UNSW Embryology

Development of the Reproductive System

© Dr Mark Hill (2008)

Acknowledgements

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 (Müllerian Duct) contribute the majority of male and female internal genital tract respectively.

Y Chromosome	Indifferent stage	Human Male (stage 22)

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.

3 stages:

1. Differentiation of gonad (Sex determination)
2. Differentiation of internal genital organs
3. 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)

Page Links: Introduction | Some Recent Findings | Reading | Development Overview | Objectives | Learning activities | Computer Activities | Movies | References | Glossary

Some Recent Findings

Yamada G, Suzuki K, Haraguchi R, Miyagawa S, Satoh Y, Kamimura M, Nakagata N, Kataoka H, Kuroiwa A, Chen Y. Molecular genetic cascades for external genitalia formation: An emerging organogenesis program. Dev Dyn. 2006 Jul;235(7):1738-52.

"External genitalia are anatomical structures located at the posterior embryonic region as part of several urogenital/reproductive organs. The embryonic anlage of the external genitalia, the genital tubercle (GT) develops as a bud-shaped structure with an initial urethral plate and later urethra. Embryonic external genitalia are considered to be one of the appendages. Recent experiments suggest that essential regulatory genes possess similar functions for the outgrowth regulation of the GT and limb appendages."

Internal Genital Differentiation

Common	Female	Male
Müllerian Duct (paramesonephric) - blue Wolffian Duct (mesonephric) - red

Reading

• Human Embryology (2nd ed.) Larson Ch10 p261-306
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch13 p303-346
• Before We Are Born (5th ed.) Moore and Persaud Ch14 p289-326
• Essentials of Human Embryology, Larson Ch10 p173-205
• Human Embryology, Fitzgerald and Fitzgerald Ch21-22 p134-152
• Developmental Biology (6th ed.) Gilbert Ch14 Intermediate Mesoderm
• UNSW Embryology References

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.

Learning activities

• Study the developmental overview of gonad/genital development.
• Study the early stage 13/14 embryo urogenital region and identify mesonephric duct, genital ridge.
• Study the late stage 22 male embryo urogenital region and identify mesonephric duct, paramesonephric duct, genital tubercle, scrotal swellings.
• Study the early female fetal (week 10) urogenital region and identify paramesonephric duct, mesonephric duct, , ovary, developing uterus/vagina, genital tubercle.
• Watch the animations (listed under movies) of male/female genital development.

Computer Activities

Abnormalities | Y chromosome | X chromosome | Ovary | Stage 13/14 Embryo | Stage 22 Embryo | Stage 22 Highpower | Urogenital Movies | References | Text only page | WWW Links

Embryo Images Unit: Embryo Images Online | Urongenital Development | Internal Genitalia | Definitive Kidney | External Genitalia

Movies:

Urogenital Movies

Primordial Germ Cell (PGC) migration	Germ Cell Migration (440 Kb)
Female Gonad (228 Kb)	Male Gonad (288 Kb)
Female External (288 Kb)	Male External (288 Kb)
Aortic Branches to Glands (Gonads only) (765Kb)	Testes Descent (172 Kb)

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

• All embryos initially same (indifferent)
• Testosterone differentiates male

Glossary

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Quick Links

Urogenital Pages:

Abnormalities | References | OMIM | Questions | Medline | Pig (stage13/14) | Human (Stage22) | Selected Human highpower
Text only page | WWW Links

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Genes/DNA Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Urogenital Musculoskeletal Integumentary

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

Other Embryos ----------------- Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G