 Let's look at our layers. So I'm going to draw in the last slide what we saw was an actual tube, a cross section of a tube with a little lumen in it. And even though the lumen was all squishy and funky looking, do you agree that this is essentially what we had? I'm going to draw you a piece of digestive tubing when I talk about all the different layers that we have. Basically, I'm going to take a little cross section like this. And do you agree that if I have the lumen up here, I can draw this little space flanked by red? Do you see what I'm doing here? And I can actually draw my layers this way. Do you agree with that? So here's the lumen and here's the lumen. And it's the same thing. So now I'm going to look at my layers from luminal to basolateral in this direction. Okay, you got where I was going with all that. The first layer that we have is called the mucosa. And I'm just going to... In fact, the mucosa has several layers. So I'm going to draw it like this. The mucosa. So the mucosa is first. But I'm going to show you the different layers. Now, you tell me, what is one guaranteed layer in the mucosa? Maybe I should ask it like this. What is one guaranteed tissue type that you're going to find in the mucosa? We're lining in lumen dog bounds. That means it must be... It must be an epithelial tissue layer as part of the mucosa. And it's a true story. The epithelial tissue varies depending on what part of the tube you're in. So it's actually kind of a handy way to identify where you are in your tube. But for our purposes, we're just going to have this looks cuboidal. Most of the digestive tube is lined with simple columnar epithelium. The shape to the mucosa is a layer of loose connective tissue. Look at my connective tissue fun times. It's loose connective tissue, and it's called the lamina propria. Now, do you agree that I could take this shape and like smash it up, fold it up, twirl it up? It's endless, deep to whatever kind of epithelial tissue we have. That next layer of messiness is going to be my lamina propria. Also part of the mucosa is a relatively thin layer of tissue. It's actually smooth muscle. This is our first exposure to smooth muscle tissue. We're studying muscle until much farther down the line. So we're not actually going to look at our smooth muscle in histological detail. But I'm telling you right now, if you can identify smooth muscle in your digestive slides, you are going to be one happy human. What kind of tissue is this? That smooth muscle tissue. What is the name of the layer? The smooth muscle makes up the muscularis mucosi. The muscularis mucosi is the smooth muscle layer. Now, a luminal to muscularis mucosi, what's the name of the layer that's luminal to muscularis mucosi? That's the lamina propria. That kind of tissue is luminal to muscularis mucosi, a loose connective tissue. Do you see the difference there? Of course you do. That's it. Those are your parts of the mucosa. Now, the next layer is deep to the mucosa. And we're going to talk about that. Oh, next.