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The human penis is an external male
intromittent organ An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs e ...
that additionally serves as the urinary duct. The main parts are the root (radix); the body (corpus); and the
epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
of the
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...
including the shaft skin and the foreskin (prepuce) covering the
glans penis In male human anatomy, the glans penis, commonly referred to as the glans, is the bulbous structure at the distal end of the human penis that is the human male's most sensitive erogenous zone and their primary anatomical source of sexual pl ...
. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the
dorsal side Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...
and corpus spongiosum between them on the
ventral side Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
. The human male
urethra The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra ...
passes through the
prostate gland The prostate is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, chemically, and physi ...
, where it is joined by the ejaculatory duct, and then through the penis. The urethra traverses the corpus spongiosum, and its opening, the meatus (), lies on the tip of the glans penis. It is a passage both for
urination Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...
and
ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential compo ...
of
semen Semen, also known as seminal fluid, is an organic bodily fluid created to contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. Sem ...
(''see'' male reproductive system.) Most of the penis develops from the same embryonic tissue as the
clitoris The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the op ...
in females. The skin around the penis and the urethra share the same embryonic origin as the labia minora in females. An
erection 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, a ...
is the stiffening expansion and orthogonal reorientation of the penis, which occurs during sexual arousal. Erections can occur in non-sexual situations; spontaneous non-sexual erections frequently occur during adolescence and sleep. In its flaccid state the penis is smaller, gives to pressure, and the glans is covered by the foreskin. In its fully erect state the corpus becomes rigid and the glans becomes engorged but not rigid. An erect penis may be straight or curved and may point at an upward angle, a downward angle, or straight ahead. , the average erect human penis is 13.12 cm (5.17 inches) long and has a circumference of 11.66 cm (4.59 inches). Neither age nor size of the flaccid penis accurately predicts erectile length. There are several common body modifications to the penis, including
circumcision Circumcision is a procedure that removes the foreskin from the human penis. In the most common form of the operation, the foreskin is extended with forceps, then a circumcision device may be placed, after which the foreskin is excised. Top ...
and
piercings Body piercing, which is a form of body modification, is the practice of puncturing or cutting a part of the human body, creating an opening in which jewelry may be worn, or where an Implant (medicine), implant could be inserted. The word ''pier ...
.


Anatomy


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 For their anterior three-fourths the corpora cavernosa penis lie in intimate apposition with one another, but behind they diverge in the form of two tapering processes, known as the crura, which are firmly connected to the ischial rami. Traced f ...
, one on either side of the bulb. It lies within the superficial perineal pouch. The crus of penis is attached to the pubic arch. * Body of the penis (corpus): The pendulous part of the penis. 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 the penile raphe. The base of the body of penis is supported by the suspensory ligament which is attached to the pubic symphysis. *
Epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
of the penis consists of the shaft
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...
, the foreskin, and the
preputial mucosa The preputial mucosa of the penis is the epithelium of the inside of the prepuce, or foreskin. To differentiate it from the cutaneous skin of the outside of the prepuce, it is sometimes referred to as the inner mucosa. It starts at the ridged ...
on the inside of the foreskin and covering the
glans penis In male human anatomy, the glans penis, commonly referred to as the glans, is the bulbous structure at the distal end of the human penis that is the human male's most sensitive erogenous zone and their primary anatomical source of sexual pl ...
. The epithelium is not attached to the underlying shaft so it is free to glide to and fro.


Structure

The human penis is made up of three columns of tissue: two corpora cavernosa lie next to each other on the
dorsal side Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...
and one corpus spongiosum lies between them on the
ventral side Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
. The corpus cavernosum forms most of the penis and contains blood vessels that fill with blood to help make an erection. The crus of penis is the proximal parts of the corpora cavernosum. The corpus spongiosum is an erectile tissue surrounding the urethra. The proximal parts of the corpus spongiosum form the bulb of penis and the distal ends form the glans penis. The enlarged and bulbous-shaped end of the corpus spongiosum forms the glans penis with two specific types of sinusoids, 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. The rounded base of the glans is called the corona. The
perineal raphe The perineal raphe is a visible line or ridge of tissue on the body that extends from the anus through the perineum to scrotum (male) or labia majora (female). It is found in both males and females, arises from the fusion of the urogenital folds, a ...
is the noticeable line along the underside of the penis. The
urethra The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra ...
, which is the last part of the
urinary tract The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, c ...
, traverses the corpus spongiosum, and its opening, known as the meatus , lies on the tip of the glans penis. It is a passage both for urine and for the ejaculation of semen.
Sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, ...
are produced in the
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...
and stored in the attached
epididymis The epididymis (; plural: epididymides or ) is a tube that connects a testicle to a vas deferens in the male reproductive system. It is a single, narrow, tightly-coiled tube in adult humans, in length. It serves as an interconnection between the ...
. 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 gland The bulbourethral glands or Cowper's glands (named for English anatomist William Cowper) are two small exocrine glands in the reproductive system of many male mammals (of all domesticated animals, they are absent only in dogs). They are homolo ...
s add further secretions, and the semen is expelled through the penis. The raphe is the visible ridge between the
lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...
halves of the penis, found on the ventral or underside of the penis, running from the meatus (opening of the urethra) across the
scrotum The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum co ...
to the
perineum The perineum in humans is the space between the anus and scrotum in the male, or between the anus and the vulva in the female. The perineum is the region of the body between the pubic symphysis (pubic arch) and the coccyx (tail bone), includi ...
(area between scrotum and
anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
). The human penis differs from those of most other mammals, as it has no
baculum The baculum (also penis bone, penile bone, or ''os penis'', ''os genitale'' or ''os priapi'') is a bone found in the penis of many placental mammals. It is absent from the human penis, but present in the penises of some primates, such as the ...
(or erectile bone) and instead relies entirely on engorgement with blood to reach its erect state. A distal ligament buttresses the glans penis and plays an integral role to the penile fibroskeleton, and the structure is called "os analog," a term coined by Geng Long Hsu in the Encyclopedia of Reproduction. It is a remnant of
baculum The baculum (also penis bone, penile bone, or ''os penis'', ''os genitale'' or ''os priapi'') is a bone found in the penis of many placental mammals. It is absent from the human penis, but present in the penises of some primates, such as the ...
evolved likely due to change in mating practice. The human penis cannot be withdrawn into the groin, and it is larger than average in the animal kingdom in proportion to body mass. The human penis is reciprocating from a cotton soft to a bony rigidity resulting from penile arterial flow varied between 2–3 to 60-80 mL/Min implies the most ideal milieu to apply Pascal's law in the entire human body; the overall structure is unique.


Size

Penile measurements vary, with studies that rely on self-measurement reporting a significantly higher average size than those which rely on measurements taken by health professional. A 2015 systematic review of 15,521 men in which the subjects were measured by health professionals concluded that the average length of an erect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches). Among all primates, the human penis is the largest in girth, but is comparable to the
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative t ...
penis and the penises of certain other primates in length. Penis size is affected by
genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar work ...
, but also by environmental factors such as
fertility medication Fertility medications, also known as fertility drugs, are medications which enhance reproductive fertility. For women, fertility medication is used to stimulate follicle development of the ovary. There are very few fertility medication options a ...
s and chemical/pollution exposure. The longest officially documented human penis was found by physician
Robert Latou Dickinson Robert Latou Dickinson (1861–1950) was an American obstetrician and gynecologist, surgeon, maternal health educator, artist, sculptor and medical illustrator, and research scientist. Early life Robert Latou Dickinson was born on February 21, ...
. It was long and in circumference.


Normal variations

* ''Pearly penile papules'' are raised bumps of somewhat paler color around the base (sulcus) of the glans which typically develop in men aged 20 to 40. As of 1999, different studies had produced estimates of incidence ranging from 8 to 48 percent of all men. They may be mistaken for warts, but are not harmful or infectious and do not require treatment. *
Fordyce's spot Fordyce spots (also termed Fordyce granules)James, William; Berger, Timothy; Elston, Dirk (2005). ''Andrews' Diseases of the Skin: Clinical Dermatology''. (10th ed.). Saunders. . are visible sebaceous glands that are present in most individuals ...
s are small, raised, yellowish-white spots 1–2 mm in diameter that may appear on the penis, which again are common and not infectious. *''Sebaceous prominences'' are raised bumps similar to Fordyce's spots on the shaft of the penis, located at the
sebaceous gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest n ...
s and are normal. * Phimosis is an inability to retract the foreskin fully. It is normal and harmless in infancy and pre-pubescence, occurring in about 8% of boys at age 10. According to the British Medical Association, treatment (topical steroid cream and/or 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 Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal pene ...
. 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 Peyronie's disease is a connective tissue disorder involving the growth of fibrous plaques in the soft tissue of the penis. Specifically, scar tissue forms in the tunica albuginea, the thick sheath of tissue surrounding the corpora cavernosa, c ...
.


Development


Differences between female and male organs

In the developing fetus, the genital tubercle develops into the glans of the penis in males and into the clitoral glans in females; they are homologous. The urogenital fold develops into the skin around the shaft of the penis and the urethra in males and into the labia minora in females.Keith L. Moore, T. V. N. Persaud, Mark G. Torchia, The Developing Human: Clinically Oriented Embryology 10th Ed. Elsevier Health Sciences, 2015
pp 267-69
/ref> 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 majora The labia majora (singular: ''labium majus'') are two prominent longitudinal cutaneous folds that extend downward and backward from the mons pubis to the perineum. Together with the labia minora they form the labia of the vulva. The labia maj ...
; and the foreskin, homologous to the clitoral hood. The raphe does not exist in females, because there, the two halves are not connected.


Growth in puberty

On entering
puberty Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a ...
, the penis, scrotum and
testicles A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testosteron ...
will enlarge toward maturity. During the process,
pubic hair Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bon ...
grows above and around the penis. A large-scale study assessing penis size in thousands of 17- to 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.


Physiological functions


Urination

In males the expulsion of urine from the body is done through the penis. The urethra drains the bladder through the
prostate gland The prostate is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, chemically, and physi ...
where it is joined by the ejaculatory duct, and then onward to the penis. At the root of the penis (the proximal end of the corpus spongiosum) lies the external sphincter muscle. This is a small sphincter of striated muscle tissue and is in healthy males under voluntary control. Relaxing the urethra sphincter allows the urine in the upper urethra to enter the penis properly and thus empty the urinary bladder. Physiologically, urination involves coordination between the
central Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known a ...
, autonomic, and somatic nervous systems. In infants, some elderly individuals, and those with neurological injury, urination may occur as an involuntary reflex. Brain centers that regulate urination include the pontine micturition center, periaqueductal gray, and the
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...
. During erection, these centers block the relaxation of the sphincter muscles, so as to act as a physiological separation of the excretory and reproductive function of the penis, and preventing urine from entering the upper portion of the urethra during ejaculation.


Voiding position

The distal section of the urethra allows a human male to direct the stream of urine by holding the penis. This flexibility allows the male to choose the posture in which to urinate. In cultures where more than a minimum of clothing is worn, the penis allows the male to urinate while standing without removing much of the clothing. It is customary for some boys and men to urinate in seated or crouched positions. The preferred position may be influenced by cultural or religious beliefs. Research on the medical superiority of either position exists, but the data are heterogenic. A
meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting m ...
summarizing the evidence found no superior position for young, healthy males. For elderly males with
LUTS Lower urinary tract symptoms (LUTS) refer to a group of clinical symptoms involving the bladder, urinary sphincter, urethra and, in men, the prostate. The term is more commonly applied to men—over 40% of older men are afected—but lower urin ...
, however, the sitting position when compared to the standing position is differentiated by the following: * the post void residual volume (PVR, ml) was significantly decreased * the maximum urinary flow (Qmax, ml/s) was increased * the voiding time (VT, s) was decreased This urodynamic profile is related to a lower risk of urologic complications, such as cystitis and
bladder stones A bladder stone is a stone found in the urinary bladder. Signs and symptoms Bladder stones are small mineral deposits that can form in the bladder. In most cases bladder stones develop when the urine becomes very concentrated or when one is d ...
.


Erection

An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. Spontaneous erections frequently occur during adolescence due to friction with clothing, a full bladder or large intestine, hormone fluctuations, nervousness, and undressing in a nonsexual situation. It is also normal for erections to occur during sleep and upon waking. (See nocturnal penile tumescence.) The primary physiological mechanism that brings about erection is the autonomic
dilation Dilation (or dilatation) may refer to: Physiology or medicine * Cervical dilation, the widening of the cervix in childbirth, miscarriage etc. * Coronary dilation, or coronary reflex * Dilation and curettage, the opening of the cervix and surgi ...
of
arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...
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. The scrotum will usually tighten during erection. 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, out of a sample of 81 males aged 21 through 67. 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.


Ejaculation

Ejaculation is the ejection of semen from the penis. It is usually accompanied by
orgasm Orgasm (from Greek , ; "excitement, swelling") or sexual climax is the sudden discharge of accumulated sexual excitement during the sexual response cycle, resulting in rhythmic, involuntary muscular contractions in the pelvic region chara ...
. A series of muscular contractions delivers semen, containing male
gametes A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
known as sperm cells or
spermatozoa A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromos ...
, from the penis. Ejaculation usually happens as the result of sexual stimulation, but it can be due to prostatic disease in rare cases. 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 The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of t ...
, while the ejaculatory phase is under control of a spinal reflex at the level of the
spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
s S2–4 via the pudendal nerve. A refractory period succeeds the ejaculation, and sexual stimulation precedes it.


Evolved adaptations

The human penis has been argued to have several evolutionary adaptations. The purpose of these adaptations is to maximise reproductive success and minimise sperm competition. Sperm competition is where the sperm of two males simultaneously resides within the reproductive tract of a female and they compete to fertilise the egg. If sperm competition results in the rival male's sperm fertilising the egg,
cuckold A cuckold is the husband of an adulterous wife; the wife of an adulterous husband is a cuckquean. In biology, a cuckold is a male who unwittingly invests parental effort in juveniles who are not genetically his offspring. A husband who is a ...
ry could occur. This is the process whereby males unwittingly invest their resources into offspring of another male and, evolutionarily speaking, should be avoided. The most researched human penis adaptations are testis and
penis size Human penises vary in size on a number of measures, including length and circumference when flaccid and erect. Besides the natural variability of human penises in general, there are factors that lead to minor variations in a particular male, ...
, ejaculate adjustment and semen displacement.


Testis and penis size

Evolution has caused sexually selected adaptations to occur in
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...
and testis size in order to maximise reproductive success and minimise sperm competition. Sperm competition has caused the human penis to evolve in length and size for sperm retention and displacement. To achieve this, the penis must be of sufficient length to reach any rival sperm and to maximally fill the vagina. In order to ensure that the female retains the male's sperm, the adaptations in length of the human penis have occurred so that the ejaculate is placed close to the female cervix. This is achieved when complete penetration occurs and the penis pushes against the cervix. These adaptations have occurred in order to release and retain sperm to the highest point of the vaginal tract. As a result, this adaptation also leaves the sperm less vulnerable to sperm displacement and semen loss. Another reason for this adaptation is that, due to the nature of the human posture, gravity creates vulnerability for semen loss. Therefore, a long penis, which places the ejaculate deep in the vaginal tract, could reduce the loss of semen. Another evolutionary theory of penis size is female
mate choice Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...
and its associations with social judgements in modern-day society. A study which illustrates female mate choice as an influence on penis size presented females with life-size, rotatable, computer generated males. These varied in height, body shape and flaccid penis size, with these aspects being examples of masculinity. Female ratings of attractiveness for each male revealed that larger penises were associated with higher attractiveness ratings. These relations between penis size and attractiveness have therefore led to frequently emphasized associations between masculinity and penis size in popular media. This has led to a social bias existing around penis size with larger penises being preferred and having higher social status. This is reflected in the association between believed sexual prowess and penis size and the social judgement of penis size in relation to 'manhood'. Like the penis, sperm competition has caused the human testicles to evolve in size through
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...
. This means that large testicles are an example of a sexually selected adaptation. The human testicles are moderately sized when compared to other animals such as gorillas and chimpanzees, placing somewhere midway. Large testicles are advantageous in sperm competition due to their ability to produce a bigger ejaculation. Research has shown that a positive correlation exists between the number of sperm ejaculated and testis size. Larger testes have also been shown to predict higher sperm quality, including a larger number of motile sperm and higher sperm motility. Research has also demonstrated that evolutionary adaptations of testis size are dependent on the breeding system in which the species resides. Single-male breeding systems—or
monogamous Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
societies—tend to show smaller testis size than do multi-male breeding systems or extra-pair copulation (EPC) societies. Human males live largely in monogamous societies like gorillas, and therefore testis size is smaller in comparison to primates in multi-male breeding systems, such as chimpanzees. The reason for the differentiation in testis size is that in order to succeed reproductively in a multi-male breeding system, males must possess the ability to produce several fully fertilising ejaculations one after another. This, however, is not the case in monogamous societies, where a reduction in fertilising ejaculations has no effect on reproductive success. This is reflected in humans, as the sperm count in ejaculations is decreased if copulation occurs more than three to five times in a week.


Ejaculate adjustment

One of the primary ways in which a male's ejaculate has evolved to overcome sperm competition is through the speed at which it travels. Ejaculates can travel up to 30–60 centimetres at a time which, when combined with its placement at the highest point of the vaginal tract, acts to increase a male's chances that an egg will be fertilised by his sperm (as opposed to a potential rival male's sperm), thus maximising his paternal certainty. In addition, males can—and do—adjust their ejaculates in response to sperm competition and according to the likely cost-benefits of mating with a particular female. Research has focused primarily on two fundamental ways in which males go about achieving this: adjusting ejaculate size and adjusting ejaculate quality.


Size

The number of sperm in any given ejaculate varies from one ejaculate to another. This variation is hypothesised to be a male's attempt to eliminate, if not reduce, his sperm competition. A male will alter the number of sperm he inseminates into a female according to his perceived level of sperm competition, inseminating a higher number of sperm if he suspects a greater level of competition from other males. In support of ejaculate adjustment, research has shown that a male typically increases the amount he inseminates sperm into his partner after they have been separated for a period of time. This is largely due to the fact that the less time a couple is able to spend together, the chances the female will be inseminated by another male increases, hence greater sperm competition. Increasing the number of sperm a male inseminates into a female acts to get rid of any rival male's sperm that may be stored within the female, as a result of her potential extra-pair copulations (EPCs) during this separation. Through increasing the amount he inseminates his partner following separation, a male increases his chances of paternal certainty. This increase in the number of sperm a male produces in response to sperm competition is not observed for masturbatory ejaculates.


Quality

Males also adjust their ejaculates in response to sperm competition in terms of quality. Research has demonstrated, for example, that simply viewing a sexually explicit image of a female and two males (i.e. high sperm competition) can cause males to produce a greater amount of motile sperm than when viewing a sexually explicit image depicting exclusively three females (i.e. low sperm competition). Much like increasing the number, increasing the quality of sperm that a male inseminates into a female enhances his paternal certainty when the threat of sperm competition is high.


Female phenotypic quality

A female's
phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
quality is a key determinant of a male's ejaculate investment. Research has shown that males produce larger ejaculates containing better, more motile sperm when mating with a higher quality female. This is largely to reduce a male's sperm competition, since more attractive females are likely to be approached and subsequently inseminated by more males than are less attractive females. Increasing investment in females with high quality phenotypic traits therefore acts to offset the ejaculate investment of others. In addition, female attractiveness has been shown to be an indicator of reproductive quality, with greater value in higher quality females. It is therefore beneficial for males to increase their ejaculate size and quality when mating with more attractive females, since this is likely to maximise their reproductive success also. Through assessing a female's phenotypic quality, males can judge whether or not to invest (or invest more) in a particular female, which will influence their subsequent ejaculate adjustment.


Semen displacement

The shape of the human penis is thought to have evolved as a result of sperm competition. Semen displacement is an adaptation of the shape of the penis to draw foreign semen away from the cervix. This means that in the event of a rival male's sperm residing within the reproductive tract of a female, the human penis is able to displace the rival sperm, replacing it with his own. Semen displacement has two main benefits for a male. Firstly, by displacing a rival male's sperm, the risk of the rival sperm fertilising the egg is reduced, thus minimising the risk of sperm competition. Secondly, the male replaces the rival's sperm with his own, therefore increasing his own chance of fertilising the egg and successfully reproducing with the female. However, males have to ensure they do not displace their own sperm. It is thought that the relatively quick loss of erection after ejaculation, penile hypersensitivity following ejaculation, and the shallower, slower thrusting of the male after ejaculation, prevents this from occurring. The coronal ridge is the part of the human penis thought to have evolved to allow for semen displacement. Research has studied how much semen is displaced by differently shaped artificial genitals. This research showed that, when combined with thrusting, the coronal ridge of the penis is able to remove the seminal fluid of a rival male from within the female reproductive tract. It does this by forcing the semen under the
frenulum A frenulum (or frenum, plural: frenula or frena, from the Latin ''frēnulum'', "little bridle", the diminutive of ''frēnum'') is a small fold of tissue that secures the motion of a mobile organ in the body. In human anatomy Frenula on the h ...
of the coronal ridge, causing it to collect behind the coronal ridge shaft. When model penises without a coronal ridge were used, less than half the artificial sperm was displaced, compared to penises with a coronal ridge. The presence of a coronal ridge alone, however, is not sufficient for effective semen displacement. It must be combined with adequate thrusting to be successful. It has been shown that the deeper the thrusting, the larger the semen displacement. No semen displacement occurs with shallow thrusting. Some have therefore termed thrusting as a semen displacement behaviour. The behaviours associated with semen displacement, namely thrusting (number of thrusts and depth of thrusts), and duration of
sexual intercourse Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal pene ...
, have been shown to vary according to whether a male perceives the risk of partner
infidelity Infidelity (synonyms include cheating, straying, adultery, being unfaithful, two-timing, or having an affair) is a violation of a couple's emotional and/or sexual exclusivity that commonly results in feelings of anger, sexual jealousy, and ri ...
to be high or not. Males and females report greater semen displacement behaviours following allegations of infidelity. In particular, following allegations of infidelity, males and females report deeper and quicker thrusting during sexual intercourse. Circumcision has been suggested to affect semen displacement. Circumcision causes the coronal ridge to be more pronounced, and it has been hypothesised that this could enhance semen displacement. This is supported by females' reports of sexual intercourse with circumcised males. Females report that their vaginal secretions diminish as intercourse with a circumcised male progresses, and that circumcised males thrust more deeply. It has therefore been suggested that the more pronounced coronal ridge, combined with the deeper thrusting, causes the vaginal secretions of the female to be displaced in the same way as rival
sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, ...
can be.


Clinical significance


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 Peyronie's disease is a connective tissue disorder involving the growth of fibrous plaques in the soft tissue of the penis. Specifically, scar tissue forms in the tunica albuginea, the thick sheath of tissue surrounding the corpora cavernosa, c ...
, anomalous scar tissue grows in the soft tissue of the penis, causing curvature. Severe cases can be improved by surgical correction. *A
thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (th ...
can occur during periods of frequent and prolonged sexual activity, especially
fellatio Fellatio (also known as fellation, and in slang as blowjob, BJ, giving head, or sucking off) is an oral sex act involving a person stimulating the penis of another person by using the mouth, throat, or both. Oral stimulation of the scrotu ...
. It is usually harmless and self-corrects within a few weeks. *Infection with the
herpes Herpes simplex is a viral infection caused by the herpes simplex virus. Infections are categorized based on the part of the body infected. Oral herpes involves the face or mouth. It may result in small blisters in groups often called cold ...
virus can occur after sexual contact with an infected carrier; this may lead to the development of herpes sores. * Balanitis is an inflammation, either infectious or not. * Pudendal nerve entrapment is a condition characterized by pain on sitting and the loss of penile 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. This can also occur in the clitoris of females. * 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 as soon as possible. Prompt medical attention lowers the likelihood of permanent penile curvature. *In
diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
,
peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...
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 Erectile dysfunction (ED), also called impotence, is the type of sexual dysfunction in which the penis fails to become or stay erect during sexual activity. It is the most common sexual problem in men.Cunningham GR, Rosen RC. Overview of ma ...
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, most notably including the phosphodiesterase type 5 inhibitor drugs (such as ''
sildenafil Sildenafil, sold under the brand name Viagra, among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. It is unclear if it is effective for treating sexual dysfunction in women. It is taken by ...
citrate'', marketed as Viagra), which work by
vasodilation Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstrictio ...
. * Priapism is a painful and potentially harmful medical condition in which the erect penis does not return to its flaccid state. Priapism lasting over four hours is a medical emergency. The causative mechanisms are poorly understood but involve complex neurological and vascular factors. Potential complications include
ischaemia Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...
,
thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (th ...
, and impotence. In serious cases the condition may result in
gangrene Gangrene is a type of tissue death caused by a lack of blood supply. Symptoms may include a change in skin color to red or black, numbness, swelling, pain, skin breakdown, and coolness. The feet and hands are most commonly affected. If the gan ...
, which may result in
amputation Amputation is the removal of a limb by trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on indi ...
. However, that is usually only the case if the organ is broke out and injured because of it. The condition has been associated with a variety of drugs including
prostaglandin The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are deriv ...
. Contrary to common knowledge,
sildenafil Sildenafil, sold under the brand name Viagra, among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. It is unclear if it is effective for treating sexual dysfunction in women. It is taken by ...
(Viagra) will not cause it. * Lymphangiosclerosis is a hardened
lymph vessel The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes), structured like blood vessels, that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vesse ...
, 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 Penile cancer is cancer that develops in the skin or tissues of the penis. Symptoms may include abnormal growth, an ulcer or sore on the skin of the penis, and bleeding or foul smelling discharge. Risk factors include phimosis (inability to retr ...
is rare with a reported rate of 1 person in 100,000 in developed countries. Some sources state that circumcision can protect against this disease, but this notion remains controversial among medical circles.


Developmental disorders

*
Hypospadias Hypospadias is a common variation in fetal development of the penis in which the urethra does not open from its usual location in the head of the penis. It is the second-most common birth abnormality of the male reproductive system, affecting ab ...
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 Micropenis is an unusually small penis. A common criterion is a dorsal (measured on top) penile length of at least 2.5 standard deviations smaller than the mean human penis size (stretched penile length less than 9.3 cm (3.67 in) in adults ...
is a very small penis caused by developmental or congenital problems. *
Diphallia Diphallia, penile duplication (PD), diphallic terata, or diphallasparatus, is an extremely rare developmental abnormality in which a male is born with two penises. The first reported case was by Johannes Jacob Wecker in 1609. Its occurrence is 1 ...
, or penile duplication (PD), is the rare condition of having two penises.


Alleged and observed psychological disorders

* Penis panic (''koro'' in Malaysian/ Indonesian)—delusion of shrinkage of the penis and retraction into the body. This appears to be culturally conditioned and largely limited to Ghana, Sudan, China, Japan, Southeast Asia, and West Africa. * In April 2008,
Kinshasa Kinshasa (; ; ln, Kinsásá), formerly Léopoldville ( nl, Leopoldstad), is the capital and largest city of the Democratic Republic of the Congo. Once a site of fishing and trading villages situated along the Congo River, Kinshasa is now one of ...
, Democratic Republic of Congo, West Africa's 'Police arrested 14 suspected victims (of penis snatching) and sorcerers accused of using black magic or witchcraft to steal (make disappear) or shrink men's penises to extort cash for cure, amid a wave of panic. Arrests were made in an effort to avoid bloodshed seen in Ghana a decade before, when 12 penis snatchers were beaten to death by mobs. * Penis envy—the contested
Freudian Sigmund Freud ( , ; born Sigismund Schlomo Freud; 6 May 1856 – 23 September 1939) was an Austrian neurologist and the founder of psychoanalysis, a clinical method for evaluating and treating pathologies explained as originating in conflicts i ...
belief of all women inherently envying men for having penises.


Society and culture


Terminology

In many cultures, referring to the penis is considered taboo or vulgar, and a variety of slang words and euphemisms are used to talk about it. In English, these include ''member'', ''
dick Dick, Dicks, or Dick's may refer to: Media * ''Dicks'' (album), a 2004 album by Fila Brazillia * Dicks (band), a musical group * ''Dick'' (film), a 1999 American comedy film * "Dick" (song), a 2019 song by Starboi3 featuring Doja Cat Names ...
'', ''cock'', ''prick'', ''johnson'', ''dork'', ''peter'', ''pecker'', ''manhood'', ''stick'', ''rod'', ''thing'', ''third/middle leg'', ''dong'', ''willy'', ''schlong'', and ''todger.'' Many of these are used as
insult An insult is an expression or statement (or sometimes behavior) which is disrespectful or scornful. Insults may be intentional or accidental. An insult may be factual, but at the same time pejorative, such as the word " inbred". Jocular ex ...
s—though sometimes playfully—meaning an unpleasant or unworthy person. Among these, historically, most commonly used euphemism for penis in English literature and society was ''member''.


Alteration

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 palang ( iba, crossbar), or ampallang is a male genital piercing that penetrates horizontally through the entire glans of the penis. History Penis piercings of proto-Malay origin predated European contact with tribes in (among others) t ...
, the dydoe, and the frenum piercing.
Foreskin restoration Foreskin restoration is the process of expanding the skin on the penis to reconstruct an organ similar to the foreskin, which has been removed by circumcision or injury. Foreskin restoration is primarily accomplished by stretching the residual ski ...
or stretching is a further form of body modification, as well as implants under the shaft of the penis.
Trans women A trans woman or a transgender woman is a woman who was assigned male at birth. Trans women have a female gender identity, may experience gender dysphoria, and may transition; this process commonly includes hormone replacement therapy and s ...
who undergo
sex reassignment surgery Gender-affirming surgery (GAS) is a surgical procedure, or series of procedures, that alters a transgender or transsexual person's physical appearance and sexual characteristics to resemble those associated with their identified gender, and a ...
have their penis surgically modified into a vagina via vaginoplasty.
Trans men A trans man is a man who was assigned female at birth. The label of transgender man is not always interchangeable with that of transsexual man, although the two labels are often used in this way. ''Transgender'' is an umbrella term that inclu ...
who undergo such surgery 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 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 Aboriginal Australians are the various Indigenous peoples of the Australian mainland and many of its islands, such as Tasmania, Fraser Island, Hinchinbrook Island, the Tiwi Islands, and Groote Eylandt, but excluding the Torres Strait Isla ...
, although it is now done by some in the U.S. and Europe.


Circumcision

The most common form of body modification related to the penis is
circumcision Circumcision is a procedure that removes the foreskin from the human penis. In the most common form of the operation, the foreskin is extended with forceps, then a circumcision device may be placed, after which the foreskin is excised. Top ...
: removal of part or all of the foreskin. It is most commonly performed as an
elective procedure Elective surgery or elective procedure (from the la, eligere, meaning to choose) is surgery that is scheduled in advance because it does not involve a medical emergency. Semi-elective surgery is a surgery that must be done to preserve the pati ...
for prophylactic,
cultural Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups.T ...
, or
religious Religion is usually defined as a social- cultural system of designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that generally relates humanity to supernatur ...
reasons. For infant circumcision, modern devices such as the
Gomco clamp Circumcision surgical procedure in males involves either a conventional "cut and stitch" surgical procedure or use of a circumcision instrument or device. In the newborn period (less than 2 months of age), almost all circumcisions are done by g ...
, Plastibell, and
Mogen clamp Circumcision surgical procedure in males involves either a conventional "cut and stitch" surgical procedure or use of a circumcision instrument or device. In the newborn period (less than 2 months of age), almost all circumcisions are done by g ...
are available. 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. In some African countries, male circumcision is often performed by non-medical personnel under non-sterile conditions. After hospital circumcision, the foreskin may be used in biomedical research, consumer skin-care products, skin grafts, or β-interferon-based drugs. In parts of Africa, the foreskin may be dipped in brandy and eaten by the patient, eaten by the circumciser, or fed to animals. According to
Jewish law ''Halakha'' (; he, הֲלָכָה, ), also transliterated as ''halacha'', ''halakhah'', and ''halocho'' ( ), is the collective body of Jewish religious laws which is derived from the written and Oral Torah. Halakha is based on biblical comman ...
, after a ''
Brit milah The ''brit milah'' ( he, בְּרִית מִילָה ''bərīṯ mīlā'', ; Ashkenazi pronunciation: , " covenant of circumcision"; Yiddish pronunciation: ''bris'' ) is the ceremony of circumcision in Judaism. According to the Book of Genes ...
'', the foreskin should be buried. Circumcision plays a major role in many of the world's cultures and religions. When performed for religious reasons, it is most common among both
Jews Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
and
Muslims Muslims ( ar, المسلمون, , ) are people who adhere to Islam, a monotheistic religion belonging to the Abrahamic tradition. They consider the Quran, the foundational religious text of Islam, to be the verbatim word of the God of Abrah ...
, among whom it is near-universal. There are variant cultural, social, ethical, and religious views on circumcision. Among the world's major medical organizations, there is an overwhelming consensus that circumcision reduces heterosexual HIV infection rates in high-risk populations, and differing perspectives on the prophylactic efficacy and
cost effectiveness Cost-effectiveness analysis (CEA) is a form of economic analysis that compares the relative costs and outcomes (effects) of different courses of action. Cost-effectiveness analysis is distinct from cost–benefit analysis, which assigns a moneta ...
of circumcision in developed nations. The World Health Organization (WHO; 2007), the
Joint United Nations Programme on HIV/AIDS The Joint United Nations Programme on HIV and AIDS (UNAIDS) (, ONUSIDA) is the main advocate for accelerated, comprehensive and coordinated global action on the HIV/ AIDS pandemic. The mission of UNAIDS is to lead, strengthen and support an ...
(UNAIDS; 2007), and the
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
(CDC; 2008) state that evidence indicates 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. In 2010, the World Health Organization released a statement encouraging a higher rate of circumcision:
There are significant benefits in performing male circumcision in early infancy, and programmes that promote early infant male circumcision are likely to have lower morbidity rates and lower costs than programmes targeting adolescent boys and men.
''Bolnick, Koyle & Yosha (2012)'' projects that worldwide circumcision rates will significantly rise "in the first half of the twenty-first century".


Potential regeneration

There are efforts by scientists to partially or fully regenerate the structures of the human penis. Patients who can benefit most from this field are those who have congenital defects, cancer, and injuries that have excised parts of their
genitalia A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
. Some organizations which perform research into, or conduct regeneration procedures, include the
Wake Forest Institute for Regenerative Medicine The Wake Forest Institute for Regenerative Medicine (WFIRM) is a research institute affiliated with Wake Forest School of Medicine and located in Winston-Salem, North Carolina, United States WFIRM's goal is to apply the principles of regenerative ...
and the
United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national sec ...
. The first successful penis allotransplant surgery was done in September 2005 in a military hospital in
Guangzhou Guangzhou (, ; ; or ; ), also known as Canton () and Chinese postal romanization, alternatively romanized as Kwongchow or Kwangchow, is the Capital city, capital and largest city of Guangdong Provinces of China, province in South China, sou ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
. A man at 44 sustained an injury after an accident and his penis was severed;
urination Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...
became difficult as his urethra was partly blocked. A recently brain-dead man, aged 23, was selected for the transplant. Despite
atrophy Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply ...
of blood vessels and nerves, the
arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...
,
veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...
, nerves and the corpora spongiosa were successfully matched. But, on 19 September (after two weeks), the surgery was reversed because of a severe
psychological Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries bet ...
problem (rejection) by the recipient and his wife. In 2009 researchers Chen, Eberli, Yoo and Atala have produced
bioengineered Biological engineering or bioengineering is the application of principles of biology and the tools of engineering to create usable, tangible, economically-viable products. Biological engineering employs knowledge and expertise from a number o ...
penises and implanted them on rabbits. The animals were able to obtain
erection 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, a ...
and
copulate Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...
, with 10 of 12 rabbits achieving
ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential compo ...
. This study shows that in the future it could be possible to produce artificial penises for replacement surgeries or phalloplasties. In 2015 the world's first successful penis transplant took place in
Cape Town Cape Town ( af, Kaapstad; , xh, iKapa) is one of South Africa's three capital cities, serving as the seat of the Parliament of South Africa. It is the legislative capital of the country, the oldest city in the country, and the second largest ...
, South Africa in a nine-hour operation performed by surgeons from Stellenbosch University and
Tygerberg Hospital Tygerberg Hospital is a tertiary hospital located in Parow. The hospital was officially opened in 1976 and is the largest hospital in the Western Cape and the second largest hospital in South Africa, with the capacity for 1899 beds. It acts as ...
. The 21-year-old recipient, who had been sexually active, had lost his penis in a botched circumcision at 18.


Additional images

Image:Sobo 1906 490.png, Dissection showing the fascia of the penis as well as several surrounding structures Image:Sobo 1909 571.png, Image showing innervation and blood-supply of the human male external genitalia


References


External links


Kinsey Institute on the penis
{{Authority control Human anatomy Men's health Urinary system