Female External Genitalia

The female external genitalia include the mons pubis, labia majora (enclosing the pudendal cleft), labia minora (enclosing the vestibule of vagina), clitoris, bulbs of vestibule, and greater and lesser vestibular glands. The synonymous terms vulva and pudendum include all these parts; the term pudendum is commonly used clinically. The vulva serves:

• As sensory and erectile tissue for sexual arousal and intercourse.

• To direct the flow of urine.

• To prevent entry of foreign material into the urogenital tract.

Mons Pubis

The mons pubis is the rounded, fatty eminence anterior to the pubic symphysis, pubic tubercles, and superior pubic rami. The eminence is formed by a mass of fatty subcutaneous tissue. The amount of fat increases at puberty and decreases after menopause. The surface of the mons is continuous with the anterior abdominal wall. After puberty, the mons pubis is covered with coarse pubic hairs.

Labia Majora

The labia majora are prominent folds of skin that indirectly protect the clitoris and urethral and vaginal orifices. Each labium majus is largely filled with a finger-like "digital process" of loose subcutaneous tissue containing smooth muscle, and the termination of the round ligament of the uterus. The labium majus passes inferoposteriorly from the mons pubis toward the anus.

The labia majora lie on the sides of a central depression (a narrow slit when the thighs are adducted), the pudendal cleft, within which are the labia minora and vestibule. The external aspects of the labia majora in the adult are covered with pigmented skin containing many sebaceous glands, and are covered with crisp pubic hairs. The internal aspects of the labia are smooth, pink, and hairless.

The labia majora are thicker anteriorly where they join to form the anterior commissure. Posteriorly, in nulliparous women (those never having borne children), they merge to form a ridge, the posterior commissure, which overlies the perineal body and is the posterior limit of the vulva. This commissure usually disappears after the first vaginal birth.

Labia Minora

The labia minora are rounded folds of fat-free, hairless skin. They are enclosed in the pudendal cleft and immediately surround and close over the vestibule of vagina into which both the external urethral and vaginal orifices open. They have a core of spongy connective tissue containing erectile tissue at their base and many small blood vessels. Anteriorly, the labia minora form two laminae. The medial laminae of each side unite as the frenulum of the clitoris. The lateral laminae unite anterior to (or often anterior and inferior to, thus overlapping and obscuring) the glans clitoris, forming the prepuce (foreskin) of the clitoris. In young women, especially virgins, the labia minora are connected posteriorly by a small transverse fold, the frenulum of the labia minora (fourchette). Although the internal surface of each labium minus consists of thin moist skin, it has the pink color typical of mucous membrane and contains many sebaceous glands and sensory nerve endings.

Clitoris

The clitoris is an erectile organ located where the labia minora meet anteriorly. The clitoris consists of a root and a small, cylindrical body, which are composed of two crura, two corpora cavernosa, and the glans clitoris. The crura attach to the inferior pubic rami and perineal membrane, deep to the labia. The body of the clitoris is covered by the prepuce. Together, the body and glans clitoris are approximately 2 cm in length and <1 cm in diameter.

In contrast to the penis, the clitoris is not functionally related to the urethra or to urination. It functions solely as an organ of sexual arousal. The clitoris is highly sensitive and enlarges on tactile stimulation. The glans clitoris is the most highly innervated part of the clitoris and is densely supplied with sensory endings.

Vestibule of Vagina

The vestibule of the vagina is the space surrounded by the labia minora into which the orifices of the urethra and vagina and the ducts of the greater and lesser vestibular glands open. The external urethral orifice is located 2-3 cm postero-inferior to the glans clitoris and anterior to the vaginal orifice. On each side of the external urethral orifice are the openings of the ducts of the para-urethral glands. Openings of the ducts of the greater vestibular glands are located on the upper, medial aspects of the labia minora, in 5 and 7 o'clock positions relative to the vaginal orifice in the lithotomy position.

The size and appearance of the vaginal orifice vary with the condition of the hymen, a thin anular fold of mucus membrane, which partially or wholly occludes the vaginal orifice. After its rupture, only remnants of the hymen, hymenal caruncles (tags), are visible. These remnants demarcate the vagina from the vestibule. The hymen has no established physiological function. It is considered primarily a developmental vestige, but its condition (and that of the frenulum of the labia minora) often provides critical evidence in cases of child abuse and rape.

Bulbs of Vestibule

The bulbs of the vestibule are paired masses of elongated erectile tissue, approximately 3 cm in length. The bulbs lie along the sides of the vaginal orifice, superior or deep to (not within) the labia minora, immediately inferior to the perineal membrane. They are covered inferiorly and laterally by the bulbospongiosus muscles extending along their length. The bulbs are homologous with the bulb of the penis.

Vestibular Glands

The greater vestibular glands (Bartholin glands), approximately 0.5 cm in diameter, are located in the superficial perineal pouch. They lie on each side of the vestibule of the vagina, posterolateral to the vaginal orifice and inferior to the perineal membrane; thus they are in the superficial perineal pouch. The greater vestibular glands are round or oval and are partly overlapped posteriorly by the bulbs of the vestibule. Like the bulbs, they are partially surrounded by the bulbospongiosus muscles. The slender ducts of these glands pass deep to the bulbs of the vestibule and open into the vestibule on each side of the vaginal orifice. These glands secrete mucus into the vestibule during sexual arousal.

The lesser vestibular glands are small glands on each side of the vestibule of the vagina that open into it between the urethral and vaginal orifices. These glands secrete mucus into the vestibule, which moistens the labia and vestibule.

Arterial Supply and Venous Drainage of Vulva

The abundant arterial supply to the vulva is from the external and internal pudendal arteries. The internal pudendal artery supplies most of the skin, external genitalia, and perineal muscles. The labial arteries are branches of the internal pudendal artery, as are those of the clitoris.

The labial veins are tributaries of the internal pudendal veins and accompanying veins of the internal pudendal artery. Venous engorgement during the excitement phase of the sexual response causes an increase in the size and consistency of the clitoris and the bulbs of the vestibule of the vagina.

Innervation of Vulva

The anterior aspect of the vulva (mons pubis, anterior labia) is supplied by derivatives of the lumbar plexus: the anterior labial nerves, derived from the ilio-inguinal nerve, and the genital branch of the genitofemoral nerve.

The posterior aspect of the vulva is supplied by derivatives of the sacral plexus: the perineal branch of the posterior cutaneous nerve of the thigh laterally, and the pudendal nerve centrally. The latter is the primary nerve of the perineum. Its posterior labial nerves (terminal superficial branches of the perineal nerve) supply the labia. Deep and muscular branches of the perineal nerve supply the orifice of the vagina and superficial perineal muscles. The dorsal nerve of the clitoris supplies deep perineal muscles and sensation to the clitoris.

The bulb of the vestibule and erectile bodies of the clitoris receive parasympathetic fibers via cavernous nerves from the uterovaginal nerve plexus. Parasympathetic stimulation produces increased vaginal secretion, erection of the clitoris, and engorgement of erectile tissue in the bulbs of the vestibule.

Lymphatic Drainage of Female Perineum

The vulva contains a rich network of lymphatic vessels. Lymph from the skin of the perineum, including the anoderm inferior to the pectinate line of the anorectum and the inferiormost vagina, vaginal orifice, and vestibule, drains initially to the superficial inguinal lymph nodes. Lymph from the clitoris, vestibular bulb, and anterior labia minora drains to the deep inguinal lymph nodes, or directly to the internal iliac lymph nodes, and that from the urethra drains to the internal iliac or sacral lymph nodes.