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Foreskin

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This article is about human foreskin. For foreskin in other mammals, see Penile sheath.
Foreskin
Foreskin partially retracted over the glans penis, with a ridged band visible at the end of the foreskin
Details
PrecursorGenital tubercle, urogenital folds
ArteryDorsal artery of the penis
VeinDorsal veins of the penis
NerveDorsal nerve of the penis
Identifiers
LatinPraeputium
MeSHD052816
TA98A09.4.01.011
TA23675
FMA19639
Anatomical terminology

In male human anatomy, the foreskin is the double-layered fold of smooth muscle tissue, blood vessels, neurons, skin, and mucous membrane part of the penis that covers and protects the glans penis and the urinary meatus. 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. The highly innervated mucocutaneous zone of the penis occurs near the tip of the foreskin. The foreskin is mobile, fairly stretchable, and acts as a natural lubricant.

The foreskin of adults is typically retractable over the glans. Coverage of the glans in a flaccid and erect state varies depending on foreskin length. The foreskin is attached to the glans at birth and is generally not retractable in infancy. Inability to retract the foreskin in childhood should not be considered a problem unless there are other symptoms.[1]

The World Health Organization debates the precise functions of the foreskin, which may include "keeping the glans moist, protecting the developing penis in utero, or enhancing sexual pleasure due to the presence of nerve receptors".[2]

The foreskin may become subject to a number of pathological conditions.[3] Most conditions are rare, and easily treated. In some cases, particularly with chronic conditions, treatment may include circumcision, a procedure where the foreskin is partially or completely removed.

Description

File:Male anatomy.png
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. The ridged band of highly innervated tissue is located just inside the tip of the foreskin. Like the eyelid, the foreskin is free to move after it separates from the glans, which usually occurs before or during puberty. The foreskin is attached to the glans by a frenulum, a highly vascularized tissue of the penis.[2] The World Health Organization states that "[t]he frenulum forms the interface between the outer and inner foreskin layers, and when the penis is not erect, it tightens to narrow the foreskin opening.[2]

The human foreskin contains a sheath of muscle tissue just below the skin, formerly known as the peripenic muscle and now called the dartos fascia, most of which is contained in the foreskin. Elastic fibers are contained in the dartos fascia, which form a whorl at the tip of the foreskin. The whorl of fibers acts as a sphincter in infants, which opens to allow the passage of urine, but closes to protect the glans penis from foreign matter and contaminants. The dartos fascia is sensitive to temperature and expands and contracts with temperature changes. The dartos fascia is only loosely connected with the underlying tissue so it provides the skin mobility and elasticity of the penile skin.

The College of Physicians and Surgeons of British Columbia has 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."[4]

Development

The foreskin is present in non-human primates, including the chimpanzee.[2]

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.

Once the foreskin has naturally separated from the glans, the foreskin's two layers of outer skin and inner mucosa can be retracted to reveal the glans, inner foreskin, and ridged band.

In children, the foreskin usually covers the glans completely but in adults it may not. During erection, the degree of automatic foreskin retraction varies considerably; in some adults, the foreskin remains covering all or some of the glans until retracted manually or by sexual activity. This variation was regarded by Chengzu (2011) as an abnormal condition named 'prepuce redundant'. Frequent retraction and washing under the foreskin is suggested for all adults but particularly for those with a long, or 'redundant' foreskin.[5] When the foreskin is longer than the erect penis, it will not spontaneously retract upon erection.

It is shown that manual foreskin retraction during childhood or even adulthood serves as a stimulant to normal development and automatic retraction of the foreskin, which suggests that many conditions affecting the foreskin may be prevented or cured behaviorally.

Some males, according to Xianze (2012), may be reluctant for their glans to be exposed because of discomfort when it chafes against clothing, although the discomfort on the glans was reported to diminish within one week of continuous exposure.[6] Guochang (2010) states that for those whose foreskins are too tight to retract or have some adhesions, forcible retraction should be avoided since it may cause injury.[7]

Functions

The foreskin typically covers the glans when the penis is not erect (top image), but generally retracts upon erection (bottom image). Coverage of the glans in a flaccid and erect state varies depending on foreskin length

The World Health Organization (2007) states 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".[2] The foreskin helps to provide sufficient skin during an erection.[8]

The foreskin protects the glans.[4] The foreskin protects the glans of infants from ammonia and feces in diapers, which reduces the incidence of meatal stenosis, and continues to protect the glans from abrasions and trauma throughout life.[8] The fold of the prepuce maintains sub-preputial wetness, which mixes with exfoliated skin to form smegma.[citation needed]

The American Academy of Pediatricians' 2012 technical report on circumcision found that the foreskin tends to harbor micro-organisms that can lead to urinary tract infections in infants and tend to contribute to the transmission of sexually transmitted diseases in adults.[9]

Sensitivity and sexual sensation

The foreskin is specialized tissue that is packed with nerves and stretch receptors.[10] The foreskin contains Meissner's corpuscles, which are nerve endings involved in fine-touch sensitivity. They are most concentrated in the "ridged band", where the inner and outer foreskin layers meet, and least concentrated in the smooth inner layer of foreskin. Compared to other hairless skin areas on the body, the Meissner's index was highest in the finger tip (0.96) and lowest in the foreskin (0.28). The foreskin is the least sensitive hairless tissue of the body. A study also found that "the number of these nerve endings decreases significantly after the teenage to young adult years when sexual activity begins. This makes it very difficult to propose any sexual function for Meissner's corpuscles. A more feasible hypothesis is to regard them as a juvenile phenomenon, perhaps serving to protect the penis until the onset of puberty reveals its sexual function."[11] Charles Darwin speculated that the sensitivity of the foreskin to fine touch might have served as an "early warning system" in our naked ancestors while it protected the glans from the intrusion of biting insects and parasites.[12]

Moses and Bailey (1998), say that "it has not been demonstrated that [the foreskin] is associated with increased male sexual pleasure."[13] A 2015 study in sexual sensation concluded that the glans, not the foreskin, is involved in sexual sensation, particularly the corona and frenular (the area under the frenulum) areas.[11] Morris and Krieger state, "Thus, speculation and outdated opinion pieces claiming special properties of the foreskin, such as in penile function and masturbation, should be viewed with skepticism."[14] Contrary to popular belief and opinion, two studies conducted in 2013 that examined sexual penile sensitivity before and after circumcision both found higher penile sensitivity post circumcision. It was deduced that even a retracted foreskin would tend to reduce the stimulus to the corona and frenular areas, particularly on the outward stroke of intercourse. However, both studies concluded that there were no significant differences in sexual function between circumcised and uncircumcised men.[15][16] The 2015 study determined that "any sexual effect of circumcision must depend solely on the exposure of the glans and not on the absence of the prepuce."[11] The study concluded that male circumcision has no adverse effect on parameters relevant to sexual function, sensation, sensitivity, satisfaction, or pleasure.[11]

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."[2] There is controversy about whether the epithelium of the glans of an uncircumcised penis is keratinised; some authors claim that it is not,[17] while one study examined the glans of seven circumcised and six uncircumcised men and found the epithelia to be equally keratinised.[18]

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'."[19]

Evolution

In primates, the foreskin is present in the genitalia of both sexes and likely has been present for millions of years of evolution.[20] The evolution of complex penile morphologies like the foreskin may have been influenced by females.[21][22][23]

In modern times, there is controversy regarding whether the foreskin is a vital or vestigial structure.[24] In 1949, British physician Douglas Gairdner noted that the foreskin plays an important protective role in newborns. He wrote, "It is often stated that the prepuce is a vestigial structure devoid of function... However, it seems to be no accident that during the years when the child is incontinent the glans is completely clothed by the prepuce, for, deprived of this protection, the glans becomes susceptible to injury from contact with sodden clothes or napkin."[24] During the physical act of sex, the foreskin reduces friction, which can reduce the need for additional sources of lubrication.[24] "Some medical researchers, however, claim circumcised men enjoy sex just fine and that, in view of recent research on HIV transmission, the foreskin causes more trouble than it’s worth."[24] The area of the outer foreskin measures between 7–100 cm2,[25] and the inner foreskin measures between 18–68 cm2,[26] which is a wide range. Regarding vestigial structures, Charles Darwin wrote, "An organ, when rendered useless, may well be variable, for its variations cannot be checked by natural selection."[12] In the March 2017 publication of the Global Health Journal: Science and Practice, Morris and Krieger wrote, "The variability in foreskin size is consistent with the foreskin being a vestigial structure."[14]

Conditions

The foreskin can be involved in balanitis, phimosis, sexually transmitted infection and penile cancer.[27]

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. Phimosis can be treated by using topical steroid ointments and using lubricants during sex; for severe cases circumcision may be necessary.[1] 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 ischemia of the glans penis.[1]

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.[28]

Some birth defects of the foreskin can occur; all of them are rare. In aposthia there is no foreskin at birth,[29]: 37–39  in micropathia the foreskin doesn't cover the glans,[29]: 41–45  and in macroposthia, also called and congenital megaprepuce, the foreskin extends well past the end of the glans.[29]: 47–50 

It has been found that larger foreskins place uncircumcised men at an increased risk for HIV infection[30] most likely due to the larger surface area of inner foreskin and the high concentration of Langerhans cells.[18]

Surgical and non-surgical modifications of the foreskin

Preputioplasty:
Fig 1. Penis with tight phimotic ring making it difficult to retract the foreskin.
Fig 2. Foreskin retracted under anaesthetic with the phimotic ring or stenosis constricting the shaft of the penis and creating a "waist".
Fig 3. Incision closed laterally.
Fig 4. Penis with the loosened foreskin replaced over the glans.

Preputioplasty is the most common foreskin reconstruction technique, most often done when a boy is born with a foreskin that is too small;[31]: 177  a similar procedure is performed to relieve a tight foreskin without resorting to circumcision.[31]: 181 

Circumcision is the removal of the foreskin, either partially or completely. For newborns, it may be done for religious requirements or personal preferences surrounding hygiene and aesthetics.[32]: 257  Circumcision may also be performed on children or adults to treat phimosis, balanitis, or to prevent transmission of sexually transmitted disease.[33]: 166  As of 2012 no successful technique to reconstruct a circumcised foreskin had been published.[31]: 181  Some men have used weights to stretch the skin of the penis to regrow a foreskin; the resulting tissue does cover the glans but does not replicate the features of a foreskin.[34]

Other cultural or aesethetic practices include genital piercings involving the foreskin and slitting the foreskin.[35]

Langerhans cells

Langerhans cells are immature dendritic cells that are found in all areas of the penile epithelium,[36] but are most superficial in the inner surface of the foreskin.[36]

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.[37]

Foreskins of babies are also used for skin graft tissue,[38][39][40] and for β-interferon-based drugs.[41]

Foreskin fibroblasts have been used in biomedical research.[42]

See also

References

  1. ^ a b c "Phimosis (tight foreskin)". NHS Choices. 26 August 2015. Retrieved 21 September 2017.
  2. ^ a b c d e f "Male circumcision: Global trends and determinants of prevalence, safety and acceptability" (PDF). World Health Organization. 2007.
  3. ^ Manu Shah (January 2008). The Male Genitalia: A Clinician's Guide to Skin Problems and Sexually Transmitted Infections. Radcliffe Publishing. pp. 37–. ISBN 978-1-84619-040-7.
  4. ^ a b College of Physicians; Surgeons of British Columbia (2009). "Circumcision (Infant Male)" (PDF). Archived from the original (PDF) on May 31, 2012. Retrieved April 22, 2012.
  5. ^ Chengzu, Liu (2011). "Health Care for Foreskin Conditions". Epidemiology of Urogenital Diseases. Beijing: People's Medical Publishing House.
  6. ^ Xianze, Liang (2012). Tips on Puberty Health. Beijing: People's Education Press.
  7. ^ Guochang, Huang (2010). General Surgery. Beijing: People's Medical Publishing House.
  8. ^ a b Dobanovacki D, Lucić Prostran B, Sarac D, Antić J, Petković M, Lakić T (2012). "[Prepuce in boys and adolescents: what when, and how?]". Medicinski Pregled. 65 (7–8): 295–300. PMID 22924249.
  9. ^ American Academy of Pediatrics Task Force on Circumcision (September 2012). "Male circumcision". Pediatrics. 130 (3): e756–85. doi:10.1542/peds.2012-1990. PMID 22926175.. The technical report was published in conjunction with an updated statement of policy on circumcision: American Academy of Pediatrics Task Force on Circumcision (September 2012). "Circumcision policy statement" (PDF). Pediatrics. 130 (3): 585–6. doi:10.1542/peds.2012-1989. PMID 22926180.
  10. ^ Human Sexuality: An Encyclopedia. Routledge; 14 January 2014. ISBN 978-1-135-82502-7. p. 120–.
  11. ^ a b c d Cox, Guy; Krieger, John N.; Morris, Brian J. (June 2015). "Histological Correlates of Penile Sexual Sensation: Does Circumcision Make a Difference?". Sexual Medicine. 3 (2): 76–85. doi:10.1002/sm2.67. ISSN 2050-1161. PMC 4498824. PMID 26185672.
  12. ^ a b Darwin C. The Origin of Species by Means of Natural Selection. London, UK: John Murray; 1859.
  13. ^ Moses S; Bailey RC; Ronald AR (1998). "Male circumcision: assessment of health benefits and risks". Sexually Transmitted Infections. 74 (5): 368–373. Retrieved 2007-04-28. There is indirect evidence suggesting that the foreskin may have an important sensory function, although aside from anecdotal reports, it has not been demonstrated that this is associated with increased male sexual pleasure.
  14. ^ a b Morris BJ, Krieger JN, Klausner JD (March 2017). "CDC's Male Circumcision Recommendations Represent a Key Public Health Measure". Global Health, Science and Practice. 5 (1): 15–27. doi:10.9745/GHSP-D-16-00390. PMC 5478224. PMID 28351877.
  15. ^ Morris, B.J. and Krieger, J.N. Does male circumcision affect sexual function, sensitivity or satisfaction?—A systematic review. J Sex Med. 2013; 10: 2644–2657.
  16. ^ Tian, Y., Liu, W., Wang, J.Z., Wazir, R., Yue, X., and Wang, K.J. Effects of circumcision on male sexual functions: A systematic review and meta-analysis. Asian J Androl. 2013; 15: 662–666.
  17. ^ Barreto J, Caballero C, Cubilla A. Penis. In: Sternberg SS, editor. Histology for pathologists. 2nd ed. Philadelphia: Lippincott-Raven; 1997.
  18. ^ a b Szabo, R., & Short, R. V. (2000). How does male circumcision protect against HIV infection? BMJ : British Medical Journal, 320(7249), 1592–1594.
  19. ^ "Non-therapeutic circumcision of male minors (2010)". KNMG. 12 June 2010.
  20. ^ Martin, Robert D. (1990). Primate Origins and Evolution: A Phylogenetic Reconstruction. New Jersey: Princeton University Press. ISBN 978-0-691-08565-4.
  21. ^ Diamond, Jared M. (1997). Why Sex is Fun: The Evolution of Human Sexuality. London: Weidenfeld & Nicolson. ISBN 978-0-465-03126-9.
  22. ^ Darwin, Charles (1871). The Descent of Man and Selection in Relation to Sex. London: Murray. ISBN 978-1-148-75093-4.
  23. ^ Short, RV (1981). "Sexual selection in man and the great apes". Graham CE, ed. Reproductive Biology of the Great Apes: Comparative and Biomedical Perspectives. New York: Academic Press. ISBN 9780323149716.
  24. ^ a b c d Collier, Roger (2011-11-22). "Vital or vestigial? The foreskin has its fans and foes". CMAJ. 183 (17): 1963–1964. doi:10.1503/cmaj.109-4014. ISSN 0820-3946. PMC 3225416. PMID 22025652.
  25. ^ Kigozi G, Wawer M, Ssettuba A, et al. . Foreskin surface area and HIV acquisition in Rakai, Uganda (size matters). AIDS. 2009; 23(16):2209–2213. 10.1097/QAD.0b013e328330eda8.
  26. ^ Werker PMN, Terng ASC, Kon M. The prepuce free flap: dissection feasibility study and clinical application of a super-thin new flap. Plast Reconstr Surg. 1998; 102(4):1075–1082. 10.1097/00006534-199809020-00024.
  27. ^ Simmons MN, Jones JS (May 2007). "Male genital morphology and function: an evolutionary perspective". The Journal of Urology. 177 (5): 1625–31. doi:10.1016/j.juro.2007.01.011. PMID 17437774.
  28. ^ Chi C, Kirtschig G, Bakio M, et aL.. Topical interventions for genital lichen sclerosus. Cochrane. 2011. doi:10.1002/14651858.CD008240.pub2. PMID 22161424.
  29. ^ a b c Fahmy, Mohamed (2017). Congenital Anomalies of the Penis – Springer. Springer. ISBN 978-3-319-43310-3.
  30. ^ Morris BJ, Krieger JN.. Letter from Morris and Kriger Re: Examining penile sensitivity in neonatally circumcised and intact men using quantitative sensory testing: J.A. Bossio, C.F. Pukall and S.S. Steele J Urol 2016; 195:1848–1853. J Urol. 2016;196(6):1824–1825. 10.1016/j.juro.2016.05.127.
  31. ^ a b c Snodgrass, Warren T. (2012). "Chapter 15: Foreskin Reconstruction". In Bolnick, David A.; Koyle, Martin; Yosha, Assaf (eds.). Surgical Guide to Circumcision. London: Springer-Verlag. pp. 177–181. ISBN 978-1-4471-2858-8.
  32. ^ Cox, Guy; Morris, Brian J. (2012). "Chapter 21: Why Circumcision:From Prehistory to the Twenty-First Century". In Bolnick, David A.; Koyle, Martin; Yosha, Assaf (eds.). Surgical Guide to Circumcision. London: Springer-Verlag. pp. 243–259. ISBN 978-1-4471-2858-8. {{cite book}}: Unknown parameter |name-list-format= ignored (|name-list-style= suggested) (help)
  33. ^ McClung, Chris; Voelzke, Bryan (2012). "Chapter 14: Adult Circumcision". In Bolnick, David A.; Koyle, Martin; Yosha, Assaf (eds.). Surgical Guide to Circumcision. London: Springer-Verlag. pp. 165–175. ISBN 978-1-4471-2858-8. {{cite book}}: Unknown parameter |name-list-format= ignored (|name-list-style= suggested) (help)
  34. ^ Collier R. Whole again: the practice of foreskin restoration. CMAJ. 2011;183(18):2092–3. doi:10.1503/cmaj.109-4009. PMID 22083672.
  35. ^ "Paraphimosis : Article by Jong M Choe, MD, FACS". eMedicine. Retrieved 2012-07-16.
  36. ^ a b McCoombe SG, Short RV. Potential HIV-1 target cells in the human penis. AIDS. 2006;20(11):1491–5. doi:10.1097/01.aids.0000237364.11123.98. PMID 16847403.
  37. ^ McKie, Robin (1999-04-04). "Foreskins for Skin Grafts". The Toronto Star.
  38. ^ High-Tech Skinny on Skin Grafts; 1999-02-16 [archived October 10, 2008].
  39. ^ Grand DJ. Medscape. Skin Grafting; August 15, 2011.
  40. ^ Amst, Catherine; Carey, John (July 27, 1998). "Biotech Bodies". www.businessweek.com. The McGraw-Hill Companies Inc. Archived from the original on December 24, 2013. Retrieved 2017-09-17. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  41. ^ Cowan, Alison Leigh (April 19, 1992). "Wall Street; A Swiss Firm Makes Babies Its Bet". New York Times:Business. New York Times. Retrieved 2008-08-20.
  42. ^ Hovatta O, Mikkola M, Gertow K, Strömberg AM, Inzunza J, Hreinsson J, Rozell B, Blennow E, Andäng M, Ahrlund-Richter L (July 2003). "A culture system using human foreskin fibroblasts as feeder cells allows production of human embryonic stem cells". Human Reproduction. 18 (7): 1404–9. doi:10.1093/humrep/deg290. PMID 12832363.
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