WOMEN: REPRODUCTIVE ORGANS DEVELOPMENT
The reproductive organs don’t always develop properly. Many defects are minor and may never cause problems or can be easily corrected. Others may have a profound effect on sexual development and the ability to have children. To understand the congenital abnormalities that are possible, we must know something of reproductive development before birth.
Beginning around the sixth week of pregnancy, the female foetus’s XX sex genes stimulate the development of its ovaries. Two pairs of foetal structures – the Wolffian ducts and the genital ridges on each side – contribute tissue to the ovaries. The ova and ovarian stroma come from the genital ridge. The Wolffian duct makes only a small contribution to each ovary. Its lower part regresses.
It is the Y chromosome in the male foetus that leads to the development of the testis. The tissues that produce sperm and hormones come from the genital ridge, and the Wolffian duct contributes the collecting tubules of the testis, the epididymis, the vas deferens and the seminal vesicles.
In both sexes, the Wolffian ducts make a large contribution to the development of the kidneys.
The tubes, uterus and upper vagina develop from another pair of structures in the foetus – the Müllerian ducts – which run the length of the developing abdominal cavity near the Wolffian ducts. This development begins around the eighth week of pregnancy. The upper ends of the Müllerian ducts remain separate, forming the fallopian tubes. The remainder fuses in the middle to form the uterus, cervix and upper vagina. The development of the Müllerian ducts in female foetuses is independent of ovarian hormones. In male foetuses, this development is suppressed by the Mullerian inhibitory hormone (MIH) produced by the foetal testis.
The external genitals and lower vagina develop from the foetal structure that also forms the lower urinary system. The difference between female and male genital development is determined mainly by the effect of male hormones from the foetal testis.
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