Development of the Sexual Organs in the Embryo and Fetus

The human embryo is bipotential, allowing the formation of either male or female reproductive organs.

During the fifth week of embryonic development, the gonads originate from gonadal ridges in the intermediate mesoderm.

Alongside these ridges, the mesonephric ducts, also known as Wolffian ducts, and the paramesonephric ducts, or Müllerian ducts, also develop.

Now, the embryo's genetic makeup guides further development.

In a genetically male embryo, the mesonephric ducts form male reproductive organs.

The sex-determining region on the Y chromosome or SRY gene triggers the development of male-specific organs. 

Its activation leads to the differentiation of sustentacular cells into the testes and the secretion of Müllerian-inhibiting substances, causing the Müllerian ducts to degenerate.

Conversely, in a genetically female embryo, the paramesonephric ducts, in the absence of the SRY gene, develop into the uterus, fallopian tubes, and the upper two-thirds of the vagina.

By the eighth week, the female external genitalia, like the clitoris, labia minora, and labia majora, develop.