JACOPIN / SCIENCE PHOTO LIBRARY JACOPIN / SCIENCE PHOTO LIBRARY
FETAL GROWTH Foetal development of internal reproductive organs and the possibility of abnormalities occurring. In the 6th week of gestation, the gonads are identical in the future girl or boy foetus. In the 8th week, the boy's mullerian duct begins to shrink and the mesonephric duct to develop, while the testicles appear under the influence of the testosterone-producing Leydig's cells. In the girl, the mesonephric duct shrinks and the ovaries begin to form. Up through week 16, the boy's mesonephric duct becomes the vas deferens and the penis develops under the influence of the hormones testosterone and dihydrosterone. In the girl, the mullerian duct becomes the uterus and the Fallopian tubes. At month 7, both the ovaries and testicles descend. At each stage in foetal development, abnormalities and malformations may occur.
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