 All right, we're in stomach land. Now I'm going to show you some of the unique characteristics of the stomach. First of all, this is probably the most significant, although sometimes it's hard to find all three layers. There are three layers. Oops, I forgot my little trick. There are three layers of muscularis externa, and you'll see them right here. One, two, three. I couldn't, for the life of me, explain to you how these fibers are moving through this structure. I've got this way, I've got that way, and then I've got like me, way. But regardless, they're moving a different way, and they call them oblique fibers. I just don't have a sense. My spatial challenge meant doesn't let me understand that. So, um, luminal to muscularis externa, we've got our submucosa, and you can usually not much significant in the submucosa, but usually muscularis mucosi is also well-defined in the stomach. So this is all part of the mucosa. Muscularis mucosi is usually easier to find in the stomach than other places. So that's another thing that I kind of, sort of focus in on. Another really significant and sort of obvious characteristic that you'll notice, it isn't super obvious right here, but in the lamina propria, there are a lot of glands in the stomach. So the reason why is even though these sort of, don't they kind of look like villi? They're not villi. Take a look, villi stick out like this. They're little finger-like projections that extend out. The lamina propria is down here, and the fingers can float around in the mush and gush and do their absorbing. This, look at my surface. My surface is not wispy and wavy with finger-like projections. My surface is actually flat with holes in it. These things right here, these are gah. Why does it do that? I don't know. These are actually gastric glands, and the glands are down in the lamina propria. They're producing substances. I'm going to show you a picture of a gland and talk to you a little bit about what they're producing. And then the substances that they produce are being secreted into the lumen of the stomach up here. So the stomach, the lamina propria of the stomach looks extremely glandular. The tissue looks puffy to me, and I'll show you when we look at the slides. And sometimes it looks like there are villi and there aren't villi. One thing that there are are rugi, or what were the gastric folds in the stomach. And that is just those places that they will look like extensions up and out. They tend to look a little more square than finger-like. But remember that the rugi were just there so that we could stretch. So fill up with the chocolate chip cookies that your son makes every single night because he loves baking. And then you fill up with them. And my rugi do a good job of expanding because I'm a good mama. I'm going to eat those chocolate chip cookies that my kid made for me. Let me talk to you a little bit about a little bit of physio. So there are two cells that are found in these gastric glands. We are, let's see, the superficial or the luminal cell is called a parietal cell. And we will not be able to tell these cells apart. Some people can. Awesome. We're not going to spend our time trying to identify them, but you should know them and know what they do because it's actually pretty cool. The parietal cells are luminal. The chief cells are basal. And they're found in these gastric glands. Now, the chief cells are producing a substance that they are secreting into the lumen of the gastric gland and it's called pepsinogen. And it's actually a protein-digesting enzyme. Now, you tell me, protein-digesting enzyme, do you want that hanging out close to your cells? Why or why not? That would be a great exam question. The answer is no thank you. I do not want a protein-digesting enzyme close to my cells because it will digest my cells. Totally true. So pepsinogen is actually inactive. It cannot digest protein yet, but guess what? The parietal cells are doing some magic, too. Guess what they're producing? Hydrochloric acid. What stomach acid? The parietal cells are producing stomach acid. When pepsinogen moses on by and comes in contact with a pH of one because it's hydrochloric acid, it activates and it turns into pepsin, but not until it's exited the gastric gland. And now it's pepsin in the lumen of the stomach and it's going to go to town-digesting proteins. It's active. How cool is that? Digests proteins. Let's go look at our diagram or our chart or whatever that thing was. I'm going to make a note that we have simple columnar, columnar epithelium, and then I'm not going to note it anymore because it's not significant. The laminopropria is full of glands, and that is significant. I think the muscularous mucosae is thick and definitely muscularous externa has three layers. Sub mucosa, whatever. And then you tell me. Advantisha or cirrhosa for the stomach? Definitely cirrhosa. It is the stomach is intraparitoneal. All right. Now let's take a look at histoland. Check this out. Can you see sort of blocky? Like, these are probably my rugi, these blocky chunks of tissue, and if we zoom in here, you will be able to see, like, oh, good graciousness. I think the slices look kind of, oh, here's a good one. Here's a place where you can get a sense that, oh yeah, it looks like simple columnar epithelium, which means that all of this is lamina propria. If you go deep, I'm going to zoom out just a little bit, look at that glandular tissue. You can imagine that if I had cut, if I'd made the cut right or on the correct plane, I could have cut and made it look like the diagram, the drawing, the cartoon that we were labeling. The cut is crazy, and so we've got all these lumens for all these glands, and ultimately they're going to dump into those pits that are going to empty their goodies out into the lumen. You would expect to see parietal cells closer to the lumen and chief cells closer, farther away from the lumen, and I believe in this slide the different colored cells are the chief cells in the parietal cells. If we zoom back out again and look at these layers a little more clearly, you can see your subucosa, it just looks messy, right? And then, whoa, look at how thick that smooth muscle, muscularis externa is, and we can see some different layers there. I don't think I see three layers, but someone might want to fight me about that and go demonstrate, like that might be a third layer, or maybe even that might be, those kind of look like blood vessels. What's that? What's that? What's that? That's a lymphatic nodule there in the stomach, too. Okay, how are you feeling? Awesome, should we go on to the small intestine? Let's do it.