Paramesonephric duct derivatives in the female
In typical female development, the paramesonephric ducts, a pair of embryonic tubes, are not removed and go on to form the uterus, the fallopian tubes and the upper vagina.
Remember
In a typical female embryo there are no testes, so nothing makes the paramesonephric ducts break down, and they build the uterus, the fallopian tubes and the upper vagina. The lower vagina comes from the urogenital sinus.
Memory aid
Müllerian ducts make the Mother's organs
Use it to link the Müllerian ducts with the uterus and tubes, and the Wolffian ducts with the male tubes.
Every early embryo has two pairs of ducts, which are tubes, running alongside the mesonephros (the embryonic kidney). They are the mesonephric (Wolffian) ducts and the paramesonephric (Müllerian) ducts. Hormones from the testes decide which pair survives.
In a male, the Sertoli cells (the supporting cells of the testis) make anti-Müllerian hormone, which makes the paramesonephric ducts degenerate (break down). The Leydig cells (the testosterone-making cells) make testosterone, which keeps the mesonephric ducts.
A typical female embryo has no testes, so it has neither hormone. Without testosterone, the mesonephric ducts degenerate. Without anti-Müllerian hormone, the paramesonephric ducts persist and carry on developing. Their upper parts become the fallopian tubes. Their lower parts fuse (join) in the midline to form the uterus, the cervix (the neck of the uterus) and the upper vagina.
The lower vagina has a different origin. It comes from part of the urogenital sinus (the embryonic chamber from which the bladder also develops), which joins the ducts to complete the vagina. If the two ducts fuse incompletely, the uterus can end up with two horns, called a bicornuate uterus.
Key facts
- Why they persist
- In a typical female embryo there is no anti-Müllerian hormone, so the paramesonephric ducts do not degenerate.
- Derivatives
- In typical female development, the paramesonephric ducts form the fallopian tubes, uterus, cervix and upper vagina.
- Lower vagina
- It is formed by part of the urogenital sinus, which fuses with the paramesonephric ducts to complete the vagina.
- Not from the ducts
- The ovary develops from the gonad itself (the early structure that can become either an ovary or a testis), not from the paramesonephric ducts.
- Male pattern
- In the male, testosterone keeps the mesonephric (Wolffian) ducts, which are the male duct system.
- Missing uterus
- Absence of the uterus and upper vagina with normal ovaries points to failed development of the paramesonephric (Müllerian) ducts, as in Müllerian aplasia (aplasia means that a structure has failed to form).
Exam traps
- The mesonephric (Wolffian) ducts do not form the female internal genital tract: they need testosterone to survive, and without it they degenerate in the female.
- The lower vagina does not come from the paramesonephric ducts, because it develops from the urogenital sinus, and only the upper vagina receives a contribution from the Müllerian ducts.
- The ovary is the gonad itself, so it is not made from the paramesonephric ducts, even though the ducts run alongside it.
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