Fetal genital development
A few weeks after fertilization, the initial appearance of the human fetal genitalia is basically feminine: a pair of "urogenital folds" with a small protuberance in the middle, and the urethrabehind the protuberance.
In typical fetaldevelopment, the presence of the SRY genecauses the fetal gonadsto become testes; the absence of it allows the gonads to continue to develop into ovaries. Thereafter, the development of the internal reproductive organsand the external genitaliais determined by hormones produced by fetal gonads (ovaries or testes) and the cells' response to them.
If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings swell, wrap around the penis, and fuse in the midline to form the penile urethra.
If testosterone is not present, normal female development continues, with the development of a perineal urethraand the formation of a uterus, clitorisand vagina.
The Müllerian ducts, which are paired ducts of the embryo which empty into the cloaca, and which develop into the upper vagina, cervix, uterusand oviducts; in the male they disappear except for the vestigial vagina masculinaand the appendix testis.
Because of their common origin in fetal anatomy, a number of male and female anatomical features are said to be homologous; for example, the clitoris and penis are homologous with one another, as are Skene's glandsin females and the prostate glandin males.
Most of the time, the result of fetal genital development follows the stereotypical male or stereotypical female development path. However, in a small but significant minority of cases, the path of development follows an intermediate or other pathway, leading to what are called "ambiguous genitalia", a condition known as intersex.
See congenital anomalies of the genitaliafor a list of congenital disorderscaused by problems with fetal genital development.
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It uses material from the http://en.wikipedia.org/wiki/Fetal+genital+development Wikipedia article Fetal genital development.