During the fifth week of fetal life, formation of the genital ridges starts in the posterior abdominal wall, in response to colonization by primordial germ cells, migrating from the yolk sac. By the end of the sixth week, the male and female gonads are indifferent. Differentiation of the gonads is triggered by the sex-determining-region on the Y-chromosome. The first step in male gonadal development is differentiation of Sertoli cells, which produce anti-Müllerian hormone (AMH). Subsequently, between the eighth and tenth week, AMH induces regression of the Müllerian ducts. Thereafter, mesenchymal cells differentiate into Leydig cells, which produce testosterone. Further differentiation of the urogenital system into male derivatives is then ensured by testosterone. In absence of the sex-determining-region on the Y-chromosome, producing the testis determining factor, the gonad differentiates into a female genital system. In addition, production of AMH is lacking and Müllerian ducts, also called the paramesonephric ducts, continue to differentiate into fallopian tubes, uterus and upper part of the vagina. From the seventh week of fetal life onwards, germ cells differentiate into oogonia. Through mitotic cell divisions, the number of oogonia increases steadily and during the third month, the first oogonia begin to transform into oocytes. From the fifth month onwards, the oogonia enter meiosis. In addition, the oocytes are encapsuled by a single layer of pregranulosa cells, forming the primordial follicles. Meiosis is arrested during the first prophase of the first meiotic division, when the homologous chromosomes pair and the primordial follicles enter a dormant state.

, ,
A.P.N. Themmen (Axel) , J.S.E. Laven (Joop)
Erasmus University Rotterdam
Erasmus MC: University Medical Center Rotterdam

Lie Fong, S. (2012, April 27). Clinical Applications of Serum Anti-Müllerian Hormone. Retrieved from http://hdl.handle.net/1765/32515