Reproductive System Development

EMBRYOLOGICAL DEVELOPMENT OF THE GENITAL TRACT

Early embryo

• Small indifferent gonads.
• Primitive structures which will become gonads and genital tract are identical at this stage.
• Paired mesonephric ducts (Wolffian) or paramesonephric (Mullerian) ducts fuse caudally with urogenital sinus.

(Metanephros - becomes the kidney).

Gonadal differentiation

• Determined by the presence of the SRY gene of the Y chromosome (sex determining region of the Y chromosome) which encodes “testicular determining factor” protein (TDF).
• Lack of SRY gene (i.e. XX females) leads to ovarian differentiation.

Development of phenotypic sex

• The sex of the embryonic gonad normally determines which reproductive duct system develops.
• Testes induce development of mesonephric (Wolffian) duct system in to epididymis and vas deferens and cause regression of paramesonephric (Mullerian) duct by ”mullerian inhibitory substance”, (MIS).
• Absence of testes in presence of ovaries allows paramesonephric ducts to develop under influence of oestrogen to oviduct, uterus, cervix and cranial vagina.

Summary of determinants of sexual development

Chromosomal or genetic sex = sex chromosomes
Gonadal sex = ovary or testis
Phenotypic sex = usually determined by gonad

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Information by permission of Professor RW Else