Endoderm – 3 Germ Layers

by John McLachlan, PhD

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    00:00 Now, let’s have a look at the third layer, the endoderm, the lower layer of the three.

    00:05 This will form the linings of a number of other structures. For instance, the gut, lungs, the liver, the pancreas, and the bladder are all lined with cells derived from the endoderm.

    00:18 But as these linings grow out, often in the form of buds, what happens is that mesoderm will condense roundabout them. So, the final adult got an adult lung, adult liver, and so on that are composed of an endodermal lining, but with a mesodermal grown substance which fills up the bulk of the organ itself. If we look at the folding process in transverse section, so that’s a cross-section across the body of the embryo. In this image, you can see the amniotic cavity at the top, and the lower part is the yolk sac. As the folding of the embryo proceeds, the amniotic cavity sweeps around and begins to pinch off a small part of the yolk sac and that small part being pinched off will form the gut tube. Perhaps, it’s easier to understand this in a view from the side. So, here again, we have the amniotic cavity at the top and the yolk sac at the bottom. You have to imagine the amniotic cavity sweeping around as the embryo rises up into the amniotic cavity and the effect this has on the foregut and the hindgut is to gradually enclose them as the gut sweeps around. We’ve indicated that by shading in this particular image. So, that indicates the fore and hindgut.

    About the Lecture

    The lecture Endoderm – 3 Germ Layers by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Endoderm – 3 Germ Layers

     John McLachlan, PhD

    John McLachlan, PhD

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