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

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 in 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 tissues 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 are 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 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 so that's what makes them cube shape. 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 at 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.

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.

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 four 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 epithelium. Again, it’s simple because it’s just one single layer of cells, as you can see by the nuclei being organized into one 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.