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Penis

Human penis
Labelled flaccid penis.jpg
Latin 'penis, penes'
Gray's subject #262 1247
Artery Dorsal artery of the penis, deep artery of the penis, artery of the urethral bulb
Vein Dorsal veins of the penis
Nerve Dorsal nerve of the penis
Lymph Superficial inguinal lymph nodes
Precursor Genital tubercle, Urogenital folds
MeSH Penis

The penis (plural penises, penes) is an external sexual organ of certain biologically male animals, in both vertebrates and invertebrates.

The penis is a reproductive organ, technically an intromittent organ, and for placental mammals, additionally serves as the external organ of urination. The penis is generally found on mammals and reptiles.

Contents

Etymology

The word "penis" is taken from the Latin word for "tail." Some derive that from Indo-European pesnis, and the Greek word πέος = "penis" from Indo-European pesos. Prior to the adoption of the Latin word in English the penis was referred to as a "yard". The Oxford English Dictionary cites an example of the word yard used in this sense from 1379,[1] and notes that in his Physical Dictionary of 1684, Steven Blankaart defined the word penis as "the Yard, made up of two nervous Bodies, the Channel, Nut, Skin, and Fore-skin, etc."[2]

The Latin word "phallus" (from Greek φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describe images, pictorial or carved, of the penis.[3]

The adjectival form of the word penis is penile. This adjective is commonly used in describing the male copulatory organ's various accessory structures that are commonly found in many kinds of invertebrate animals.

As with nearly any aspect of the human body that is involved in sexual or excretory functions, the word penis is considered humorous from a juvenile perspective, and there are many slang words and euphemisms for the penis.

Humans

Parts

  • Root of the penis (radix): It is the attached part, consisting of the bulb of penis in the middle and the crus of penis, one on either side of the bulb. It lies within the superficial perineal pouch.
  • Body of the penis (corpus): It has two surfaces: dorsal (posterosuperior in the erect penis), and ventral or urethral (facing downwards and backwards in the flaccid penis). The ventral surface is marked by a median raphe.

Structure

The human penis is made up of three columns of tissue: two corpora cavernosa lie next to each other on the dorsal side and one corpus spongiosum lies between them on the ventral side.

The enlarged and bulbous-shaped end of the corpus spongiosum forms the glans penis, which 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).

Anatomical diagram of a human penis

The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum, and its opening, known as the meatus (pronounced /miːˈeɪtəs/), lies on the tip of the glans penis. It is a passage both for urine and for the ejaculation of semen. Sperm are 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 underside of the penis, running from the meatus (opening of the urethra) across the scrotum to the perineum (area between scrotum and anus).

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

Penile growth and puberty

On entering puberty, the penis, scrotum and testicles will begin to develop. During the process, pubic hair grows above and around the penis. A large-scale study assessing penis size in thousands of 17–19 year old males found no difference in average penis size between 17 year olds and 19 year olds. From this, it can be concluded that penile growth is typically complete not later than age 17, and possibly earlier.[4]

Sexual homology

In short, this is a known list of sex organs that evolve from the same tissue in females and males.

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; the scrotum, homologous to the labia minora and labia majora; and the foreskin, homologous to the clitoral hood. The raphe does not exist in females, because there, the two halves are not connected.

Erection

Erection Development, with foreskin (skin covering at the end) sliding all the way back to reveal the rounded glans underneath

An erection is the stiffening and rising (see Erection Angle) of the penis, which occurs during sexual arousal, 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 than leaves the penis until an equilibrium is reached where an equal volume of blood flows into the dilated arteries and out of the constricted veins; a constant erectile size is achieved at this equilibrium.

Erection facilitates sexual intercourse though it is not essential for various other sexual activities.

Erection angle

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 or even horizontally straight forward, all depending on the tension of the suspensory ligament that holds it in position. The following table shows how common various erection angles are for a standing male. In the table, zero degrees is pointing straight up against the abdomen, 90 degrees is horizontal and pointing straight forward, while 180 degrees would be pointing straight down to the feet. An upward pointing angle is most common.[5]

Occurrence of Erection Angles
Angle (degrees) Percent
0–30 5
30–60 30
60–85 31
85–95 10
95–120 20
120–180 5

Ejaculation

Ejaculation is the ejecting of semen from the penis, and is usually accompanied by orgasm. A series of muscular contractions delivers semen, containing male gametes known as sperm cells or spermatozoa, from the penis (and into the vagina, if for reproductive intention via sexual intercourse). It is usually the result of sexual stimulation, which may include prostate stimulation. Rarely, it is due to prostatic disease. Ejaculation may occur spontaneously during sleep (known as a nocturnal emission or wet dream). Anejaculation is the condition of being unable to ejaculate.

Ejaculation has two phases: emission and ejaculation proper. The emission phase of the ejaculatory reflex is under control of the sympathetic nervous system, while the ejaculatory phase is under control of a spinal reflex at the level of the spinal nerves S2–4 via the pudendal nerve. A refractory period succeeds the ejaculation, and sexual stimulation precedes it.

Normal variations

  • Pearly penile papules are raised bumps of somewhat paler color around the base of the glans and are normal.
  • Fordyce's spots are small, raised, yellowish-white spots 1–2 mm in diameter that may appear on the penis.
  • 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 is an inability to retract the foreskin fully, is harmless in infancy and pre-pubescence, occurring in about 8% of boys at age 10. According to the British Medical Association, treatment (steroid cream, manual stretching) does not need to be considered until age 19.
  • Curvature: few penises are completely straight, with curves commonly seen in all directions (up, down, left, right). Sometimes the curve is very prominent but it rarely inhibits sexual intercourse. Curvature as great as 30° is considered normal and medical treatment is rarely considered unless the angle exceeds 45°. Changes to the curvature of a penis may be caused by Peyronie's disease.

Disorders

Paraphimosis is an inability to move the foreskin forward, over the glans. It can result from fluid trapped in a foreskin left retracted, perhaps following a medical procedure, or accumulation of fluid in the foreskin because of friction during vigorous sexual activity.

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.

Infection with the herpes virus can occur after sexual contact with an infected carrier; this may lead to the development of herpes sores.

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 bicycle seats and accidents.

Penile fracture can occur if the erect penis is bent excessively. A popping 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 is the inability to develop and maintain an erection sufficiently firm for satisfactory sexual performance. Diabetes is a leading cause, as is natural aging. A variety of treatments exist, including drugs, such as sildenafil citrate (marketed as Viagra), which works by vasodilation.

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. The condition has been associated with a variety of drugs including prostaglandin but not sildenafil (Viagra).[6]

Lymphangiosclerosis is a hardened lymph vessel, although it can feel like a hardened, almost calcified or fibrous, vein. It tends not to share the common blue tint with a vein however. It can be felt as a hardened lump or "vein" even when the penis is flaccid, and is even more prominent during an erection. It is considered a benign physical condition. It is fairly common and can follow a particularly vigorous sexual activity for men, and tends to go away if given rest and more gentle care, for example by use of lubricants.

Carcinoma of the penis is rare with a reported rate of 1 person in 100,000 in developed countries. Circumcision is said to protect against this disease but this notion remains controversial.[7]

Developmental disorders

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.[8] It is usually corrected by surgery. The Intersex Society of North America classifies hypospadias as an intersex condition. They believe in halting all medically unnecessary surgeries, including many of those done on people with hypospadias.

A micropenis is a very small penis caused by developmental or congenital problems. Diphallia, or penile duplication (PD), is the condition of having two penises. However, this disorder is exceedingly rare.

Alleged and observed psychological disorders

Altering the genitalia

The penis is sometimes pierced or decorated by other body art. Other than circumcision, genital alterations are almost universally elective and usually for the purpose of aesthetics or increased sensitivity. Piercings of the penis include the Prince Albert, the apadravya, the ampallang, the dydoe, and the frenum piercing. Foreskin restoration or stretching is a further form of body modification, as well as implants under the shaft of the penis.

Male to female transsexuals who undergo sex reassignment surgery, have their penis surgically modified into a neovagina. Female to male transsexuals may have a phalloplasty.

Other practices that 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.

Circumcision

A circumcised penis

The most common form of genital alteration is circumcision: removal of part or all of the foreskin for various cultural, religious, and more rarely medical reasons. For infant circumcision, modern devices such as the Gomco clamp, Plastibell, and Mogen clamp are available.[10]

With all modern devices the same basic procedure is followed. First, the amount of foreskin to be removed is estimated. The foreskin is then opened via the preputial orifice to reveal the glans underneath and ensured that it is normal. The inner lining of the foreskin (preputial epithelium) is then separated from its attachment to the glans. The device is then placed (this sometimes requires a dorsal slit) and remains there until blood flow has stopped. Finally, part, or all, of the foreskin is then removed.

Adult circumcisions are often performed without clamps and require 4 to 6 weeks of abstinence from masturbation or intercourse after the operation to allow the wound to heal.[11] In some African countries, male circumcision is often performed by non-medical personnel under unsterile conditions.[12] After hospital circumcision, the foreskin may be used in biomedical research,[13] consumer skin-care products,[14] skin grafts,[15][16][17] or β-interferon-based drugs.[18] In parts of Africa, the foreskin may be dipped in brandy and eaten by the patient, eaten by the circumciser, or fed to animals.[19] According to Jewish law, after a Brit milah, the foreskin should be buried.[20]

Dorsal view of a circumcised penis (semi-erect)

There is controversy surrounding circumcision. Advocates of circumcision argue, for example, that it provides important health advantages that outweigh the risks, has no substantial effects on sexual function, has a low complication rate when carried out by an experienced physician, and is best performed during the neonatal period.[21] Opponents of circumcision argue, for example, that it is a practice that has historically been, and continues to be, defended through the use of various myths; that it interferes with normal sexual function; is extremely painful; and, when performed on infants and children, violates the individual's human rights.[22]

The American Medical Association stated in 1999: "Virtually all current policy statements from specialty societies and medical organizations do not recommend routine neonatal circumcision, and support the provision of accurate and unbiased information to parents to inform their choice."[23]

The World Health Organization (WHO; 2007), the Joint United Nations Programme on HIV/AIDS (UNAIDS; 2007), and the Centers for Disease Control and Prevention (CDC; 2008) state that evidence indicates male circumcision significantly reduces the risk of HIV acquisition by men during penile-vaginal sex, but also state that circumcision only provides partial protection and should not replace other interventions to prevent transmission of HIV.[24][25]

Surgical replacement

The first successful penis allotransplant surgery was done in September 2005 in a military hospital in Guangzhou, China.[26] 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, age 23, was selected for the transplant. Despite atrophy of blood vessels and nerves, the arteries, veins, nerves and the corpora spongiosa were successfully matched. But, on 19 September, the surgery was reversed because of a severe psychological problem (rejection) by the recipient and his wife.[27]

In 2009 researchers Chen, Eberli, Yoo and Atala have produced bioengineered penises and implanted them on rabbits.[28] The animals were able to obtain erection and copulate, with 10 of 12 rabbits achieving ejaculation. This study shows that in the future it could be possible to produce artificial penises for replacement surgeries.

Size

Results from LifeStyles condom manufacturer's study of penis size, displayed in inches. The data is listed by percentile (i.e. a male with a 6 in (15.24 cm) penis is greater in length than 70 percent of those measured.)

While results vary across studies, the consensus is that the average erect human penis is approximately 12.9–15 cm (5.1–5.9 in) in length with 95% of adult males falling within the interval (10.7 cm, 19.1 cm) or (4.23 in, 7.53 in).[29][30][31] The typical girth or circumference is approximately 12.3 cm (4.84 in) when fully erect. The average penis size is slightly larger than the median size (i.e., most penises are below average in size).

A research project, summarizing dozens of published studies conducted by physicians of different nationalities, shows that, worldwide, erect-penis size averages vary between 9.6 and 16 cm (3.8 and 6.3 in). It has been suggested that this difference is caused not only by genetics but also by environmental factors such as culture, diet, chemical/pollution exposure,[32][33][34] etc. Endocrine disruption resulting from chemical exposure has been linked to genital deformation in both sexes (among many other problems).

The longest officially documented human penis was found by Doctor Robert Latou Dickinson. It was 34.3 cm (13.5 in) long and 15.9 cm (6.26 in) around.[35]

Species morphology

The penis of a stallion
A selection of penises from different species

As a general rule, an animal's penis (pizzle) 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 4 cm (1.5 in) in length; an adult chimpanzee, significantly smaller (in body size) than a gorilla, has a penis size about double that of the gorilla. In comparison, the human penis is larger than that of any other primate, both in proportion to body size and in absolute terms.[36]

The penis of a Bean weevil, Callosobruchus analis, is spiked. Researchers have found that each act of mating scars the female beetle's reproductive tract. Traumatic insemination is an extreme mating technique that some insects have developed.

As with any other bodily attribute, the length and girth of the penis can be highly variable between individuals of the same species. In many animals, especially mammals, the size of a flaccid penis is much smaller than its erect size.

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.[citation needed]

In the realm of absolute size, the smallest vertebrate penis belongs to the common shrew (5 mm or 0.2 inches). Accurate measurements of the blue whale are difficult to take because the whale's erect length can only be observed during mating.[citation needed]

The Icelandic Phallological Museum is devoted entirely to collecting penis specimens from all sorts of land and sea mammals.

Echidnas have a four-headed penis, but only two of the heads are used during mating. The other two heads "shut down" and do not grow in size. The heads used are swapped each time the mammal has sex.[37]

Most male birds (e.g., roosters and turkeys) have a cloaca (also present on the female), but not a penis. Among bird species with a penis are paleognathes (tinamous and ratites), Anatidae (ducks, geese and swans), and a very few other species (including ostriches and flamingoes). 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. It is usually partially feathered and in some species features spines and brush-like filaments, and in flaccid state curls up inside the cloaca. The Argentine Blue-bill has the largest penis in relation to body size of all vertebrates; while usually about half the body size (20 cm), a specimen with a penis 42.5 cm long is documented.

Male specimens of the Squamata order of reptiles have two paired organs called hemipenes. In fish, the gonopodium, andropodium, and claspers are various organs developed from modified fins. In male insects, the structure analogous to a penis is known as aedeagus. The male copulatory organ of various lower invertebrate animals is often called the cirrus.

The record for the largest penis to body size ratio is held by the barnacle. The barnacle's penis can grow to up to forty times its own body length. This enables them to reach the nearest female.[38]

Cultural aspects

Uses of non-human animal penises

  • Culinary, e.g., in Chinese gastronomy
  • Magical and therapeutic, in medicine and/or superstition, especially as an alleged aphrodisiac or even cure for impotence – for example the deer penis and tiger penis.
  • Punitive implements, such as the bull pizzle
  • Dog chew toys, such as the bull pizzle

Uses of human penises in cultural traditions

See also

References

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  2. ^ Simpson, John, ed (2005). "penis, n.". Oxford English Dictionary (Draft revision September 2005 ed.). Oxford University Press. Online edition. http://dictionary.oed.com/cgi/entry/50174565.  (1989 second edition: ISBN 978-0-19-861186-8, CD-ROM ISBN 978-0-19-861016-8)
  3. ^ Online Etymology Dictionary
  4. ^ Ponchietti R, Mondaini N, Bonafè M, Di Loro F, Biscioni S, Masieri L (February 2001). "Penile length and circumference: a study on 3,300 young Italian males". European Urology 39 (2): 183–6. doi:10.1159/000052434. PMID 11223678. 
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  19. ^ Anonymous (editorial) (1949-12-24). "A ritual operation". British Medical Journal 2: 1458–1459. ""...in parts of West Africa, where the operation is performed at about 8 years of age, the prepuce is dipped in brandy and eaten by the patient; in other districts the operator is enjoined to consume the fruits of his handiwork, and yet a further practice, in Madagascar, is to wrap the operation specifically in a banana leaf and feed it to a calf."". 
  20. ^ Shulchan Aruch, Yoreh Deah, 265:10
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  26. ^ Guangzhou Daily
  27. ^ Sample, Ian (2006-09-18). "Man rejects first penis transplant". The Guardian (London). http://www.guardian.co.uk/science/2006/sep/18/medicineandhealth.china. Retrieved 2010-05-22. 
  28. ^ Chen KL, Eberli D, Yoo JJ, Atala A (November 2009). "Regenerative Medicine Special Feature: Bioengineered corporal tissue for structural and functional restoration of the penis". Proceedings of the National Academy of Sciences of the United States of America 107 (8): 3346–50. doi:10.1073/pnas.0909367106. PMID 19915140. 
  29. ^ Wessells H, Lue TF, McAninch JW (September 1996). "Penile length in the flaccid and erect states: guidelines for penile augmentation". The Journal of Urology 156 (3): 995–7. doi:10.1016/S0022-5347(01)65682-9. PMID 8709382. 
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  31. ^ "ANSELL RESEARCH – The Penis Size Survey". March 2001. http://www.free-condom-stuff.com/education/research.htm. Retrieved 2006-07-13. 
  32. ^ Swan SH, Main KM, Liu F, et al. (August 2005). "Decrease in anogenital distance among male infants with prenatal phthalate exposure". Environmental Health Perspectives 113 (8): 1056–61. doi:10.1289/ehp.8100. PMID 16079079. PMC 1280349. http://ehp.niehs.nih.gov/members/2005/8100/8100.html. 
  33. ^ Montague, Peter. "PCBs Diminish Penis Size". Rachel's Hazardous Waste News 372. http://copa.org/library/articles/rhwn/penis.htm. 
  34. ^ "Hormone Hell". DISCOVER. http://discovermagazine.com/1996/sep/hormonehell865/. Retrieved 2008-04-05. 
  35. ^ Dickinson, R.L. (1940). The Sex Life of the Unmarried Adult. New York: Vanguard Press. [page needed]
  36. ^ Human penis is larger than that of any other primate. Darwin's legacy: scenarios in human evolution, p. 121. S.T. Parker, K.E. Jaffe.
  37. ^ Shultz, N. (2007-10-26). "Exhibitionist spiny anteater reveals bizarre penis". New Scientist website. http://environment.newscientist.com/article.ns?id=dn12838. Retrieved 2006-10-27. 
  38. ^ The Largest Penis in the World – Both for humans and animals, size does matter! – Softpedia
  39. ^ Fritscher, Jack; Anton Szandor La Vey (2004). Popular witchcraft: straight from the witch's mouth. Popular Press. pp. 161. ISBN 9780299203047. http://books.google.com/?id=OZm3tdWMgbIC&pg=PA161. 

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