Identifying Types of Epithelial Tissue - Online Tutor, Practice Problems & Exam Prep

Understanding epithelial tissue is crucial for identifying its types through a systematic flowchart. Begin by determining if the cells are tightly packed next to an open space. If yes, assess the number of layers: two or more indicates stratified tissue, while one layer suggests simple tissue. Simple squamous, cuboidal, and columnar tissues can be identified based on cell shape and arrangement. Stratified tissues, such as squamous and transitional, are characterized by multiple layers and specific cell shapes. Recognizing these features aids in understanding their functions in various body systems.

Epithelium Identification Flow Chart

In this video, we're going to put together a lot of the helpful ID tips from our previous lesson videos as we begin our lesson on identifying the types of epithelial tissue by using the epithelium identification flowchart that you can see down below right here. And so, this flowchart is designed to help you better identify the type of epithelial tissue in a micrograph or an actual image of the tissue under a microscope. And so, this flowchart starts at the top, and we work our way downwards. And what you'll notice is that as we go through this flowchart, we're going to encounter these decision-making points where we'll need to closely analyze the tissue in the micrograph to make decisions because the flowchart is going to split based on our decision. And so, hopefully, you can use this epithelium identification flowchart a few times and let us know in the comments how well it works for you.

And if you have any suggestions for modifications that could help improve the flowchart. And so, that being said, let's go ahead and get started with this epithelium identification flowchart. And so, of course, we're going to need to start with a micrograph of epithelial tissue. And so, go ahead, find a micrograph of epithelial tissue and let's see if this flowchart can help us properly identify it. And so, notice at the beginning of our flowchart, we have this question that's asking, are the cells in the micrograph tightly packed with one side or surface of the tissue beside an open space?

And so, recall from our previous lesson videos that one of the key defining features of most epithelial tissue is that it consists of a single sheet or multiple sheets of tightly packed cells that form a boundary immediately adjacent to open space. And so, being able to identify the open space in a micrograph of epithelial tissue is going to be really important. And so, if we can say yes to this question here, then we can move forward in our flowchart. But if we need to say no, then the micrograph is probably not showing epithelial tissues. It's probably showing some other type of tissue.

Now moving forward in our flowchart here, we're encountered with another question, which is asking, are there clearly greater than or equal to 2 layers of cells in the micrograph? Or, in other words, are there clearly multiple layers of cells in the micrograph? Now, if we can say yes to this question, then we're limiting our options to stratified epithelial tissue. But if we say no because it's not super clear that there are multiple layers of cells, then we're limiting ourselves to these simple epithelial tissues. And so, let's first explore the branch with the simple epithelial tissues, and then once we finish going through that branch, we'll come back up and revisit the branch with the stratified epithelial tissue.

And so, let's assume that we say no, it's not super clear that there are indeed multiple layers of cells. Well, then we encounter ourselves with the next question here, which is asking, do the cells in the micrograph either look flat or squish or like ribbons between open space? Now, if they look either flat or like ribbons in open space, then we can say yes to this question. And that means, of course, we're going to have squamous-shaped cells. Now, again, because we've already identified that there's not multiple layers of cells that are clear, then we can say that this is a simple type of epithelia, simple squamous epithelia.

And recall from our previous lesson videos that usually, the micrograph is going to be of the air sacs of the lungs, which means that the simple squamous tissue is going to look like ribbons between open space. And so, you can kinda see those ribbons kinda falling between the open space here. Now, recall simple squamous epithelia is going to be the thinnest layer of epithelial tissue, which means that it's going to allow for rapid diffusion and can be found in areas of the body where rapid diffusion is critical. Such as lining the air sacs of the lungs and also lining the capillaries for example. Now, if we have to say no to the previous questions because the cells don't look flat or the cells don't look like ribbons between open space, then we move on to the next question here, which is asking, are the cells in the micrograph tall and narrow?

And so, if they're tall and narrow, of course, they are going to look like a column, and they are going to be columnar tissue. And so, if we say yes to this question, then we're going to be limited to columnar-shaped tissue. But if we say no, then of course, this this means that we have one layer of cells that's not flat and again, it's not tall and narrow. And that means that we must have these cube-shaped cells, cuboidal tissue. And again, because it's one layer, it must be simple cuboidal tissue.

And so, notice here in this micrograph, it's not very clear to see but you can see the open space is right here highlighted in green, and the simple cuboidal epithelial tissue is forming a ring around the open space. And again, these cells are going to be equally tall as they are wide, and sosthat's what makes them cube-shaped. And again, they're often going to be in a ring because they can form the smaller parts of the ducts of glands and also they can form the smaller tubules that are found in the kidneys. Now, if we say yes, once again, we're limited to the columnar tissue, and we're going to need to look at this next question, which is asking us to specifically focus on the nuclei of the cells. And so, if the nuclei of the cells are in a single row, then we can limit ourselves to simple columnar tissue.

But if the nuclei are in different levels, then we most likely are going to have pseudostratified columnar epithelial tissue. And so, notice that with the nuclei being in a single row, here you can see that these nuclei are in a single row. And again, this is going to, make it very clear that it's just one single layer of cells. Notice that they are columnar-shaped because they are tall and narrow. And notice that the nuclei are actually slightly shifted downwards toward the basal surface.

And so those are all little ID tips that can help you identify simple columnar tissue. Now, sometimes the simple columnar tissue are going to have microvilli on their surface, and that will be really important for absorption. And so, we find simple columnar lining pretty much the entire digestive system from the stomach to the anus, and, especially in the intestines, such as the small intestine, where absorption of nutrients from the diet is going to be critical. But these simple columnar tissues can also have cilia on their surface, which help to move substances through the open space that they are aligned. Now, recall that if the nuclei are at different levels, then again, it's going to be pseudostratified columnar.

So, notice that here, the nuclei seem to be all over the place and seem to be creating a set stratified tissue. But, again, recall the root pseudo is a root that means false or fake. And so, pseudostratified is a false or fake stratified tissue that may appear to be stratified, but it's not actually stratified because all of the cells are going to come into direct contact with the underlying basement membrane. And so notice that with pseudostratified columnar epithelial tissue, again, the nuclei are going to be scattered all over in different levels. And it's not super apparent that these nuclei are organizing themselves into a specific row.

And so, some of these cells are going to be, shorter, whereas other cells are going to be taller, as you see here. Some of the cells will reach the apical surface, whereas other cells are not going to reach the apical surface. Usually pseudostratified columnar, or often it is going to have cilia, these little tiny hair-like structures that can move like oars and move substances through the open space. And recall pseudostratified columnar is found in the upper respiratory tracts, for example, where it can, also contain, goblet cells. And the goblet cells can also be found in simple columnar as well.

And recall these goblet-shaped cells, which you can actually see one of them right over here, they're actually shaped like a goblet or shaped like a wine glass, if you will. And, they actually secrete a product that ends up forming mucus, and that mucus can help to lubricate the tissue and also to protect the tissue as well. And so, really that concludes the branch of simple epithelial tissue. And now we can move forward with the branch with stratified tissue. Again, if we were to answer this question, are there clearly greater than or equal to 2 layers of cells with a yes, then we are saying that there are clearly multiple layers of cells, and that means that we have stratified tissues.

So then we are encountered with this next question, which is asking, are there many or several layers of cells, or are there just approximately 2 to 3 layers of cells? Now if there are many layers of cells, then we know we're either going to have stratified squamous or transitional epithelial tissue. But if there's only 2 to 3 layers of cells, then we've limited ourselves to either stratified columnar or stratified cuboidal, which we'll get to here shortly. But first, let's focus on if there are many layers of cells. In stratified squamous, there can actually be dozens of layers of cells.

Now, transitional epithelia have fewer layers of cells, but they still have many more than just 2 or 3. So, if there are many layers of cells, then notice we're going to be encountered with this next question, which is asking, are the surface cells that are on the apical surface flat and flaking off, or are the surface cells more pillow-shaped? And so, if the apical surface cells are flat, then that's suggesting that the tissue is going to be stratified squamous. And so stratified squamous, notice that looking at the apical surface, these cells here are actually flat and appear squished. And notice once again with stratified tissues, the term that indicates the shape of the tissue cells only applies to the cells on the apical surface that are closest to the open space.

So, notice you can see the open space above up here. And the cells that are deeper in the tissue may not necessarily be squamous in their shape. But clearly here there are many layers of cells, much more than just 2 or 3. And again, the cells are flat and flaking off on the surface. And the flaking off of cells is going to be a key feature that helps us identify stratified squamous epithelia.

And recall from our previous lesson videos that there are really two main types of stratified squamous epithelia, the keratinized form, which contains the protein keratin and is found in the outermost layers of our skin. And then we have the unkeratinized form that does not have the protein keratin, which is found in the orifices that are near the skin, such as the mouth, for example. Now, if the cells again are flat, it's stratified squamous. But if the cells are not flat and the surface cells appear pillow-shaped, then that's going to indicate that it is transitional epithelium. And so recall that transitional epithelium is sometimes called urothelium because it is found only in the urinary system, lining the bladder, for example.

And transitional epithelium is known for its elasticity, its ability to be able to stretch, but then return back to its original shape. And the cells transition from a cuboidal shape when they are in a relaxed form to a squamous shape when they are in a stretched form. And so notice that here we're showing you some transitional epithelium. And again, you can see the open space up above. And so notice focusing in on the surface cells, they are somewhat pillow-shaped.

You can kind of see that they are roundish like that, somewhat like a pillow. And the cells on the surface are larger than the cells that are immediately beneath. And so again, if we said that the cells only had 2 to 3 layers, instead of having many, many layers like stratified squamous or transitional, then we're limiting ourselves to either stratified columnar or stratified cuboidal. And so we're encountered with this final question here, which is asking, once again, are the surface cells going to be tall and narrow, or are the surface cells more cube-shaped? If the surface cells are tall and narrow, then we have stratified columnar.

But if the surface cells are more cube-shaped, then, of course, we have stratified cuboidal. And so, notice here that the stratified columnar, the cells on the apical surface are going to be columnar-shaped. But again, the cells that lie deeper to the apical surface can be irregularly shaped and have taken on different shapes. And recall stratified columnar epithelium is going to be found in areas of the body that are going to transition different types of epithelial tissue. So, in areas of the body, for example, where the tissue transitions from simple columnar to stratified squamous, right in between you'll find the stratified columnar.

And with stratified cuboidal, notice once again that we have, the open space right over here, and we have these cuboidal-shaped cells or these cube-shaped cells immediately on the apical surface. And, notice that we have 2 layers of cells, so we have multiple layers making it a stratified tissue. And recall that this stratified cuboidal is going to provide a little bit more protection than the simple cuboidal. And so, they're both going to be found, forming, the ducts of glands, but the stratified cuboidal is going to be found in larger spaces of the ducts of glands. Whereas the simple cuboidal is found more so in the smaller spaces of glands.

And, again, one other important note is that stratified columnar and stratified cuboidal are both relatively rare or uncommon tissues in the body. And so this here concludes our epithelium identification flowchart. And hopefully, it was helpful for you to identify your epithelial tissue in your micrograph. But if not, once again, leave some feedback in the comments. Let us know how helpful it was for you and what modifications you might suggest to help improve the flowchart.

That being said, I'll see you all in our next video.

Identifying Types of Epithelial Tissue Example 1

So here we have an example problem that says identify the following epithelial tissues. And so notice down below we have these 3 micrographs of epithelial tissue. And so let's start with the first one on the far left. And so when we're looking at micrographs of epithelial tissue, it can be really helpful to identify the open space because that will allow us to identify the polarity of the tissue. Which side is the apical surface versus which side is the basal surface.

And so if we take a look at the micrograph on the far left over here, notice that we have a lot of open space toward the top as we can see highlighted here. But you may have also noticed that there seems to be a little bit of open space toward the bottom. And so which one of these spaces is going to be considered the open space? And which side of the tissue is considered the apical surface? And so in order to answer that question, we need to look really closely at this micrograph.

Because notice that this surface of the tissue over here actually has these little tiny hair-like structures that are called cilia. And recall that cilia can actually move like oars in coordination in order to move substances such as mucus, for example, through the open space. And so these cilia are only found on the apical surface of the tissue. They are not found on the basal surface. And so just based on that, of course, this means that the space up above here must be the open space since again, the cilia structures are going to be on the apical surface.

And we know the apical surface is the surface that is immediately adjacent to the open space. And so that must mean that this open space down below is not going to be the open space that we're focusing on. Maybe it's a result of the preparation of this tissue for microscopy. And so, what you'll notice is that this tightly packed tissue that you see here immediately adjacent to the open space that you see here, that is going to be the epithelial tissue that we're focusing on. And so notice that down below there seems to be tissue that takes on a different organization.

We can assume that that is going to be the connective tissue. And so recall that the basement membrane is going to separate the connective tissue that underlies from the epithelial tissue that is up above here in this micrograph. Now, in terms of the shape of the cells in this tissue, what you'll notice is that they tend to be pretty elongated, pretty columnar shaped. And what you'll also notice is that the nuclei of these cells seem to be pretty scattered all throughout. We've got nuclei at the bottom, some nuclei toward the top, nuclei kind of all over the place and they're not really neatly organized into very clearly distinct rows.

And so, because of that, we can actually assume that this is going to be pseudostratified columnar epithelium. Because recall that in pseudostratified columnar epithelium, the root pseudo is a root that means false or fake. And so, pseudostratified is going to be a false or a fake stratified tissue that appears to be multiple layers because the nuclei are all at different levels. But, it's not actually a stratified tissue because all of the cells come into direct contact with the underlying basement membrane. And so, we can say this is pseudostratified columnar epithelium.

And so, now that we've identified this tissue in the far left micrograph, let's move on to the next tissue here. And so once again, we want to identify the open space and here it's pretty clear this is the open space right here. And so once again, what we can see pretty clearly in this micrograph is that there are certainly multiple layers of cells.

It's very clear that there are multiple layers of cells here. And so we know that this must be one of the 4 stratified tissue. Now, what you'll also notice is looking at the apical surface and looking at the cells on the apical surface that these cells are fairly pillow-shaped, if you will. And recall that these pillow-shaped cells is an indication that this is transitional epithelium. And so we can actually label this as transitional epithelium.

Now, recall that with transitional epithelium when it is in a relaxed state that is not stretched, the cells are going to be more cuboidal in their shape. But if you can imagine grabbing the tissue and stretching the tissue out, then these cells here are going to be elongated. They're going to widen and flatten and they're going to look more like squamous shaped cells. And so, recall that is why it's called transitional epithelium because when it is in a relaxed state, the shape is more cuboidal. But, when the tissue is stretched, the shape transitions from cuboidal to squamous.

And so, that allows the tissue to stretch in order to accommodate something like the bladder stretching when it's filled with urine. And so now that we've identified this epithelial tissue here, let's move on to the last one on the far right here. And so, what you'll notice is once again, the open space can be found right here in this region, you can also see open space here, in this area as well. And so, the epithelial tissue that we're looking at that's immediately lining this open space is going to be this area right here. And so, what you'll notice about the epithelial tissue here, is that these cells seem to be cube shaped or cuboidal because they are pretty much just as tall as they are wide.

And notice that the nuclei are pretty round or circular and they're also centrally located. And so what we can see here is that this is going to be just one single layer of cells since the nuclei seem to be organized into 1 curved layer. And also, notice that the cells are forming what appears to be a ring if this were to completely round out in the micrograph. And so this is all an indication that this is going to be simple cuboidal epithelia. Again, it's simple because it's just one single layer of cells, as you can see by the nuclei being organized into 1 single row.

And it's cuboidal once again because the shape of the cells is pretty box-shaped or pretty cube-like. And so this here concludes this example problem, 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.

Identify the tissue indicated in the slide:  

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

Identify the tissue indicated in the slide:  

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

Identify the tissue indicated in the slide:

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

Here’s what students ask on this topic:

What are the key features of simple squamous epithelial tissue?

Simple squamous epithelial tissue consists of a single layer of flat, thin cells that resemble scales or ribbons. These cells are tightly packed and form a boundary adjacent to open spaces, such as the air sacs of the lungs and the lining of capillaries. This tissue type is the thinnest among epithelial tissues, allowing for rapid diffusion of gases and nutrients. Its primary function is to facilitate efficient exchange processes, making it crucial in areas where quick diffusion is essential, like the respiratory and circulatory systems.

How can you differentiate between simple and stratified epithelial tissues?

To differentiate between simple and stratified epithelial tissues, examine the number of cell layers. Simple epithelial tissue has a single layer of cells, while stratified epithelial tissue has two or more layers. In a micrograph, simple tissues will show a uniform layer of cells, whereas stratified tissues will display multiple layers stacked on top of each other. The function of simple tissues often involves absorption, secretion, and filtration, while stratified tissues provide protection against abrasion and are found in areas subject to wear and tear, like the skin and mouth.

What is the function of pseudostratified columnar epithelial tissue?

Pseudostratified columnar epithelial tissue appears to have multiple layers due to the varying positions of nuclei within the cells, but it is actually a single layer with all cells in contact with the basement membrane. This tissue type often has cilia on its surface, which help move mucus and trapped particles out of the respiratory tract. It also contains goblet cells that secrete mucus, providing lubrication and protection. Pseudostratified columnar epithelium is primarily found in the upper respiratory tract, where it plays a crucial role in filtering and moving debris out of the airways.

Where is transitional epithelium found and what is its function?

Transitional epithelium, also known as urothelium, is found exclusively in the urinary system, including the bladder, ureters, and part of the urethra. Its primary function is to accommodate fluctuating volumes of liquid in these organs. The cells of transitional epithelium can stretch and change shape from cuboidal when relaxed to squamous when stretched. This elasticity allows the bladder to expand as it fills with urine and contract when it empties, providing a protective barrier that prevents urine from diffusing back into the surrounding tissues.

What are the distinguishing characteristics of stratified squamous epithelial tissue?

Stratified squamous epithelial tissue is characterized by multiple layers of cells, with the apical (surface) cells being flat and squamous in shape. This tissue type provides protection against abrasion, dehydration, and microbial invasion. There are two forms: keratinized and non-keratinized. Keratinized stratified squamous epithelium contains the protein keratin, making it tough and water-resistant, and is found in the outer layer of the skin. Non-keratinized stratified squamous epithelium lacks keratin and is found in moist areas subject to abrasion, such as the mouth, esophagus, and vagina.