Embryology and Congenital Malformations of the Female Genital Tract

Abstract

In mammalian embryos the first indication of sex differentiation appears in the form of the primordial germ cells. Although for a long time considerable controversy has existed on whether these cells arise within the gonad or in an extragonadal site, it is now generally accepted that they originate in the wall of the yolk sac close to the allantois^8,21 (Figure l.1a). From various experimental and histochemical studies^5,19 it has been concluded that the germ cell line begins with the primordial germ cells and that these cells appear at an early stage of development in the yolk sac entoderm. Subsequently they are incorporated into the wall of the hindgut and finally migrate through the dorsal mesentery to the gonadal ridges. In these ridges they multiply, differentiate, and give rise to the definitive germ cells (Figure 1.1b). Hence, the early primordial germ cells form a continuous cell line from early embryonic development to the definitive germ cells in the adult stages of life.⁹