Stratified Epithelial Tissues - Video Tutorials & Practice Problems

Four Stratified Epithelial Tissues

So now that we've covered the 4 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 8 types of epithelial tissues, and half of them, or 4 of them, are simple epithelial tissues that we've already covered. The other half, or the other four, are going to be tissues that are structurally categorized as stratified epithelial tissues. 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 4 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. Recall from our previous lesson videos that 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. 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. 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. 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. 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. As you go deeper into the tissue closer to the basement membrane, the cell shape can vary from cuboidal to even columnar. 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.

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 place. Of course, what this means is that not all of the cells are going to come into direct contact with the underlying basement membrane. This is what defines this tissue as a stratified tissue with multiple layers of cells.

In terms of the functions of stratified squamous epithelium, it's going to be the structure of the tissue and the structure of the cells that dictates the functions of the tissue. With stratified tissues that have multiple layers of cells, these tissues tend to be thicker in nature. These thick tissues are going to be great for protection. As we move forward talking about stratified epithelial tissues, the thick nature of the tissue is going to allow it to function in protection in many cases. That's actually going to be the case here with stratified squamous epithelium. 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. This means that we're going to find stratified squamous epithelium in locations of the body where protection is going to be important. For example, we are going to find 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 drinks that we consume. In the anus, it's encountering physical stresses from the passage of feces. In the vagina, it encounters physical stresses from sexual intercourse.

When it comes to the function of stratified squamous epithelium, what's important to note is that some of the cells in some of the stratified squamous epithelium can actually produce a tough and waterproof fibrous protein that's called keratin. This keratin protein, when it is present in the stratified squamous epithelium, can actually increase the toughness of the tissue and can help to prevent water loss from the underlying tissue. But the keratin itself is a waterproof protein. In the tissues where the keratin 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 apical surface. This is important to keep in mind about this protein keratin. Later in our course, when we talk about the skin or the integumentary system in more detail, we're going to revisit this protein keratin and talk about it in more detail.

This really leads us to two main types of stratified squamous epithelium. The first main type is going to be keratinized stratified squamous epithelium, which, of course, as its name implies, is going to contain the protein keratin. The second type is going to be unkeratinized or non-keratinized stratified squamous epithelium, which as its name implies, is not going to have the protein keratin. The keratinized stratified squamous epithelium can actually be found in the outermost layers of our skin. The skin pretty much covers our entire body. The unkeratinized stratified squamous epithelium that does not have the protein keratin 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. Again, because this protein keratin is waterproof and creates a dry surface on the apical surface of keratinized stratified squamous epithelium, this is why our skin is usually going to be dry in its nature. Whereas the unkeratinized stratified squamous epithelium that does not have the protein keratin is going to have more moist tissue. That's why the mouth, esophagus, anus, and vagina are associated with being moist, more so than dry like the skin.

Notice over here in our image, we're actually focusing on the skin of this person here. You can see a micrograph showing the outermost layers of the skin. What you'll notice is that all of this that's being highlighted here is going to be the stratified squamous epithelial tissue. What you'll notice again is that it's the outermost layers of the tissue that are going to be squamous, flat, and squished. As you go lower into the tissue, deeper into the tissue, the shapes of the cells can vary from cuboidal to even columnar. What you'll notice is that in stratified squamous epithelial tissue, because they serve a protective role 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. The cells that have been rubbed off need to be replaced by dividing cells that are down beneath. 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. 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 has blood vessels that supply nutrients. 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. As the cells get further and further away from the basal surface, they are going to have less access to the underlying nutrients from the connective tissue and so they're going to have less capacity to divide. Also, with this keratinized tissue here, as the cells get further and further away from the underlying connective tissue, again, they're going to have less access to nutrients and things of that nature and also they're going to become more keratinized. It's really the outermost layers of the stratified squamous epithelial tissue that's going to be keratinized in keratinized stratified squamous epithelial tissue. Also, these cells that are towards the top can actually even be dead in many cases. These dead cells can help to protect the living epithelial tissue that's below as well.

We also have some helpful ID tips here when it comes to stratified squamous epithelial tissue. 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. Once again, it's only the cells that are near the apical surface that are going to be flat in their nature. Again, these cells 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. Once again, the cells near the basement membrane are not necessarily going to be flat in their nature. 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 columnar. This 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. 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. 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 where all of the cells are not going to come into direct contact with the underlying basement membrane. The reason that we're covering transitional epithelium at this point in our lesson is that structurally and functionally, transitional epithelium is similar to stratified squamous epithelium, which we covered in our last lesson video. We'll be able to point out some of those similarities in this video shortly. Transitional epithelium is called transitional because its cells have the ability to transition in shape depending on the conditions. 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. This transition of the transitional epithelial tissue cells from a cuboidal shape to a squamous shape occurs when the tissue is stretched. 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. In terms of its function, it's going to be the structure of the tissue and the structure of the cells that make up the tissue that determines its function. Once again, transitional epithelium is a type of stratified tissue with many layers of cells. 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, it's no surprise that one of its primary functions is going to be protection. Transitional epithelium provides its protection by blocking the diffusion of harmful molecules.

In terms of the location, we can expect to find transitional epithelium in areas of the body that rely on the elasticity or the ability for this 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. Transitional epithelium is only found in the urinary system. We can find transitional epithelium lining the bladder, which stores the urine until it needs to be excreted. The bladder needs to have the ability to stretch when full and then return back to its original shape when not full. We can also find transitional epithelium in the ureters, which are the tubes that carry urine from the kidneys to the bladder, and in parts of the urethra that are closer to the bladder, which is the tube that allows for the excretion of urine from the body. Transitional epithelium is sometimes referred to as urothelium because it is only found in the urinary system. It provides protection by blocking the diffusion of harmful molecules in the urine so that those molecules cannot diffuse back into the internal regions of our body and cause harm.

In our image, we've broken it up into two sections separated by a dotted line. We have a top half and a bottom half of the image, both showing transitional epithelium. In the top half of the image, we're showing an empty bladder. You can see the bladder here and the ureters coming in. In this empty form of the bladder that does not have any urine in it, the transitional epithelium is more in a relaxed state. 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. Over here, we have a micrograph of some actual transitional epithelium. Notice that here, this open space is being labeled as the inside of the bladder. Notice that in the full bladder, when the bladder is filled with urine, the transitional epithelial tissue cells transition from a cuboidal shape to a squamous shape, a squished or flat-like shape. This is because when the bladder is filled, the pressure of the urine is going to stretch the tissue. When the tissue is stretched, it's going to allow the cells to widen and flatten. That's why we see the transitional epithelium transitions to a squamous shape where the cells are wider and flatter. The tight junctions and the desmosomes make sure that the cells are still held together. So the cells are not going to separate, but they are going to be stretched. This stretching is going to cause the cells to widen and flatten so that they become more of a squamous shape.

On the apical surface of the empty bladder version of the transitional epithelium, when in a relaxed state, these cells on the apical surface are going to appear to be pillow-shaped. 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 curved shape. And this curved shape resembles a pillow. That's why we have this pillow right here; 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, you can see our pillow being stretched. Notice that the pillow is widening and flattening, just like what we talked about with the transitional epithelium.

We have some helpful ID tips for transitional epithelium. Transitional epithelia are going to have more layers of cells than stratified cuboidal epithelia, which we have not yet covered, but we will discuss in our next video. However, transitional epithelia will have fewer layers of cells than stratified squamous epithelia. The surface cells on the apical surface of transitional epithelia in their relaxed state, when the bladder is empty, are going to be pillow-shaped, just like what we talked about earlier with these cells having a curved shape. This concludes our lesson on transitional epithelium, and moving forward, we'll be able to apply these concepts in practice problems and learn about other stratified epithelial tissues. 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 micrographs, 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 micrographs 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.

In this tissue, it's going to be up here, which will be the apical 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 micrographs is that clearly they are stratified tissues. You can tell that there are multiple layers of cells because of all 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 micrographs, the term that indicates the shape of the cells is actually only going to apply to the cells that are on the apical surface.

In stratified squamous epithelium, the term squamous indicates that the shape of the cells on the apical surface is going to be squamous or squished or flat-shaped cells. And so when we closely analyze the shape of the cells in the left diagram, 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 these flat squamous shaped cells on the apical surface. Whereas, when we closely analyze the shape of the cells on the apical surface in the micrograph on the right, notice that these cells on the apical surface are more cuboidal in shape.

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 epithelium when the tissue is in a relaxed state. Again, when the bladder is empty.

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, 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. For example, the stratified squamous epithelium that makes up our skin, our skin is constantly flaking off. And so that is a good indication of stratified squamous.

This here concludes this particular example. Again, the 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 3rd 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. Also, this is why this is the 3rd stratified tissue in our lesson instead of being the 1st stratified tissue in our lesson, for example. 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. Also, 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. 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. 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. Also, notice that the cells on the apical surface of this stratified tissue are going to be cuboidal in their shape, cube-shaped or box-shaped. 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 apical surface. 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. That can be a really helpful ID tip when it comes to stratified cuboidal epithelium. Notice over here, we're only showing you 2 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. 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 cells.

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 these 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. 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, it's just one single layer of cube-shaped cells, recall 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 cells. But in stratified tissues that have multiple layers of cells, they are not going to 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 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 in absorption like simple cuboidal epithelia might have.

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 a thicker tissue that allows for protection and because it can function in secretion as well, we can expect to find it 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, of 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 pressure, 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 going to 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 ducts, 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 ducts. Notice over here in our image, we're showing you this person 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.

So what you should notice is that right here in the middle, we have this open space. And immediately, 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-shaped or box-shaped. 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-shaped or cuboidal. And again, we have multiple layers of cells as you can see right here. 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 4th 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 4th 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 apical 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 2 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 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 can find stratified columnar epithelia, 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 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 apical 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 apical surface of the tissue are going to be columnar shaped, tall and narrow like a column. But again, the cells that are 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 here 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.