 So, let's think about pseudo-stratified columnar epithelium with cilia next. And I have a micrograph here of a trachea slide that shows the pseudo-stratified columnar epithelial tissue. And it's a little hard to make out on this particular slide. If I drop back, you can get oriented a little better, perhaps. And so here you can see that we have a trachea, and the hollow portion of the trachea is called the lumen. Now, we don't have the entire trachea here. You can see that it's been cut. But if you look, you can see that it's roughly circular, and so this space that it is encircling is the lumen. And that's what your air moves through when you breathe in. So the pseudo-stratified columnar epithelium with cilia lines the lumen of the trachea. And so we want to go up on a higher power and observe this tissue lining the lumen. So click up, it's if we can get it in focus, find the tissue, and I'm going to go up one more. Now the thing about the microscope slides is when these are made, you're cutting through different planes, and we just want to find an area where we're looking at the tissue in a way that will help us understand exactly how it's put together. I also want to find a spot that shows the cilia really nicely. So let's look at this spot. In particular, I want you to notice the cilia, and the cilia are right here. Cilia are found on the free surface of these cells, and they're just little, some people call them hair-like projections, but they're really, they're short. And what they do is, you can sort of picture them as fingers, and they wave back and forth and back and forth, and within the pseudo-stratified tissue we have some cells called goblet cells. And these goblet cells may secrete a mucus, and as the cilia beat back and forth, they distribute that mucus across the surface of the tissue. And if you're doing something dusty, like chopping up leaves with a lawnmower, you may have a piece of dust that gets stuck in your trachea and the cilia can move that up towards your larynx, and when it gets to your larynx you can cough, and then, well, you can swallow or spit, but either way, you get that piece of debris out of your trachea and somewhere that's more appropriate. So look in this area for the cilia, and I'm going to adjust the magnification just a little bit, which will help you pick up those cilia. Really fine and hard to see on this particular slide. Now the other thing about the tissue we've talked about before is that it's pseudo-stratified or falsely layered, and so I'm going to just try and draw an outline around some of these cells so you can sort of see what we're talking about. So here are three cells, we have the cilia attached to them, and here's the nucleus of one cell. You can see it's sort of in the middle of the cell. Here's a nucleus of another cell that's more towards the top, and here's a nucleus of another cell. So when we look at this tissue under the microscope, we may have a nucleus here, a nucleus here, one here, here, here, that kind of thing, and so that gives the tissue, when we look at it microscopically, the appearance of being layered. But it's not actually layered, it's actually a simple tissue that's attached to the basement membrane on this side. So pseudo-stratified columnar epithelium with cilia, thick cell helps to protect the lining of the trachea, has cilia helps to distribute mucus, which is secreted by this tissue, it's involved with moving debris, it may be involved with moving cells if you inhale some bacterial cells for example, and so it's a tissue that we find in the trachea, and also we find this tissue in the fallopian tubes or the uterine tubes.