Development of genital system

 

Indifferent gonads

  • A genital ridge forms from intermediate mesoderm (medial to mesonephros) – forms stroma of gonads
  • Primitive sex cords form from mesodermal coelomic epithelium covering the genital ridge
  • Primordial germ cells (endodermal) develop in wall of yolk sac ⇒ pass through dorsal mesentery ⇒ lie inbetween primitive sex cords
  • Gonads don’t acquire male or female characteristics until week 7

 

Image result for primitive sex cords and yolk sac

 


 

Testis

  • Primitive sex cords branch and anastomose to from testis cordis
  • Primordial germ cells incorporate in the testis cordis
  • Testis cordis lose connection with the surface epithelium – form seminiferous tubules
  • Straight ends of seminiferous tubules anastomose at hilum of testis and form rete testis
  • Rete testis connect to mesonephric duct via 8-12 mesonephric tubules – forms head of epididymis
  • Surface epithelium disappears, testis surrounded by thick fibrous capsule – tunica albuginea

 

Image result for primitive sex cords and yolk sac

 

Descent of testis:

  • Testis develop on posterior abdominal wall behind peritoneum
  • A gubernacular cord extends from lower pole of testis to scrotal pouch
  • Gubernacular cord shortens due to chorionic gonadotropins and increased intraabdominal pressure
  • Goes through inguinal canal
  • Remnant of gubernaculum disappears
  • An evagination of peritoneal cavity called vaginal process enters scrotum
  • Forms serous cavity for testis called tunica vaginalis
  • Proximal part of vaginal process obliterated

 

Image result for descent of testis       Image result for descent of testis

 

Anomalies of testis:

  1. Cryptorchidism – undescended testis
  2. Maldescended testis – lying somewhere over the normal line of descent
  3. Ectopic testis – outside that line
  4. Congenital inguinal hernia – failure of obliteration of proximal vaginal process

 

Male genital ducts

1. Mesonephric tubules:

  • Upper – degenerate, form appendix of epididymis
  • Middle – 6-12 form head of epididymis and are connected to rete testis
  • Lower – degenerate, form paradidymis

2. Mesonephric duct:

  • Body and tail of epididymis
  • Vas deferens
  • Seminal vesicle
  • Ejaculatory duct

3. Mullerian duct (notes in female):

Degenerates completely except the upper end – forms appendix of testis


 

Ovaries

  • Primitive sex cords break into clusters of cells – form primary medullary cords
  • Which is replaced by vascular stroma to form – medulla of ovary
  • Coelomic epithelium proliferates again – forms 2nd generation of ovary (sex) cords
  • Which will divide into clusters of cells – follicular cells of primary follicle
  • Primordial germ cells incorporate into primary follicles – form oogonia
  • Primitive cortex becomes secondary cortex containing primary follicles
  • Medulla is just vascular stroma, no follicles

 

Image result for development of ovaries

 

Descent of ovaries:

  • Ovary develops in posterior abdominal wall
  • Gubernacular cord from lower pole of ovary to labia majora
  • Pulls ovary to its level on pelvis
  • Uterus develops, gubernaculum divides into 2 parts:
  1. Ovarian ligament – ovary to uterus
  2. Round ligament – uterus to labia majora (goes through inguinal canal)

Image result for round ligament from where to where

 

Congenital anomalies of ovaries:

  1. Congenital absence – Turner’s syndrome
  2. True hermaphroditism – gonads of both sex present
  3. Imperfect descent – in inguinal canal
  4. Vagina agenesis

 

Female genital ducts

 

  • 2 mullerian (paramesonephric) ducts arise from coelomic epithelium, lateral to mesonephric ducts
  • Grow caudally, curve medially infront of mesonephric duct, meet each other and grow caudally

 

Image result for development of uterus

  • The 2 ducts fuse to form uterovaginal canal
  • The lower tip of uterovaginal canal grows downwards and protrudes posterior wall of urogenital sinus
  • 2/3 of mullerian ducts form oviducts
  • Uterovaginal canal forms uterus and upper 4/5 vagina
  • Where the 2 ducts unite, forms fundus of uterus
  • Lower 1/5 vagina forms from definitive urogenital sinus

Union between upper 4/5 and lower 1/5 vagina is demarcated by hymen

Mesonephric tubules and mesonephric duct degenerates

 

Congenital anomalies:

  1. Double uterus, double vagina – complete failure of fusion
  2. Double uterus, single vagina – partial failure of fusion
  3. Agenesis of uterus – failure of both mullerian ducts to develop
  4. Rudimentary horn – failure of one mullerian ducts to develop, therefore one fallopian tube, and half body of uterus connected to rudimentary horn
  5. Atresia of cervix/vagina
  6. Imperforate hymen – cells between junction fail to degenerate
  7. Remnants of mesonephric tubules – enlarge and form cysts
  8. Remnants of mesonephric duct – Gartner’s duct
  9. Infantile uterus – small uterus, large cervix

Image result for Gartner's duct

 

 

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