The gonads develop in two paired ridges of mesenchyme at the medial aspect of the mesonephros during the 5th–7th weeks of gestation (Byskov and Høyer 1988; Wartenberg 1989). The primordial germ cells originate from the yolk sac and migrate to the gonadal ridges. Regardless of the karyotype, all embryos have, after 6–7 weeks of gestation, indifferent gonads consisting of germ cells, coelomic surface epithelium and mesenchyme. At this stage also internal Müllerian (paramesonephric) and Wolffian (mesonephric) ducts, a urogenital sinus and an undifferentiated external genitalia can be identified (Fig. 20.1). The subsequent sex-specific development of internal and external genitalia is primarily dependent on the karyotype, but is also influenced by the endocrine function of the gonads. It has long been known that presence of a Y chromosome is decisive for testicular differentiation. Recently, the essential DNA sequence on the short arm of the Y chromosome has been cloned and called the sex-determining region of the Y (Sinclair et al. 1990).
KeywordsMigration Testosterone Androgen Meso Hypospadias
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- Byskov AG, Høyer PE (1988) Embryology of mammalian gonads and ducts. In: Knobil E, Neill J, Ewing LL, Greenwald GS, Markert CL, Pfaff DW (eds) The physiology of reproduction, Raven Press, New York, pp 265–302Google Scholar
- Grumbach MM, Conte FA (1985) Disorders of sexual differentiation. In: Wilson JD, Foster DW (eds) Textbook of endocrinology, 7th edn. Saunders, Philadelphia, pp 312–401Google Scholar
- Kerr JB (1989) The cytology of the human testis. In: Burger H, de Kretser D (eds) The testis, 2nd edn. Raven Press, New York, pp 197–229Google Scholar
- Nielsen J, Wohlert M (1991) Sex chromosome abnormalities found among 34910 newborn children: results from a 13-year incidence study in Århus, Denmark. In: Evans JA, Hamerton JL, Robinson A (eds) Children and young adults with sex chromosome aneuploidy. Wiley-Liss, New York, pp 209–223Google Scholar
- Simpson JL, Jirásek JE, Speroff L, Kase NG (1976) Disorders of sexual differentiation. Academic Press, New York, pp 341–359Google Scholar
- Wartenberg H (1989) Differentiation and development of the tests. In: Burger H, de Kretser D (eds) The testis, 2nd edn. Raven Press, New York, pp 67–118Google Scholar