• Week 1-6
    • embryo is sexually indifferent
    • genetically male and female embryos are phenotypically the same
    • both male and female have mesonephric (Wolffian) ducts at this stage
  • Week 7
    • sexual differentiation occurs
  • Week 12
    • sex of embryo can be distinguished based on external genitalia 
  • Week 20
    • phenotypical differentiation is complete
Male vs. Female Differentiation
  • Mesonephric (wolffian) duct
    • needs to be induced to develop
      • by testosterone from the Leydig cells of testes
    • forms male internal sexual organs: Seminal vesicles, Epididymis, Ejaculatory duct, Ductus deferens
  • Paramesonephric (müllerian) duct
    • default development but can be suppressed
    • forms female internal sexual organs: fallopian tube, uterus, upper 1/3 of vagina (lower 2/3 from urogenital sinus
  • Female 
    • default phenotypic differentiation
    • mesonephric duct degenerates and paramesonephric duct develops
  • Male 
    • SRY gene (Y chromosome) produces testis-determining factor which is necessary for testes development
    • testes gives rise to
      • sertoli cells: produces Müllerian inhibitory factor suppressing the development of paramesonephric ducts
      • leydig cells: produces androgens stimulating development of mesonephric ducts 
Male/Female Genital Homologues
Dihydrotestosterone Results in Development
Common Precursor
Estrogen Results in Development
Glans penis
  • Genital tubercle
  • Glans clitoris
Corpus cavernosum and spongiosum
  • Vestibular bulbs
Bulbourethral glands (of Cowper)
  • Urogenital sinus
  • Greater vestibular glands (of Bartholin)
Prostate gland
  • Urethral and paraurethral glands (of Skene)
Ventral shaft of penis (penile urethra)
  • Urogenital folds
  • Labia minora
  • Labioscrotal swelling
  • Labia majora


Female Genital Abnormalities


  • Unicornate Uterus
    • one paramesonephric fails to develop
  • Bicornuate Uterus
    • due to incomplete/partial fusion of the paramesonephric ducts
    • associated with urinary tract abnormalities and infertility
  • Uterus didelphys
    • no fusion between the two paramesonephric ducts resulting in a "double uterus"
  • Müllerian agenesis 
    • failure of paramesonephric ducts to develop resulting in abnormalities of the upper portion of the vagina, cervix, uterus, and fallopian tubes
Male Genital Abnormalities
  • Hypospadias
    • failure of urethral folds to fuse
    • resulting in opening of penile urethra on inferior side of penis
    • susceptible to UTI's
    • surgery is recommended for treatment
  • Epispadias
    • faulty positioning of genital tubercle
    • resulting in penile urethra opening on superior side of penis
    • associated with exstrophy of the bladder
  • Cryptochidism
    • failure of testes to descend into scrotum (undescended testes)
    • testes can be found in inguinal canal or abdominal canal
    • can lead to infertility if both are undescended
    • observable within 3 months of birth
  • Hydrocele
    • processus vaginalis remains patent allowing fluid to flow in
    • resulting in a fluid filled sac in the scrotum
    • can differentiate from tumor by shining light through testes
    • hydrocele allows light to flow through whereas a tumor does not

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