Development of the Uterine Tubes, Uterus, and Vagina

The female reproductive tract

Includes the uterine tubes, uterus, and vagina

Paramesonephric ducts (aka, Mullerian Ducts)

• Emerged as a groove in the intermediate mesoderm, parallel to the mesonephric ducts, during week 6.
• The following genetic signals aid in their cranial to caudal growth:
  • Wnt4 is necessary for early growth of the paramesonephric ducts
  • Wnt9b ensures growth in the caudal direction
  • Wnt7a is thought to be essential for their normal development
• Ducts grow towards, and make contact with, the urogenital sinus (an endoderm-derived structure).
• ~Week 10, paramesonepheric ducts begin to fuse
  • Uterine septum temporarily lies in midline, where the edges of the two paramesonephric ducts meet.
  • Cranial ends remain open
  • Where caudal ends meet urogenital sinus, the vaginal plate forms
• Mesonephros degnerates

Mature Form

• Uterine tubes derive from cranial portions of the paramesonephric ducts
• Uterine cavity and upper vagina derive from caudal portions of paramesonephric ducts
  • Uterine ligaments = broad ligament extending laterally and round ligament attaching to labia majora
  • Fornices of vagina extend outward, over cervix of uterus
• Lower vagina (possibly) derives from urogenital sinus
  • Hymen = membranous covering of vagina
• Ovaries lie between uterus and distal ends of uterine tubes
• Descend from abdominal cavity, guided and stabilized by genital ligaments
  • Ovarian ligaments = suspensory ligament of the ovary and ovarian ligament

Four models used to explain origin of epithelia of vagina:

1. The upper 2/3 of the vaginal epithelia derives from the paramesonephric ducts, and the lower 1/3 derives from the urogenital sinus. Recall that the urogenital sinus is of endodermal origins; therefore, according to this model, the vaginal epithelium has both mesodermal and endodermal origins.

Because this is the model many medical textbooks use, this is the we've followed, here.

2. Only the paramesonephric ducts contribute to the vaginal epithelium.
3. The epithelium is mostly derived from the paramesonephric ducts, but also from remnants of the mesonephros.
4. Vaginal epithelium derives solely from the urogenital sinus, which would mean that the vagina has purely endodermal origins (this model appears to be relatively unpopular).

Clinical Correlation:

• The cellular origin of the vaginal epithelium has implications for understanding normal and abnormal development.
• Surrounding mesenchyme gives rise to the musculature and peritoneal coverings of the vagina and uterus.