So now that we've covered the characteristics and functions of epithelial tissue. In this video, we're going to begin our lesson on the structural naming of epithelial tissue. And so structurally, humans have eight main types of epithelial tissue. And most of them, in fact, six out of eight of them are named using a two word naming system where both the first word and the second word of this two word naming system will reveal structural characteristics of the tissue. And so the first word of this two word naming system will tell us the number of cell layers in the tissue. More specifically, the first word of this two word naming system will indicate whether the tissue has just one layer of cells or if the tissue has multiple layers of cells. And the second word of this two word naming system is going to indicate the cell shape. And so let's take a look at our image down below where we can start to piece things together here. And so just to orient you on this diagram, notice that across the top here, what we have is the first word of our two word naming system and across the side. What we have is the second word of our two word naming system. And then notice that down below what we have are the two naming exceptions to this two word naming system. But we'll talk about the exceptions to the two word naming system a little bit later toward the end of this video. For now, let's focus on these two words of this two word naming system. And so once again, the first word of this two word naming system will tell us the number of cell layers. More specifically, it will tell us whether there is just one layer of cells in the tissue or if there are multiple layers of cells in the tissue. And so the first word of this two word naming system can either be the word simple or the word stratified. Now the word simple will indicate that the tissue has just one cell layer as you can see right here. And so in this little diagram right here, notice that the cell layer is this layer at the top here and the purple thing at the bottom here is supposed to represent the basement membrane. Now, if the first word is stratified, that would indicate that there are multiple layers of cells in the tissue as you can see here in this diagram. Now, in terms of the second word, recall that the second word will reveal the cell shape of the tissue cells. And so there are three possibilities. For the second word, it can either be squamous, cuboidal or columnar. Now, the term squamous is literally meaning scales in Latin and scales are pretty flat. And so the word squamous will indicate that the shapes of the cells are flat or squished if you will. And so you can think squamous is or squished. And so if we take a look at the shape of the cells here in this diagram, notice that they are pretty flattened or squished. And in fact, they remind me a little bit of fried eggs if you will. Now, the term cuboidal as its name implies is going to reveal that the cell shape is cube like or boxlike if you will. And so notice looking at the diagram here, the cell shape is cube like or boxlike. And then of course, the term columnar is going to reveal that the shape of the cells is tall and narrow like a column. And so you can think columnar cells are going to be shaped like a column. And so notice that the diagram here shows these elongated, tall and narrow column shaped cells. And so what we can start to do is pair first words with second words to reveal the epithelial tissues. And so for example, if we take this first word, simple as we have right here, and we pair this first word simple with the second word over here. Squamous as we have right here, then we should expect to have one cell layer of flat or squished cells. And so take a moment to imagine what this tissue might look like. Well, it should look something like this right here. One layer of these flat or squished cells and so simple squamous, epithelial tissue is going to look something like this. Now, this time, imagine using the first word stratified and pairing it with the second word squamous so that we have stratified squamous, like what we see over here. Well, in this case, we would expect to see multiple layers of these flat or squished cells. And so take a moment to imagine what this tissue might look like. Well, it should look something like this right here. And so notice that we have lots and lots and lots of cell layers here and these cells are going to be flat or squished. Now, one thing to keep in mind about these stratified tissues is that usually the naming system is going to be uh looking at the shape of the cells that are on the apical surface of the tissue. And so uh the shapes of the cells that are deeper in the tissue can actually change and be different. And so really when you're focusing on stratified tissue that has multiple layers of cells, you want to be focusing on the shapes of the cells that are on the apical surface, which again are the cells that are facing toward the open space And so keeping that in mind, we can continuously pair these first words with second words to reveal these epithelial tissues. And so for example, if we take the first word simple and we pair it with the second word cuboidal, then we should expect to see one layer of cube shape shaped cells. And so it should look something like this right here. And then if you take the first word stratified and pair it with the second word cuboidal, then you should expect to see multiple layers of cube shaped cells, which would look something like this right here. And then if you take the first word simple and pair it with the second word columnar, then you should expect to see one layer of these tall and narrow column shaped cells. And so it should look something like this right here. And then if you take the first word stratified and pair it with the second word columnar, then you should expect to see multiple layers of column shaped cells. And so that would look something like this right here. And so what you'll notice is that from pairing the first words with the second words, we were able to get these six different epithelial tissues, simple squamous, simple cuboidal, simple columnar and stratified, squamous, stratified cuboidal and stratified alumni. And so really there are only two exceptions to this naming system and that's what we have down below right here. The two exceptions are going to be pseudostratified columnar, which is actually a type of simple epithelial tissue, meaning that it's going to have just one layer of cells. And then the other exception is transitional epithelial tissue, which is a type of stratified epithelial tissue, meaning that it has multiple layers of cells. And so moving forward in our course, we're going to talk about each of these eight epithelial tissues in their own separate videos covering a lot more of their characteristics and features. Uh But one thing that you should note here is that although pseudo stratified has the word stratified in it, it is categorized as a simple epithelial tissue, meaning that it has one cell layer. And so what can help you remember this is that the root pseudo is actually a root that means false or fake. And so really this is just saying a fake stratified or a false stratified columnar epithelial tissue. And so, although it may appear to be multiple layers of cells, it's actually just one layer of cells. So pseudostratified is still a type of simple epithelial tissue. And then once again, transitional is a type of stratified epithelial tissue because it has multiple layers of cells. And so this here concludes our brief lesson on the structural naming of epithelial tissue. And we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video
