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External Genitals – Genital System Development

by John McLachlan, PhD
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    00:00 where the testicle lies. Now, let?s have a look at the external genitalia. Again, in the early stages, these are identical between males and females. The significant features are a large genital tubercle present in both males and females, and swellings on either side, cloacal folds, which are more medial, and the more lateral, labioscrotal swellings.

    00:25 Later on, as the urogenital sinus and the anal canal become separate, then we can see a division between these structures with the urogenital sinus at the upper part of these diagrams, and the anal canal or rectum in the lower part. Let?s look again at the female.

    00:43 Essentially, the rearrangements are relatively minor. And because the rearrangements are relatively minor, this is less likely to go wrong than it might do in developing male.

    00:55 So the genital tubercle will become the clitoris and the villous labia will form as the labia minora and the labia majora on the outside. If we look at the male, then the rearrangements are more significant. Effectively, the original urogenital sinus has to zip up as it were, and you can see that in section view in the upper images. So it?s gradually closing over and it will enclose the urethra in the very center of the developing genital tubercle, which, of course, will give rise to the penis. There will also be an invasion of the ectoderm from the very tip, which will meet the developing urethra to form the final adult penal urethra all the way from the urethra to the exit of the penis. This line of zipping up, as it were, is a classic example of where things can go wrong in development, where folds have to come together and fuse and any disturbance in the timing of exact process is involved mainly to a deficiency. If we look at this picture of which there?s a section through the embryo from the side, we can see just the size and significance of the genital tubercle. It is a well-formed structure in both males and females.

    02:09 In fact, if we look at a scanning electron micrograph, you can see that it?s very well developed even if it?s in a different stage. It?s even sometimes possible to mistake a female fetus for a developing male fetus because of the size of the genital tubercle.

    02:24 In this image, we can also see the opening of the urogenital sinus, which is not yet zipped up, but this will zip up towards the tip of the genital tubercle in males. There is variety


    About the Lecture

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


    Author of lecture External Genitals – Genital System Development

     John McLachlan, PhD

    John McLachlan, PhD


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