Overview 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 Developement Common Precursor Estrogen Results in Development Glans penis Genital tubercle Glans clitoris Corpus cavernosum and spongiosum Genital tubercle Vestibular bulbs Bulbourethral glands (of Cowper) Urogenital sinus Greater vestibular glands (of Bartholin) Prostate gland Urogenital sinus Urethral and paraurethral glands (of Skene) Ventral shaft of penis (penile urethra) Urogenital folds Labia minora Scrotum 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