Testis and epididymis
General
Embryology

Author: Turki Al-Hussain, M.D. (see Authors page)

Revised: 5 April 2017, last major update August 2012

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Testis and epididymis [title] Embryology

Table of Contents
Definition / general
Cite this page: Embryology. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/testisembryology.html. Accessed November 21st, 2017.
Definition / general
  • Presence of Y chromosome (possibly sex determining region Y) determines formation of testis
  • Germ cells migrate to genital ridge, tubules formed by day 45; Wolffian ducts (form epididymis, vas deferens, seminal vesicles and ejaculatory ducts) develop by day 25, Müllerian ducts (form uterus and upper vagina) by day 43
  • If no Y, gonad becomes an ovary; if Y present becomes a testis
  • If Y present, Sertoli cells develop from genital ridge and secrete anti-Müllerian hormone / Müllerian inhibiting factor (AMH) by day 62, causing ipsilateral regression of Müllerian duct by day 75 - 80; lack of Sertoli cells means no AMH, no regression and presence of uterus and upper vagina
  • If Y present, Leydig cells arise by day 64 and produce testosterone, which causes development of Wolffian duct structures (epididymis, vas deferens, seminal vesicles and ejaculatory ducts) if functional androgen receptors are also present
  • If no testosterone is produced, Wolffian duct structures degenerate
  • Exogenous androgens or their production by maternal tumor or congenital adrenal hyperplasia cause development of Wolffian duct system regardless of presence of Y chromosome
  • Development of external genitalia requires testosterone plus androgen receptors plus 5 alpha reductase, which converts testosterone to dihydrotestosterone (DHT), which causes development of external genitalia between days 120 - 140, including elongation of phallus
  • If ovaries or no gonads present, internal ducts are female
  • If DHT not present, external genitalia is female