Tuesday, September 11, 2012

Foreskin -more than just a sex toy


Foreskin

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Foreskin
Foreskin of a human penis.jpg
A partially retracted foreskin, revealing some of the glans penis. The ridged band toward the end of the foreskin is clearly visible.
Latinprepucium, præputium
Gray'ssubject #262 1250
ArteryDorsal artery of the penis
VeinSuperficial dorsal vein of the penis
NerveDorsal nerve of the penis
PrecursorGenital tubercle, Urogenital folds
MeSHForeskin
Dorlands/ElsevierPreupuce
In male human anatomy, the foreskin is a generally retractable double-layered fold of skin and mucous membrane that covers the glans penis and protects the urinary meatus (play /mˈtəs/) when the penis is not erect. It is also described as the prepuce, a technically broader term that also includes the clitoral hood in women, to which the foreskin is embryonically homologous.

Contents

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Description

Diagram of a portion of the male anatomy
The outside of the foreskin is a continuation of the skin on the shaft of the penis, but the inner foreskin is a mucous membrane like the inside of the eyelid or the mouth. The mucocutaneous zone occurs where the outer and inner foreskin meet. Like the eyelid, the foreskin is free to move after it separates from the glans, usually by puberty. Smooth muscle fibres keep it close to the glans but make it highly elastic.[1] The foreskin is attached to the glans by a frenulum, which helps return the foreskin over the glans.
The presence of a type of nerve ending called Meissner's corpuscles has been reported. Their density is reportedly greater in the ridged band (a region of ridged mucosa at the tip of the foreskin) than in the larger area of smooth mucosa.[2] They are affected by age: their incidence decreases after adolescence.[3] Meissner's corpucles could not be identified in all individuals.[4] Bhat et al studied Meissner's corpuscles at a number of different sites, including the "finger tips, palm, front of forearm, sole, lips, prepuce of penis, dorsum of hand and dorsum of foot". They found the lowest Meissner's Index (density) in the foreskin, and also reported that corpuscles at this site were physically smaller. Differences in shape were also noted. They concluded that these characteristics were found in "less sensitive areas of the body".[5] In the late 1950s, Winkelmann suggested that some receptors had been wrongly identified as Meissner's corpuscles.[6][7]
The College of Physicians and Surgeons of British Columbia have written that the foreskin is "composed of an outer skin and an inner mucosa that is rich in specialized sensory nerve endings and erogenous tissue."[8] According to a study by Sorrells et al. (2007), the five most sensitive areas of the penis are on the foreskin and the glans is more sensitive in the uncircumcised penis.[9] The study has been criticized by Waskett and Morris, who argue that re-analysis of Sorrells' data shows no significant differences.[10] In 2009, Schober et al reported on self-assessed sexual sensitivity in 81 men, 11 of whom were not circumcised. When assessing areas producing sexual pleasure, the foreskin was ranked 7th, after the glans, lower and upper shaft, and the left and right sides of the penis, but above the area between scrotum and anus, the scrotum itself, and the anus.[11]

Development

Eight weeks after fertilization, the foreskin begins to grow over the head of the penis, covering it completely by 16 weeks. At this stage, the foreskin and glans share an epithelium (mucous layer) that fuses the two together. It remains this way until the foreskin separates from the glans.[12]
At birth, the foreskin is usually still fused with the glans.[12] As childhood progresses the foreskin and the glans gradually separate, a process that may not be complete until late puberty.[13] Thorvaldsen and Meyhoff (2005) reported that average age of first foreskin retraction in Denmark is 10.4 years.[14] Wright (1994) argues that forcible retraction of the foreskin should be avoided and that the child himself should be the first one to retract his own foreskin.[15] Attempts to forcibly retract it can be painful and may injure the foreskin.[16]
In children, the foreskin usually covers the glans completely but in adults, this need not be so. Schöberlein (1966) [17] found that about 50% of young men had full coverage of the glans, 42% had partial coverage, and, in the remaining 8%, the glans was uncovered. After adjusting for circumcision, he stated that, in 4% of the young men, the foreskin had spontaneously atrophied (shrunk). There is considerable variation in the degree to which the foreskin retracts during erection; in some adults the foreskin remains covering the glans until retracted by sexual activity.

Functions

The foreskin typically covers the glans when the penis is flaccid (top image), but generally retracts upon erection (bottom image).
The World Health Organization state that there is "debate about the role of the foreskin, with possible functions including keeping the glans moist, protecting the developing penis in utero, or enhancing sexual pleasure due to the presence of nerve receptors".[18]

Sexual

The Royal Australasian College of Physicians states that the foreskin protects the glans, and that "the foreskin is a primary sensory part of the penis, containing some of the most sensitive areas of the penis. The effects of circumcision on sexual sensation however are not clear, with reports of both enhanced and diminished sexual pleasure following the procedure in adults and little awareness of advantage or disadvantage in those circumcised in infancy."[19] The Royal Dutch Medical Association (2010) states that many sexologists view the foreskin as "a complex, erotogenic structure that plays an important role ‘in the mechanical function of the penis during sexual acts, such as penetrative intercourse and masturbation’."[20]
Taylor et al. (1996) described the foreskin in detail, documenting a ridged band of mucosal tissue. They stated: "This ridged band contains more Meissner's corpuscles than does the smooth mucosa and exhibits features of specialized sensory mucosa."[2] In 1999, Cold and Taylor stated: "The prepuce is primary, erogenous tissue necessary for normal sexual function."[21] Boyle et al. (2002) state that "the complex innervation of the foreskin and frenulum has been well documented, and the genitally intact male has thousands of fine touch receptors and other highly erogenous nerve endings."[22] The AAP noted that the work of Taylor et al. (1996) "suggests that there may be a concentration of specialized sensory cells in specific ridged areas of the foreskin."[23]
Moses and Bailey (1998) describe the evidence of sensory function as "indirect," and state that, "aside from anecdotal reports, it has not been demonstrated that this is associated with increased male sexual pleasure."[24] The World Health Organization (2007) states that "Although it has been argued that sexual function may diminish following circumcision due to the removal of the nerve endings in the foreskin and subsequent thickening of the epithelia of the glans, there is little evidence for this and studies are inconsistent."[25] Fink et al. (2002) reported "although many have speculated about the effect of a foreskin on sexual function, the current state of knowledge is based on anecdote rather than scientific evidence."[26] Masood et al. (2005) state that "currently no consensus exists about the role of the foreskin."[27] Schoen (2007) states that "anecdotally, some have claimed that the foreskin is important for normal sexual activity and improves sexual sensitivity. Objective published studies over the past decade have shown no substantial difference in sexual function between circumcised and uncircumcised men."[28]
The term 'gliding action' is used in some papers to describe the way the foreskin moves during sexual intercourse. This mechanism was described by Lakshamanan & Prakash in 1980, stating that "[t]he outer layer of the prepuce in common with the skin of the shaft of the penis glides freely in a to and fro fashion..."[29] Several people have argued that the gliding movement of the foreskin is important during sexual intercourse.[30] Warren & Bigelow (1994) state that gliding action would help to reduce the effects of vaginal dryness and that restoration of the gliding action is an important advantage of foreskin restoration.[31] O'Hara (2002) describes the gliding action, stating that it reduces friction during sexual intercourse, and suggesting that it adds "immeasurably to the comfort and pleasure of both parties".[32] Taylor (2000) suggests that the gliding action, where it occurs, may stimulate the nerves of the ridged band,[33] and speculates (2003) that the stretching of the frenulum by the rearward gliding action during penetration triggers ejaculation.[34]
Whiddon (1953), Foley (1966), and Morgan (1967) all believed that the presence of the foreskin made sexual penetration easier.[35][36][37]

Protective and immunological

Gairdner (1949) states that the foreskin protects the glans.[12] The fold of the prepuce maintains sub-preputial wetness, which mixes with exfoliated skin to form smegma. Some authors believe that smegma contains antibacterial enzymes,[38] though their theory has been challenged.[39] The American Academy of Pediatrics (1999) state that "no controlled scientific data are available regarding differing immune function in a penis with or without a foreskin."[40] Inferior hygiene has been associated with balanitis,[41] though excessive washing can cause non-specific dermatitis.[42][43]

Evolution

In primates, the foreskin is present in the genitalia of both sexes and likely has been present for millions of years of evolution.[44] The evolution of complex penile morphologies like the foreskin may have been influenced by females.[45][46][47]

Conditions

Simmons et al. (2007) report that the foreskin's presence "frequently predisposes to medical problems, including balanitis, phimosis, venereal disease and penile cancer", and additionally state that "because we now are able to effectively treat foreskin related maladies, some societies are shifting toward foreskin preservation."[48]
Frenulum breve is a frenulum that is insufficiently long to allow the foreskin to fully retract, which may lead to discomfort during intercourse. Phimosis is a condition where the foreskin of an adult cannot be retracted properly. Before adulthood, the foreskin may still be separating from the glans.[49] Phimosis can be treated by gently stretching the foreskin, by changing masturbation habits,[50] using topical steroid ointments, preputioplasty, or by the more radical option of circumcision. Posthitis is an inflammation of the foreskin.
A condition called paraphimosis may occur if a tight foreskin becomes trapped behind the glans and swells as a restrictive ring. This can cut off the blood supply, resulting in ischaemia of the glans penis.
Lichen sclerosus is a chronic, inflammatory skin condition that most commonly occurs in adult women, although it may also be seen in men and children. Topical clobetasol propionate and mometasone furoate were proven effective in treating genital lichen sclerosus. [51]
Aposthia is a rare condition in which the foreskin is not present at birth.

Surgical and other modifications of the foreskin

Circumcision is the removal of the foreskin, either partially or completely. It may be done for religious requirements, health reasons such as to treat a medical disorder, or personal preferences surrounding hygiene and aesthetics. Preputioplasty is a minor procedure designed to relieve a tight foreskin without resorting to circumcision.
Foreskin restoration techniques (developed to help circumcised men 'regrow' a skin covering for the glans by tissue expansion) can be used by men with short foreskins to lengthen the natural foreskin so that it covers the glans. A narrow foreskin may also be widened by tissue expansion.[52]
Other practices include genital piercings involving the foreskin and slitting the foreskin.[53]

Langerhans cells

Langerhans cells are immature dendritic cells that are found in all areas of the penile epithelium,[54] but are most superficial in the inner surface of the foreskin.[54] A study by Szabo and Short (2000) targets Langerhans cells as receptors of HIV, and states that these cells "must be regarded as the most probable sites for viral entry in primary HIV infection in men."[55] Langerhans cells are also known to express the c-type lectin langerin, which may play a role in transmission of HIV to nearby lymph nodes.[54] However, de Witte et al. (2007) suggested that langerin, produced by Langerhans cells, might block the transmission of HIV to T cells.[56]

Foreskin-based medical and consumer products

Foreskins obtained from circumcision procedures are frequently used by biochemical and micro-anatomical researchers to study the structure and proteins of human skin. In particular, foreskins obtained from newborns have been found to be useful in the manufacturing of more human skin.[57]
Human growth factors derived from newborns' foreskins are used to make a commercial anti-wrinkle skin cream, TNS Recovery Complex.[58]
Foreskins of babies are also used for skin graft tissue,[59][60][61] and for β-interferon-based drugs.[62]
Foreskin fibroblasts have been used in biomedical research.[63]

Foreskin in non-human species

In koalas, the foreskin contains naturally occurring bacteria that play an important role in fertilization.[64] Almost all mammal penises have foreskins, although in non-human cases the foreskin is usually a sheath into which the whole penis is retracted. Only monotremes (the platypus and the echidna) lack foreskins.[65]

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