Submucosa and Muscularis Externa

00:00 and mitochondria, of course, to provide the energy. Let's just lastly look at the submucosa, which is fairly uninteresting tissue really. It's just general loose in some areas, dense connective tissue in other areas, containing the blood vessels I mentioned earlier that are going to supply the mucosa. It's that area that can expand or contract or change its dimensions to accommodate the increased luminal space, during swallowing or during increasing content of food as you would have in the stomach. And then on the right-hand side is the section through the muscularis externa. The muscularis externa here has an inner circular and an outer longitudinal layer. You can't really tell that from this section because you can't see the orientation of the lumen. But I know because I actually took the image from the section through this stomach, and now I know the orientation of the lumen. So you can trust me to say, that there is, at the top, the section through the inner circular and the more longitudinal layer as you can see just below that.

01:18 And then you have the serosa, the covering, the mesothelial covering, cuboidal squamous cells that are going to be part of the visceral peritoneum.

01:34 That muscularis externa is controlled by a nerve plexus, the enteric plexus that goes all the way through the gut wall and controls that independently of the central nervous system. And we'll see evidence of that as we look at other organs of the digestive system in later lectures. It's called Auerbach's plexus between the muscle layers and the muscularis externa, and the submucosal or Meissner's plexus in this submucosa that controls the contraction of the muscle in the muscularis mucosa layer. Well, in summary, it's important that you understand the wall of the gut is composed of those layers listed there. And I went through these layers and explained, particularly in relation to the stomach and the esophagus, how the mucosa changes. And also, I pointed out the role of the other layers in the general function of the gut wall, particularly, moving food along it, mixing food within it, and then the mucosa layers that have secretory functions, and as we'll see later on also, absorptive functions in other lectures. The esophagus was specialized to pass food through to the stomach. It's a tube, a muscular tube that is lined by a wear and tear epithelium.

03:10 And we learned that the stomach has a special gastric glands within it, that secrete a number of different components, pepsinogen, acid, and the intrinsic factor, that's important for the absorption of Vitamin B12 lower down in other parts of digestive tract. And the importance of that mucous layer, lining the surface, protecting the surface from the abrasion of chyme moving about during the mixing of the food, and also, concentrating bicarbonate on there to protect the epithelium from the damage of hydrochloric acid. So, I hope you now know something about the histology of the esophagus and the stomach. And certainly, I hope you now understand all the structures that comprise the wall of the gut. So thank you very much for listening and I hope you enjoyed this lecture.