Foreskin

Foreskin
A penis with a partially-retracted foreskin, revealing some of the glans penis. The ridged band toward the end of the foreskin is clearly visible.
Latin prepucium, præputium
Gray's subject #262 1250
Artery Dorsal artery of the penis
Vein Superficial dorsal vein of the penis
Nerve Dorsal nerve of the penis
Precursor Genital tubercle, Urogenital folds
MeSH Foreskin
Dorlands/Elsevier Preupuce

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 ( /miːˈeɪtəs/) 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

Description

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] In the late 1950s, Winkelmann suggested that some receptors had been wrongly identified as Meissner's corpuscles.[5][6]

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 [7]. The study has been criticized by Waskett and Morris, who argue that re-analysis of Sorrells' data shows no significant differences.[8] 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.[9]

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.[10]

At birth, the foreskin is usually still fused with the glans.[10] As childhood progresses the foreskin and the glans gradually separate, a process that may not be complete until late puberty.[11] Thorvaldsen and Meyhoff (2005) reported that average age of first foreskin retraction in Denmark is 10.4 years.[12] 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.[13] Attempts to forcibly retract it can be painful and may injure the foreskin.[14]

In children, the foreskin usually covers the glans completely but in adults, this need not be so. Schöberlein (1966) [15] 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 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".[16]

Sexual

For more details on this topic, see Sexual effects of circumcision.

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."[17] 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—many of which are lost to circumcision, with an inevitable reduction in sexual sensation experienced by circumcised males."[18] 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."[19]

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."[20] The World Health Organization (2007) states that there is little evidence for diminished sexual function, adding that studies have been inconsistent.[21] Fink et al. (2002) reported "[a]lthough 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."[22] Masood et al. (2005) state that "[c]urrently no consensus exists about the role of the foreskin or the effect circumcision has on penile sensitivity and overall sexual satisfaction."[23] Schoen (2007) states that "[a]necdotally, 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."[24]

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..."[25] Several people have argued that the gliding movement of the foreskin is important during sexual intercourse.[26] 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.[27] 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".[28] Taylor (2000) suggests that the gliding action, where it occurs, may stimulate the nerves of the ridged band,[29] and speculates (2003) that the stretching of the frenulum by the rearward gliding action during penetration triggers ejaculation.[30]

Whiddon (1953), Foley (1966), and Morgan (1967) all believed that the presence of the foreskin made sexual penetration easier.[31][32][33]

Other

Gairdner (1949) states that the foreskin protects the glans[10] however, several studies find that inflammation of the glans is more common when the foreskin is present.[34][35][36][37][38][39][40][41] In contrast, Van Howe (2007) found more inflammation in circumcised boys.[42]

Meatitis, meatal ulcer, and meatal stenosis are thought to be less common if the foreskin is present.[43][44][45] Among circumcised males, reported incidence figures of meatal stenosis include 0%,[46] 0.01%,[47] 0.55%,[48] 0.9%,[49] 2.8%,[50] 7.29%,[51] 9-10%,[52] and 11%.[53]

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,[54] though their theory has been challenged.[55] 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."[56] Inferior hygiene has been associated with balanitis,[57] though excessive washing can cause non-specific dermatitis.[58]

Evolution

In primates, the foreskin is present in the genitalia of both sexes and likely has been present for millions of years of evolution.[59] The evolution of complex penile morphologies like the foreskin may have been influenced by females.[60][61][62]

Conditions

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.[63] Phimosis can be treated by gently stretching the foreskin, by changing masturbation habits,[64] 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.

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.[65]

Other practices include genital piercings involving the foreskin and slitting the foreskin.[66]

Langerhans cells

Langerhans cells are immature dendritic cells that are found in all areas of the penile epithelium,[67] but are most superficial in the inner surface of the foreskin.[67] 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."[68] 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.[67] However, de Witte et al. (2007) suggested that langerin, produced by Langerhans cells, might block the transmission of HIV to T cells.[69]

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.[70]

Human growth factors derived from newborns' foreskins are used to make a commercial anti-wrinkle skin cream, TNS Recovery Complex.[71]

Foreskins of babies are also used for skin graft tissue,[72][73][74] and for β-interferon-based drugs.[75]

Foreskin fibroblasts have been used in biomedical research.[76]

Foreskin in non-human species

In koalas, the foreskin contains naturally-occurring bacteria that play an important role in fertilization.[77] 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.[78]

Additional images

See also

References

  1. ^ Lakshmanan, S; Prakash, S (1980). "Human prepuce - structure & function". Indian J Surg 44: 134–7. http://www.cirp.org/library/anatomy/lakshmanan/. 
  2. ^ a b Taylor, JR; Lockwood, AP; Taylor, AJ (1996). "The prepuce: specialized mucosa of the penis and its loss to circumcision". Br J Urol 77 (2): 291–5. doi:10.1046/j.1464-410X.1996.85023.x. PMID 8800902. http://www.blackwell-synergy.com/doi/pdf/10.1046/j.1464-410X.1996.85023.x. 
  3. ^ Dong, GUO; XU Sheng-mei, JIANG Hai-yang, TAN Ming-bo, LUAN Hua (2007-01). "Observation of Meissner's corpuscle on fused phimosis". Journal of Guangdong Medical College. CNKI:. http://en.cnki.com.cn/Article_en/CJFDTOTAL-GDYY200701004.htm. Retrieved 2010-05-07. 
  4. ^ Haiyang, Jiang; Wang Guxin, Guo Dong, Tan Mingbo, Xu Shengmei (2005-04). "Observation of Meissner's corpuscle in abundant prepuce and phimosis". Journal of Modern Urology. http://en.cnki.com.cn/Article_en/CJFDTOTAL-MNWK200504018.htm. Retrieved 2010-05-07. 
  5. ^ Winkelmann, R. K. (1956-1). "The cutaneous innervation of human newborn prepuce". Journal of Investigative Dermatology 26 (1): 53–67. doi:10.1038/jid.1956.5. PMID 13295637. http://www.cirp.org/library/anatomy/winkelmann2/index.html. 
  6. ^ Winkelmann RK (1957). "The mucocutaneous end-organ: the primary organized sensory ending in human skin". AMA Arch Dermatol 76 (2): 225–35. doi:10.1001/archderm.1957.01550200069015. 
  7. ^ Sorrels, Morris; James L. Snyder, Mark D. Reiss, Christopher Eden, Marilyn F. Milos, Norma Wilcox and Robert S. Van Howe. (2007). "Fine-touch pressure thresholds in the adult penis" (PDF). Bjuinternational 99 (4): 864–869. doi:10.1111/j.1464-410X.2006.06685.x. PMID 17378847. http://onlinelibrary.wiley.com/doi/10.1111/j.1464-410X.2006.06685.x/full. 
  8. ^ Waskett, Jake H.; Brian J. Morris (May 2007). "Fine touch pressure thresholds in the adult penis". BJU International 99 (6): 1551–1552. doi:10.1111/j.1464-410X.2007.06970_6.x. PMID 17537227. http://www3.interscience.wiley.com/cgi-bin/fulltext/118508593/HTMLSTART. 
  9. ^ Schober JM, Meyer-Bahlburg HF, Dolezal C (April 2009). "Self-ratings of genital anatomy, sexual sensitivity and function in men using the 'Self-Assessment of Genital Anatomy and Sexual Function, Male' questionnaire". BJU Int. 103 (8): 1096–103. doi:10.1111/j.1464-410X.2008.08166.x. PMID 19245445. 
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    Friction is not entirely eliminated during natural intercourse but it is largely eliminated. Friction can take place in the lower vagina, but only if the man uses a stroke that exceeds the (forward and backward) gliding range of the shaft's extra skin. And in such a case, there will be friction only to the extent that the shaft exceeded its extra skin, which is uncommon since the natural penis has a propensity for short strokes. Primarily, it is the penis head that makes frictional contact with the vaginal walls, usually in the upper vagina where there is ample lubrication. [...] The gliding principle of natural intercourse is a two-way street—the vagina glides on the shaft skin while the shaft skin massages the penis shaft as it glides over it."     
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