 Okay, everybody, Dr. O. This is going to be the last video where I cover all these epithelial tissue types. These two don't really have anything in common, I just need to put them somewhere. So we're going to cover the pseudo-stratified columnar epithelium and transitional epithelium. So let's go ahead and dive in. So pseudo means false or fake. So pseudo-stratified columnar epithelium looks like it's stratified, but it's not. And the reason being is to see how the nuclei are scattered in that image. So some are high, some are low. So if you look at the nuclei of the cells, it looks like there's more than one layer. But each of those cells is attached to the basement membrane. So that's what it means to be pseudo-stratified columnar. But you're usually going to hear this called pseudo-stratified ciliated columnar epithelium. So in the last video we talked about simple columnar epithelium can either have microvilli like in your gut for absorption secretion or cilia, which cilia moves material. So if we were single-celled organisms, cilia would move us like ores on a boat. Since our cells are attached to that connected tissue layer underneath it, it moves material. So the key examples of pseudo-stratified columnar epithelium are all going to be ciliated. These are going to be the cells lining your respiratory tract. So you see trachea, much of the upper respiratory tract, these ciliated cells, they move material. So in the AMP2 we'll talk about the mucociliary escalator or the mucous escalator or whatever you want to call it. So the cells in your respiratory tract, they capture debris, whatever you're inhaling in mucous, then these ciliated cells beat to carry it up. They carry it to the back of your throat where you can spit it out or swallow it. So that's going to be what the cilia do here. So that is pseudo-stratified columnar epithelium and all the ones we care about are going to be pseudo-stratified ciliated columnar epithelium. Think respiratory tract first. Some of them, there are other places like the male, we talk about it a tiny bit next semester, the male reproductive tract will have some of these cells as well because sperm is carried for a while until it turns itself on and the flagella start to beat. Sperm is going to be carried like a boat that doesn't have a motor yet. So there are going to be some ciliated cells in the male reproductive tract there. All right, here's just another picture. You see pseudo-stratified because the nuclei are scattered. I mentioned goblet cells, the cells that make mucous. These cells have to constantly be lubricated to keep them safe. And that's what the mucous producing goblet cells do. Then we have transitional epithelium. So it's called that because it transitions or changes. You only see this in the urinary system. The bladder and the ureters are the two key examples of transitional epithelium. Called that because when, let's say the bladder, when the bladder is empty, the cells are scrunched up together and they look cuboidal, like you see here in the picture. But when the bladder fills, they're going to stretch and they will look squamous. So it's called transitional epithelium because they change depending on whether the bladder is full or empty. So the urinary bladder, by far the key example of transitional epithelium. All right, so these last four videos have covered each of the types of epithelial tissue. I hope this helps. Have a wonderful day. Be blessed.