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Vulva


The vulva (from the Latin vulva, plural vulvae, see etymology) consists of the external genital organs of the female mammal.[1] This article deals with the vulva of the human being, although the structures are similar for other mammals.

The vulva has many major and minor anatomical structures, including the labia majora, mons pubis, labia minora, clitoris, bulb of vestibule, vulval vestibule, greater and lesser vestibular glands, and the opening of the vagina. Its development occurs during several phases, chiefly during the fetal and pubertal periods of time. As the outer portal of the human uterus or womb, it protects its opening by a “double door”: the labia majora (large lips) and the labia minora (small lips). The vagina is a self-cleaning organ, sustaining healthy microbial flora that flow from the inside out; the vulva needs only simple washing to assure good vulvovaginal health, without recourse to any internal cleansing.

The vulva has a sexual function; these external organs are richly innervated and provide pleasure when properly stimulated. In various branches of art, the vulva has been depicted as the organ that has the power both to “give life” (often associated with the womb), and to give sexual pleasure to humankind.[2]

The vulva also contains the opening of the female urethra, and thus serves the vital function of passing urine.

Structure

In human beings, major structures of the vulva are:[3]

  • the mons pubis
  • the labia, consisting of the labia majora and the labia minora
  • the external portion of the clitoris (Latin: Clitoral glans) and the clitoral hood
  • the vulval vestibule
  • the pudendal cleft
  • the frenulum labiorum pudendi or the fourchette
  • the opening (or urinary meatus) of the urethra
  • the opening (or introitus) of the vagina
  • the hymen and

Other structures:

  • the perineum
  • the sebaceous glands on labia majora
  • the vaginal glands:
  • Bartholin’s glands
  • Paraurethral glands called Skene’s glands

The soft mound at the front of the vulva is formed by fatty tissue covering the pubic bone, and is called the mons pubis. The term mons pubis is Latin for “pubic mound” and it is gender-nonspecific. There is, however, a variant term that specifies gender: in human females, the mons pubis is often referred to as the mons veneris, Latin for “mound of Venus” or “mound of love”. The mons pubis separates into two folds of skin called the labia majora, literally “major (or large) lips”. The cleft between the labia majora is called the pudendal cleft, or cleft of Venus, and it contains and protects the other, more delicate structures of the vulva. The labia majora meet again at a flat area between the pudendal cleft and the anus called the perineum. The color of the outside skin of the labia majora is usually close to the overall skin color of the individual, although there is considerable variation. The inside skin and mucus membrane are often pink or brownish. After the onset of puberty, the mons pubis and the labia majora become covered by pubic hair. This hair sometimes extends to the inner thighs and perineum, but the density, texture, color, and extent of pubic hair coverage vary considerably, due to both individual variation and cultural practices of hair modification or removal.

The labia minora are two soft folds of skin within the labia majora. While labia minora translates as “minor (or small) lips”, often the “minora” are of considerable size, and may protrude outside the “majora”. Much of the variation among vulvas lies in the significant differences in the size, shape, and color of the labia minora.

The clitoris is located at the front of the vulva, where the labia minora meet. The visible portion of the clitoris is the clitoral glans. Typically, the clitoral glans is roughly the size and shape of a pea, although it can be significantly larger or smaller. The clitoral glans is highly sensitive, containing as many nerve endings as the analogous organ in males, the glans penis. The point where the labia minora attach to the clitoris is called the frenulum clitoridis. A prepuce, the clitoral hood, normally covers and protects the clitoris, however in women with particularly large clitorises or small prepuces, the clitoris may be partially or wholly exposed at all times. The clitoral hood is the female equivalent of the male foreskin.[4] Often the clitoral hood is only partially hidden inside of the pudendal cleft.

The area between the labia minora is called the vulval vestibule, and it contains the vaginal and urethral openings. The urethral opening (meatus) is located below the clitoris and just in front of the vagina. This is where urine passes from the urinary bladder to be disposed of.

The opening of the vagina is located at the bottom of the vulval vestibule, toward the perineum. The term introitus is more technically correct than “opening”, since the vagina is usually collapsed, with the opening closed, unless something is inserted. The introitus is sometimes partly covered by a membrane called the hymen. The hymen will rupture during the first episode of vigorous sex, and the blood produced by this rupture has been seen as a sign of virginity. However, the hymen may also rupture spontaneously during exercise (including horseback riding) or be stretched by normal activities such as use of tampons and menstrual cups, or be so minor as to be unnoticeable. In some rare cases, the hymen may completely cover the vaginal opening, requiring a surgical incision. Slightly below and to the left and right of the vaginal opening are two Bartholin glands which produce a waxy, pheromone-containing substance, the purpose of which is not yet fully known.

The appearance of the vulva and the size of the various parts varies a great deal from one female to another, and it is also common for the left and right sides to differ in appearance.

Fluids and odor

There are a number of different secretions associated with the vulva, including urine, sweat, menses, skin oils (sebum), Bartholin’s and Skene’s gland secretions, and vaginal wall secretions. These secretions contain a mix of chemicals, including pyridine, squalene, urea, acetic acid, lactic acid, complex alcohols, glycols, ketones, and aldehydes. During sexual arousal, vaginal lubrication increases.

Smegma

Smegma is a white substance formed from a combination of dead cells, skin oils, moisture and naturally occurring bacteria, that forms in mammalian genitalia. In females it collects around the clitoris and labial folds.

Aliphatic acids

Approximately one third of women produce aliphatic acids. These acids are a pungent class of chemicals which other primate species produce as sexual-olfactory signals. While there is some debate, researchers often refer to them as human pheromones. These acids are produced by natural bacteria resident on the skin. The acid content varies with the menstrual cycle, rising from one day after menstruation, and peaking mid-cycle, just before ovulation.

Sexual arousal

Sexual arousal results in a number of physical changes in the vulva. Arousal may be broken up into four somewhat arbitrary phases: Excitement, Plateau, Orgasm, and Resolution.

Excitement

Vaginal lubrication begins first. This is caused by vasocongestion of the vaginal walls. Increased blood pooling there causes moisture to seep from the walls. These droplets collect together and flow out of the vagina, moistening the vulva. The labia majora flatten and spread apart, and the clitoris and labia minora increase in size.

Unlike an average man, whose sexual excitement will cause an obvious erection, a woman experiencing arousal may not be aware that her vagina has produced lubrication and has been engorged with blood.

Plateau

Increased vasocongestion in the vagina causes it to swell, decreasing the size of the vaginal opening by about 30%. The clitoris becomes increasingly erect, and the glans moves towards the pubic bone, becoming concealed by the hood. The labia minora increase considerably in thickness, approximately 2–6 times, causing them to spread apart, displaying the vaginal opening. The labia minora sometimes change considerably in color, going from pink to red in lighter skinned women who have not borne a child, or red to dark red in those that have.[citation needed]

Orgasm

Immediately prior to the female orgasm, the clitoris becomes exceptionally engorged, causing the glans to appear to retract into the clitoral hood. This is thought to protect the sensitive glans during orgasm. However, there is some doubt that this is the case, since the same engorgement prior to orgasm occurs in the male homologous structure, the penis, the function of which is thought to be to extend the penis as close to the cervix as possible prior to ejaculation.

Rhythmic muscle contractions occur in the outer third of the vagina, as well as the uterus and anus. They occur initially at a rate of about one every 0.8 seconds, becoming less intense and more randomly spaced as the orgasm continues. An orgasm may have as few as one or as many as 15 or more contractions, depending on its intensity. Orgasm may be accompanied by female ejaculation, causing liquid from either the Skene’s gland or bladder to be expelled through the urethra.

Immediately after orgasm the clitoris may be so sensitive that any stimulation is either exciting or uncomfortable.

Resolution

The pooled blood begins to dissipate, although at a much slower rate if an orgasm has not occurred. The vagina and vaginal opening return to their normal relaxed state, and the rest of the vulva returns to its normal size, position and color.

Development

Fetus

During the first eight weeks of life, both male and female fetuses have the same rudimentary reproductive and sexual organs, and maternal hormones control their development. Male and female organs begin to become distinct when the fetus is able to begin producing its own hormones, although visible determination of the sex is difficult until after the twelfth week.

During the sixth week, the genital tubercle develops in front of the cloacal membrane. The tubercle contains a groove termed the urethral groove. The urogenital sinus (forerunner of the bladder) opens into this groove. On either side of the groove are the urogenital folds. Beside the tubercle are a pair of ridges called the labioscrotal swellings.

Beginning in the third month of development, the genital tubercle becomes the clitoris. The urogenital folds become the labia minora, and the labioscrotal swellings become the labia majora.

Childhood

At birth, the neonate’s vulva (and breast tissue—see witch’s milk) may be swollen or enlarged as a result of having been exposed, via the placenta, to her mother’s increased levels of hormones. The clitoris is proportionally larger than it is likely to be later in life. Within a short period of time as these hormones wear off, the vulva will shrink in size.

From one year of age until the onset of puberty, the vulva does not undergo any change in appearance, other than growing in proportion with the rest of her body.

Puberty

The onset of puberty produces a number of changes. The structures of the vulva become proportionately larger and may become more pronounced. Coloration may change and pubic hair develops, first on the labia majora, and later spreading to the mons pubis, and sometimes the inner thighs and perineum.

In preadolescent girls, the vulva appears to be positioned further forward than in adults, showing a larger percentage of the labia majora and pudendal cleft when standing. During puberty the mons pubis enlarges, pushing the forward portion of the labia majora away from the pubic bone, and parallel to the ground (when standing). Variations in body fat levels affect the extent to which this occurs.

Childbirth

During childbirth, the vagina and vulva must stretch to accommodate the baby’s head (approximately 9.5 cm or 3.7 in). This can result in tears in the vaginal opening, labia, and clitoris. An episiotomy (a preemptive surgical cutting of the perineum) is sometimes performed to limit tearing, but its appropriateness as a routine procedure is under question.

Some of the changes to the vagina and vulva that occur during pregnancy may become permanent.

Post-menopause

During menopause, hormone levels decrease, and as this process happens, reproductive tissues which are sensitive to these hormones shrink in size. The mons pubis, labia, and clitoris are reduced in size in post-menopause, although not usually to pre-puberty proportions.

Sexual homology

Most male and female sex organs originate from the same tissues during fetal development; this includes the vulva. The anatomy of the vulva is related to the anatomy of the male genitalia by a shared developmental biology. Organs that have a common developmental ancestry in this way are said to be homologous.

The clitoral glans is homologous to the glans penis in males, and the clitoral body and the clitoral crura are homologous to the corpora cavernosa of the penis. The labia majora, labia minora, and clitoral hood are homologous to the scrotum, shaft skin of the penis, and the foreskin, respectively. The vestibular bulbs beneath the skin of the labia minora are homologous to the corpus spongiosum, the tissue of the penis surrounding the urethra. The Bartholin’s glands are homologous to the Cowper’s glands in males.

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