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Penis
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Penis

The Penis (plural penises or penes) or phallus is the male copulatory organ, and, in mammals, the 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.

Table of contents
1 The human penis
2 Animal penises
3 See also
4 External link

The human penis

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erectile bone, instead relying entirely on engorgement with blood to reach its erect state, lacking the ability to be withdrawn into the groin, and being larger than average in proportion to body mass.

Structure

The human penis is built of three columns of erectile tissue:


An uncircumcised penis, a circumcised penis

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. It aids in sexual insertion, keeps the glans moist and provides a gliding action which is said to increase sexual pleasure for the man and his partner as well. (Sometimes it is removed by circumcision, see below.) The inner portion of the foreskin near the sulcus is a highly innervated area known as the ridged band. The area on the underside of the penis, where the foreskin attaches, 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 foreskin of the penis is homologous to the clitoral hood, the corpora cavernosa are homologous to the body of the clitoris, skin on the shaft of the penis is homologous to the labia minora, the corpus spongiosum is homologous to the vestibular bulbs beneath the labia minora, and the scrotum is homologous to the labia majora. The raphe does not exist in females, because there the two halves are not connected.

Erection

Erection is a stiffening and rising of the penis which occurs in the sexually aroused male. Erection enables sexual intercourse, though it is not essential, and some other sexual activities.

Although the average erect penis points approximately horizontally, it is common and normal for an erect penis to have 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.

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 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 predict the size of a fully aroused member. 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 known by the slang terms as "showers" and "growers" respectively.

See penis size for a more thorough treatment of this topic.

Normal variations of the penis

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:

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)

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.

Pudendal nerve entrapment is a condition characterized by pain on sitting and loss of penis (or clitoris) sensation and orgasm. In fact, sometimes there is a total loss of sensation and orgasm. The pudendal nerve can be damaged by narrow hard cycle seats and accidents. In females it commonly occurs as a result of childbirth. It is treated in France (the leaders in this area), America and Egypt.

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, preventative 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 disfunction or ED, is the inability to have and maintain a sufficiently firm erection for some activities. A wide variety of generally effective treatments are available. Diabetes is a leading cause, as is normal aging.

Developmental disorders of the penis

Hypospadias is a developmental disorder of the penis, where the meatus is positioned wrongly at birth. It is usually corrected by surgery.

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

Psychological disorders related to the penis

Body modification

The most common form of penile body modification is circumcision: for various cultural, religious, and more rarely medical reasons, the foreskin is partly or completely removed (usually during infancy). This procedure is controversial and is considered by some to be a form of mutilation. Removal of the same tissue in females is considered by far more people to be mutilation and is outlawed in many countries. Removal of the foreskin by circumcision also usually removes the ridged band and injures or removes the frenulum.

Less commonly, the penis is sometimes pierced and modified by other body art. Piercings of the penis include the Prince Albert piercing, the Apadravya piercing, the Ampallang piercing, the dydoe piercing, the frenum piercing and others.

Other physical modifications to the penis are also performed by some people, although they are considered very extreme. Apart from a penectomy, perhaps the most radical of these is subincision, in which the urethra is bifurcated along the underside of the penis. This modification was originally done among Australian Aborigines, although it is now done by some in the U.S. and Europe.

A small number of men who are circumcised attempt to restore their foreskin through various means, including surgical. This is called foreskin restoration.

Fears and reassurance

Possibly due to shame incolcated 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 China, Japan, and South-east Asia.

As mentioned earlier, the normal human penis has a raphe, what appears to be a scar leading from the foreskin (or from the scar that remains after circumcision) to the perineum along the underside of the penis and across the scrotum. 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. In order to close the urethra all the way to the tip of the penis, surgery must be used. Treatment may involve multiple surgeries, attending pain, and an air of mystery about the entire procedure if the adults involved feel shame about the "abnormal" condition of the infant. The reconstructive surgery may sometimes leave scars. The pain, fear, memory of visits to the hospital perhaps accompanied by an air of mystery, and (possibly) the scarring may cause the individual to believe that something terrible happened to him during his early childhood.

Adolescent males trying to masturbate successfully for the first time, and ignorant of the utility of lubricants, may chafe themselves and become fearful due to having learned "myths" about penile cancer. Other such beliefs involve the idea that masturbation can cause insanity or blindness.

Penis size myths and legends

(see also the more detailed article on penis size)

Many people are highly concerned with penis size. Some men seek penis enlargement, as they perceive that their penis is "too small". Studies have shown that most men seeking penis enlargement have normal-sized penises.

Many cultures have a persistent urban legend that the penis size of some minority groups is larger than the norm. In the United States, the minority group chosen are African-Americans. This appears not to be supported by anything other than anecdote. Fanon covers this subject in some detail in "Black Skin, White Masks", and tends to agree that this is a myth (which he backs up with statistics).

The only reliable penis-size studies commonly quoted in the literature are the Kinsey study, the UCSF study, and an Italian study, none of which even attempted to correlate with race. There is an ongoing government study in India as well (commissioned with the goal of helping reduce the high condom failure rate there), but it too is unlikely to answer the question. There have been many other studies and claims of varying rigor--for example, the LifeStyles condoms study, but they are generally flawed by selection bias.

Animal penises

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 in Reykjavik is devoted entirely to the study of animal penises.

See also

impotence, lingam, penis envy, priapism, list of severed penises, circumcision, sexual intercourse, sexual slang, penis sheath, and the movie Percy.

External link


Reproductive system
Female: Cervix - Clitoris - Fallopian tubes - Bartholin's glands - Hymen - Mammary glands - Ovaries - Skene's glands - Urethra - Uterus - Vagina
Male: Bulbourethral glands - Ejaculatory duct - Epididymis - Penis - Prostate - Seminal vesicles - testes - Urethra - Vas deferens