Midgut Loop and Hindgut Development – Stomach, Midgut and Hindgut Development

by John McLachlan, PhD

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    00:00 the course of stomach development. What we’re going to look at now is the extension and return of the midgut loop. Now, this process is quite complicated, so to help you understand it, we prepared an animation. As you can see here, we’re looking at an embryo roundabout the beginning of the embryonic period. And at this stage, the midgut loop has been pulled out into the extraembryonic cavity by the yolk stalk. In this position, it has an upper limb, the cranial limb, and a lower limb, the caudal limb. Now, what’s going to happen is that this loop will rotate through 90 degrees counterclockwise as seen from in front.

    00:38 So it will rotate so that the cranial limb comes to lie on the right-hand side of the body, and the caudal limb on the left-hand side of the body. In this position, what will now happen is that the cranial limb will become much more complicated and convoluted as it forms the small intestine. The caudal limb remains much simpler and will form the transverse ascending and descending colons. Once this is complete, then the abdominal cavity will open again, and the midgut loop will begin to return. First of all, the small intestine will return. So that’s the parts derived from the cranial limb. And then the parts derived from the caudal limb will return and lie unto above them. So the caudal limb will form the ascending, transverse and descending colon. While this process is taking place, we must bear in mind that the gut is suspended by its mesentery all the way through the process.

    01:37 This mesentery, the dorsal mesentery, carries the major blood vessels which supply the gut.

    01:44 We can see that the stomach is supplied by the celiac artery, the midgut loop is supplied by the superior mesenteric artery, and the hindgut is supplied by the inferior mesenteric artery. These arteries come off eventually from the aorta. When the gut loops and twists, there’s always a possibility that one of these arteries may be cut off or kinked, and if that were to happen, then an area of the gut would be deprived of blood supply and may well develop the process. Now, let’s look at the hind end of the gut. Originally, the cloaca is a large open space at the hind end of the gut, closed off by a cloacal membrane.

    02:27 During the course of development, urorectal septum will grow towards the tail end, and finally, divide the original cloaca into a urogenital sinus anteriorly, and the anal canal or rectum posteriorly. The openings are initially closed by membranes, but subsequently, these will open.

    About the Lecture

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

    Author of lecture Midgut Loop and Hindgut Development – Stomach, Midgut and Hindgut Development

     John McLachlan, PhD

    John McLachlan, PhD

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