 So I have a chart and this is actually attached to the back of your lab, or it's in your external brain handout. So this chart, the whole purpose of this thing is to help you gather, quantify, solidify. I don't know what a phi you're going to do a phi, but you're going to do something with this chart if you remember the key characteristics of each one of these parts of the digestive tube. So the esophagus, we're going to start with the esophagus. Why? Because it's first. And the esophagus might be the easiest one to tell. And let me tell you why. It is the only part of the tube that has a different kind of epithelial tissue lining the lumen. The esophagus is lined with stratified, squamous epithelial tissue. All of them are lined with epithelial tissue because you only find epithelia along a lumen and all of them have lumens in the middle. So the esophagus has stratified squamous. Now think about that for a second and tell me what is the function of the esophagus? Well, it pretty much did nothing more than pass food from here, from the pharynx, to the belly zone. And you probably are going to want to have some decent muscle in order to go through the process of motilitying. So the esthalsis is the process of moving food through the tube. So I'm not sure that we're going to see anything significant in the laminopropria. Muscularis mucosae is probably noticeable. In some of the parts of the digestive tube, the muscularis mucosae is, if you can find it, you're stoked, but often you can't find it. The mucosa has some glands in it, and here's the key. You might find glands in the submucosa. So we'll just put a little question mark, glands. Maybe they'll be here. We'll see. But honestly, if you see stratified squamous epithelium, you are no longer asking yourself what part of the tube you're in. You know. Today, in the future, if we're dealing with other kinds of tubes like vaginas, then there's other tubes out there that have stratified squamous epithelium lining the lumen. So vagina, esophagus, I don't want to mess that up. Muscularis externa is usually in our tubes made of smooth muscle, but in the esophagus, and I think you know this already, the esophagus at the superior end, the mouth end, there's skeletal muscle. At the inferior end or the stomach end, it's smooth muscle. So if you actually see skeletal muscle, striated those long fibers with nuclei all around the edges, if you see skeletal muscle in the muscularis externa, that's a pretty good hint that you are also in esophagus. You probably aren't going to need to determine that because the fact is that if you see stratified squamous epithelium or you see not simple columnar epithelium, then you pretty much know you're in the esophagus. You tell me, I told you that adventitia was found somewhere and cirrhosa was found somewhere else. What did I tell you? Cirrhosa is peritoneal. If the structure is found in the peritoneal cavity, if it is intraperitoneal, then it's going to be the outermost layer or the most superficial layer or the most basal from the lumen of the tube is going to be cirrhosa. If it is not in the peritoneum and you tell me esophagus, what's the story? Is it in the peritoneum? Most of it is not. Some of it is. As soon as it passes through the diaphragm and into the stomach, there's a little brief period where it is in the peritoneal cavity and at that point it is covered with cirrhosa, most of its life it is covered with adventitia. And I said most of its life, most of its length is probably a nicer way to put that. Okay, I didn't put anything in the laminopropria because the laminopropria is, there's nothing unique or interesting. Really, submucosa, I probably could have skipped that too. Knowing that it's adventitia, that's a good thing to know. That tells me that this is not going to be found in the peritoneal cavity. And like I said, stratified squamous epithelium, that's your go-to. So let's go check it out. Here I am in my favorite land, University of Michigan, Histo, woof woof, what are the Michigan? Wolverines, wolves, woofs, woof woofs, doggies. All right, check this out. First of all, Histo review. Every time we're in Histo land, try to identify as many tissues as you can. What is that? Come on, home pounds, lacuna, clear, glassy looking. This is hyaline cartilage, you guys. So are we expecting hyaline cartilage in the esophagus? No, no. But what might we expect hyaline cartilage in that might be near the esophagus? You can feel it, right there, your trachea. You could totally have your trachea and we will be looking at the trachea soon. But I want to show you this too really fast. Look at what these are. Our slides at College of the Redwoods, I can never find these structures on our slides of trachea, but these are tracheal glands and they're actually found in the submucosa of the trachea. So that's the kind of thing you're looking for if you're looking for some glands. But yeah, this is not the tissue you're looking for. This is not the tube you are looking for. Let's go look somewhere else. Now, trachea, probably pretty close to esophagus. Look, another lumen. Shall we check it out? Let's do it. Let's zoom in here. Doesn't this, here's a lumen. Doesn't this look like epithelial tissue? And sure enough, my friends, what kind of tissue is this? Like, oh dude, this is awesome. I'm trying to move around and I'm zooming in and out. What kind of tissue is that? No question. This is stratified squamous epithelium, done. As soon as you find stratified squamous epithelium, you know you're in the esophagus. There's some other things that are interesting here though. This would be my basement membrane, which means what is going to be basal to that? We should see the submucosa, and I mean the laminopropria, and it's true. This is an interesting structure right here. This is actually a lymphatic nodule, and it's a little bit different structurally from a lymph node, but it has a lot of similarities. It's a little less structure than a lymph node. A lymph node would be more nodule-like and have some additional structures in it, but most of your digestive tract has these lymphatic nodules in it because the lymphocytes hang out there. Why? Because it's the outside world, and lymphocytes are part of your immune system, and they're hanging out there to be like, dude, if anybody comes in here, I'm going to get ready to fight. Fight, it's time to fight. Awesome, that's perfect. So they are just guarding the door to make sure that nothing funky happens. You can see that this is, that right there is probably our muscularis mucosi. This is the laminopropria, and then that might be submucosa right here. It looks pretty messy. There looks like some open holes here, and then doesn't this look like, oh, it changed, didn't it? Can you see that layer change? Let's zoom out a little bit. There, you can totally see that layer change. This is smooth muscle here. This was my submucosa. submucosa has all sorts of stuff going on. There's another layer of smooth muscle. So we could probably look in there and get closer and see if any of it could possibly be skeletal, I don't know. The smooth muscle of muscularis externa comes in two layers, and you can see it right here. You can see these fibers are rolling one way, and these fibers are rolling another way. So you've got both your layers, and it's looking pretty fabulous, and you are at a zone where you cut a slice of esophagus and trachea. You got both of them in the mix, which brilliant to do that as often as possible. All right, esophagus, the easiest one there is. All right, let's do another one.