questions 5

Genital Embryology

Topic updated on 07/30/17 11:38am

  • 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


Qbank (3 Questions)

(M1.EB.11) A 4-day-old healthy male infant is born with normal internal and external male reproductive organs. Karyotype analysis reveals a 46XY genotype. Production of what substance by which cell type is responsible for the development of the normal male seminal vesicles, epididymides, ejaculatory ducts, and ductus deferens? Topic Review Topic

1. Testis-determining factor; Sertoli cells
2. Testis-determining factor; Leydig cells
3. Testosterone; Sertoli cells
4. Testosterone; Leydig cells
5. Mullerian inhibitory factor; Sertoli cells

(M1.EB.35) A newborn infant with karyotype 46, XY has male internal and external reproductive structures. The lack of a uterus in this infant can be attributed to the actions of which of the following cell types? Topic Review Topic

1. Leydig
2. Sertoli
3. Theca
4. Granulosa
5. Reticularis

(M1.EB.36) A 22-year-old G2P1 female presents to the clinic at the beginning of her third trimester for a fetal ultrasound. The sonographer is unable to visualize any of the structures arising from the mesonephric duct. This infant is at risk for malformation of which of the following? Topic Review Topic

1. Fallopian tubes
2. Uterus
3. Upper 1/3 of vagina
4. Lower 2/3 of vagina
5. No malformation would be expected

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