 Now we're going to look at the three parts of the small intestine. Let's go ahead and jot them down. What comes first? Duodenum. What comes next? Jejunum, that's the jejunum. What comes next? Ilium with an E like eat. Now, I'm going to tell you the characteristic things that you're going to look for in each of these. They're all parts of the small intestine. They're all going to have villi. They're all going to have microvilli. They're all going to have all of our layers. All of them are lined with simple columnar epithelium. All of them have two layers of muscularis mucosi. To distinguish between them, here's what you're going to look for. In the duodenum, holy, in fact, I'm writing that down, holy glands, not in the mucosi, not in the lamina propria, like in the stomach. The stomach was full of glands. These glands are in the submucosa. If you see a submucosa and it's like, it looks like a bubbly bubble land, then you know you're in the duodenum. And I'm going to show you a picture here and in fact, dude, I better just go show you a picture right now. How are you going to know if you're in the submucosa? You have to find muscularis mucosi. And so, look, here, this is my epithelial tissue. Look, simple columnar epithelium, which means that all of this is lamina propria. And we do have some glands in there, but look, look at that line. That is muscularis mucosi. Now, zoom out, what? Look at this glandular tissue. You've got to be, I mean, holy gland madness. If you see that kind of glandular tissue in, like, deep to muscularis mucosi, here was our line of muscularis mucosi. If you see that, you know you're in the duodenum. Just look for those glands. I mean, that's crazy talk. That doesn't even look like stomach. That's even crazier than that. Holy glands, right? Perfectly clear. Let's do the ilium next, because the ilium has one that is really, really obvious. Lymphatic nodules. Holy lymphatic nodules. Not modules, nodules. Those lymphatic nodules are called pyrus patches. Sometimes the pyrus patches are found in the mucosa. Sometimes they're found in the submucosa. And so where they're located doesn't tell you anything. The number of them tells you something. The more pyrus patches there are, the more lymphatic nodules there are, the more you know that, okay, I'm probably in the ilium. Lymphatic nodules are everywhere. They're all over the digestive system. In fact, lymphatic nodules are part of the immune system. They're part of... It's almost like a little lymph node type structure. And your lymphocytes hang out there. And in fact, what is it? Like, 80% of all of your lymphocytes hang out in your digestive system, because they're making sure that, dude, who knows what you ate, especially if you're my smallest child. That kid, I mean, everything goes in his mouth. And so you know that there's going to be something gnarly in there that you want to protect. Do not let this substance into my body. So let's put a whole bunch of troops guarding the area. So, yeah, absorb as much as you want from the lumen of your gut. But let's have the troops there to make sure that what you're absorbing isn't going to make you sick. I just saw a lymphatic nodule in the duodenum. And so I want to show... Oh, wait, come back. I want to show it to you so that you can get a sense of what it looks like. Check it out. This is awesome. Don't go by color. Never go by color when you're studying histology. But look at the shape. These are my duodenal glands all over in the submucosa. Look at this. I mean, it's just weird. It's almost like dense, but regular. It's not connective tissue. It's really dense cellular tissue. This is a lymphatic nodule. And look at how the tissue is different. Here's my glandular tissue. This looks like maybe even a smooth muscle layer. Possibly dense irregular connective tissue. Let's zoom out. Do you see how... I mean, that tissue looks really different, doesn't it? That's what your lymphatic tissue is going to look like. I'm wondering if there's any other... Oh, do you see another one? Totally. You've got another one in here. Now, here's another one right there. I mean, you don't even have to zoom in to confirm. Let's do... We'll totally zoom in here and make sure that it looks like that same kind of dense polka dotty. How do you describe that? I describe it like lymphatic tissue. Do you want to see how many lymphatic nodules are found in the ilium zooming way out? You can still see these things. There's one, there's one. These guys are actually all in the semi-cosa. There's one. Cool. Along with all those duodenal glands, there's like three or four of them. Ready? I'm not going to believe this. What? There's one. Now, I can't zoom in here. This is an ilium. I'm not fond of the ilium example that they have in the Michigan slide. So, I went out into the world. Oh, and it looks like I can't see. I'm not cool with that. But check it out. Look at how many there are. One, two, three, four. Don't they look like big, globular structures? And if we could zoom in, we'd see that they're made up of that really dense stuff. These look like they're actually in the semi-cosa. Sometimes pyrus patches extend into the mucosae. I mean the laminopropria. And so, you can't really tell based just on that. But look, here we have villi. We have normal structures that we find all the way out around in the other parts of the small intestine. But if I'm going to ask you to identify the ilium, I'm going to make sure that there are billions of pyrus patches for you to see and that it's really obvious. Sometimes the pyrus patches are just on one side of the tube. But again, it's really obvious. So, the last one. I'm thinking that the last one is almost the process of elimination. There are a couple of characteristics that are really distinctive about the jejunum. They have really long, thin villi. All of them have villi. For whatever reason, the jejunum, and we can actually try and speculate on why that is the case, the jejunum has really, really lots and lots of long, thin ones. Something that happens. Now, imagine you have a tube and in your tube it's lined with all these crazy, long, spaghetti-like tentacles, the villi. And then I take a section and my villi kind of move over a little bit and they smear and I end up taking a section of villi like that. Do you agree that if I had that, I would actually, what I would see is a whole bunch of kind of circle-y shapes. I can't remember if I have a jejunum for you to look at. It almost looks like zebra, I mean not zebra, but giraffe skin, like the shape of a giraffe. Okay, I got to go see if I have any jejunum. I don't think I got jejunum. Why didn't I? That makes me kind of want to go see if I can find some jejunum. This is a giant, like what are the chances that it looks how I want to show you what it looks like? Okay, this kind of works. Does it work for you? Look, that's that giraffe-y-looking shape that I was imagining, but it's more like in this space. See how, like we take, you can imagine, that doesn't look like long thin villi to me, but it's because we cut a slice and they were all in a tangle when we cut the slice. We've got all different kinds of angles on our tangles. Ah. When you look at jejunums, you will be like, oh yeah, okay, you will get a sense for this kind of, that something that looks like this actually means that we have long thin villi. The jejunum is kind of a process of elimination. I think jejunum and stomach are equally challenging and I think easy to confuse, but if you look for those long, thin crazies, that's what you're aiming for. That was our small intestine. Let's do our large intestine.