Female Genital System – Genital System Development

by John McLachlan, PhD

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    00:01 Of course, for a human kind, the baseline condition is female. It will start off as female, and some of these are diverted away from that pathway to become male under the influence of the Y-chromosome and this will lead to differences later on. So in the early stages, there is essentially no difference between embryos of male and female gender, but later on, there will be. And in particular, in the female, the paramesonephric ducts were going to persist and contribute to the developmental apparatus, and the mesonephric ducts will disappear. In the male, the mesonephric ducts will persist and the paramesonephric ducts will disappear. The paramesonephric ducts will meet and fuse in the midline.

    00:45 And as we can see in the diagram on the left, as they meet there, they will gradually differentiate into the uterus, and they?ll also form the upper part of the vagina. So the cervix, the uterus, and the vagina in the upper third are all coming from the paramesonephric ducts as they come together and fuse in the midline. In this diagram, we can also see the degenerating mesonephric system in the female, and you can also see that perhaps, some remnants may remain along the way. So these may give rise to little anomalies which can be identified by surgeons, such as Gartner's cysts and Gartner's ducts.

    01:24 The ovaries will also shift their position slightly. They begin relatively high up inside the abdominal cavity, and they will shift down towards the lower end of the body cavity subsequently. This is partly due to the relative growth of different parts of the body.

    01:40 The embryo is curved as a C-shape, and the outer parts grow more quickly than the inner parts and therefore, the structures towards the midline can actually displace with respect to the back. If we look at this process in transverse section and cross-sections across the body of the embryo, we can see the urogenital ridges with the gonads on the inner aspect of them seen in an early view in the diagram marked A. As we move down the body, these are moving towards each other, so they?re swinging in till eventually they will come in contact with each other. When they come in contact, they will fuse, and of course we?ve already looked at the fusion of the paramesonephric ducts giving rise to the uterus and the upper part of the vagina. The mesonephric ducts, of course, as we said, will subsequently disappear. So this fusion process will give rise to the broad ligament of the ovary.

    02:36 This diagram summarizes the changes that are taking place. If we start with the gonadal ridge, we can see that the mesoderm of the gonadal ridge will give rise to the ovarian medulla.

    02:46 The epithelium on the outside will give rise to, first, the primary sex cords. But in females, this will degenerate, and secondary sex cords will arise, and the secondary sex cords in females will give rise to the follicular cells. The nephrons of the mesonephros will degenerate and regress. The mesonephric ducts themselves will regress apart from a few remnants such as Gartner?s cyst, the epoophoron, and the paroophoron. The paramesonephric ducts, as we?ve indicated, will give rise to the oviducts, to the uterus, to the cervix, and to the upper third of the vagina. Now, let?s have a look at the developing male genital system.

    About the Lecture

    The lecture Female Genital System – Genital System Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.

    Author of lecture Female Genital System – Genital System Development

     John McLachlan, PhD

    John McLachlan, PhD

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