UG Development 3

Question 1

What is the sexually indifferent stage?

Answer 1

At 8 weeks, all embryos have a single, common set of UG structures.

Question 2

What are the common structures at the indifferent stage?

Answer 2

• metanephros
• mesonephros
• gonads attached medially to the mesonephros (from the genital ridges)
• mesonephric (wolffian) ducts
• paramesonephric (mullerian) ducts
• UG sinus
• genital tubercle (phallus)
• labioscrotal folds

Question 3

What do the following develop into?

Medulla of primitive gonads?

Primary sex cords?

Cortex of primitive gonads?

Secondary sex cords?

Answer 3

• Medulla - testis, diminishes in females
• Primary sex cords - seminiferous tubules, disappear or retained as rete ovarii
• Cortex of primitive gonads - ovary
• Secondary sex cords - epithelial ovarian follicles surrounding the oocytes

Question 4

What happens to the mesonephric duct and paramesonephric duct in males?

Answer 4

• Mesonephric duct - retained as ductus deferens and epididymus
• Paramesonephric duct - disappears

Question 5

What happens fo the following structures in the female?

Paramesonephric ducts?

Mesonephric ducts?

Answer 5

• Paramesonephric ducts
  
  • uterine tubes
  • uterus
  • upper part of vagina
    
    • lower part derived from extension of endoderm of the UG sinus - sinovaginal bulbs form a solid vaginal plate
• Mesonephric ducts
  
  • ​ducts and tubules disappear

Question 6

What happens when the paired paramesonephric ducts fail to use in a female?

Answer 6

vertical septae in the uterus/vagina or double uterus (bicornuate or Didelphys if complete)

Question 7

What happens in a female when there is agenesis of one or both paramesonephric ducts?

Answer 7

unicornate uterus or complete absence of the uterus/vagina

Question 8

In the male, what is the role of the fibrous gubernaculum?

Answer 8

• Guides descent of the testis through the deep body wall via the inguinal canal
• Descends behind the processus vaginalis (pouch of parietal peritoneum)
• Pinches off as the tunica vaginalis testis - coelomic sac that envelops the testis with visceral and parietal layers