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The penis (plural penises) or phallus (plural phalli) is the external male sexual organ of some animals, and, in mammals, the external male organ of urination.

In humans, the penis is homologous to the female clitoris, as it develops from the same embryonic structure. It is capable of erection for use in copulation.

Linguistics

Etymology

The word is derived from the Latin word for tail, also used to describe the organ, "penis". The Latin word "phallus" (from the Greek "phallos") is sometimes used to describe the penis, though the word originally was used to describe images, pictoral or carved, of the penis .

Some derive the Latin word penis from earlier *pesnis, and the Greek word peos = "penis" from earlier *pesos.

Synonyms

For a far more exhaustive and multi-lingual thesaurus, see the entry on WikiSaurus.

The human penis

The human penis differs from those of some other mammals. It has no baculum, or erectile bone; instead it relies entirely on engorgement with blood to reach its erect state. It cannot be withdrawn into the groin, and is larger than average in proportion to body mass.

Structure

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

• the two corpora cavernosa (singular: corpus cavernosum) and
• one corpus spongiosum

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

Erection is the stiffening and rising of the penis which occurs in the sexually aroused male, though it can also happen in non-sexual 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.

Inability to attain a satisfactory erection is known medically as erectile dysfunction, or ED in short. A drug against this condition, sildenafil citrate (marketed as Viagra®) works by vasodilation.

Erection facilitates sexual intercourse though it is not essential for some other sexual activities. Although many erect penises point upwards (see illustration), it is common and normal for the erect penis to point nearly vertically upwards or nearly vertically downwards, depending on the tension of the suspensory ligament that holds it in position. Stiffness of erectile angle also varies.

Size

See main article Human penis size

As a general rule, an animal's penis is proportional to its body size, but this varies greatly between species — even between closely related species. For example, an adult gorilla's erect penis is about 1.5 inches (4 cm) in length; an adult chimpanzee, significantly smaller (in body size) than a gorilla, has a penis size about double that of the gorilla. The common chimpanzee, or pan troglodytes, has the third largest penis size among the great apes: in comparison, the human penis is somewhat larger than the common chimpanzee, both proportional to body size and in absolute terms; one study has found that the average human penis is 5 inches (12.7 cm) in length when fully engorged with blood during arousal.

As with any other bodily attribute, the length and girth of the penis is highly variable between individuals of the same species. In many animals, especially mammals, the size of a flaccid penis is much smaller than its size when erect. In humans and some other species, flaccid vs. erect penis size varies greatly between individuals, such that penis size when flaccid is not a reliable predictor of size when erect.

Except for extreme cases at either end of the size spectrum, penis size does not correspond strongly to reproductive ability in almost any species.

Normal variations

Depending on temperature, a flaccid (not erect) penis of average size can withdraw almost completely within the body. During erection the penis will return to its normal (erect) size.

Other variations:

• Pearly penile papules are raised bumps of somewhat paler colour around the base of the glans and are normal. See sidebar picture and picture at article.
• 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.
• Sebaceous prominences are raised bumps similar to Fordyce's spots 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.

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 depending on the seriousness 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 is 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. Prompt medical attention lowers likelihood of permanent penile curvature.

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.

Erectile dysfunction, formerly known as impotence, 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. It is usually corrected by surgery.

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

Penis replacement

The first successful penis allotransplant surgery was done on September 2005 in a military hospital in Guangzhou, China. (Guangzhou Daily, source) A man at 44 sustained an injury after an accident and his penis was severed. Urination became difficult as his urethra was partly blocked. A newly brain-dead man, at 23, was tracked down and his penis selected for the transplant. Despite atrophy of blood vessels and nerves after a protracted period of time had elapsed (exact length not given), the arteries, veins, nerves and the corpora spongiosa were successfully matched. After seven hours' surgery, the penis regained its function and even managed to attain erection.

The difficulty in this surgery is attributable to these demands: The shape of the donor's penis must sufficiently match that of the receiver's and the duration between detaching and attaching the penis must be short.

It remains to be observed if infection or rejection has occurred after the transplant and how much sexual function the man would regain. Urination ability, however, is predicted to resume after a week.

Alleged and observed penis-related psychological disorders

• penis panic (koro in Malaysian/Indonesian) - delusion of shrinkage of the penis and retraction into the body.
• penis envy - the contested Freudian belief of a woman envying men for having a penis.

Altering the male genitalia

Uncircumcised penis (L), circumcised penis (R).

Main article: genital modification and mutilation

The most prevalent form of genital alteration in some countries is circumcision: removal of part or all of the foreskin for various cultural, religious, and more rarely medical reasons. In many cases, such as in some United States hospitals, the frenulum and part of the shaft skin is also removed. Circumcision likely arose in the Middle East desert to avoid the effects of desert sand getting under the foreskin; the practice has been incorporated into organised religions which originated in desert areas such as Islam and Judaism. Secular reasons for circumcision, however, have been disputed.

Less commonly, the penis is sometimes pierced or decorated by other body art. Such alterations are almost universally elective and 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 Southeast 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 ridge 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)

Non-human penises

Most marsupials, except for the two largest species of kangaroos, have a bifurcated penis. That is, it separates into two columns, and so the penis has two ends. The barnacle has the longest penis for its own length: up to twenty times the length of the animal. Urban legend alleges that the dolphin has prehensile control over his penis. In the realm of absolute size, the smallest penis belongs to the common shrew (5 mm or 0.2 inches). The largest penis belongs to the blue whale estimated at over 2 m (about 6 feet). Accurate measurements are difficult to take because the whale's erect length can only be observed during mating.

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.

In male insects, the structure homologous to a penis is known as aedeagus. Male specimes of the Squamata order of reptiles have two paired organs called hemipenes.

Gorillas have relatively small penises, so it is an often used subtle insult in countries such as Australia to insinuate or directly state that one is 'hung like a gorilla'.

Cultural aspects involving penises

Uses of animal penises

• Culinary, e.g., in Chinese gastronomy
• Magical and therapeutic, in medicine and/or superstition, especially as an aphrodisiac or even cure against impotence
• Also used for dog toys, such as the bull pizzle

Uses of human penises in cultural traditions

• Esthetical, e.g., Body modification
• For the symbolic and artistic use, see under phallus
• In humor, e.g., in scatology - considered indecent or completely taboo in various cultures

See also

• Baculum
• Circumcision
• Impotence
• Masturbation
• Penis Day
• Penis enlargement
• Penis envy
• Penis game
• Penis panic
• Penis removal
• Penis sheath
• Phallic symbol
• Priapism
• Sexual intercourse
• Smiling Bob
• PDE5 - Viagra, Cialis and Levitra
• WikiSaurus:penis — the WikiSaurus list of synonyms and slang words for penis in many languages

External links

• The Icelandic Phallological Museum, collection of over one hundred and fifty penises and penile parts belonging to almost all the land and sea mammals that can be found in Iceland
• Penis Size Chart (actual-size chart suitable for printing out and comparing)
• AfraidToAsk.com's Male Genitalia Guide
• All About the Penis
• The Penis Website
• Shagnasty's Penis Owners Manual
• A Website About the Penis and Male Sexuality
• Summary Penis Size data
• Details Penis Size Data
• Kinsey Institute on the penis
• Ask Men about penis
• A Glossary of the Penis Note: This is an anti-circumcision website.
• Anatomy of the Penis - Mechanics of Intercourse Note: This is an anti-circumcision website.
• A gallery of uncircumcised penises

• Andrology
• Reproductive system
• Sexual anatomy