External Female Genitalia
External female genitalia are part of the female reproductive system, and include:
- mons pubis
- labia majora
- labia minora
- vestibular bulb
- vestibular glands
External genitalia of a female occupy much of the perineum and are collectively referred to as the vulva (pudendum).
The mons pubis consists of a mass of subcutaneous adipose tissue anterior to the pubic symphysis, and bears most of the pubic hair.
The labia majora (singular, labium majus) are a pair of thick folds of skin and adipose tissue found inferior to the mons. The fissure between the folds is called the pudendal cleft. Pubic hair can be found on the lateral surfaces of the labia majora once puberty hits, while the medial/internal surfaces will remain hairless. The round ligament of the uterus passes through the inguinal canal and continues into the labia majora, where the nerve fibers spread and mix with the tissue of the mons pubis. The labia majora are thicker in the front where they form by joining the anterior commisure, and is found below the mons pubis. The posterior commisure of the labia majora is the rear joining of the labia majora, and is located above the perineum.
Found medial to the labia majora are the labia minora (singular, labium minus), which are much thinner devoid of fat and entirely hairless. Their frontal ends split to form upper and lower layers. The upper layer goes superior to the clitoris and forms a fold called prepuce. The lower layer passes inferior to clitoris and forms the frenulum of the clitoris.
The clitoris is analogous to the structure of the penis but it does not contain urethra and has no urinary role. It is richly supplied with autonomic efferent motor nerve endings via the cavernosal nerve of the clitoris and is highly sensitive to sexual stimulation. Also unlike the penis, the clitoris is nearly entirely internal and does not have a corpus spongiosum or enclose the urethra.
The clitoris has a pair of corpora cavernosa which consist of erectile tissue enclosed in dense fibrous tissue. Each corpus (body) passes internally, and is attached to the ischiopubic ramus by a crus. The suspensory ligament and two small muscles (ischiocavernosi) are attached to the crura just like the penis. The glans (head) of the clitoris is a small tubercle, which protrudes slightly from the prepuce. Arteries here include the dorsal and clitoral cavernosal arteries, which arise from the iliohypogastric pudendal bed.
The labia minora enclose an area called the vestibule, which contains the urinary and vaginal orifices along with the openings of the greater and lesser vestibular glands. The prepuce is found at the anterior margin of the vestibule.
The hymen is a structure that stretches across the vaginal opening. It possesses one or more openings to allow for the discharge of menstrual fluid, and is usually ruptured to allow for sexual intercourse.
Vestibular bulbs are located on each side of the vestibule. They consist of a pair of subcutaneous erectile tissues which correspond to the penile bulb and corpus spongiosum. Both bulbs join in front of urethral orifices under the vestibule of the vagina. Each one is covered with bulbospongiosus muscles.
Bartholin’s (greater vestibular) glands are pea-sized with a short duct that opens into the vestibule or lower vagina. One is found on each side of the vagina. Bartholin’s glands are homologous to the bulbourethral glands in the male, and function to keep the vulva moist, providing lubrication for sexual intercourse during sexual excitement. Additionally, lesser vestibular glands lubricate the vestibule. Finally, a pair of Skene’s (paraurethral) glands, homologous to the male prostate, open into the vestibule nears the external urethral orifice.
Vasculature of the external female genitalia is primarily supplied by the internal pudendal arteries, which are branches of the anterior division of the internal iliac artery.
Lymphatic drainage of the external female genitalia is via the superficial and deep inguinal lymph nodes. Lymph from the clitoris, vestibular bulb and anterior labia minora can alternatively drain into the internal iliac lymph nodes.
The vulva is innervated from a variety of sources. The mons pubis and anterior labia is innervated via the anterior labial nerves, which derive from the lumbar plexus. The posterior aspect of the vulva is innervated via the pudendal nerve and its branches (posterior labial nerves), together with branches from the posterior cutaneous nerve of the thigh. Sensitive innervation to the clitoris is provided by the dorsal nerve of the clitoris.