Page 666 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat
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622 SectioN iii RepRoductive ` REPRODUCTIVE—EmbRyOlOgy RepRoductive ` REPRODUCTIVE—EmbRyOlOgy
Genital embryology
Female Default development. Mesonephric duct
degenerates and paramesonephric duct
develops.
Male SRY gene on Y chromosome—produces testis- Mesonephros Gubernaculum
determining factor testes development. Paramesonephric duct
Sertoli cells secrete Müllerian inhibitory factor Mesonephric duct
(MIF, also called antimullerian hormone) that Urogenital sinus
suppresses development of paramesonephric
ducts.
Leydig cells secrete androgens that stimulate Testis-determining factor
development of mesonephric ducts. Androgens No androgens
MIF
Paramesonephric Develops into female internal structures— Epididymis
(Müllerian) duct fallopian tubes, uterus, upper portion of vagina Testis Ovary
(lower portion from urogenital sinus). Male Metanephric
kidney
remnant is appendix testis.
Müllerian agenesis (Mayer-Rokitansky-
Küster-Hauser syndrome)—may present Oviduct
as 1° amenorrhea (due to a lack of uterine Urinary Ureter
development) in females with fully developed bladder
2° sexual characteristics (functional ovaries). Degenerated
mesonephric
Degenerated
Mesonephric Develops into male internal structures (except paramesonephric duct duct
(Wolffian) duct prostate)—Seminal vesicles, Epididymis, Vas deferens Uterus
Ejaculatory duct, Ductus deferens (SEED). Vagina
Female remnant is Gartner duct.
Sexual differentiation
Undi erentiated Absence of Sertoli cells or lack of Müllerian
gonads
inhibitory factor develop both male and
Medulla Cortex female internal genitalia and male external
Mesonephric XY XX Paramesonephric genitalia (streak gonads)
(Wolan) duct (SRY) (no SRY) (Müllerian) duct
5α-reductase deficiency—inability to convert
testosterone into DHT male internal
Leydig Sertoli
cells Testes cells Ovaries genitalia, ambiguous external genitalia until
Q
puberty (when testosterone levels cause
Testosterone MIF Estradiol
masculinization)
R
In the testes:
5α-reductase
Leydig Leads to male (internal and external)
Dihydrotestosterone sexual differentiation.
Sertoli Shuts down female (internal) sexual
Internal male External male External female Internal female differentiation.
genitalia genitalia genitalia genitalia
Seminal vesicle Penis Clitoris Fallopian tubes
Epididymis Scrotum Labia Uterus
Ejaculatory duct + Prostate Distal vagina Proximal vagina
Ductus deferens
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