Structures of the Stomach – Esophagus and Stomach

by James Pickering, PhD

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    00:00 So let’s move on now to the stomach. The stomach is specialized for this mechanical and chemical digestion. So it's a muscular sack that churns, contracts and squashes, like I say churns the ingested bolus of food. It also carries out significant chemical digestion that release pepsinogen which is an enzyme, which is converted into pepsin helps the break down of our gastric juices. And it converts this bolus of food into a semi-liquid which is known as chyme. If we look at the diagram we can see here we have got the oesophagus joining the stomach and this region of the stomach we know is the cardiac region.

    00:45 So this region here is known as the cardiac region and it opens up via the cardiac orifice. That's the junction between the oesophagus and the stomach. We can then look at some other regions of the stomach.

    01:00 Superior to this junction, this region here we have the Fundus so we have the Fundus in this region. We have the cardiac region here.

    01:10 The fundus is usually filled with gas that has been produced via this chemical digestion. And then we have this large space in here which is the body of the stomach. And we can see on the internal structure of the stomach, it's flowing into this series of folds called rugae.

    01:26 And that helps to increase the ability of the stomach to distend outer in size we got these elevation. We can also see in this region here we have what's known as the pylorus and this is a narrowing of the body of the stomach that leads it towards the duodenum and importantly, in this region we have what's known as the pyloric sphincter. Really important sphincter that regulates the passage of chyme through this space into the duodenum and that’s the pyloric sphincter. When the pressure within the stomach becomes so high, then food passes through this chyme, passes through this sphincter and enabling it to carry on through the gastrointestinal tract and fit to be digested. We can also recognize a few other landmarks or boundaries; external features of this stomach. We have this nice long curvature around here as called a greater curvature. I am going to appreciate the series of blood vessels that run along here later on. And we can also see that here we have a lesser curvature Another important landmark is that it has a peritoneal attachment with the liver. We can see we have the other structure of cardiac notch this junction between the Fundus and the oesophagus. And we can see where the lesser curvature take us down towards the pylorus, where we have the Angular incisure so we can see that down here. On this side of screen we can actually see this muscular bag and all its smooth muscle fibers arranged either longitudinally or align or arranged kind of circular that surround the muscles. And these muscles contracting enable that mechanical digestion to occur.

    03:15 So we can see the various layers of muscles that are surrounding the stomach. If we look at the internal surface of the stomach so here we can see the section through the stomach. We have got the outer surface of the stomach here and we have got the internal surface here. We can see in this thickness of the stomach, we can see the various muscle layers we can see the circular and longitudinal muscle layers which we can see here.

    03:41 And we can also see the mucosa, this most inner lining of the stomach and that’s really important, this inner surface, this mucosa.

    03:50 It’s important because it contains what are known as the gastric pits. The gastric pits that communicate with some gastric glands. And deep within these gastric glands we can just may count some gastric glands down at here, right bottom of these pits. We can see these individual pits that open up onto the surface of the stomach. This two types of cells. This is not the Physiology course so we are not going into too much detail here. But briefly these two different types of cells - these parietal and these chief cells are important in that chemical digestion. The parietal cells secrete Hydrochloric acid. So secretes hydrochloric acid as protons, as Hydrogen ions and as Chlorine ions into the lumen of the stomach. This reduces the pH to around about 1 or 2. The importance of this is it kills micro-organisms it denatures proteins, and it helps to break down the plant cell walls.

    04:55 It also importantly, this acidic environment activates the pepsin. Pepsin is released by this second group of cells called chief cells and these secrete pepsinogen.

    05:08 Pepsinogen is inactive Pepsinogen is inactive and it requies the acidic pH created by the parietal cells to become active. So this acidic lumen converts pepsinogen to pepsin. And it is the pepsin that breaks down the proteins. So without this acidic lumen, created by the parietal cells, proteins in the ingested bolus wouldn't be able to be digested.

    About the Lecture

    The lecture Structures of the Stomach – Esophagus and Stomach by James Pickering, PhD is from the course Abdomen.

    Included Quiz Questions

    1. Pepsinogen
    2. Trypsinogen
    3. Chymotrypsinogen
    4. Amylase
    5. Glucagon
    1. Fundus of the stomach
    2. Heart
    3. Esophagus
    4. Duodenum
    5. Pylorus
    1. Lesser curvature
    2. Greater curvature
    3. Cardiac orifice
    4. Fundus
    5. Body

    Author of lecture Structures of the Stomach – Esophagus and Stomach

     James Pickering, PhD

    James Pickering, PhD

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