Erection

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Erection
A Erect human penis.JPG
Erection of an uncircumcised male human
Figure 28 01 06.jpg
Three columns of erectile tissue make up most of the volume of the penis.
Identifiers
MeSH D010410
TE E1.0.0.0.0.0.8
Anatomical terminology
Erection blood vessels
Identifiers
MeSH D010410
TE E1.0.0.0.0.0.8
Anatomical terminology

An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with sexual arousal, sexual attraction or libido, although erections can also be spontaneous. The shape, angle, and direction of an erection vary considerably between humans.

Contents

Physiologically, an erection is required for a male to effect penetration or sexual intercourse and is triggered by the parasympathetic division of the autonomic nervous system, causing the levels of nitric oxide (a vasodilator) to rise in the trabecular arteries and smooth muscle of the 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 subsides when parasympathetic activity reduces to baseline.

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. Erections during sleep or upon waking up are known as nocturnal penile tumescence (NPT), also known as "morning wood". Absence of nocturnal erection is commonly used to distinguish between physical and psychological causes of erectile dysfunction and impotence.

The state of a penis which is partly, but not fully, erect is sometimes known as semi-erection (clinically: partial tumescence); a penis which is not erect is typically referred to as being flaccid, or soft.

Physiology

Erection stages
Erection Development V2.jpg
Circumcised human penis erection stages.jpg
Different penis sizes.jpg
Lateral view of an un-circumcised human penis during various stages of erection.png
Side views and comparison of the stages of both uncircumcised and circumcised human penis erection.

An erection is necessary for natural insemination as well as for the harvesting of sperm for artificial insemination, and is common for children and infants. After reaching puberty, erections occur much more frequently. [1] [2] An erection occurs when two tubular structures, called the corpora cavernosa, that run the length of the penis, become engorged with venous blood. This may result from any of various physiological stimuli, also known as sexual stimulation and sexual arousal. 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.

In some cases, the scrotum becomes tightened during an erection, and in most uncircumcised males, the foreskin automatically and gradually retracts throughout the various stages of erection, exposing the glans, though some individuals have to manually retract their foreskin.

Autonomic control

In the presence of mechanical stimulation, erection is initiated by the parasympathetic division of the autonomic nervous system 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 release acetylcholine, which in turn causes the release of nitric oxide from endothelial cells in the trabecular arteries. [3] Nitric oxide diffuses to the smooth muscle of the arteries (called trabecular smooth muscle [4] ), acting as a vasodilating agent. [5] The arteries dilate, filling the corpus spongiosum and corpora cavernosa with blood. The ischiocavernosus and bulbospongiosus muscles also compress the veins of the corpora cavernosa, limiting the venous drainage of blood. [6] Erection subsides when parasympathetic stimulation is discontinued; baseline stimulation from the sympathetic division of the autonomic nervous system causes constriction of the penile arteries and cavernosal sinosoids, forcing blood out of the erectile tissue through erection-related veins which include one deep dorsal vein, a pair of cavernosal veins, and two pairs of para-arterial veins between Buck's fascia and the tunica albuginea. [7] [8] Erection rigidity is mechanically controlled by reduction blood flow through theses veins, and thereby building up the pressure of the corpus cavernosum and corpus spongiosum, an integral instructure, the distal ligament, buttresses the glans penis. [9]

After ejaculation or cessation of stimulation, erection usually subsides, but the time taken may vary depending on the length and thickness of the penis. [10]

Voluntary and involuntary control

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. [11] The cortex may suppress erection, even in the presence of mechanical stimulation, as may other psychological, emotional, and environmental factors. [12]

Nocturnal erection

The penis may become erect during sleep or be erect on waking up. Such an erection is medically known as nocturnal penile tumescence (informally: morning wood or morning glory). [13] [14] [15] [16]

Socio-sexual aspects

Social

Though an erection can have many causes, it is most commonly seen as an indicator of sexual arousal and is therefore considered taboo or inappropriate for a public setting in many societies. This taboo is lesser than that surrounding public sex but higher than that surrounding nudity. Erectile dysfunction is often considered a flaw, eliciting shame in individuals affected.

The penile plethysmograph, which measures erections, has been used by some governments and courts of law to measure sexual orientation. An unusual aversion to the erect penis is sometimes referred to as phallophobia.

Spontaneous or random erections

A male wearing fishnet underpants (cropped).jpg
Visible erection through clothing.jpg
Erection visible beneath clothing

Spontaneous erections, also known as involuntary, random or unwanted erections, are commonplace and a normal part of male physiology. Socially, such erections can be embarrassing if they happen in public or when undesired. [1] Such erections can occur at any time of day, and if clothed may cause a bulge which (if required) can be disguised or hidden by wearing close-fitting underwear, a long shirt, or baggier clothes. [17]

Size

The length of the flaccid penis is not indicative of the length of the penis when it becomes erect, with some smaller flaccid penises growing much longer, and some larger flaccid penises growing comparatively less. [18] Generally, the size of an erect penis is fixed throughout post-pubescent life. Its size may be increased by surgery. [19]

Though the size of a penis varies considerably between males, the average length of an erect human penis is 13.12 cm (5.17 inches), while the average circumference of an erect human penis is 11.66 cm (4.59 inches). [20]

Direction

Although many erect penises point upwards, it is common and normal for the erect penis to point nearly vertically upwards or horizontally straight forward or even nearly vertically downwards, all depending on the tension of the suspensory ligament that holds it in position. An erect penis can also take on a number of different shapes, ranging from a straight tube to a tube with a curvature up or down or to the left or right. An increase in penile curvature can be caused by Peyronie's disease. This may cause physical and psychological effects for the affected individual, which could include erectile dysfunction or pain during an erection. Treatments include oral medication (such as colchicine) or surgery, which is most often performed only as a last resort.

Various erection angle and shape of penises Erection angle and shape of penises.jpg
Various erection angle and shape of penises

The following table shows how common various erection angles are for a standing male. In the table, zero degrees (0°) is pointing straight up against the abdomen, 90° is horizontal and pointing straight forward, and 180° is pointing straight down to the feet. An upward pointing angle is most common and the average erection angle is 74.3 degrees. The penile curvature was measured same time. 63% men have straight penis. 22.2% men have upwards curvature and 14.8% men have downwards curvature. [21]

Occurrence of erection angles
Angle (°)Percent of population
0–304.9
30–6029.6
60–8530.9
85–959.9
95–12019.8
120–1804.9

Medical conditions

Erectile dysfunction

Erectile dysfunction (also known as ED or "(male) impotence") is a sexual dysfunction characterized by the inability to develop and/or maintain an erection. [22] [23] The study of erectile dysfunction within medicine is known as andrology, a sub-field within urology. [24]

Erectile dysfunction may occur due to physiological or psychological reasons, most of which are amenable to treatment. Common physiological reasons include diabetes, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, vascular disease, including arterial insufficiency and venogenic erectile dysfunction, [25] and neurologic disease which collectively account for about 70% of ED cases. [5] Some drugs used to treat other conditions, such as lithium and paroxetine, may cause erectile dysfunction. [23] [26]

Erectile dysfunction, tied closely as it is to cultural notions of potency, success and masculinity, can have devastating psychological consequences including feelings of shame, loss or inadequacy. [27] There is a strong culture of silence and inability to discuss the matter. Around one in ten men experience recurring impotence problems at some point in their lives. [28]

Priapism

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 lasting over four hours is a medical emergency.

Hard flaccid syndrome

Hard flaccid syndrome is a rare, chronic condition characterized by a flaccid penis that remains in a firm, semi-rigid or semi-erect state in the absence of sexual arousal.

Other animals

A stallion with an erect penis Medimurski konj (vranac) na sajmu MESAP 2015.jpg
A stallion with an erect 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. After the male achieves penetration, he will often hold the female tighter and thrust faster, and it is during this time that the male's penis expands, unlike human sexual intercourse, where the male penis commonly becomes erect before entering the female. [29]

An elephant's penis is S-shaped when fully erect and has a Y-shaped orifice. [30]

Given the small amount of erectile tissue in a bull's penis, there is little enlargement after erection. The penis is quite rigid when non-erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of the retractor penis muscle and straightening of the sigmoid flexure. [31] [32]

A male fossa's penis reaches to between his forelegs when erect. [33]

When not erect, a horse's penis is housed within the prepuce, 50 centimetres (20 in) long and 2.5 to 6 centimetres (0.98 to 2.36 in) in diameter with the distal end 15 to 20 centimetres (5.9 to 7.9 in). The retractor muscle contracts to retract the penis into the sheath and relaxes to allow the penis to extend from the sheath. [34] When erect, the penis doubles in length [35] and thickness and the glans increases by 3 to 4 times. [34] Erection and protrusion take place gradually, by the increasing tumescence of the erectile vascular tissue in the corpus cavernosum penis . [36] [37] Most stallions achieve erection within 2 minutes of contact with an estrus mare, and mount the estrus mare 5–10 seconds afterward. [38]

A bird penis is different in structure from mammal penises, being an erectile expansion of the cloacal wall and being erected by lymph, not blood. [39] The penis of the lake duck can reach about the same length as the animal himself when fully erect, but more commonly is about half the bird's length. [40] [41]

Terminology

Clinically, erection is often known as "penile erection", and the state of being erect, and process of erection, are described as "tumescence" or "penile tumescence". The term for the subsiding or cessation of an erection is "detumescence".

Colloquially and in slang, erection is known by many informal terms. Commonly encountered English terms include 'stiffy', 'hard-on', 'boner' and 'woody'. [42] There are several slang words, euphemisms and synonyms for an erection in English and in other languages (see also: The WikiSaurus entry).

See also

Related Research Articles

Erectile dysfunction (ED), also referred to as impotence, is a form of sexual dysfunction in males characterized by the persistent or recurring inability to achieve or maintain a penile erection with sufficient rigidity and duration for satisfactory sexual activity. It is the most common sexual problem in males and can cause psychological distress due to its impact on self-image and sexual relationships.

<span class="mw-page-title-main">Priapism</span> Medical condition where an erection lasts excessively long

Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases are ischemic. Ischemic priapism is generally painful while nonischemic priapism is not. In ischemic priapism, most of the penis is hard; however, the glans penis is not. In nonischemic priapism, the entire penis is only somewhat hard. Very rarely, clitoral priapism occurs in women.

Erectile tissue is tissue in the body with numerous vascular spaces, or cavernous tissue, that may become engorged with blood. However, tissue that is devoid of or otherwise lacking erectile tissue may also be described as engorging with blood, often with regard to sexual arousal.

<span class="mw-page-title-main">Corpus spongiosum (penis)</span> Spongy tissue within the human penis

The corpus spongiosum is the mass of spongy tissue surrounding the male urethra within the penis. It is also called the corpus cavernosum urethrae in older texts.

<span class="mw-page-title-main">Bulbospongiosus muscle</span> Superficial muscle of the perineum

The bulbospongiosus muscles are a subgroup of the superficial muscles of the perineum. They have a slightly different origin, insertion and function in males and females. In males, these muscles cover the bulb of the penis, while in females, they cover the vestibular bulbs.

Tumescence is the quality or state of being tumescent or swollen. Tumescence usually refers to the normal engorgement with blood of the erectile tissues, marking sexual excitation, and possible readiness for sexual activity. The tumescent sexual organ in males is the penis and in females is the clitoris and other parts of the genitalia like the vestibular bulbs. Arteries in the penis dilate to increase blood volume.

<span class="mw-page-title-main">Deep shaft piercing</span> Type of genital piercing

Deep shaft piercings are piercings which pass through the penile shaft. They are most commonly seen in the form of deeply placed ampallangs, apadravyas, and reverse shaft Prince Alberts. They are more rare piercings due to associated pain, difficulty, bleeding and long healing times. Common placement is directly behind the head of the penis, but they can be placed farther back.

<span class="mw-page-title-main">Corpus cavernosum penis</span> Sponge-like region of erectile tissue

A corpus cavernosum penis (singular) is one of a pair of sponge-like regions of erectile tissue, which contain most of the blood in the penis during an erection.

<span class="mw-page-title-main">Corpus cavernosum of clitoris</span> One of a pair of regions in the clitoris that contain the blood during erection

The corpus cavernosum of the clitoris is one of a pair of sponge-like regions of erectile tissue that engorge with blood during an erection. This is homologous to the corpus cavernosum of the penis. The term corpora cavernosa literally means "cave-like bodies".

<span class="mw-page-title-main">Dorsal veins of the penis</span>

In human male anatomy, the dorsal veins of the penis are blood vessels that drain the shaft, the skin and the glans of the human penis. They are typically located in the midline on the dorsal aspect of the penis and they comprise the superficial dorsal veinof the penis, that lies in the subcutaneous tissue of the shaft, and the deep dorsal veinof the penis, that lies beneath the deep fascia.

Nocturnal penile tumescence (NPT) is a spontaneous erection of the penis during sleep or when waking up. Along with nocturnal clitoral tumescence, it is also known as sleep-related erection. Colloquially, the term morning wood, or less commonly, morning glory is also used, although this is more commonly used to refer specifically to an erection beginning during sleep and persisting into the period just after waking. Men without physiological erectile dysfunction or severe depression experience nocturnal penile tumescence, usually three to five times during a period of sleep, typically during rapid eye movement sleep. Nocturnal penile tumescence is believed to contribute to penile health.

Venous leak, also called venogenic erectile dysfunction and penile venous insufficiency, is one category of vasculogenic impotence — a cause of erectile dysfunction in males. It affects all ages, being particularly awkward in young men. Much about venous leaks has not reached a consensus among the medical community, and many aspects of the condition, particularly its treatment strategies, are controversial. The prevalence of the condition is still unknown, although some sources claim it to be a common cause of erectile dysfunction.

<span class="mw-page-title-main">Tunica albuginea (penis)</span> Anatomical structure of the penis

The tunica albuginea is the fibrous envelope that extends the length of the corpus cavernosum penis and corpus spongiosum penis. It is a bi-layered structure that includes an outer longitudinal layer and an inner circular layer.

<span class="mw-page-title-main">Helicine arteries of penis</span> Arteries of the penis

The helicine arteries of penis are arteries in the penis. They are found in the corpora cavernosa penis.

<span class="mw-page-title-main">Human penis</span> Human male external reproductive organ

In human anatomy, the penis is an external male sex organ that serves as a passage for excretion of urine and ejaculation of semen. The main parts are the root, body, the epithelium of the penis including the shaft skin, and the foreskin covering the glans. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side. The urethra passes through the prostate gland, where it is joined by the ejaculatory ducts, and then through the penis. The urethra goes across the corpus spongiosum and ends at the tip of the glans as the opening, the urinary meatus.

<span class="mw-page-title-main">Body of penis</span> Part of the penis located outside of the pelvic cavity

The body or shaft of the penis is the free portion of the human penis that is located outside of the pelvic cavity. It is the continuation of the internal root, which is embedded in the pelvis and extends to the glans. It is made up of the two corpora cavernosa and the corpus spongiosum on the underside. The corpora cavernosa are intimately bound to one another with a dorsally fenestrated septum, which becomes a complete one before the penile crura. The body of the penis is homologous to the female clitoral body.

<span class="mw-page-title-main">Root of penis</span> Internal portion of the human penis

In human male anatomy, the radix or root of the penis is the internal and most proximal portion of the human penis that lies in the perineum. Unlike the pendulous body of the penis, which is suspended from the pubic symphysis, the root is attached to the pubic arch of the pelvis and is not visible externally. It is triradiate in form, consisting of three masses of erectile tissue; the two diverging crura, one on either side, and the median bulb of the penis or urethral bulb. Approximately one third to one half of the penis is embedded in the pelvis and can be felt through the scrotum and in the perineum.

<span class="mw-page-title-main">Clitoral erection</span> Physiological phenomenon involving the engorgement of the clitoris

Clitoral erection is a physiological phenomenon where the clitoris becomes enlarged and firm.

Penile ultrasonography is medical ultrasonography of the penis. Ultrasound is an excellent method for the study of the penis, such as indicated in trauma, priapism, erectile dysfunction or suspected Peyronie's disease.

<span class="mw-page-title-main">Glans insufficiency syndrome</span> Medical condition

Glans insufficiency syndrome, also known as the soft glans, cold glans, or glans insufficiency, is a medical condition that affects male individuals. This condition is characterized by the persistent inability of the glans penis to achieve and maintain an erect or turgid state during sexual arousal, remaining soft and cold. This condition can have an impact on a person's sexual function, including decreased sensitivity, difficulty in maintaining an erection, and overall quality of life.

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