.

Human penis

penispenisesdick
An erection is the stiffening and rising of the penis, which occurs during sexual arousal.

Stallion

stallionssireHorse
When not erect, a horse's penis is housed within the prepuce, 50 cm long and 2.5 to 6 cm in diameter with the distal end 15 to 20 cm.

Baculum

baculapenis boneos penis
At the time of penetration, the canine penis is not erect, and only able to penetrate the female because it includes a narrow bone called the baculum, a feature of most placental mammals.
In humans, the rigidity of the erection is provided entirely through blood pressure in the corpora cavernosa.

Sexual function

functionsexual functioningsexual response
The aspects of sexual function defined as being relevant to the assessment include sexual desire, erection, orgasm and ejaculation.

Tumescence

detumescencetumescentflaccid
Erection and protrusion take place gradually, by the increasing tumescence of the erectile vascular tissue in the corpus cavernosum penis.
Something that causes an erection is sometimes referred to as a tumefier (tumefyer) or tumescer.

Sexual attraction

sex appealsexual attractivenesssexual interest
Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with sexual arousal or sexual attraction, although erections can also be spontaneous.