Stratified Epithelial Tissues - Video Tutorials & Practice Problems

Four Stratified Epithelial Tissues

So now that we've covered the four simple epithelial tissues in this video, we're going to begin our lesson on the stratified epithelial tissues. And so once again, recall from our previous lesson videos that structurally humans have eight types of epithelial tissues and half of them or four of them are simple epithelial tissues that we've already covered. And the other half or the other four are going to be tissues that are structurally categorized as stratified epithelial tissues. And recall that this term stratified indicates that these four tissues have multiple layers of cells. And so we'll get to talk about each of these four stratified epithelial tissues in their own separate videos. And in our next video, we'll get to talk about the very first type in our lesson, which is going to be stratified squamous epithelium. So I'll see you all there.

Stratified Squamous Epithelia

In this video, we're going to talk about the first type of stratified epithelial tissue in our lesson, which is stratified squamous epithelium. And so recall from our previous lesson videos, the term stratified indicates this tissue has multiple layers of cells or many layers of cells where all of the cells are not going to come into direct contact with the underlying basement membrane. And so recall that the term squamous here indicates that the apical surface of the tissue has cells with cell shapes that appear to be squished or flat. And so we can say that stratified squamous epithelium consists of many layers of these flat or squished cells just like what you can see over here in our diagram. Now, once again, it's worth emphasizing that when it comes to stratified epithelial tissues that have multiple layers of cells, the term that indicates the cell shape only applies to the cells that are closest to the apical surface of the tissue or the cells that are closest to the open space immediately adjacent to the tissue. And so what we're saying here is that when it comes to stratified squamous epithelium, it's only going to be the cells that are closest to the apical surface that are going to have shapes that appear to be squished or flat. And so as you go deeper into the tissue, closer to the basement membrane, the cell shape can vary from cuboidal to even columnar. And so again, it's important to note that when it comes to these stratified epithelial tissues with multiple layers of cells, the term that indicates the cell shape once again only applies to the cells closest to the apical surface of the tissue. Now notice here in our little diagram, it's very clear that this tissue has multiple layers of cells. You can see these nuclei are pretty much all over the plates. And of course, what this means is that not all of the cells are going to come into direct contact with the underlying basement membrane. And really this is what defines this tissue as a stratified tissue with multiple layers of cells. Now, in terms of the functions of stratified squamous epithelium, again, it's going to be the structure of the tissue and the structure of the cells that dictates the sh the functions of the tissue. And so with stratified tissues that have multiple layers of cells, these tissues tend to be thicker in nature and these thick tissues are going to be great for protection. And so what we're going to see as we move forward talking about stratified epithelial tissues is that the thick nature of the tissue is going to allow it to function in protection in many cases. And so that's actually going to be the case here with stratified squamous epithelium again, because it has so many layers of cells, it's going to be a relatively thick tissue. And so its primary function is going to be in protection. And so this means that we're going to find the stratified squamous epithelium in locations of the body where protection is going to be important. And so, uh for example, we are going to find the stratified squamous epithelium in areas that encounter a lot of physical stresses and also areas that require protection such as our skin, for example, and also in areas such as our mouth, esophagus, anus and vagina, which encounter physical stresses in our mouth and esophagus. It's encountering physical stresses from the foods that we eat and the, the drinks that we drink in the anus. It's encountering, encountering physical stresses from the passage of feces and in the vagina, it encounters physical stresses from sexual intercourse. And so, uh when it comes to the function of stratified squamous epithelium, what's important to note is that some of the cells and some of the stratified squamous epithelium can actually produce a tough and waterproof fibrous protein that's called carin. And so this Carotin protein. When it is present in the stratified squamous epithelium, it can actually increase the toughness of the tissue and it can help to prevent water loss from the underlying tissue. But the Carotin itself is a waterproof protein. And so what this means is that in the tissues where the Carotin is present, it's actually going to help create a waterproof surface and that waterproof surface is going to make the tissue dry on the April surface. And so, um this is important to keep in mind about this protein Carotin. Now, later in our course, when we talk about the skin or the inte system, in more detail, we're going to revisit this protein carrot and talk about it in more detail. Now, this really leads us to two main types of stratified squamous epithelium. The first main type is going to be carin stratified squamous epithelium, which of course, as its name implies, is going to contain the protein Carotin. And then the second type is going to be unchains or non carin stratified squamous epithelium, which as its name implies, is not going to have the protein carrot. Now, the carin stratified squamous epithelium can actually be found in the outermost layers of our skin. And so the skin pretty much covers our entire body. Now, the un characterized stratified squamous epithelium that does not have the protein Carotin is going to be found in orifices or openings that are near the skin, for example, again, the mouth, the esophagus, the anus or the vagina, for example, now again, because this protein Carotin is waterproof and creates a dry surface on the apical surface of carrot, stratified squamous epithelium. This is why our skin is usually going to be dry in its nature. Whereas the unchains stratified squamous epithelium that does not have the protein Carotin is going to have more moist tissue. And so that's why the mouth esophagus, anus and vagina are associated with being moist more so than being dry like the skin. And so notice over here in our image, we're actually focusing in on the skin of this person here. And so you can see a micrograph showing the outermost layers of the skin. And what you'll notice is that all of this that's being highlighted here is going to be the stratified epithelial, the stratified squamous epithelial tissue. And so uh what you'll notice again is that it's the outermost layers of the tissue that are going to be squamous or flat and squished. And again, as you go lower into the tissue deeper into the tissue, the shapes of the cells can vary uh from cuboidal to even columna. Now, uh what you'll notice is deeper to the epithelial tissue here is going to be the connective tissue. And so you can see that here in this light blue color. Now, over here, what we have is a micrograph that's zooming into this specific region. And once again, what you'll notice here is that the outermost layers of this tissue are going to be flat in their nature, they're so flat here that you can barely um you know, tell them apart, they're flat and really squished together here. Um Again, these cells here are also pretty flat in their nature. But again, as you go deeper into the tissue, the cell shape in varied. Now, uh what you'll notice is that in stratified squamous epithelial tissue, um because they serve a protective role uh where they're going to be protecting against physical stresses and abrasions and things of that nature. What that means is that the cells that are on the surface are going to encounter a lot of physical stresses that can actually kill the cells and rub the cells off. And so the cells that have been rubbed off actually need to be replaced by dividing cells that are down beneath. And so it turns out that the cells that are closer to the basal surface or closer to the basement membrane are going to have a higher capacity to divide. And the reason for that recall from our previous lesson videos is because these cells that are closer to the basal surface are going to be closer to the underlying vascular connective tissue that have blood vessels that supply nutrients. And so the cells closer to the basal surface here are going to have more direct access to the nutrients. And so they'll be able to have a higher capacity to divide. And as the cells get further and further away from the basal surface, they are going to have a uh they're going to have less access to the underlying nutrients from the connective tissue. And so they're going to have less capacity to divide. And also with this characterized tissue here, um as the cells get further and further away from the underlying connective tissue again, um they are going to have less access to nutrients and things of that nature and also they're going to become more characterized. And so it's really the outermost layers of the stratified squamous epithelial tissue that's going to be characterized in characterized stratified squamous epithelial tissue. And also these cells that are towards the top, they can actually even be dead in many cases. And so these dead cells can help to protect the living epithelial tissue that's below as well. Now, we also have some helpful ID tips here when it comes to stratified squamous epithelial tissue. And the biggest tip that we have for you is that this tissue is going to be relatively thick. It's going to have lots and lots of cell layers and again, appear relatively thick as you can see in these images. Now, once again, it's only the cells that are near the april surface that are going to be flat in their nature. And again, these cells that are uh near the apical surface are going to encounter all of the physical trauma and abrasions. And so those are the ones that are most likely going to be flaking off and falling off or rubbing off And again, that's why they need to be replaced by dividing cells that are closer to the basal surface. And so the cells that are near the basement membrane, once again, are not necessarily going to be flat in their nature. Again, as you go deeper into the tissue, closer to the basement membrane, these cells that are closer to the basement membrane can vary in shape from cuboidal to alumni. And so this here concludes our lesson on stratified squamous epithelium. And we'll be able to learn more about other stratified epithelial tissues and get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Transitional Epithelia

So it may be a little bit of a surprise to you that the second type of stratified epithelial tissue in our lesson is transitional epithelium because it is an exception to our structural naming system from our previous lesson video. And so transitional epithelium is the only stratified epithelial tissue that does not have the term stratified in its name. But again, it is a stratified tissue which means that it's made of multiple layers of cells or many layers of cells where all of the cells are not going to come into direct contact with the underlying basement membrane. And so the reason that we're covering transitional epithelium at this point in our lesson is because structurally and functionally transitional epithelium is similar to stratified squamous epithelium, which we covered in our last lesson video. And so we'll be able to point out some of those similarities in this video here shortly. And also transitional epithelium is called transitional because its cells have the ability to transition in shape depending on the conditions. And so more specifically transitional epithelial tissue cells have the ability to transition from a cuboidal or a cube shape as you can see here in this region of our diagram up above to a squamous or a squished flat shape, as you can see down below in this part of our diagram. And so this transition of the transitional epithelial tissue cells from a cuboidal shape to a squamish shape occurs when the tissue is stretched. In fact, a notable characteristic of transitional epithelium is its elasticity or its ability to be stretched, but then return back to its original shape after being stretched. And so, in terms of its function, again, it's going to be the structure of the tissue and the structure of the cells that make up the tissue that determine its function. And so, once again, transitional epithelium is a type of stratified tissue with many layers of cells and so like stratified squamous tissue. From our last lesson video, because it's made of many layers of cells. This tissue is going to be relatively thick and because it is a relatively thick tissue, again, like stratified squamous tissue, it's no surprise that one of its primary functions is going to be protection. Now, transitional epithelium is going to provide its protection by blocking the diffusion of harmful molecules. And so in terms of the location, we can expect to find transitional epithelium in areas of the body that are going to rely on the elastic ability or the ability for this transitional a bit uh tissue to stretch and return back to its original shape. And that rely on the ability for the tissue to provide protection by blocking the diffusion of harmful molecules. And so it turns out that transitional epithelium is only found in the urinary system. And so we can find transitional epithelium lining the bladder, which is going to be storing the urine until it needs to be excreted. And so the bladder needs to have that ability to stretch when the bladder is full and then return back to its original shape when the bladder is not full. And also we can find transitional epithelium in the ureters, which are going to be the tubes that carry urine from the kidneys to the bladder. And we can also find transitional epithelium in the parts of the urethra that are closer to the bladder, which is the tube that allows for the excretion of urine from the body. And so, what I want you to notice is that because transitional epithelium is only found in the urinary system, sometimes transitional epithelium is referred to as urothelium. And again, transitional epithelium is going to provide protection by blocking the diffusion of harmful molecules in the urine so that those harmful molecules in the urine cannot diffuse back into the internal regions of our body and causes harm. And so notice that in our image, we've broken it up into two sections that are separated by this dotted line here. So we have a top half of our image and then we have a bottom half of the m and notice that they're both showing transitional epithelium. And so notice that in the top half of the image, we're showing an empty bladder. And so you can see the bladder is here and the ureters are coming in. And so again, this is an empty form of the bladder that does not have any urine in it. And so when the bladder is empty, the transitional epithelium is more in a relaxed state. And so in this relaxed state, the transitional epithelial tissue cells are going to be in a cuboidal or a cube like shape, just like what we can see here in our diagram. Now, over here, what we have is a micrograph of some actual transitional epithelium and notice that here, this open space here is being labeled as the inside of the bladder. And so again, the transitional epithelia is found lining the bladder. And what you'll notice here looking at this micrograph is again, it is certainly a stratified epithelial tissue. You can see all of these different layers of nuclei here. So clearly there are mark multiple layers of cells. And uh what you'll notice is that down below in the full bladder, when the bladder is filled with urine, notice that the transitional epithelial tissue cells transition from a cuboidal shape to a squamous shape, a sh uh squished or flat like shape. And this is because when the bladder is filled, the pressure of the urine is actually going to stretch the tissue. And so when the tissue is stretched, it's actually going to allow the cells to widen and Latin. And so that's why we see that in the full bladder, the transitional epithelia transitions to this squamous shape where the cells are wider and flatter. But again, the tight junctions and the desmosome make sure that the cells are still held together. So the cells are not going to separate, they still are held together, but they are going to be stretched. And that stretching is going to cause the cells to widen and Latin so that they become more of a squamous shape. And so uh one thing to note is that on the surface of the empty bladder version of the transitional epithelia, when the transitional epithelia is in a relaxed state, the cells on the apical surface are going to appear to be pillow shape. And so you'll notice that they're going to be a little bit larger than the cells that are deeper to them. And you'll also notice that they have this kind of curved shape to them. And this curved shape here is kind of going to look a little bit like a pillow, you can put your head on it and take a nap. And so that's exactly why we have this pillow right here is because again, the cells on the apical surface of transitional epithelia, kind of resemble the shape of a pillow with this kind of curved like shape that you see here. And so, uh, notice that here, we have the pillow in a relaxed state when the bladder is empty. But then again, when the bladder is filled with urine, it is going to apply pressure that stretches the tissue. And when the tissue is stretched again, you can see that our pillow is being stretched and, uh indicated by these arrows here, uh showing the stretching and notice that the uh the pillow here is widening and flattening just like what we talked about with the transitional epithelia. And so notice that we have some helpful ID tips for transitional epithelia. And so, one of the things to note is that uh transitional epithelia is going to have more layers of cells than stratified cuboidal epithelia, which we have not yet covered. But we will talk about in our next video, our next lesson video. Uh but although they have more layers of cells than stratified cuboidal epithelia, transitional epithelia will have fewer layers of cells than stratified squamous epithelia. Um And also the surface cells on the apical surface of transitional epithelia in its relaxed state when the bladder is empty, uh those cells are going to be pillow shaped just like what we talked about earlier with these cells having somewhat of a curve to them. And so this year concludes our lesson on transitional epithelium and moving forward, we'll be able to apply these concepts and practice problems and we'll also be able to learn about the other stratified epithelial tissue. So I'll see you all in our next video.

Stratified Epithelial Tissues Example 1

So here we have an example problem that says to students stratified squamous epithelium and transitional epithelium tissues often look similar, identify each tissue below and highlight the difference or the differences between the tissues that helps you tell them apart. And so notice that we've got this micrograph on the left and another micrograph on the right. And our job is to fill in these interactive blanks with the appropriate tissue type, either stratified squamous epithelium or transitional epithelium. And so when I look at these micro graphs, the first thing that stands out to me is actually all of this open space that you can see highlighted in these regions of the image. And so notice that identifying the open space when we're looking at micro graphs of epithelial tissue is going to be key because it's going to help us identify the polarity of the tissue, which side of the tissue is the apical surface versus which side of the tissue is the basal surface. And so of course, the apical surface is going to be the surface that is closer to the open space. And so in this tissue, it's going to be up here that will be the april surface. And in this tissue over here, the apical surface is actually curving, but it's going to be that surface right there of the tissue. And so what we can clearly see in both of these micro graphs is that clearly they are stratified tissues. You can tell that there are multiple layers of cells because of all of the nuclei that you can see and you can see those multiple layers again in both of these tissues. And so not all of these tissue cells are going to be in direct contact with the underlying basement membrane. Now, the real part that is going to help us tell these two tissues apart is focusing on the apical surface. And so recall from our previous lesson videos that when it comes to stratified epithelial tissues that have multiple layers of cells, like both of these micro grafts. Uh The the term that indicates the shape of the cells is actually only going to apply to the cells that are on the apical surface. And so in stratified squamous epithelium, the term squamous indicates that the shape of the cells on the surface are going to be squamous or squished or flat shaped cell. And so when we closely analyze the shape of the cells in the left a diagram uh that are closest to the apical surface, what you'll notice is that these cells are pretty flat in their shape. And so they do have this flat squamous shaped cells on the apical surface. Whereas when we closely analyze the shape of the cells on the apical surface and the um micrograph on the right notice that these cells on the april surface are more cuboidal in shape. And so already just by looking at that feature right there, we can clearly see that the stratified squamous epithelium is going to be the micrograph on the left. And so for that reason, we can actually write in stratified squamous on this micrograph. And so, of course, what that means is that this right tissue must be the transitional epithelium. Now, another key feature that we could have looked at is again, these cells on the apical surface are somewhat pillow shaped. And so you can see these kind of roundish pillow shaped cells. And that is a key feature of transitional epi when the tissue is in a relaxed state. Again, when the bladder is empty. And usually in most cases, the transitional epithelium that is going to be shown is the transitional epithelium in that relaxed state where again the bladder would be empty. And so uh another key feature that we could have identified is that in the stratified squamous epithelia, the apical surface has cells that are flaking off and the cells flaking off on the apical surface is very characteristic of stratified squamous epithelium. Uh for example, the stratified squamous epithelium that makes up our skin, uh our skin is constantly flaking off. And so uh that is a good indication of stratified squamous. And so this here concludes this particular example. Again, the uh micrograph on the right is transitional, the micrograph on the left is stratified squamous. And so we'll be able to get some practice applying these concepts moving forward. So I'll see you all in our next video.

Before rubber was used in inflatable balls used in sports, people would inflate animal bladders to make the inner part of a ball. Which tissue type would make this possible? 

• A. Stratified squamous epithelium. 
• B. Transitional epithelilum.
• C. Pseudostratified columnar epithelium.
• D. Simple squamous epithelium.

When you look at another person, what do you see?

• A. Stratified squamous epithelium. 
• B. Transitional epithelilum.
• C. Pseudostratified columnar epithelium.
• D. Simple squamous epithelium.

What is different about the epithelium found inside the mouth and the epithelium found on the face?

• A. Inside the mouth has simple squamous epithelium while the face has stratified squamous epithelium. 
• B. The epithelium inside the mouth has goblet cells, while the skin will not. 
• C. The epithelium of the skin has a basement membrane, while the epithelium inside the mouth will not.  
• D. The epithelium on the face has keratinized cells, while inside the mouth will not.

Stratified Cuboidal Epithelia

In this video, we're going to talk about the third type of stratified epithelial tissue in our lesson, which is stratified cuboidal epithelium, which is actually a relatively rare or uncommon tissue in the human body, which is why we have the word rare in parentheses right after it. And also this is why this is the third stratified tissue in our lesson instead of being the first stratified tissue in our lesson, for example. And so recall the term stratified indicates this tissue has multiple layers of cells or more than one layer of cells where all of the cells are not going to come into direct contact with the underlying basement membrane. And recall the term cuboidal indicates that the cells on the apical surface of this stratified tissue are going to be cube shaped or box shaped. And so we can say stratified cuboidal epithelium is going to consist of more than one layer of these cube shaped cells just like what we can see over here in our diagram. And so notice that we have these multiple layers of cells where all of the cells are not going to come into direct contact with the underlying basement membrane, which is really what makes this a stratified tissue with multiple layers of cells. And also notice that the cells on the apy surface of this stratified tissue are going to be cuboidal in their shape or cube shape or box shape. And again, when it comes to stratified tissues that have multiple layers of cells, the term that indicates the shape of the cells is only going to apply to the cells that are closest to the A and the cells that are deeper in the tissue may not necessarily take on that same cuboidal shape. Now, one thing to notice is that in comparison to stratified squamous epithelia, which can have dozens of layers of cells. And in comparison to transitional epithelia, which can also have several layers of cells, not as much as stratified squamous, but still several layers of cells when it comes to stratified cuboidal epithelium. Yes, it is a stratified tissue with multiple layers of cells, but usually it's only going to have just 2 to 3 layers of cells instead of dozens of layers of cells. And so that can be a really helpful ID tip when it comes to stratified cuboidal epithelium. And so notice over here, we're only showing you two layers of cells. Now, when it comes to the functions, of course, it's going to be the structure of the tissue and the structure of the cells of the tissue that determine the function. And so of course, this is a stratified tissue with multiple layers of cells. And because it has multiple layers of cells, of course, it's going to be a thicker tissue, especially in comparison to its single layered cell counterpart, the simple cuboidal epithelia, which again consists of just one single layer of these cube shaped cell. And so because stratified cuboidal epithelia is going to be a thicker tissue than simple cuboidal epithelia. Of course, it's no surprise that it's going to function in protection and support. And also because the cells on the apical surface of the tissue are going to be cube shaped in comparison to squamous cells which are squished and flat. These cuboidal shaped cells are going to have more cytoplasm and more room for organelles. And those additional organelles can allow for the function of secretion, which is an important function for glands and the ducts of glands. Now, when it comes to simple cuboidal epithelia, which we covered in our previous lesson videos. And again, is just one single layer of cube shaped cells, recall one of their one of their functions was absorption. And what you'll notice is that in tissues that have just one single layer of cells, it's going to make it a lot easier for substances to be absorbed through the tissue. Because again, those substances only need to be absorbed through just one single layer of cell. But in stratified tissues that have multiple layers of cells, they are going to not function as well in absorption, because the substances that need to be absorbed need to go through multiple layers of cells. And that makes it more difficult and less efficient for absorption to take place. Now, it is important to note that again, stratified cuboidal epithelium only consists of just 2 to 3 layers of cells. And so because it only has 2 to 3 layers of cells, it may still have some limited functions in absorption, but it's not going to have a primary function and of absorption like simple cuboidal epithelia might have. And so keeping that in mind in terms of the locations where we can expect to find stratified cuboidal epithelia. Again, because it's going to be stratified and allow for uh a a thicker tissue that allows for protection and because it can function in secretion as well, we can expect to find it in the parts of the ducts of glands that are going to be larger and need to be able to handle larger volumes of secretions that create more pressures and things of that nature. And so we can expect to find stratified cuboidal epithelium in the larger parts of the ducts of sweat glands and mammary glands, for example, whereas again, recall with simple cuboidal epithelia, because it's just one single layer of cells, it's going to be found in the smaller parts of ducts, glands and tubules. And again, those smaller parts are going to have smaller volumes of secretions passing through them, for example. And so those smaller volumes create less pressures. And so one single layer of cells is sufficient for those simple cuboidal epithelia. But again, stratified cuboidal epithelia is going to have multiple layers of cells. It's gonna provide a little bit more protection. So they are going to be found in the larger parts of ducts, for example. And so another helpful ID tip to keep in mind is that because these stratified cuboidal epithelia can be found in ducks, for example, usually they're going to be arranged in a ring. And again, it's going to be adjacent to the open space in the middle because again, it's going to be forming the larger parts of the ducks. And so notice over here in our image, we're showing you this woman here that is sweating pretty profusely. You can see these big drops of sweat and we're actually zooming in on one of the sweat glands. And that's what we're showing you here is the micrograph of one of the sweat glands. And so what you should notice is that right here in the middle, we have this open space and uh immediately uh we can determine the polarity of the surrounding tissue. We know that the tissue that is immediately around the open space here is going to be the epithelial tissue, the stratified cuboidal epithelia because the cells that are on the apical surface here are cube shape or box shape. And so notice that we do have multiple layers of cells. Again, you can see here, there's a ring of cells here and a second layer of a ring of cells right there. And so over here on the right, what we have is a sketch of the same exact micrograph just to make it a little bit easier for you to see. And once again, you can see that right in the middle here, we have the open space or the lumen, which is going to be the open space in the duct of the sweat gland. And again, notice that the cells that are on the apical surface are going to be cube shape or cuboidal. And again, we have multiple layers of cells as you can see right here. And so this year concludes our lesson on stratified cuboidal epithelium. And we'll be able to get some practice applying these concepts and talk about the last type of stratified epithelia as we move forward in our course. So I'll see you all in our next video.

Stratified Columnar Epithelia

In this video, we're going to talk about the fourth and final stratified epithelial tissue in our lesson, which is stratified columnar epithelium, which like stratified cuboidal epithelium. From our last lesson video is a relatively rare or uncommon tissue in the human body, which is why we have the word rare in parentheses right after it. And this is partially why this is the fourth stratified tissue in our lesson instead of being the first stratified tissue in our lesson, for example. And so we know that the term stratified indicates this tissue has multiple layers of cells or more than one layer of cells where all of the cells are not going to come into direct contact with the underlying basement membrane. And recall the term columnar indicates that the cells on the apical surface of this stratified tissue are going to be tall and narrow like a column. And so we can say that stratified columnar epithelium is going to consist of more than one layer of cells where again, it's the cells that are on the surface of the stratified tissue that are going to be columnar cells and be tall and narrow, shaped like a column, just like what we can see over here in our diagram. And so notice once again that we have multiple layers of cells here making it a stratified tissue because not all of the cells are going to come into direct contact with the underlying basement membrane. And also notice that the term columnar is only going to apply to the shape of the cells on the apical surface of the tissue or the cells that are closest to the open space that's immediately adjacent to the tissue. And so the cells that are deeper to the apical surface can take on different shapes and can even be irregularly shaped now like simple cuboidal epithelia. From our last lesson video again, simple columnar epithelia is relatively rare and uncommon in the body. And it's also only going to consist of just 2 to 3 layers of cells instead of dozens of layers of cells like stratified squamous epithelia, for example. And so again, this can be a really helpful ID tip. And notice here in our diagram, we're only showing you two layers of cells. Now, in terms of the function, of course, it's going to be the structure of the tissue and the structure of the cells that make up the tissue that determine the function. And once again, because this is a stratified epithelial tissue with multiple layers of cells. This is going to be a thicker tissue, especially in comparison to its single layered cell counterpart the simple columnar epithelia. And so because stratified columnar epithelia is multilayered and a thicker tissue, it is actually no surprise that one of its primary functions is going to be in protection and support. Now, what you'll also notice is that it does have absorption ability but it is limited. And so recall that with stratified tissues that have multiple layers of cells, absorption is going to be a little bit less efficient because the materials that need to be absorbed need to go through multiple layers of cells, which is a little bit more inefficient than having to go through, you know, only one single layer of cells. But again, stratified columnar epithelia only have 2 to 3 layers of cells. And so going through just 2 to 3 layers of cells is going to be better for absorption than having to go through dozens of layers of cells. So again, it does function in absorption but it does have a limited capacity in absorption. Now, in some areas of the body stratified columnar epithelia can also function in secretion. We know that these cells are going to be columnar shaped and because they are columnar shaped, there's plenty of cytoplasm, plenty of room for organelles. And so they can function in secretion and in some areas of the body, these columnar epi stratified columnar epithelia can be sprinkled with some goblet cells which we know can secrete a product that ends up forming mucus. But those goblet cells are not always going to be found in the stratified columnar epithelia. And so, in terms of the location, some example locations of where stratified columnar epithelia can be found. We can actually find it in some parts of the male urethra, which is the tube that allows for the excretion of urine from the body. And we actually, we actually can find stratified columnar epithelia uh transitioning between other epithelial tissues. For example, when simple columnar epithelia is transitioning to stratified squamous epithelia, we can actually find some stratified columnar epithelia in between them helping to transition these uh other types of epithelial tissue. Now, in terms of the ID tips, once again, usually stratified columnar epithelium is only going to have 2 to 3 layers of cells. And once again, only the top layer or only the apy layer is going to have those columnar shaped cells. The cells that are deeper to the apical layer can be irregularly shaped. And so notice here we have a micrograph of some stratified columnar epithelia. And notice the first thing that you can see here is all of this open space. And so only the cells that are on the surface of the tissue are going to be columnar shaped, tall and narrow like a column. But again, the cells that are deep deeper to the apical surface can take on different shapes and irregular shapes. And so over here, what we have is a sketch of the same exact micrograph just so that you can see it a little bit easier. And again, the cells on the apical surface take on this column shape, whereas the cells deeper to that can take on different shapes. And so this year concludes our brief lesson on stratified columnar epithelium. 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.

Which type of epithelial tissue has more than one cell shape in a single layer? 

• A. Simple cuboidal epithelium.
• B. Simple columnar epithelium.
• C. Stratified squamous epithelium.
• D. Pseudostratified columnar epithelium.

Which of the following functions is stratified squamous epithelial tissue best suited to?

• A. Rapid diffusion.
• B. Absorption.
• C. Protection.
• D. Lining internal organs.