Development of the Vulva

embryology of the female external genitalia

Aka, the vulva

During gestation, development is influenced by estrogen from the placenta, and, possibly, the developing fetal ovaries.

Weeks 3-4

Undifferentiated primordial genitalia

During weeks 3-4 the genital tubercle, which is the precursor to the clitoris, emerges.

• Recall that the cloacal membrane covers the opening of the cloaca prior to separation of the distal urinary and digestive tracts.
• Primordia of the genital tubercle borders the membrane.
• Anterior fusion of the primordia forms the definitive genital tubercle.
• Posteriorly, the unfused portion gives rise to the genital (aka, urogenital) folds, which enclose the cloacal membrane.
• Lateral to the folds the genital swellings (aka, labioscrotal swellings) take form.

Weeks 7-9

Elongation of the urorectal septum divided the cloaca into urogenital and digestive tracts.

• By this stage, the genital tubercle and folds are enlarged.
• Perineal body lies posterior to the genital folds
  • Perineal body is where the urorectal septum connected to the cloacal membrane, it separates the genital folds from the anal folds.
  • Aka, the central tendon of the perineum
• Division of the cloacal membrane gives rise to the urogenital membrane, enclosed by the genital folds, and, the anal membrane, enclosed by the anal folds.
• By the end of week nine, the urogenital and anal membranes disappear.
• Genital tubercle is now the glans of the clitoris.
• Urogenital groove appears where urogenital membrane was.
• Anus appears where the anal membrane was.
• The area between the urogenital groove and anus is the perineum.

Weeks 11-12

Final stages of vulva formation.

• Glans of the clitoris recedes.
• The genital folds give rise to the labia minora
  • Prepuce of labia minora covers body of clitoris
  • Vestibule of vagina is area between right and left labia minora; urethra and vagina open to vestibule.
• The genital swellings give rise to the labia majora
  • Anterior fusion = mons pubis
  • Posterior fusion = posterior labial commissure
• Deeper structures
  Clitoris
  • Glans
  • Body
  • Crus
    Bulb of the vestibule
  • Deep to clitoral crura and vestibule of the vagina.

Summary

The genital tubercle gives rise to the clitoris and bulbs of the vestibule
The genital folds give rise to the labia minora
The genital swellings give rise to the labia majora