Genital Development

Introduction

This section of notes covers genital development. Differences in development are dependent on a protein product of the Y chromosome SRY gene. Mesonephric duct (Wolffian Duct) and paramesonephric (Mullerian Duct) contribute the majority of male and female internal genital tract respectively.

Stage 22 mesonephros

Objectives

Understand the role of the Y chromosome in sex determination.
Understand the differences in male/female duct develpoment (mesonephric/paramesonephric).
Compare the development of the cloaca in the male and female.
Understand the developmental abnormalities in male and female development.

Textbooks

Human Embryology (2nd ed.) Larson Ch10 p261-306
The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 13 p303-346

Three Stages

The mesonephric/paramesonephric duct changes are one of the first male/female differences that occur in development, while external genitaila remain indeterminate in appearance for quite a while.

Differentiation of gonad (Sex determination)
Differentiation of internal genital organs
Differentiation of external genital organs

The 2nd and 3rd stages dependent on endocrine gonad. Reproductive development has a long maturation timecourse, begining in the embryo and finishing in puberty. (More? Puberty)

Development Overview

Sex Determination

Humans (week 5-6)
Germ cells migrate into gonadal ridge
Gonads (male/female) identical at this stage, indifferent

Gonad development

dependent on sex chromosome
Y testes
No Y ovary

SRY

SRY protein (Testes determining factor, TDF) binds DNA
Transcription factor, Bends DNA 70-80 degrees

Internal Genital Organs

All embryos form paired
Mesonephric duct, see kidney development
Paramesonephric duct, Humans 7th week Invagination of coelomic epithelium Cord grows and terminates on urogenital sinus
Male Gonad (testes) secretes Mullerian duct inhibitory factor (MDIF) which causes regression of paramesonephric duct
Male Gonad (testes) secretes Testosterone which retains mesonephric duct

External Genital Organs