A Practical Approach to Intersex

M. David Bomalaski

Disclosures

Urol Nurs. 2005;25(1):11-18, 23-24. 

In This Article

Gonadal Differentiation

Traditional teaching is that chromosomal sex predetermines gonadal sex, which determines phenotypic sex. It is in the basis of this concept that the development of the genitalia will be explored. Figure 1 shows an overview of the hormonal stimuli that lead to genital development. It has been appreciated since the 1950s that the genetic material for male differentiation is located on the Y chromosome (Hughes, 2002). Genital development is a stepwise process that is determinate on both sequence and timing starting with the presence or absence of the testis-determining factor on the Y chromosome, in the SRY gene region.

Gonadal and Genital Differentiation

Starting about the 5th week of development, the primary germ cells migrate from the yolk sac to the retroperitoneum where they form a germinal epithelium referred to as the urogenital ridge. Dependent upon the XY or XX chromosomal material, gonadal induction at the 6th week leads to selected germ cell growth into the underlying mesenchyme. This gives rise to primary sex cords and seminiferous tubules in the testis during the 7th week or the primary follicles in the ovary during the 10th week (Hughes, 2002). Two X chromosomes are needed for normal ovarian differentiation.

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