••• Chapter 2^ Embryology of the Genital Tract^19
❍ What enzyme must be present in target tissues for masculinization to occur?
5 a-reductase.
❍ What is 5a-reductase deficiency?
46XY, autosomal-recessive deficiency resulting in decreased conversion of testosterone to the more active
dihydrotestosterone (DHT), which is the necessary androgen for the target tissues at the urogenital sinus.
❍ What are the clinical manifestations of 5a-reductase deficiency?
Decreased DHT and normal testosterone levels. Ambiguous genitalia or phenotypically female and male internal
genitalia present. During puberty, increased testosterone may cause virilization with growth of a penis and descent
of testes.
❍ What is the treatment of 5a-reductase deficiency?
Individual should be raised female and undergo gonadectomy.
❍ Do male germ cells begin meiotic division prior to puberty?
No.
❍ Which cells surround fetal spermatogonia?
Sertoli cells.
❍ In females, androgen exposure at what gestation period may cause external ambiguity of the female
phenotype?
9 to 14 weeks’ gestation.
❍ Do Leydig cell numbers remain constant throughout fetal life?
No. Leydig cell numbers peak at 15 to 18 weeks.
❍ What is the name of the indifferent structure, which later divides into the anorectal canal and the
urogenital sinus?
The cloaca.
❍ What are the swellings on each side of the urethral fold that later develop into the scrotum in the male and
labia majora in the female?
Genital swellings.
❍ How does the phallus develop?
Rapid elongation of the genital tubercle.
❍ Are the scrotal swellings in the male developed outside the abdominal cavity?
No. The scrotal swellings are located initially in the inguinal region and then migrate caudally.