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[[File:Vulva Diversity.jpg|thumb|right|300px|Variation in the appearance of women's labia]]
[[File:Vulva Diversity.jpg|thumb|right|300px|Variation in the appearance of women's labia]]
The coloration, size, length, and shape of the inner labia can vary extensively from woman to woman.<ref name="OurSexuality" /> In some women the ''labia minora'' are almost non-existent, and in others they can be fleshy and protuberant. They can range in color from a light pink in some women to brownish black in others.<ref name="HumanReproductiveBiology">{{cite book | url=http://books.google.ca/books?id=LqG5ngEACAAJ | title=Human reproductive biology | publisher=Elsevier Science | last1=Jones | first1=Richard E. last2=Lopez first2=Kristin H. | year=2006 | pages=55}}</ref> Symmetry varies greatly also, and some women only have one labium minora. Some differences are purely personal, while others may be genetically linked; a striking example of the latter is the [[elongated labia|elongated labia minora]] of the [[Khoisan]] peoples, whose "khoikhoi aprons" can hang down up to 10&nbsp;cm (four inches) past their labia majora when they are standing.
The coloration, size, length, and shape of the inner labia can vary extensively from woman to woman.<ref name="OurSexuality" /> In some women the ''labia minora'' are almost non-existent, and in others they can be fleshy and protuberant. They can range in color from a light pink in some women to brownish black in others.<ref name="HumanReproductiveBiology">{{cite book | url=http://books.google.ca/books?id=LqG5ngEACAAJ | title=Human reproductive biology | publisher=Elsevier Science | last1=Jones | first1=Richard E. last2=Lopez first2=Kristin H. | year=2006 | pages=55}}</ref> Symmetry varies greatly also, and some women only have one labium minora. Some differences are purely personal, while others may be genetically linked; a striking example of the latter is the [[elongated labia|elongated labia minora]] of the [[Khoisan]] peoples, whose "khoikhoi aprons" can hang down up to 10&nbsp;cm (four inches) past their labia majora when they are standing.

===Embryonic development===
[[File:Stages in the development of the external sexual organs in the female (from Gray1119).png|thumb|left|225px|[[Development of the reproductive system#External genitalia|Stages in the development of the female genitals]]]]<!-- TODO: It would be beneficial to replace this image with a labelled version -->
The biological sex of an individual is determined at [[conception]], which is the moment a [[sperm]] fertilizes an [[ovum]],<ref name="OurSexuality" /> creating a [[zygote]].<ref name="SexualityNow" /> The chromosome type contained in the sperm determines the sex of the zygote. A [[Y chromosome]] results in a male, and an [[X chromosome]] results in a female. A male zygote will later grow into an [[embryo]] and form [[testes]], which produce [[androgens]] (male hormones), causing male genitals to be formed. Female genitals will be formed if androgens are absent.

The genitals begin to develop after approximately 4 to 6 weeks of [[gestation]].<ref name="SexualityNow" /> Initially, the external genitals develop the same way regardless of the sex of the embryo, and this period of development is called the ''sexually indifferent'' stage.<ref name="HumanReproductiveBiology" /> The embroyo develops three distinct external genital structures: a [[genital tubercle]]; two [[urogenital folds]], one on either side of the tubercle; and two [[labioscrotal swellings]], each bounding one of the urogenital folds.<ref name="TheVulvaAnatomyPhysiologyPathology" />

[[Sexual differentiation]] starts on the internal sex organs at about 5 weeks of gestation, resulting in the formation of either testes in males, or ovaries in females. If testes were formed, they begin to secrete androgens that affect the external genital development at about week 8 or 9 of gestation.<ref name="SexualityNow" /> With the presence of androgens, male genitals will be formed, and female genitals will be formed otherwise. The urogenital folds form the labia minora in females, or penile shaft in males. The labioscrotal swellings become the labia majora and mons pubis in females, or fuse to become the scrotum in males. Sexual differentiation is complete at around 12 weeks of gestation.<ref name="OurSexuality" />


===Homology===
===Homology===
The labia majora are [[homology (biology)|homologous]] to the [[scrotum]] in males, and the labia minora are homologous to male's [[penile urethra]] and part of the penile skin.<ref name="VulvaAnatomyPhysiologyPathology" />
Because they develop from the same tissues, the labia minora are said to be [[homology (biology)|homologous]] with the penile shaft, and the labia majora are homologous with the scrotum.<ref name="OurSexuality" /><ref name="SexualityNow" />


===Changes over time===
===Changes over time===

Revision as of 19:48, 2 April 2014

For other uses, see Labia (disambiguation).
Human Labia (pubic hair has been removed from the labia majora in these pictures):
Top: Woman in standing position, labia minora partly covered
Bottom: Exposing labia minora by spreading labia majora

The labia are anatomical structures that are part of the female genitalia; they are the major externally visible portions of the vulva. In humans, there are two pairs of labia: the outer labia, or labia majora are larger and fattier, while the labia minora are folds of skin between the outer labia. The labia surround and protect the clitoris and the openings of the vagina and urethra.

Etymology

Labium (plural labia) is a Latin-derived term meaning "Lip". Labium and its derivatives (including labial, labrum) are used to describe any lip-like structure, but in the English language, labium often specifically refers to parts of the vulva.

Anatomy

Left: In their resting state, the labia protect the inner areas of the vulva.
Right: Spreading the labia apart exposes the vulvar vestibule, clitoris, vagina and urethra. The upper portion of each labium minora splits to join with both the clitoral glans, and the clitoral hood. The lower portion of each labium minora joins to form the fourchette. The shiny, pink inner surface of the labia majora can be seen in the left corner of the righthand image, between the outer labia majora and the labia minora.

The labia majora, also commonly called outer labia or outer lips, are lip-like structures consisting mostly of skin and adipose (fatty) tissue, which extend on either side of the vulva to form the pudendal cleft through the middle. The labia majora often have a plump appearance, and are thicker towards the anterior.[1] The anterior junction of the labia majora is called the anterior commissure, which is below the mons pubis and above the clitoris. To the posterior, the labia majora join at the posterior commissure, which is above the perineum and below the frenulum of the labia minora.

When standing or with the legs together, they usually entirely or partially cover the moist, sensitive inner surfaces of the vulva, which indirectly protects the vagina and urethra,[1] much like the lips protect the mouth.

The outer surface of the labia majora is pigmented skin, and develops pubic hair during puberty. The inner surface is smooth, hairless skin, which resembles a mucous membrane, and is only visible when the inner and outer labia are drawn apart. Both the inner and outer surfaces contain sebaceous glands (oil glands), apocrine sweat glands, and eccrine sweat glands. The labia majora have fewer superficial nerve endings than the rest of the vulva, but the skin is highly vascularized.[2]

The labia minora (obsolete: nymphae), also called inner labia or inner lips, are two soft folds of fat-free, hairless skin between the labia majora. They enclose and protect the vulvar vestibule, urethra and vagina. The upper portion of each labium minora splits to join with both the clitoral glans, and the clitoral hood. The labia minora meet posterially at the frenulum of the labia minora (also known as the fourchette), which is a fold of skin below the vaginal orifice. The fourchette is more prominent in younger women, and often recedes after sexual activity[2] and childbirth.[1]

The internal surface of the labia minora is a thin moist skin, with the appearance of a mucous membrane. They contain many sebaceous glands, and occasionally have eccrine sweat glands. The labia minora have many sensory nerve endings, and have a core of erectile tissue.[1]

Diversity

File:Vulva Diversity.jpg
Variation in the appearance of women's labia

The coloration, size, length, and shape of the inner labia can vary extensively from woman to woman.[3] In some women the labia minora are almost non-existent, and in others they can be fleshy and protuberant. They can range in color from a light pink in some women to brownish black in others.[4] Symmetry varies greatly also, and some women only have one labium minora. Some differences are purely personal, while others may be genetically linked; a striking example of the latter is the elongated labia minora of the Khoisan peoples, whose "khoikhoi aprons" can hang down up to 10 cm (four inches) past their labia majora when they are standing.

Embryonic development

Stages in the development of the female genitals

The biological sex of an individual is determined at conception, which is the moment a sperm fertilizes an ovum,[3] creating a zygote.[5] The chromosome type contained in the sperm determines the sex of the zygote. A Y chromosome results in a male, and an X chromosome results in a female. A male zygote will later grow into an embryo and form testes, which produce androgens (male hormones), causing male genitals to be formed. Female genitals will be formed if androgens are absent.

The genitals begin to develop after approximately 4 to 6 weeks of gestation.[5] Initially, the external genitals develop the same way regardless of the sex of the embryo, and this period of development is called the sexually indifferent stage.[4] The embroyo develops three distinct external genital structures: a genital tubercle; two urogenital folds, one on either side of the tubercle; and two labioscrotal swellings, each bounding one of the urogenital folds.[6]

Sexual differentiation starts on the internal sex organs at about 5 weeks of gestation, resulting in the formation of either testes in males, or ovaries in females. If testes were formed, they begin to secrete androgens that affect the external genital development at about week 8 or 9 of gestation.[5] With the presence of androgens, male genitals will be formed, and female genitals will be formed otherwise. The urogenital folds form the labia minora in females, or penile shaft in males. The labioscrotal swellings become the labia majora and mons pubis in females, or fuse to become the scrotum in males. Sexual differentiation is complete at around 12 weeks of gestation.[3]

Homology

Because they develop from the same tissues, the labia minora are said to be homologous with the penile shaft, and the labia majora are homologous with the scrotum.[3][5]

Changes over time

The genital tissues are greatly influenced by natural fluctuations in hormone levels, which lead to changes in labia size, appearance, and elasticity at various life stages. At birth, the labia minora are well-developed, and the labia majora appear plump due to being exposed to maternal hormones in the womb. The labia majora have the same color as the surrounding skin. Labial adhesions can occur between the ages of 3 months and 2 years, and may make the vulva look flat. These adhesions are not usually a cause for concern, and usually disappear without treatment. Treatment options may include estrogen cream, manual separation with local anesthesia, or surgical separation under sedation.[2]

During early childhood, the labia majora look flat and smooth because of decreasing levels of body fat, and the diminished effects of maternal hormones. The labia minora become less prominent.

During puberty, increased hormone levels often significantly change the appearance of the labia. The labia majora regain fat, and begin growing pubic hair. The labia minora become more elastic, prominent, and wrinkled.

By adulthood, the outer surface of the labia majora may be darker than the surrounding skin, and may have wrinkles similar to those on a male's scrotum. During the reproductive years, if a woman delivers a child, the fourchette will flatten. Pregnancy may cause the labia minora to darken in color.[3]

Later in life, the labia majora once again gradually lose fat, becoming flatter and more wrinkled, and pubic hair turns grey. Following menopause, falling hormone levels cause further changes to the labia. The labia minora atrophy, making them become less elastic, and pubic hair on the labia majora becomes more sparse.[2]

Sexual arousal and response

Left: A vulva in the resting, unaroused state.
Right: The woman is sexually aroused, causing the inner and outer labia to swell, the labia majora to recede slightly, and the vulva to become lubricated.

The labia are one of a woman's erogenous zones. The labia minora are sexually responsive,[7] and sensitivity varies greatly between women. In some women, they are so sensitive that anything other than light touch may be uncomfortable, whereas stimulation may elicit no sexual response in others. The labia may be sexually stimulated as part of masturbation or with a sex partner, such as by fingering or oral sex. Moving the labia minora can also stimulate the extremely sensitive clitoris.

During sexual arousal, the labia majora swell due to increased blood flow to the region,[5] and draw back,[3] opening the vulva slightly. The labia minora become engorged with blood, causing them to expand in diameter by two to three times, and darken or redden in color.[5] Because pregnancy and childbirth increase genital vascularity, the inner and outer labia will engorge faster in women who have had children.[5]

After a period of sexual stimulation, the labia minora will become further engorged with blood approximately 30 seconds to 3 minutes before orgasm,[5] causing them to redden further.[5][8] In women who have had children, the labia majora may also swell significantly during this period, becoming a dark red. Continued stimulation can result in an orgasm, and the orgasmic contractions help remove blood trapped in the inner and outer labia, as well as the clitoris and other parts of the vulva, which causes pleasurable orgasmic sensations. Following orgasm or when a woman is no longer sexually aroused, the labia return to their unaroused state.[5]

Society and culture

In many cultures and locations all over the world, the labia, as part of the genitalia, are considered private, or intimate parts, whose exposure (especially in public) is governed by fairly strict socio-cultural mores. In many cases, public exposure is limited, and often prohibited by law.[9][10]

Labia with pubic hair

Views on pubic hair differ between people and between cultures. Some women prefer the look or feel of pubic hair, while others may choose to trim or remove it for aesthetic or personal reasons.

In some cultures, any of several areas of the female genitals are surgically altered or removed for religious, cultural, perceived hygienic or aesthetic purposes. Terms for these types of procedures include female circumcision, Pharaonic circumcision, intubation, infibulation, and female genital mutilation or cutting.[11][dead link][12] In many parts of the world the practice is believed to have ancient origins, but even in countries where it has been widespread in the past, it is now mostly illegal.

Labiaplasty is a controversial plastic surgery procedure that involves the creation or reshaping of the labia.[13] The clinical procedure of labiaplasty alters the appearance of the labia, for cosmetic or medical reasons.

Labia piercing is a cosmetic piercing, usually with a special needle under sterile conditions, of either the inner labia (labia minora) or the outer labia (labia majora). Jewelry is worn in the resulting opening.

Additional images

See also

References

  1. ^ a b c d Keith L. Moore, Anne M.R. Agur, Arthur F. Dalley II (2010). Essential Clinical Anatomy, Fourth Edition. ISBN 9781609131128.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ a b c d Farage, Miranda A.; Maibach, Howard I. (2006). The Vulva - Anatomy, Physiology, and Pathology. ISBN 0-8493-3608-2.
  3. ^ a b c d e f Crooks, Robert L. (2005). Our Sexuality. Cengage Learning. ISBN 0495812943.
  4. ^ a b Jones, Richard E. last2=Lopez first2=Kristin H. (2006). Human reproductive biology. Elsevier Science. p. 55. {{cite book}}: Missing pipe in: |first1= (help)CS1 maint: numeric names: authors list (link)
  5. ^ a b c d e f g h i j Carroll, Janell L. (2011). Sexuality Now: Embracing Diversity. Cengage Learning. ISBN 0-495-60274-4.
  6. ^ Cite error: The named reference TheVulvaAnatomyPhysiologyPathology was invoked but never defined (see the help page).
  7. ^ Ginger, Van Anh T.; Yang, Claire C. (2011). "Functional Anatomy of the Female Sex Organs" in Cancer and Sexual Health (PDF). Humana Press. pp. 13–23.
  8. ^ Lamanna, Mary Ann; Riedmann, Agnes (2011). Marriages, Families, and Relationships: Making Choices in a Diverse Society. Cengage Learning. pp. A7.
  9. ^ 617.23, Minnesota Statute
  10. ^ 18-4116 — INDECENT EXPOSURE - Idaho 18-4116 — INDECENT EXPOSURE - Idaho Code :: Justia
  11. ^ http://www.emro.who.int/publications/Book_Details.asp?ID=58%7CWorld Health Organization website
  12. ^ Female Genital Mutilation (FGM) - Terminology and the main types of FGM
  13. ^ The Centrefold Project
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