Internal and External Genitalia Development - Anatomy & Physiology

BACK TO REPRODUCTIVE SYSTEM BACK TO MALE REPRODUCTIVE TRACT

Introduction

Sexual differenciaton by default follows a pathways for development of female internal and external genitalia, requiring no active intervention. Endocrine activity of the testes, production of Androgens by Leydig cells and Mullerian Inhibiting hormone (MIH) by Sertoli cells, is required for sexual differenciation to be diverted down the male genitalia development pathway.

Internal Genetalia

From the primitive reproductive tracts the Internal genitalia can only develop into one gender and so are termed unipotent.

• Male: The primitive male reproductive tract The Wolffian Duct developes from the Mesonephric Duct
• Female: The primitive female reproductive tract Mullarian Ducts develop from the Paramesonephric Duct
• This is dependent on appropriate hormonal influence.

Male

• MIH from Sertoli cells and Androgens from Leydig cells prevent spontaneous development of female internal genetalia.
• Androgens actively maintain Wolffian Ducts, which give rise to male internal genetalia:
  • Epididymis
  • Vas Deferens
  • Vesicular Glands/ Seminal Vesicles
• MIH causes the primitive female reproductive tract Mullarian Ducts to regress.

Female

• Wolffian Ducts spontaneously regress in the absence of Androgens.
• Mullarian Ducts persist to give rise to female internal genetalia:
  • Oviducts
  • Uterus
  • Cervix
  • Cranial Vagina
• Normal Ovarian activity is NOT essential for the development of normal female internal genetalia as this is the default development pathway.

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External Genetalia

External genitalia have the potencial to be either gender and so arebipotencial.

Male

• Potential to develop male or female external genetalia. Testosterone is required to develop male external genetalia.
• Androgen secretion from the Testes induces:
  • Urethral folds to fuse to allow enclosure of the urethral tube. This, together with the cells from the genital swelling, forms the shaft of the Penis.
  • Genital swellings fuse in the midline to allow formation of the Scrotum
  • Genital Tubercle expands to give rise to the Glans Penis

Female

• Development is ensured by the absence of Testosterone, it is independent of Ovarian endocrine activity.
• Urethral folds and Genital Swellings remain separate to form the Labia Minora and Majora.
• Genital tubercle forms the Clitoris

• Exposure of the female tract to Androgens will masculinise external genetalia.
• Failure of proper endocrine communication between the gonads, internal and external genitalia can lead to dissociation of gonadal and genital sex.

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Associated Disorders

• Turner's Syndrome

• Kleinfelter's Syndrome

• Testicular Feminisation

• Adrenogenital Syndrome

• Intersex

• Bovine Freemartinism