Vulva

The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external female sex organs. The vulva includes the mons pubis (or mons veneris), labia majora, labia minora, clitoris, vestibular bulbs, vulval vestibule, urinary meatus, the vaginal opening, hymen, and Bartholin's and Skene's vestibular glands. The urinary meatus is also included as it opens into the vulval vestibule. Other features of the vulva include the pudendal cleft, sebaceous glands, the urogenital triangle (anterior part of the perineum), and pubic hair. The vulva includes the entrance to the vagina, which leads to the uterus, and provides a double layer of protection for this by the folds of the outer and inner labia. Pelvic floor muscles support the structures of the vulva. Other muscles of the urogenital triangle also give support.

Blood supply to the vulva comes from the three pudendal arteries. The internal pudendal veins give drainage. Afferent lymph vessels carry lymph away from the vulva to the inguinal lymph nodes. The nerves that supply the vulva are the pudendal nerve, perineal nerve, ilioinguinal nerve and their branches. Blood and nerve supply to the vulva contribute to the stages of sexual arousal that are helpful in the reproduction process.

Following the development of the vulva, changes take place at birth, childhood, puberty, menopause and post-menopause. There is a great deal of variation in the appearance of the vulva, particularly in relation to the labia minora. The vulva can be affected by many disorders which may often result in irritation. Vulvovaginal health measures can prevent many of these. Other disorders include a number of infections and cancers. There are several vulval restorative surgeries known as genitoplasties, and some of these are also used as cosmetic surgery procedures.

Different cultures have held different views of the vulva. Some ancient religions and societies have worshipped the vulva and revered the female as a goddess. Major traditions in Hinduism continue this. In Western societies, there has been a largely negative attitude typified by the medical terminology of , meaning parts to be ashamed of. There has been an artistic reaction to this in various attempts to bring about a more positive and natural outlook, such as work from British, American, and Japanese artists. While the vagina is a separate part of the anatomy, it has often been used synonymously with vulva.

Structure

The main structures of the vulva are: the mons pubis, the labia majora and labia minora, the external parts of the clitoris – the clitoral hood and the glans, the urinary meatus, the vaginal opening and hymen, and Bartholin's and Skene's vestibular glands. Other features include the pudendal cleft, pubic hair, sebaceous glands, the vulval vestibule, and the urogenital triangle.

Mons pubis

The mons pubis is the soft mound of fatty tissue at the front of the vulva, in the pubic region covering the pubic bone. is Latin for "pubic mound" and is present in both sexes to act as a cushion during sexual intercourse, and is more pronounced in the female. The variant term ''mons veneris'' ('mound of Venus') is used specifically for females. The lower part of the mons pubis is divided by a fissure – the pudendal cleft – which separates the mons pubis into the labia majora. After puberty, the clitoral hood and the labia minora can protrude into the pudendal cleft in a variable degree. The mons and labia majora become covered in pubic hair at puberty.

Labia

The labia majora and the labia minora cover the vulval vestibule. The outer pair of folds, divided by the pudendal cleft, are the labia majora (New Latin for "larger lips"). They contain and protect the other structures of the vulva. The labia majora meet at the front at the mons pubis, and meet posteriorly at the urogenital triangle (the anterior part of the perineum) between the pudendal cleft and the anus. The labia minora are often pink or brownish black, relevant to the person's skin color.

The grooves between the labia majora and labia minora are called the interlabial sulci, or interlabial folds. The labia minora (smaller lips) are the inner two soft folds, within the labia majora. They have more color than the labia majora and contain numerous sebaceous glands. They meet posteriorly at the frenulum of the labia minora, a fold of restrictive tissue. The labia minora meet again at the front of the vulva to form the clitoral hood, also known as the prepuce.

The visible portion of the clitoris is the clitoral glans. Typically, this is roughly the size and shape of a pea, and can vary in size from about 6 mm to 25 mm. The size can also vary when it is erect. The clitoral glans contains as many nerve endings as the much larger homologous glans penis in the male, which makes it highly sensitive. The only known function of the clitoris is to focus sexual feelings. The clitoral hood is a protective fold of skin which varies in shape and size, and it may partially or completely cover the clitoris. The clitoris is the homologue of the penis, and the clitoral hood is the female equivalent of the male foreskin, and may be partially or completely hidden within the pudendal cleft.

Vestibule

The area between the labia minora where the vaginal opening and the urinary meatus are located is called the vulval vestibule, or vestibule of the vagina. The urinary meatus is below the clitoris and just in front of the vaginal opening which is near to the perineum. The term ''introitus'' is more technically correct than "opening", since the vagina is usually collapsed, with the opening closed. The introitus is sometimes partly covered by a membrane called the hymen. The hymen will usually rupture during the first episode of vigorous sex, and the blood produced by this rupture has been seen to signify virginity. However, the hymen may also rupture spontaneously during exercise or be stretched by normal activities such as the use of tampons and menstrual cups, or be so minor as to be unnoticeable, or be absent. In some rare cases, the hymen may completely cover the vaginal opening, requiring a surgical procedure called a hymenotomy. On either side of the back part of the vaginal opening are the two greater vestibular glands known as Bartholin's glands. These glands secrete mucus and a vaginal and vulval lubricant. They are homologous to the bulbourethral glands in the male. The lesser vestibular glands known as Skene's glands, are found on the anterior wall of the vagina. They are homologues of the male prostate gland and are also referred to as the female prostate.

Muscles

Pelvic floor muscles help to support the vulvar structures. The voluntary, pubococcygeus muscle, part of the levator ani muscle partially constricts the vaginal opening. Other muscles of the urogenital triangle support the vulvar area and they include the transverse perineal muscles, the bulbospongiosus, and the ischiocavernosus muscles. The bulbospongiosus muscle decreases the vaginal opening. Their contractions play a role in the vaginal contractions of orgasm by causing the vestibular bulbs to contract.

Blood, lymph and nerve supply

The tissues of the vulva are highly vascularised and blood supply is provided by the three pudendal arteries. Venous return is via the external and internal pudendal veins.
The organs and tissues of the vulva are drained by a chain of superficial inguinal lymph nodes located along the blood vessels.

The ilioinguinal nerve originates from the first lumbar nerve and gives branches that include the anterior labial nerves which supply the skin of the mons pubis and the labia majora. The perineal nerve is one of the terminal branches of the pudendal nerve and this branches into the posterior labial nerves to supply the labia. The pudendal nerve branches include the dorsal nerve of clitoris which gives sensation to the clitoris. The clitoral glans is seen to be populated by a large number of small nerves, a number that decreases as the tissue changes towards the urethra. The density of nerves at the glans indicates that it is the center of heightened sensation. Cavernous nerves from the uterovaginal plexus supply the erectile tissue of the clitoris. These are joined underneath the pubic arch by the dorsal nerve of the clitoris.
The pudendal nerve enters the pelvis through the lesser sciatic foramen and continues medial to the internal pudendal artery. The point where the nerve circles the ischial spine is the location where a pudendal block of local anesthetic can be administered to inhibit sensation to the vulva. A number of smaller nerves split off from the pudendal nerve. The deep branch of the perineal nerve supplies the muscles of the perineum and a branch of this supplies the bulb of the vestibule.

Variations

There is a great deal of variation in the appearance of female genitals. Much of this variation lies in the significant differences in the size, shape, and color of the labia minora. Though called the smaller lips they can often be of considerable size and may protrude outside the vagina or labia majora. This variation has also been evidenced in a large display of 400 vulval casts called the ''Great Wall of Vagina'' created by Jamie McCartney to fill the lack of information of what a normal vulva looks like. The casts taken from a large and varied group of women showed clearly that there is much variation. Pubic hair also varies in its color, texture, and amount of curl.

Researchers from the Elizabeth Garret Anderson Hospital, London, measured multiple genital dimensions of 50 women between the ages of 18 and 50, with a mean age of 35.6:Pdf.

Development

Prenatal development

In week three of the development of the embryo, mesenchyme cells from the primitive streak migrate around the cloacal membrane. Early in the fifth week the cells form two swellings called the cloacal folds. The cloacal folds meet in front of the cloacal membrane and form a raised area known as the genital tubercle. The urorectal septum fuses with the cloacal membrane to form the perineum. This division creates two areas one surrounded by the urethral folds and the other by the anal folds. These areas become the urogenital triangle and the anal triangle. The area between the vagina and the anus is known as the clinical perineum.

At the same time a pair of swellings on either side of the urethral folds known as the genital swellings develop into the labioscrotal swellings. Sexual differentiation takes place, and at the end of week 6 in the female, hormones stimulate further development and the genital tubercle bends and forms the clitoris. The urethral folds form the labia minora and the labioscrotal swellings form the labia majora. At this time the sexes still cannot be distinguished. The appearance of the external genitalia is similar in male and female embryos until the twelfth week and even then is difficult to distinguish.

The uterovaginal canal or genital canal, forms in the third month of the development of the urogenital system. The lower part of the canal is blocked off by a plate of tissue, the vaginal plate. This tissue develops and lengthens during the third to fifth months and the lower part of the vaginal canal is formed by a process of desquamation or cell shedding. The end of the vaginal canal is blocked off by an endodermal membrane which separates the opening from the vestibule. In the fifth month the membrane degenerates but leaves a remnant called the hymen.

Organs in the male and female with a shared common ancestry are said to be homologous. The clitoral glans is homologous to the male glans penis, and the clitoral body and the clitoral crura are homologous to the corpora cavernosa of the penis. The labia majora is homologous to the scrotum; the clitoral hood is homologous to the foreskin, and the labia minora is homologous to the spongy urethra. The vestibular bulbs beneath the skin of the labia minora are homologous to the corpus spongiosum, the tissue of the penis surrounding the urethra, and to the bulb of the penis. Bartholin's glands are homologous to the bulbourethral glands in males.

Childhood

The newborn's vulva may be swollen or enlarged as a result of having been exposed, via the placenta, to her mother's increased levels of hormones. The labia majora are closed. These changes disappear over the first few months. During childhood before puberty, the lack of estrogen can cause the labia to become sticky and to ultimately join firmly together. This condition is known as labial fusion and is rarely found after puberty when oestrogen production has increased.

Puberty

Puberty is the onset of the ability to reproduce, and takes place over two to three years, producing a number of changes. The structures of the vulva become proportionately larger and may become more pronounced. Pubarche, the first appearance of pubic hair develops, firstly on the labia majora, and later spreads to the mons pubis, and sometimes to the inner thighs and perineum. Pubic hair is much coarser than other body hair, and is considered a secondary sex characteristic. Pubarche can occur independently of puberty. ''Premature pubarche'' may sometimes indicate a later metabolic-endocrine disorder seen at adolescence. The disorder sometimes known as a ''polyendocrine disorder'' is marked by elevated levels of androgen, insulin, and lipids, and may originate in the fetus. Instead of being seen as a normal variant it is proposed that premature pubarche may be seen as a marker for these later endocrine disorders.

Apocrine sweat glands secrete sweat into the pubic hair follicles. This is broken down by bacteria on the skin and produces an odor, which some consider to act as an attractant sex pheromone. The labia minora may grow more prominent and undergo changes in color. At puberty the first monthly period known as menarche marks the onset of menstruation.
In prepubertal girls the skin of the vulva is thin and delicate, and its neutral pH makes it prone to irritation. The production of the female sex hormone estradiol (an estrogen) at puberty, causes the perineal skin to thicken by keratinising, and this reduces the risk of infection. Estrogen also causes the laying down of fat in the development of the secondary sex characteristics. This contributes to the maturation of the vulva with increases in the size of the mons pubis, and the labia majora and the enlargement of the labia minora.

Pregnancy

In pregnancy the vulva and vagina take on a bluish colouring due to venous congestion. This appears between the eighth and twelfth week and continues to darken as the pregnancy continues. Estrogen is produced in large quantities during pregnancy and this causes the external genitals to become enlarged. The vaginal opening and the vagina are also enlarged. After childbirth a vaginal discharge known as lochia is produced and continues for about ten days.

Menopause

During menopause, hormone levels decrease, which causes changes in the vulva known as vulvovaginal atrophy. The decreased estrogen affects the mons, the labia, and the vaginal opening and can cause pale, itchy, and sore skin. Other visible changes are a thinning of the pubic hair, a loss of fat from the labia majora, a thinning of the labia minora, and a narrowing of the vaginal opening. This condition has been renamed by some bodies as the ''genitourinary syndrome of menopause'' as a more comprehensive term.

Function and physiology

The vulva has a major role to play in the reproductive system. It provides entry to, and protection for the uterus, and the right conditions in terms of warmth and moisture that aids in its sexual and reproductive functions. The external organs of the vulva are richly innervated and provide pleasure when properly stimulated. The mons pubis provides cushioning against the pubic bone during intercourse.

A number of different secretions are associated with the vulva, including urine (from the urethral opening), sweat (from the apocrine glands), menses (leaving from the vagina), sebum (from the sebaceous glands), alkaline fluid (from the Bartholin's glands), mucus (from the Skene's glands), vaginal lubrication from the vaginal wall and smegma. Smegma is a white substance formed from a combination of dead cells, skin oils, moisture and naturally occurring bacteria, that forms in the genitalia. In females this thickened secretion collects around the clitoris and labial folds. It can cause discomfort during sexual activity as it can cause the clitoral glans to stick to the hood, and is easily removed by bathing. Aliphatic acids known as copulins are also secreted in the vagina. These are believed to act as pheromones. Their fatty acid composition, and consequently their odor changes in relation to the stages of the menstrual cycle.

Sexual arousal

The clitoris and the labia minora are both erogenous areas in the vulva. Local stimulation can involve the clitoris, vagina and other perineal regions. The clitoris is the human female's most sensitive erogenous zone and generally the primary anatomical source of human female sexual pleasure. Sexual stimulation of the clitoris (by a number of means) can result in widespread sexual arousal and, if maintained, can result in orgasm. Stimulation to orgasm is optimally achieved by a massaging sensation.

Sexual arousal results in a number of physical changes in the vulva. During arousal vaginal lubrication increases. Vulva tissue is highly vascularised; arterioles dilate in response to sexual arousal and the smaller veins will compress after arousal, so that the clitoris and labia minora increase in size. 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. 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. Immediately prior to an orgasm, the clitoris becomes exceptionally engorged, causing the glans to appear to retract into the clitoral hood. Rhythmic muscle contractions occur in the outer third of the vagina, as well as the uterus and anus. Contractions become less intense and more randomly spaced as the orgasm continues. The number of contractions that accompany an orgasm vary depending on its intensity. An orgasm may be accompanied by female ejaculation, causing liquid from either the Skene's gland or bladder to be expelled through the urethra. 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.

Distance between vagina and clitoral glans

The distance of the frenula clitoridis at the clitoral glans from the urinary meatus