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The penis (plural penises or penes) or phallus is the external male copulatory organ, and, in mammals, the external male organ of urination. It is homologous to the female clitoris, as it develops from the same embryonic structure. The penis is capable of erection for use in copulation.

The human penis

The human penis differs from some other mammalian penises by lacking a baculum, or erectile bone, instead relying entirely on engorgement with blood to reach its erect state. It also lacks the ability to be withdrawn into the groin, and is larger-than-average in proportion to body mass.

Structure

File:Male anatomy.png
Illustration of the human male anatomy.

The human penis is made up of three columns of erectile tissue:

The corpus spongiosum lies on the underside (known also as the ventral side) of the penis; the two corpora cavernosa lie next to each other on the upper side (dorsal side).

The end of the corpus spongiosum is enlarged and cone-shaped and forms the glans penis. The glans supports the foreskin or prepuce, a loose fold of skin that in adults can retract to expose the glans. The area on the underside of the penis, where the foreskin is attached, is called the frenum (or frenulum).

The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum and its opening, known as the meatus, lies on the tip of the glans penis. It is both a passage for urine and for the ejaculation of semen. Sperm is produced in the testes and stored in the attached epididymis. During ejaculation, sperm are propelled up the vas deferens, two ducts that pass over and behind the bladder. Fluids are added by the seminal vesicles and the vas deferens turns into the ejaculatory ducts which join the urethra inside the prostate gland. The prostate as well as the bulbourethral glands add further secretions, and the semen is expelled through the penis.

The raphe is the visible ridge between the lateral halves of the penis, found on the ventral or under side of the penis, running from the meatus (opening of the urethra) across the scrotum to the perineum (area between scrotum and anus).

Relation to female genitals

The glans of the penis is homologous to the clitoral glans, the corpora cavernosa are homologous to the body of the clitoris, the corpus spongiosum is homologous to the vestibular bulbs beneath the labia minora, and the scrotum is homologous to the labia minora, labia majora and clitoral hood. The raphe does not exist in females, because there the two halves are not connected.

Erection

Main article: Erection

File:Flaccid and erect human penis.jpg
An uncircumcised penis in both flaccid and fully erect states, respectively.

Erection is the stiffening and rising of the penis which occurs in the sexually aroused male, though it can also happen during non-sexual, and at times awkward situations. The primary physiological mechanism that brings about erection is the autonomic dilation of arteries supplying blood to the penis, which allows more blood to fill the three spongy erectile tissue chambers in the penis, causing it to lengthen and stiffen. The now engorged erectile tissue presses against and constricts the veins that carry blood away from the penis. More blood enters the penis than leaves until an equilibrium is reached (equal volume of blood flowing into the dilated arteries and out of the constricted veins). A constant erectile size is achieved at equilibrium.

The vasodilating effects of the drug sildenafil citrate (marketed as Viagra®) have been found to be efficacious in treating certain forms of impotence and erectile dysfunction.

Erection enables, although is not essential for, sexual intercourse and some other sexual activities. Although the average erect penis points approximately horizontally, it is common and normal for an erect penis to have any of a wide range of vertical angles, from nearly vertically upward to nearly vertically downward, depending on the tension of the suspensory ligament which holds it in position when erect.

Size

See main article penis size

In comparison to body size, the human male penis is among the largest of the primates. One study has found that the average human penis is 2-5 inches (13 cm) in length when fully engorged with blood during arousal, though this varies quite a bit. The size of a flaccid human penis has an even greater variation in both length and width that often does not correspond to the size when fully aroused. When a man with a relatively large flaccid penis has a normal or below average length penis when fully aroused, or when a man with a relatively small flaccid penis has a normal or above average length penis when fully aroused, they are sometimes known by the slang terms "showers" and "growers" respectively.

Normal variations

Depending on temperature, a flaccid (not erect) penis of normal size can withdraw almost completely within the body. Such a penis will be of normal size when erect - not unusually small.

Other variations:

  • Pearly penile papules are raised bumps of somewhat paler color around the base of the glans and are normal. (Picture of them on a human penis)
  • Fordyce's spots are small, raised, yellowish-white spots 1-2mm in diameter that may appear on the penis, as well as the inner surface and vermilion border of the lips of the face, and are normal. See Pearly penile papules for a picture.
  • Sebaceous prominences are similar raised bumps on the shaft of the penis, located at the sebaceous glands and are normal.
  • Phimosis, an inability to retract the foreskin fully, is harmless in infants and pre-pubescent males, occurring in about 8 percent of boys at age 10. See Phimosis for a more complete discussion.

Disorders affecting the penis

Oedema (swelling) of the foreskin can result from sexual activity, including masturbation. It appears worrying but so long as the foreskin is in its normal position and blood flow is present it's harmless. See paraphimosis for situations where the foreskin can't be moved to its normal position or the swelling persists. If the condition recurrs regularly, medical advice should be obtained, since it can be a symptom of conditions such as chronic heart disease. (description of a case resulting from sexual activity, with pictures)

Pathological Phimosis--where a non-retracting foreskin is accompanied by pain or physiological distress, or affects physical hygiene, requires treatment which can be surgical or non-surgical according to the severity of the condition. See Phimosis for more details.

Paraphimosis is an inability to move the foreskin forward over the glans. It can result from fluid trapped in a foreskin which is left retracted, perhaps following a medical procedure, or accumulation of fluid in the foreskin because of friction during vigorous sexual activity. Applying pressure to compress the glans, then moving the foreskin to its normal position is the initial procedure to follow, perhaps with the assistance of a lubricant. Placing the penis in normal granulated sugar can reduce the swelling via osmosis. If the condition persists for more than several hours or there's a sign of lack of blood flow, a hard glans with no erection or an inability to urinate, it should be treated as a medical emergency.

In Peyronie's disease, anomalous scar tissue grows in the soft tissue of the penis, causing curvature. Severe cases can benefit from surgical correction.

A thrombosis can occur during periods of frequent and prolonged sexual activity, especially fellatio. It is usually harmless and self-corrects within a few weeks.

Pudendal nerve entrapment is a condition characterized by pain on sitting and loss of penile (or clitoral) sensation and orgasm. Occasionally there is a total loss of sensation and orgasm. The pudendal nerve can be damaged by narrow hard cycle seats and accidents.

Penile fracture can occur if the erect penis is bent excessively. A pop or cracking sound and pain is normally associated with this event. Emergency medical assistance should be obtained, after which long term consequences are usually prevented. In one study [1], the few patients suffering permanent penile curvature were the ones who had waited longest before seeking treatment.

In diabetes, peripheral neuropathy can cause tingling in the penile skin and possibly reduced or completely absent sensation. The reduced sensations can lead to injuries for either partner and their absence can make it impossible to have sexual pleasure through stimulation of the penis. Since the problems are caused by permanent nerve damage, preventive treatment through good control of the diabetes is the primary treatment. Some limited recovery may be possible through improved diabetes control.

Impotence, sometimes called erectile dysfunction or ED, is the inability to have and maintain an erection sufficiently firm for satisfactory sexual performance. A wide variety of generally effective treatments are available. Diabetes is a leading cause, as is normal aging.

Priapism is a painful and potentially harmful medical condition in which the erect penis does not return to its flaccid state. The causative mechanisms are poorly understood but involve complex neurological and vascular factors. Potential complications include ischaemia, thrombosis, and impotence. In serious cases the condition may result in gangrene, which may necessitate amputation.

Developmental disorders of the penis

Hypospadias is a developmental disorder where the meatus is positioned wrongly at birth. Hypospadias can also occur iatrogenically by the downward pressure of an indwelling urethral catheter.[2] It is usually corrected by surgery.

A micropenis is a very small penis caused by developmental problems.

Altering the male genitalia

File:Circpn - circumcised penis.jpg
An uncircumcised penis, a circumcised penis

Main article: genital modification and mutilation

The most prevalent form of genital alteration in some countries is circumcision: for various cultural, religious, and more rarely medical reasons, part or all of the foreskin is removed. In many cases, such as in some United States hospitals, the frenulum and part of the shaft skin is also removed.

Less commonly, the penis is sometimes pierced or decorated by other body art, usually for the purpose of aesthetics, or increased sensitivity. Piercings of the penis include the Prince Albert piercing, the Apadravya piercing, the Ampallang piercing, the dydoe piercing, and the frenum piercing. Foreskin restoration or stretching is a further form of body modification.

Other practices which alter the penis are also performed, although they are rare in Western societies without a diagnosed medical condition. Apart from a penectomy, perhaps the most radical of these is subincision, in which the urethra is split along the underside of the penis. Subincision originated among Australian Aborigines, although it is now done by some in the U.S. and Europe.

Fears and reassurance

Possibly due to shame inculcated in regard to genitalia, some people suffer from misunderstandings and resultant fear.

Penis panic is a kind of hysteria that appears to be culturally conditioned and largely limited to Sudan, China, Japan, and South-east Asia.

As mentioned earlier, the raphe is the visible ridge between the lateral halves of the penis, found on the ventral or under side of the penis, running from the meatus (opening of the urethra) across the scrotum to the perineum (area between scrotum and anus). This "scar" is actually the "biological zipper" that closes the urethra during the normal course of fetal development. When the urethra does not close normally, the resulting condition is called hypospadias. Surgery is required to close the urethra. Treatment may involve multiple surgeries and attendant pain.

Other beliefs involve the idea that masturbation can cause insanity or blindness.

In childhood, according to the study Paediatric penile trauma, male circumcision is the most common form of genital trauma; it occurred in two-thirds of the physical traumas examined (El-Bahnasawy 2002) [3]

Non-human penises

An elephant's penis is proportionally large.

Most marsupials, except for the two largest species of kangaroos, have a bifurcated penis. That is, it separates into two separate columns, and so the penis terminates in two ends. The dolphin has prehensile control over his penis, so he sometimes uses it as an sensory appendage with which to probe the ocean floor. The barnacle has the longest penis for its own length: up to twenty times the length of the animal.

The Icelandic Phallological Museum is devoted entirely to collecting penis specimens from all the land and sea mammals living in Iceland. The museum has received a legally-certified gift token for a future specimen belonging to Homo sapiens.

See also

Wikimedia Commons has media related to Penis.
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