Stratified Epithelial Tissues - Online Tutor, Practice Problems & Exam Prep

Stratified epithelial tissues consist of multiple layers of cells, enhancing protection and support. Stratified squamous epithelium features flat cells at the surface, ideal for areas subject to abrasion, such as skin and mucous membranes. Transitional epithelium, found in the urinary system, can change shape, allowing for stretching. Stratified cuboidal and columnar epithelia, though rare, serve protective and secretory functions in glandular ducts. Understanding these tissues is crucial for grasping their roles in maintaining homeostasis and protecting underlying structures.

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. And the other half or the other 4 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, the term stratified indicates this tissue has multiple layers of cells where all of the cells are not going to come into direct contact with the underlying basement membrane. The term squamous indicates that the apical surface of the tissue has cells with 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. It's worth emphasizing that, concerning 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.

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 the term that indicates the cell shape, once again, only applies to the cells closest to the apical surface of the tissue. 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, meaning not all of the cells come into direct contact with the underlying basement membrane. This defines this tissue as a stratified tissue with multiple layers of cells. In terms of the functions of stratified squamous epithelium, the structure of the tissue and the cells dictates the functions of the tissue. With stratified tissues that have multiple layers of cells, these tissues tend to be thicker in nature and are great for protection.

The thick nature of the tissue is going to allow it to function in protection in many cases. The case here with stratified squamous epithelium is that it has so many layers of cells, it's relatively thick, and its primary function is protection. This means that we are going to find the stratified squamous epithelium in locations of the body where protection is important. For example, in areas such as our skin, mouth, esophagus, anus, and vagina, which encounter physical stresses. In the mouth and esophagus, it encounters physical stresses from the foods we eat and the drinks we drink. In the anus, it encounters physical stresses from the passage of feces. In the vagina, it encounters physical stresses from sexual intercourse.

Some of the stratified squamous epithelium can produce a tough and waterproof fibrous protein called keratin. When this protein is present, it can increase the toughness of the tissue and help prevent water loss from the underlying tissue. The keratin itself is a waterproof protein that helps create a waterproof surface, making the tissue dry on the apical surface. Later in our course, when we talk about the skin or the integumentary system in more detail, we will revisit this protein keratin.

This leads us to two main types of stratified squamous epithelium. The first main type is keratinized stratified squamous epithelium, which, as its name implies, contains the protein keratin. The second type is non-keratinized stratified squamous epithelium, which does not contain the protein keratin. The keratinized type can be found in the outermost layers of our skin, which covers our entire body. The non-keratinized type is found in orifices near the skin, such as the mouth, esophagus, anus, and vagina. Since the protein keratin is waterproof and creates a dry surface on the apical surface of keratinized stratified squamous epithelium, our skin is usually dry. In contrast, the non-keratinized stratified squamous epithelium tends to have more moist tissue.

Notice our focus on the skin of this person here. You can see a micrograph showing the outermost layers of the skin. The outermost layers of this tissue are going to be flat in their nature. As you go lower into the tissue, deeper into the tissue, the shapes of the cells can vary, from cuboidal to even columnar. Deeper to the epithelial tissue here is the connective tissue, which you can see in this light blue color. The cells on the surface are going to encounter a lot of physical stresses that can kill the cells and rub them off. These cells need to be replaced by dividing cells that are closer to the basal surface. Cells closer to the basal surface are closer to the underlying vascular connective tissue with blood vessels that supply nutrients. As these cells get further from the basal surface, they have less access to nutrients and less capacity to divide. The outermost layers of the stratified squamous epithelial tissue are going to be keratinized in keratinized stratified squamous epithelial tissue. These cells towards the top can be dead in many cases, helping to protect the living epithelial tissue below.

We also have some helpful ID tips when it comes to stratified squamous epithelial tissue. This tissue is relatively thick, with lots of cell layers, and appears relatively thick as you can see in these images. The cells near the apical surface are going to be flat in their nature, encountering all the physical trauma and abrasions. These cells are the ones most likely to be flaking off and falling off or rubbing off, hence they need to be replaced by dividing cells closer to the basal surface. As you go deeper into the tissue closer to the basement membrane, the cell shape can vary from cuboidal to columnar. This concludes our lesson on stratified squamous epithelium, and we'll learn more about other stratified epithelial tissues and apply 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 do not come into direct contact with the underlying basement membrane. We're covering transitional epithelium at this point in our lesson because structurally and functionally it 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 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. The structure of the tissue and the cells that make up the tissue determine its function.

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 relatively thick. As a relatively thick tissue, its primary function is going to be protection. Transitional epithelium provides protection by blocking the diffusion of harmful molecules.

Transitional epithelium is found only in the urinary system. We can find transitional epithelium lining the bladder, which stores urine until it needs to be excreted. The bladder needs to have the ability to stretch when it is full and then return back to its original shape when it is not full. We can also find transitional epithelium in the ureters, which are 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.

Sometimes, transitional epithelium is referred to as urothelium. 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 us harm. In our image, we've divided it into two sections separated by a dotted line. There's a top half showing an empty bladder and a bottom half showing a full bladder. In the empty form of the bladder, the transitional epithelium is in a relaxed state, and the cells are in a cuboidal shape, as seen in the diagram. In the micrograph shown, the inside of the bladder is depicted, revealing the multiple layers of cells characteristic of this stratified epithelial tissue.

When the bladder is filled with urine, the transitional epithelial tissue cells transition from a cuboidal shape to a squamous shape. This happens because the pressure of the urine stretches the tissue, allowing the cells to widen and flatten. Tight junctions and desmosomes ensure that the cells remain connected. On the apical surface of the empty bladder version of the transitional epithelia, the cells appear pillow-shaped, indicating their larger size and curved shape. This analogy helps illustrate the stretching dynamics, as shown by arrows in the diagram.

Transitional epithelia have more layers of cells than stratified cuboidal epithelia, which we will cover in our next video, but fewer layers than stratified squamous epithelia. Surface cells on the apical surface of transitional epithelia in its relaxed state are pillow-shaped. This lesson concludes our discussion on transitional epithelium, and moving forward we will apply these concepts in practice problems and learn about other stratified epithelial tissues in our next video. I'll see you all then.

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 help you tell them apart. And so notice that we have 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.

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. Notice that identifying the open space when we are looking at micrographs of epithelial tissue is going to be key because it is 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.

Of course, the apical surface is going to be the surface that is closer to the open space. In this tissue, it is going to be up here that will be the apical surface. In this tissue over here, the apical surface is actually curving, but it is going to be that surface right there of the tissue. 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 of the nuclei that you can see, and you can see those multiple layers again in both of these tissues.

Not all of these tissue cells are going to be in direct contact with the underlying basement membrane. The real part that is going to help us tell these two tissues apart is focusing on the apical surface. 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 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. When we closely analyze the shape of the cells in the left diagram that are closest to the apical surface, what you will 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 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. So for that reason, we can actually write in stratified squamous on this micrograph. Therefore, the right tissue must be the transitional epithelium. Another key feature that we could have looked at is that in the stratified squamous epithelia, the apical surface has cells that are flaking off. The cells flaking off on the apical surface are very characteristic of stratified squamous epithelium, for example, the stratified squamous epithelium that makes up our skin, which is constantly flaking off. This is a good indication of stratified squamous epithelium.

This here concludes this particular example. Again, the micrograph on the right is transitional. The micrograph on the left is stratified squamous. We will be able to get some practice applying these concepts moving forward. 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. This is why this is the 3rd stratified tissue in our lesson instead of being the 1st stratified tissue in our lesson, for example. Recall that the term stratified indicates this tissue has multiple layers of cells or more than one layer of cells where all of the cells do not come into direct contact with the underlying basement membrane. 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 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 shape or cube or box shaped. 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. In comparison to stratified squamous epithelia, which can have dozens of layers of cells, and transitional epithelia, which can also have several layers of cells, stratified cuboidal epithelium usually has just 2 to 3 layers of cells instead of dozens. This can be a really helpful identification tip when it comes to stratified cuboidal epithelium. Notice over here, we're only showing you 2 layers of cells.

Of course, the structure of the tissue and the cells within determine the function. This is a stratified tissue with multiple layers of cells, and because it has multiple layers of cells, it is going to be a thicker tissue, especially in comparison to its single-layered cell counterpart, the simple cuboidal epithelia, which consists of just one single layer of these cube-shaped cells. Because stratified cuboidal epithelia is a thicker tissue than simple cuboidal epithelia, it's no surprise that it functions in protection and support. And because the cells on the apical surface of the tissue are 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, allowing for the function of secretion, an important function for glands and the ducts of glands. When it comes to simple cuboidal epithelia, one of their functions was absorption.

In tissues that have one single layer of cells, it's much easier for substances to be absorbed through the tissue because the substances only need to be absorbed through just one single layer of cells. However, in stratified tissues that have multiple layers of cells, they do not function as well in absorption because the substances that need to be absorbed must go through multiple layers of cells, making it less efficient. Stratified cuboidal epithelium consists of just 2 to 3 layers of cells, so although it has some limited functions in absorption, it's not going to have a primary function in absorption like simple cuboidal epithelium might have. Keeping in mind the locations where we can expect to find stratified cuboidal epithelia, they are going to be found in the larger parts of the ducts of sweat glands and mammary glands, where they handle larger volumes of secretions and more pressure.

Stratified cuboidal epithelia are going to be found in ducts for example, usually arranged in a ring. Again, they form the larger parts of the ducts. You can see these big drops of sweat and we're actually zooming in on one of the sweat glands. 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 the epithelial tissue, the stratified cuboidal epithelia, because the cells that are on the apical surface here are cube-shaped or box-shaped. You can see a ring of cells here and a second layer of a ring of cells right there.

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 the open space in the duct of the sweat gland. Notice that the cells that are on the apical surface are going to be cuboidal. And again, we have multiple layers of cells.

This 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 1st 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 all 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 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.