ABSTRACT
All fetuses have both ‘male’ and ‘female’ internal genitalia. Subsequent development is dependent upon the influence of hormones derived from the gonads as they develop into testis or ovary. The testis produces Müllerian inhibitory hormone, which leads to regression of the Müllerian ducts, and androgens which lead to persistence of the Wolffian ducts. Conversely, neither of these substances is produced by the ovary; therefore, the Müllerian ducts persist and the Wolffian ducts regress. The corollary of this reciprocal arrangement is that, in the absence of a Y chromosome – and hence testicular tissue – differentiation proceeds along female lines. This explains the female phenotype of patients with, for example, 45,XO (Turner’s) or 47,XXX genotypes and the male phenotype of patients with Klinefelter’s syndrome (47,XXY). The exception to this rule is the female phenotype of patients with androgen insensitivity syndromes, in which the androgens produced by normal testes in patients with an 46,XY genotype are ineffective as a result of end-organ insensitivity. Müllerian hormone is, however, produced and therefore both Wolffian and Müllerian ducts regress. These disorders are
Key Points
• The ovary forms from the indifferent gonad. • Development proceeds along female lines in the
absence of a Y chromosome. • The internal female genitalia form from the fused
paramesonephric ducts and the urogenital sinus.
