Review of the Folding of the Embryo – Stomach, Midgut and Hindgut Development

by John McLachlan, PhD

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    00:01 Hello, and welcome to one of two lectures on the development of the gut. In this particular lecture, we’ll be looking at the development of the stomach, the midgut, and in particular, the midgut loop, and then the hindgut. Finally, we’ll look at some developmental abnormalities of these structures. So, we have to begin again with the process of folding of the embryo.

    00:26 Up above in the image, you can see the amniotic cavity on a little lower down the yolk sac.

    00:31 What will happen is that the embryo begins to fold, bending upwards into the amniotic cavity. Here we can see the midgut beginning to close off as the yolk sac contracts relative to the size of the overall embryo. And as this takes place, it will narrow to begin to form a yolk stalk. A little later, the embryo is bent in a C-shape and projecting up into the amniotic cavity, and the yolk sac is beginning to pinch off as seen in this view from the side. If we look at the same process seen in a cross-section, a transverse section, here we can see the amniotic cavity up above and the yolk sac down below. The folding and sweeping around process of the amniotic cavity is taking place in this plane as well.

    01:22 So the amniotic cavity gradually extending round the embryo. And what we can see here is that the yolk sac is beginning to be pinched off just underneath the body of the embryo.

    01:33 This is what will give rise to the gut. Looking at this a little later, the folding has continued and beginning to pinch off even more of the yolk sac to form the gut. In the image marked C, we can see that the gut is beginning to be pinched off and suspended as a tube which is running forwards and backwards in the embryo, and is suspended in a mesentery of mesoderm above and below. In this slide, we can see the process has continued. And in the image marked D, the extraembryonic cavity has been completely separated from what we can now recognize as the intraembryonic coelom. This will give rise to the abdominal cavity.

    02:17 The gut is now suspended in a mesentery of mesoderm, and we can note the dorsal mesentery and the ventral mesentery attaching it to the body wall at the front and to the body itself respectively.

    02:30 Looking at this view from the side, we can see that in a particular part of the foregut, a swelling begins, an enlargement, and this is going to be the stomach. The curvature of the swelling is greater on the side towards the back, and this is known as the greater curvature of the stomach. Also visible, we can see where the yolk sac has been almost completely pinched off leaving just a stalk connecting the gut to the yolk sac in the midgut region. We’re following that important step forward in the later slide. We can also see down towards the hind end that the cloaca is present. This is a large open space of gut, and it’s connected to the allantois. The allantois is an evolutionary remnant which was originally intended to store waste products for embryos developing inside eggs. It remains an important part of the system in the human embryo, and will give rise to a variety of structures including the bladder. This is covered in another lecture. Here we see the stomach after it has undergone a rotation through 90 degrees. So if one were looking from head to tail, the stomach rotates so that the greater curvature comes to lie on the left-hand side and the lesser curvature on the right-hand side. This is the stage you can see in this image. Once this has happened, the stomach will also rotate. So it comes to lie transversely across the body axis in the direction indicated by the arrow in the image. The pyloric end of the stomach will develop powerful musculature, and this will be important later on when we look at the abnormalities that can develop during the course of stomach development. What we’re going to look at now is the extension and

    About the Lecture

    The lecture Review of the Folding of the Embryo – Stomach, Midgut and Hindgut Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.

    Author of lecture Review of the Folding of the Embryo – Stomach, Midgut and Hindgut Development

     John McLachlan, PhD

    John McLachlan, PhD

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