Female external genitalia comprises of both urinary and reproductive structures, which collectively are called as vulva. The vulva (plural: vulvas or vulvae) is a term derived from Latin which means a wrapper or covering. The external genitalia are wrapped or covered by skin folds called labia majora and labia minora which are part of vulva. The vulva consists of the mons pubis, labia majora, labia minora, clitoris, urethra, vulva vestibule, vestibular bulbs, Bartholin's glands, Skene's glands, and vaginal opening.

Vulva 

The vulva is the global term that describes all of the structures that make the female external genitalia. The components of the vulva are the mons pubis, labia majora, labia minora, clitoris, vestibular bulbs, vulva vestibule, Bartholin's glands, Skene's glands, urethra, and vaginal opening.

Vagina

The vagina is an elastic, muscular tube connected to the cervix proximally and extends to the external surface through the vulva vestibule. The term Vagina comes from the Latin for “sheath,”

The vaginal introitus is equivalent to the Level III section of the vagina, measured posteriorly from the clitoris to the anterior perineum then down the perineum to the anal verge. The anterior and posterior vestibules, with nonkeratinizing epithelium, extend laterally to the keratinized epithelium of the labia minora (Hart's line)2

Level III of the vagina, that is, those areas distal to the hymen, anterior, lateral and posterior. It incorporates the

  1. anterior vestibule: anterior and lateral areas distal to the hymen. Laterally, it extends as far as Hart's line where the labia minora commence;
  2. Posterior vestibule: posterior and posterolateral areas distal to the hymen out to Hart's line;
  3. The perineum (predominantly anterior aspects), from distal margin of posterior vestibule down to anal verge. 

The word “vestibule” comes from the Latin “vestibulum” meaning “a small cavity or a space at the entrance of a canal.

The distal opening of the vagina is usually partially covered by a membrane called the hymen. The vaginal opening is located posterior to the urethra opening. The function of the vagina is for sexual intercourse and childbirth. During sexual intercourse, the vagina acts as a reservoir for semen to collect before the sperm ascending into the cervix to travel towards the uterus and fallopian tubes. Also, the vagina also acts as an outflow tract for menses.

Mons Pubis

The mons pubis is a tissue mound made up of fat located directly anterior to the pubic bones. This mound of tissue is prominent in females and is usually covered in pubic hair. The mons pubis functions as a source of cushioning during sexual intercourse. The mons pubis also contains sebaceous glands that secrete pheromones to induce sexual attraction.

Labia Majora

The word "labia majora" is defined as the larger lips. The labia majora are a prominent pair of cutaneous skin folds that will form the lateral longitudinal borders of the vulval clefts. The labia majora forms the folds that cover the labia minora, clitoris, vulva vestibule, vestibular bulbs, Bartholin's glands, Skene's glands, urethra, and the vaginal opening. The anterior part of the labia majora folds comes together to form the anterior labial commissure directly beneath the mons pubis. While the posterior part of the labia majora comes together to form the posterior labial commissure. The labia majora engorges with blood and appears edematous during sexual arousal.

Labia Minora 

The "labia minora" is defined as the smaller lips. The labia minor are a pair of small cutaneous folds that begins at the clitoris and extends downward. The anterior folds of the labia minora encircle the clitoris forming the clitoral hood and the frenulum of the clitoris. Then the labia minor descends obliquely and downward forming the borders of the vulva vestibule. Eventually, posterior ends of the labia minora terminate as they become linked together by a skin fold called the frenulum of the labia minora. The labia minora will encircle the vulva vestibule and terminating between the labia majora and the vulva vestibule. With sexual arousal, the labia minora will become engorged with blood and appear edematous.

Clitoris

The clitoris (which is homologous to the glans penis in males) is a sex organ in females that functions as a sensory organ. The clitoris can be divided into the glans clitoris and the body of the clitoris. The underlying tissue that makes the clitoris is the corpus cavernous. The corpus cavernous is a type of erectile tissue that merges together and protrudes to the exterior of the vulva as the glans clitoris. While proximally, the two separate ends of the tissue will form the crus of the clitoris (legs of the clitoris) and the body of the clitoris. The glans clitoris is the only visible part of the clitoris. The glans clitoris is highly innervated by nerves and perfused by many blood vessels. It is estimated that glans clitoris is innervated by roughly eight thousand nerve endings. Since the glans clitoris is so highly innervated, it becomes erected and engorged with blood during sexual arousal and stimulation.

Vestibular bulbs

The vestibular bulbs (homologous to the bulb of the penis in males) are structures formed from corpus spongiosum tissue. This is a type of erectile tissue closely related to the clitoris. The vestibule bulbs are two bulbs of erectile tissue that starts close to the inferior side of the body of the clitoris. The vestibular bulbs then extend towards the urethra and vagina on the medal edge of the crus of the clitoris. Eventually, the vestibular bulbs will split and surround the lateral border of the urethra and vaginal. The vestibular bulbs are believed to function closely with the clitoris. During sexual arousal, the vestibular bulbs will become engorged with blood. The engorgement of blood then exerts pressure onto the corpus cavernosum of the clitoris and the crus of the clitoris. This exertion of pressure onto the clitoris is believed to induce a pleasant sensation during sexual arousal.

Vulva Vestibule

The area between the labia minora is the vulva vestibule. This is a smooth surface that begins superiorly just below the clitoris and ends inferiorly at the posterior commissure of the labia minora. The vulva vestibule contains the opening to the urethra and the vaginal opening. The borders of the vulva vestibule are formed from the edge of the labia minora. There is a demarcation between the vulva vestibule and the labia minora called Hart's lines. Hart's lines identify the change from the vulva vestibule to the labia minora. This change of skin appearance is visible by the smoother transitional skin appearance of the vulva vestibule to the vulvar appearance of the labia minora.

Bartholin's Glands

The Bartholin's glands also known as the greater vestibular glands (homologous to the bulbourethral glands in males) are two pea-sized glands located slightly lateral and posterior to the vagina opening. These two glands function to secrete a mucus-like substance into the vagina and within the borders of the labia minora. This mucus functions as a lubricant to decrease friction during intercourse and a moisturizer for the vulva.

Skene's Glands

The Skene's glands, which are also known as the lesser vestibular glands (homologous to the prostate glands in males), are two glands located on either side of the urethra. These glands are believed to secrete a substance to lubricate the urethra opening. This substance is also believed to act as an antimicrobial. This antimicrobial is used to prevent urinary tract infections. The function of Skene's gland is not fully understood but is believed to be the source of female ejaculation during sexual arousal.

Urethra

The urethra is an extension of a tube from the bladder to the outside of the body. The purpose of the urethra is for the excretion of urine. The urethra in females opens within the vulva vestibule located inferior to the clitoris, but superior to the vagina opening.

Blood Supply and Lymphatics

Arterial 

The internal pudendal artery perfuses the majority of the external female genitalia. The internal pudendal artery is a branch of the internal iliac artery. Once the pudendal artery branches from the internal iliac artery, it descends towards the external genitalia. The internal pudendal artery will then become the dominant blood supply to the female external genitalia. The labia majora also received blood from the superficial external pudendal artery. The superficial external pudendal artery is a tributary of the femoral artery.

Venous 

The venous drainage of the external female genitalia is via the external and internal pudendal veins. The external pudendal vein will drain towards the great saphenous vein. The saphenous vein will drain back into the femoral vein. As the femoral vein ascends pass the inguinal ligament, it becomes the external iliac vein. While the internal pudendal vein drains back into the internal iliac vein. Both the external and internal iliac veins will ascend and merge to form the common iliac veins. The common iliac veins from both sides of the body will ascend to about the level of the fourth lumbar vertebra. At the level of the fourth lumbar vertebra, the common iliac veins merge to drain venous blood back into the inferior vena cava. The inferior vena cava will ascend towards the heart. Upon reaching the heart, the inferior vena cava drains its venous blood back into the right atrium.

Lymphatic 

The lymphatic drainage of the external female genitalia drains toward the superficial inguinal lymph nodes except for the clitoris. The lymph from the clitoris will drain towards the deep inguinal lymph nodes. The lymph from the superficial and deep inguinal lymph nodes will ascend toward the common iliac lymph nodes. All of this lymph will ascend towards the distant part of the thoracic duct called the cisterna chyli. Once at the cisterna chyli, the lymph will drain into the thoracic duct and ascends toward the angle formed from the left subclavian vein and the left internal jugular vein. All of the lymph from the external female genitalia will drain back into the central circulation via the thoracic duct.

Nerves

The motor, sensory, and sympathetic nerve innervation of the external female genitalia originate from the pudendal nerve. The pudendal nerve is made up of the second, third, and fourth sacral spinal roots. The pudendal nerve will enter the pelvis via the lesser sciatic foramen. Once pass the lesser sciatic foramen, the pudendal nerve will travel in the pudendal canal towards the ischial spines. The pudendal nerve then encircles the ischial spine and form branches that innervate the perineum and the external genitalia. The pudendal nerve will branch into three main branches: the dorsal nerve for the clitoris, the perineal nerve for the external genitalia, and the inferior rectal nerve. The dorsal nerve of the clitoris provides the afferent part for clitoral erection. In addition to the dorsal nerve of the clitoris, the clitoris's cavernous tissue is innervated by the cavernous nerves from the uterovaginal plexus. As for the perineal nerve branch, it will provide sensory to the external genitalia via the posterior labial nerves. The perineal nerve also gives off a branch that provides motor innervation to the external urethral sphincter. The perineal nerve also gives off muscular nerve branches that innervate the muscles of the perineum. These muscles are the bulbospongiosus, ischiocavernosus, levator ani (iliococcygeus, pubococcygeus, and puborectalis muscle), and pubovaginalis muscles. Lastly, the inferior rectal nerve will provide innervation to the perianal skin and the external anal sphincter. The labia majora also received addition innervation from the anterior labial nerves (branches of the ilioinguinal nerve). The mons pubis also receives additional sensory innervation from the genitofemoral nerve.

It is common to anesthetize the pudendal nerve during childbirth. The landmark for the injection of anesthetic is the ischial spines. The physician will palpate for the ischial spine from the inside of the vaginal canal. Then the anesthetic will be injected towards the ischial spine to block the sensory territory of the pudendal nerve; this may be done to decrease pain sensation during child delivery, to numb the perineum before an episiotomy, or for the relief of chronic pelvic pain syndromes.

Muscles

  • Bulbospongiosus muscle
  • Ischiocavernosus muscle
  • Deep transverse perineal muscle
  • Superficial transverse perineal muscle
  • Levator ani muscle
    • Iliococcygeus muscle
    • Pubococcygeus muscle
    • Puborectalis muscle
    • Pubovaginalis muscle
    • Coccygeus muscle
  • Perineal body
  • External anal sphincter 
  • External urethral sphincter

References

  1. Nguyen JD, Duong H. Anatomy, Abdomen and Pelvis, Female External Genitalia. [Updated 2022 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK547703.
  2. Haylen BT, Vu D, Wong A. Surgical anatomy of the vaginal introitus. Neurourol Urodyn. 2022 Aug;41(6):1240-1247. doi: 10.1002/nau.24961. Epub 2022 May 20. PMID: 35592994; PMCID: PMC9544139.
  3. Haylen BT, Vu D, Wong A, Livingstone S. Surgical anatomy of the mid-vagina. Neurourol Urodyn. 2022 Aug;41(6):1293-1304. doi: 10.1002/nau.24994. Epub 2022 Jun 22. PMID: 35731184; PMCID: PMC9540639.
  4. Haylen BT, Vu D. Surgical anatomy of the vaginal vault. Neurourol Urodyn. 2022 Aug;41(6):1316-1322. doi: 10.1002/nau.24963. Epub 2022 May 27. PMID: 35620982; PMCID: PMC9543804.

 

Dr. Pawan lal
MBBS, MS, DNB (Surgery), MNAMS 
FICS, FIAS, FIMSA, FIAGES, DA
FRCS (Glasg), FACS, FACRSI
 
Professor of Surgery  
Maulana Azad Medical College
(University of Delhi)