Simple Epithelial Tissues: Study with Video Lessons, Practice Problems & Examples

Simple epithelial tissues consist of a single layer of cells in direct contact with the basement membrane. The four types include simple squamous, cuboidal, columnar, and pseudostratified columnar epithelium. Simple squamous epithelium facilitates rapid diffusion, found in areas like the lungs and capillaries. Simple cuboidal epithelium, with its cube-like cells, is involved in absorption and secretion, located in kidney tubules and glands. Simple columnar epithelium, characterized by tall cells, aids in absorption and secretion, often featuring microvilli or goblet cells. Pseudostratified columnar epithelium appears layered but is a single layer, primarily found in the respiratory tract.

Four Simple Epithelial Tissues

In this video, we're going to begin our lesson on simple epithelial tissues. Recall from our last lesson video, we said that structurally, humans have 8 types of epithelial tissues, and half of those, or 4 of those tissues, are going to be structurally categorized as simple epithelial tissues. The other half are going to be categorized as stratified epithelial tissues. But we'll talk about the stratified epithelial tissues later in our course. For now, we're focusing on simple epithelial tissues.

Recall that the term "simple" indicates that these four tissues are going to have just one single layer of cells, where all of the cells are going to come into direct contact with the basement membrane. Moving forward in our course, we're going to talk about each of these 4 simple epithelial tissues in their own separate videos. I'll see you all in our next video where we'll get to talk about the very first type of simple epithelial tissue in our lesson, which is simple squamous epithelial tissue. So, I'll see you all there.

Simple Squamous Epithelia

In this video, we're going to talk about the first type of simple epithelial tissue in our lesson, which is simple squamous epithelium. And so before we get started, I want to draw your attention to the numbering and lettering system that we're using for these tissues. Here, it's one egg. And so what I really want you to notice is that we're using the number 1 for all of the simple epithelial tissue. And so recall the term simple indicates the tissue has just one single layer of cells where all of the cells come into contact with the basement membrane.

And so we can use the number 1 in our numbering system as a memory tool to remind us that once again, all of the simple epithelial tissues have just one single cell layer where all of the cells are going to come into contact with the basement membrane. And so the letter 'a' here is indicating that this is the first type of simple epithelial tissue that we're covering in our lesson. Here, it's simple squamous epithelium. And so moving forward, when we cover the other 3 types of simple epithelial tissues, you'll notice that they're going to be numbered and lettered as 1b, 1c, and 1d, where, again, the one is indicating this is a simple epithelial tissue with just one layer of cells. And then after we cover all 4 of the simple epithelial tissues, we'll then transition to talking about the 4 stratified epithelial tissue.

And those will be numbered and lettered as 2a, 2b, 2c, and 2d. Where again, the number 2 is indicating that these stratified tissues are made of 2 or more layers of cells. But again, we'll cover these stratified epithelial tissues later in our course in different videos. And for now, we're focused on simple epithelial tissues, more specifically, simple squamous epithelium. So notice that on the left, we have some text that's showing you some of the most important characteristics, functions, and body locations of where this tissue can be found.

And we also include a helpful ID tip just in case you need to identify this tissue under the microscope. And so with each tissue, we're going to include an image to help support your understanding. And so once again, when it comes to simple squamous epithelial tissue, we know that the term simple implies that the tissue has just one single layer of cells. And so recall that the term squamous implies that the shape of the cells is going to appear squished or flat. And so simple squamous epithelium is going to consist of just one single layer of squished or flat cells.

Just like what you can see over here in our diagram. Notice that we have just one single layer of cells where all of the cells are in direct contact with the underlying basement membrane that we briefly talked about in our previous lesson videos, and you can see as indicated here in our diagram. And really, that's the defining feature that makes it one layer of cells is when all of the cells come into contact with that basement membrane. And notice that we have these flattened cells here. Again, the term squamous is Latin for scales, which are flat as well.

And so these cells are so flat or squished that they're actually going to have less cytoplasm than other tissues that have cells with different and bigger shapes. And also, these cells are so flat that they actually create a pretty flat surface that makes it really easy and smooth for liquids to be able to flow on top of this tissue. And so we tend to find simple squamous epithelial tissue in areas of the body where liquids need to be able to flow smoothly. Like for example, simple squamous epithelial tissue is found lining all of the hollow organs of the cardiovascular system, such as the capillaries and the larger blood vessels and the heart as well. Now what you'll notice is that the nuclei of these cells is pretty centrally located, And this is really what makes the simple squamous epithelial cells look like fried eggs.

And so you can think that the flat nature of the fried egg is just like the flat nature of the simple squamous cell. And notice that the yolk of the egg, which is pretty centrally located, can represent the centrally located nucleus of the simple squamous cells. And so, hopefully, thinking of fried eggs can remind you of the structure of the cells within simple squamous epithelial tissue. Now, when it comes to the functions, it's actually the structure of the tissue in the cells that's going to dictate the function. And so once again, simple squamous epithelial tissue consists of a single layer of these flat cells, and that's going to make the thinnest possible epithelial tissue.

And because it's so thin, it's not going to serve a primary protection role. Because when you think about protection, it's going to be the thicker tissues that have multiple layers of cells that are going to be better suited for protection. And so protection will be a bigger function in stratified tissue. But again, with simple squamous epithelial tissue, protection is not going to be the primary role for this tissue. And so, again, the function is going to be dictated by the structure.

And once again, simple squamous epithelial tissue is going to be the thinnest epithelial tissue. And because it's so thin, it's actually going to allow for the rapid diffusion of molecules across this thin tissue. And so, it's going to allow for the quick exchange of substances across the tissue. And so again, one of the primary functions here is going to be rapid diffusion. And so we can actually expect to find simple squamous epithelial tissue in body locations that require rapid diffusion.

For example, we can find simple squamous epithelial tissue lining the air sacs of th

Simple Cuboidal Epithelia

In this video, we're going to talk about the second type of simple epithelial tissues which is simple cuboidal epithelium. And so we already know that the term simple indicates that this tissue has just one single layer of cells. And so recall that the term cuboidal indicates that the cell shape is going to be cube-like or box-like. And so we can say that simple cuboidal epithelium is going to consist of just one single layer of these cube-shaped cells or box-shaped cells just like what we see over here in our diagram. And so notice that we have just one single layer of cells where all of the cells come into direct contact with the underlying basement membrane.

Again, this is the defining feature that makes it one single layer of cells. And notice that the cell shape is box-like or cube-like. Now in comparison to simple squamous epithelium that we covered in our last lesson video, simple cuboidal epithelium is going to have significantly more cytoplasm. Because again, the simple squamous cells from our last lesson video are squished cells that are flat. And because they're so flat, they don't have much cytoplasm, and that leaves very little room for organelles.

But with these cuboidal cells, they are more box-shaped, and so they have more volume and more spacious cytoplasm, and that makes more space for organelles. And so, those organelles are going to be important for the functions of simple cuboidal epithelium, which are for absorption and secretion. And so, absorption again indicates the uptake of nutrients, and secretion refers to the release of products. And so, this is also going to help with the locations that simple cuboidal epithelium can be found. And so, because again, it's associated with secretion and absorption, it's going to be important for areas such as the kidney, and it forms the tubules of the kidney, which are important for filtration.

Again, absorbing substances and excreting other substances. And also, it's going to be important for secretion as well. And so we know that it can be making up the ducts of many different glands. For example, simple cuboidal epithelium makes up the ducts of salivary glands and mammary glands. And it also forms the secreting portions of the thyroid gland.

And it makes up the ducts of the pancreas as well, which is another type of gland. And so, down below what we have is an ID tip to help you identify this tissue under a microscope. And so, usually, the micrograph that's going to be shown is going to show the simple cuboidal epithelium as part of a duct or a tubule. And so what this means is that the simple cuboidal epithelial cells will usually be in a ring shape. Or if they're not in a ring shape, they're going to have an open space between the two layers of cuboidal cells.

And so notice up above here, we're showing you an image of one of the kidneys. And here, what we're showing you is a micrograph. And notice that the micrograph here is a little bit difficult to see, but when we draw a sketch of the same micrograph, it makes it much easier to see the simple cuboidal epithelial tissue cells. And so notice that these simple cuboidal epithelial tissue cells are forming a ring here because they're forming the tubules of the kidney. And again, those tubules are going to form a, basically a tube.

And so notice here that we have this ring of simple cuboidal epithelial tissue cells, and you can see the open space here, which is also referred to as the lumen of the tubule. And notice that the surrounding tissue here is most likely going to be connective tissue. Now, what you'll notice is that because these simple cuboidal epithelial tissues form tubules and ducts, they are going to resemble the structure of a hose, if you will, a water hose. And so just like you can see the simple cuboidal epithelial tissue forming a ring here, you can think that that's just the ring of the hose. And if you continuously stack and layer these simple cuboidal epithelial tissue rings, you can form a hose.

Which is going to allow for the transport of liquids, just like a hose allows for the transport of liquids. And again, this is how liquid products can be secreted into these ducts and tubules and things of that nature. And so this here concludes our brief lesson on simple cuboidal epithelial tissue, 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.

Simple Epithelial Tissues Example 1

So here we have an example problem that says, the drawing shows a gas and nutrient exchange in a capillary. The missing label indicates the cells of the capillary wall. Fill in the missing label with the correct tissue type and explain how you knew the correct label. And so, notice over here we have the diagram or the drawing showing a gas and nutrient exchange in the capillary. And notice down below what we have is that missing interactive blank that we need to fill in for this problem.

That again is indicating the cells of the capillary wall. And so you can see that we have these arrows pointing from the interactive blank to the cells of the capillary wall. And so our job is to, again, identify the correct tissue type of the cells that are forming that capillary wall and then to fill in that tissue type here in this blank. And so before we do that, let's first orient you on this entire diagram. And so again, it is showing you a capillary here going through the middle of this tissue.

And so, you can see the body cells or the tissue cells surrounding the capillary here. And so, what you'll notice is that the blood within the capillary is coming from the heart. And the blood that comes from the heart is going to contain nutrients and be filled with oxygen. And so notice that the oxygen gas from the blood is going to diffuse into the surrounding tissues because those tissues need the oxygen in order to generate energy to drive their cellular processes. And also notice that food substances, such as the sugar glucose for example, can diffuse from the blood and into the surrounding tissue.

Because again, the surrounding tissues are going to need the nutrients like glucose in order to drive their cellular processes. And then notice that the actively working tissues are going to generate the waste product, carbon dioxide gas, which can diffuse from the tissues and into the blood, where the blood can transport the carbon dioxide gas to our lungs, and we can exhale that carbon dioxide waste product into the surrounding environment. And so what you'll notice is that in this capillary, there's quite a lot of diffusion and exchange occurring between the blood and the surrounding tissues. Again, we have oxygen gas diffusing from the blood into the tissues. We have food substance diffusing from the blood into the tissues.

And we have carbon dioxide gas diffusing from the tissues into the lung. And so because we have so much diffusion occurring between the tissues and the blood, this means that the cells that are forming the capillary wall are going to need to be really thin tissue. And so that is going to allow for rapid diffusion and rapid exchange between the blood and the surrounding tissue. And so recall from our previous lesson videos that the thinnest epithelial tissue is going to be simple squamous epithelial tissue. Because it consists of just one single layer of these squished or flat cells.

And so, that is going to be the correct tissue type that forms the capillary wall. And so that means that the interactive blank here for this problem is going to be simple squamous epithelia. And so that here concludes this example problem, and we'll be able to get some practice applying these concepts moving forward. So, I'll see you all in our next video.

Which features of simple squamous epithelium makes it ideal for rapid diffusion?

• A. Tight junctions usually hold the cells together.
• B. It lines body cavites.
• C. It is attached to a basement membrane.
• D. It is very thin.

What type of cell is most often found in the ducts of glands?

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

In the image to the right, what feature is the yellow arrow pointing to?

• A. Basement membrane.
• B. Cilia.
• C. Microvilli.
• D. Apical surface.

Simple Columnar Epithelia

In this video, we're going to talk about the 3rd type of simple epithelial tissue in our lesson, which is simple columnar epithelium. And so we already know that the term simple indicates this tissue has just one single layer of cells. And so recall that the term columnar indicates that the cell shape is going to be tall and narrow like a column. And so we could say that simple columnar epithelium consists of just one single layer of these tall and narrow cells that are shaped like a column. And so notice that's exactly what we can see over here in our diagram.

And so notice that we've got just one single layer of cells where all of the cells come into direct contact with the underlying basement membrane. And once again, notice that the shape of the cells is going to be tall and narrow like a column. Now unlike simple squamous and simple cuboidal epithelia from our previous lesson videos, which have nuclei that are round and circular and centrally located in the middle of the cell, here with simple columnar epithelia, notice that the nuclei are oval shaped instead of being round or circular. And notice that the nuclei are not centrally located in the middle of the cell, but instead are slightly shifted downward toward the basal surface or the basement membrane. And so this can actually be a really helpful ID tip, which is why we note that the nuclei of simple columnar epithelia are often in a neat row along the basement membrane, which you can clearly see over here in our diagram.

Now in terms of the function, of course, it's going to be the structure of the tissue and the structure of the tissue cells that are going to determine the function. And because simple columnar epithelia consists of tall and narrow cells, these cells are going to have sufficient cytoplasm to host a bunch of organelles, and that's going to be important for its functions in absorption and secretion. Now, also, because this is a simple epithelial tissue with just one single layer of cells, that's also going to be really important for its function in absorption. Because the nutrients that are being absorbed into the body only need to go through just one single layer of cells before they're absorbed into our bodies, And that's going to make it more efficient than if the tissue than if the nutrients needed to be absorbed through multiple layers of cells. Now, what you'll notice is that simple columnar epithelia is going to be similar to simple cuboidal epithelia and that they both function in absorption and secretion.

However, the simple cuboidal cells, because they are shorter in nature, they can actually fit into these tighter spaces that form the ducts of glands and the tubules. Whereas simple columnar epithelia tend to line cavities that are much larger. Now in terms of absorption, it's important to note that some simple columnar epithelial tissue cells can have structures known as microvilli on the surface, on the apical surface of the tissue. And these microvilli help to increase surface area, ultimately helping to maximize the absorption capability. And so whenever you see microvilli on the apical surface, that's an indication that absorption is going to be essential.

And again, not all simple columnar epithelia have microvilli, but the ones that do are critical for absorption. And so absorption is going to be essential in our digestive tract, especially in the linings of our intestines, such as the small intestine. And so notice over here on the right hand side, we're actually showing you the image of our intestines. And zooming into the small intestine here, notice that the small intestine lining is going to have these structures called villi, which are these folds that again help to increase surface area. And if we zoom into the villi here, the epithelial tissue that are forming the villi, that's exactly what this micrograph is showing us down below.

And so you can see that this little open space here is actually the lumen or the open space inside the intestine of, the small intestine. And so notice you can see that open space over here and that helps orient us with the tissue to identify the apical surface. We can see there's an apical surface over here and another apical surface over here. And notice over here in this diagram, this is just a sketch of the same exact micrograph. And what you'll notice is that we have the microvilli labeled.

Again, these structures on the apical surface that are going to help, increase surface area and maximize absorption. Now, in terms of the secretion function, it's important to note that simple columnar epithelia can be sprinkled with these unicellular glands called goblet cells. And so again, these goblet cells are going to be unicellular in nature and they're called goblet cells because their shape resembles that of a goblet or a wine glass if you will. And later in our course, we'll talk more details about goblet cells. Now, these goblet cells are going to be important for secreting, components that lead to mucus formation.

And so, the mucus is important for lubricating the tissues and also protecting the tissues as well. Now, what you'll notice is that in our diagram over here we're indicating where the goblet cells can be found. And so you can see the goblet cell is over here and notice again it does take on this goblet shape or this wine glass shape, if you will. And you can see that over here as well. Again, it takes this wine glass shape.

And again, it's going to be secreting components that end up leading to mucus formation. And so, that mucus formation can be found in the, lining the digestive tract and the respiratory tract, for example. Now, these simple columnar epithelial tissue cells can also be found lining the uterine tubes. And in the uterine tubes, these simple columnar epithelia instead of having microvilli on the apical surface, they actually have cilia. And those cilia are recall are little tiny hair like structures that move like oars and help to move substances through the open space.

And so, the uterine tubes are going to have cilia which help to move the oocyte or the egg that's released by the ovary and move that egg through the uterine tubes or the fallopian tubes into the uterus. Now, simple columnar epithelia is also going to be found in the gallbladder, which is an organ important for storing bile. And bile is going to be important for digesting fats. And so, the simple columnar epithelia that is found in the gallbladder is going to help with absorbing water and ions to help concentrate the bile to make the bile more effective at digesting fats. And so notice that the last ID tip that we have here for you is that the microvilli may appear as a border along the apical surface.

And so, you can tend to see these microvilli again on the apical surface as you see here. Again, not all of the simple columnar epithelial tissue is going to have microvilli. Sometimes they have cilia instead of microvilli and other times they may not have either. And so, this here concludes our brief lesson on simple columnar epithelium. And we'll be able to get some practice and learn more about other types of simple epithelial tissue as we move forward.

So I'll see you all in our next video.

Pseudostratified Columnar Epithelia

In this video, we're going to talk about the 4th type of simple epithelial tissue in our lesson, which is pseudostratified columnar epithelium. And so immediately, you'll notice that this tissue is an exception to the structural naming system that we covered earlier in our lesson. And this is because, although pseudostratified columnar epithelium is a type of simple epithelial tissue, it's the only simple epithelial tissue that does not have the term "simple" in its name. In fact, you may have realized that it actually has the term "stratified" embedded in its name, which can be really misleading because you may incorrectly think that pseudostratified columnar epithelium is a type of stratified tissue with multiple layers of cells. But again, this is not going to be the case.

Pseudostratified columnar epithelium is a type of simple epithelial tissue despite the fact that it does not have "simple" in its name. And so, this means that it's going to consist of just one single layer of cells where all the cells come into direct contact with the underlying basement membrane. And so what can be really helpful to note here is that the root "pseudo" in pseudostratified is actually a root that means false or fake. And so, once you know this, you realize that pseudostratified is really just a false stratified tissue or a fake stratified tissue where the tissue appears to be stratified with multiple layers of cells, but this is actually not the case. The tissue is going to be a simple epithelial tissue with just one single layer of cells where all the cells come into direct contact with the underlying basement membrane.

And so recall that the term "columnar" indicates that the cell shape for most of these cells is going to be tall and narrow like a column. And so we can say that pseudostratified columnar epithelium is going to consist of just a single layer of cells that are tall and narrow and shaped like a column for the most part. And so notice over here on the right, we have a diagram of this pseudostratified columnar epithelium. And notice that all of these cells are going to be coming into direct contact with the underlying basement membrane, which is, again, what makes this tissue a simple epithelial tissue with just one single layer of cells. And what you'll notice is that most of these cells are going to be tall and narrow like a column, which is where it gets the columnar term from.

But you'll also notice that not all of the cells are tall and narrow. Some of these cells are going to be shorter and are not going to reach the apical surface. And so, really, this is what makes pseudostratified columnar epithelium different from simple columnar epithelium. Because in simple columnar epithelium, all of the cells are going to be pretty much equally as tall and narrow as each other, and they're all going to reach the apical surface. Whereas this is not going to be the case with pseudostratified columnar epithelium.

And so because some of these cells are going to be shorter than others and other cells are taller than others, this is what's going to make the tissue appear to be stratified and appear to be multiple layers of cells. But again, all of these cells come into direct contact with the underlying basement membrane, and that's what makes it one single layer of cells in a simple epithelial tissue. And so notice over here, we're saying that pseudostratified columnar epithelial tissue is going to look like more than just one layer of nuclei or look like more than one layer of cells. But again, this is not going to be the case because all of the cells touch the basement membrane. And so a really helpful analogy for this is a forest.

And so notice that in a forest, we know that the trees are going to be of different heights. Some of the trees are going to be shorter trees whereas other trees we know are going to be taller trees. And so, although there are trees of different heights, we don't consider there to be multiple layers of trees in a forest. And this is because we know that all of the trees, despite the fact that they are of different heights, they're all going to be touching the ground and branching from the ground. And so the ground here is going to represent the basement membrane.

And so notice that these little holes in the trees represent the nuclei of the cells. And so, again, notice that these nuclei may appear to be in multiple layers. But, again, this is a false impression, a fake impression of stratified tissue because all of these cells come into contact with the basement membrane. And in actual stratified tissue, that's not going to be the case. Some cells will touch the basement membrane, and other cells that are in a different layer will not touch the basement membrane.

And again, this is not the case with pseudostratified columnar tissue. Now in terms of the function, again, it's going to be the structure of the tissue and the structure of the cells that make up the tissue that determine the function of the tissue. And so it turns out that the arrangement of the cells in pseudostratified columnar epithelium, because there are some cells that are shorter, other cells that are taller, and it appears to be multiple layers of cells, this arrangement of the cells actually makes this tissue a little bit thicker, a little bit more robust, and it makes it have a little bit greater stability than the simple columnar epithelial tissue that we covered in our previous lesson video. And because this is the case, pseudostratified columnar epithelium is going to have a greater role in protection, which is why we have it listed here as protective. Now, because pseudostratified columnar epithelial cells, many of them are going to be tall and narrow, this means that there's going to be plenty of cytoplasmic space for plenty of organelles and that is going to allow this tissue to function in both secretion and absorption.

And so when it comes to secretion, just like simple columnar epithelial cells, or a simple columnar epithelial ti...

Simple Epithelial Tissues Example 2

So here we have an example problem that says, this tissue is from the lining of the stomach. What type of tissue is it and what makes it unique? And so really we need to fill in these blanks that you can see down below. Now, when I take a look at this micrograph of the tissue, which again is showing the lining of the stomach, the first thing that stands out to me is actually all of this open space that you can see highlighted here in this region. And so identifying the open space is going to be really helpful to identify the polarity of the tissue.

And so notice that we have immediately adjacent to the open space, a sheet of tightly packed cells that are forming a boundary immediately adjacent to the open space. And so this layer here is actually going to be the epithelial tissue layer, and notice it's forming a curved boundary here. And what you'll notice is that the tissue that is underneath is changing its arrangement totally, so it's likely to be connective tissue, the underlying connective tissue. And that means that the basement membrane is going to be separating the two. And, again, the basement membrane is really difficult to see under the light microscope without the proper staining.

So you won't be able to see it very clearly, but we know that it's going to be present separating the epithelial tissue from the underlying connective tissue. And so over here on this side, we can see something similar. Again, the connective tissue is here and you can see the epithelial tissue again is curved. And again, the basement membrane is going to be separating the epithelial from connective tissues. And so now that we've identified those features, it's going to be really helpful to solving this problem.

And what you'll notice is that in the epithelial tissue layer here, the nuclei of the epithelial tissue appear to be all aligned in a single row here. Again, the tissue is curved, but these nuclei are all in a single row, and that implies that this is going to be a single layer of cells. And so because it's a single layer of cells, we know that this is going to be simple epithelial tissue. And what you'll also notice is that the shape of these cells is pretty long and narrow. They're much taller than they are wide.

And so because that's the case, we know that the shape is going to be columnar. And so in terms of the type of tissue, we can identify this as simple columnar epithelial tissue. And so you might recall from our previous lesson videos that simple columnar epithelial tissue actually lines the digestive system from the stomach all the way through the anus. And so here we're showing the lining of the stomach. So, of course, it's going to be simple columnar epithelial tissue.

And so we can actually add the word epithelial here to remind us that this is epithelial tissue. Now, what's unique about the tissue in the stomach here is that it's actually not going to have goblet cells. So, there are no goblet cells in the stomach. And so recall that these goblet cells are going to be unicellular glands that actually secrete a product that ends up forming mucus. But again, those goblet cells are not going to be present in the stomach, and they're more so going to be present in other areas of the digestive tract.

And also, they're present in the pseudostratified columnar epithelia that lines the upper respiratory tract. And so this here concludes our example problem and we'll be able to get some practice moving forward. So I'll see you all in our next video.

Which characteristic is true of columnar cells, but not other epithelial tissues?

• A. Columnar epithelial tissue contains the protein keratin. 
• B. Columnar epithelial tissue is found in the lungs.
• C. Columnar epithelial tissue may contain goblet cells.
• D. Columnar epithelial tissue functions in secretion.

Both the small intestine & the trachea are lined with columnar cells. Based on their location, what do you expect would be different about these cells? 

• A. Cells in the intestine will have cilia to aid in absorption. Cells in the trachea will have microvilli to move mucus. 
• B. Cells in the intestine will have cilia to move mucus. Cells in the trachea have microvilli to aid in absorption. 
• C. Cells in the intestine will have microvilli to move mucus. Cells in the trachea have cilia to aid in absorption. 
• D. Cells in the intestine will have microvilli to aid in absorption. Cells in the trachea will have cilia to move mucus.

Imagine that you are a histologist looking at a sample of cells from the lining of the human intestine. What tissue type do you expect to see?

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

Here’s what students ask on this topic:

What are the four types of simple epithelial tissues and their primary functions?

The four types of simple epithelial tissues are simple squamous, simple cuboidal, simple columnar, and pseudostratified columnar epithelium. Simple squamous epithelium consists of a single layer of flat cells and facilitates rapid diffusion, found in areas like the lungs and capillaries. Simple cuboidal epithelium, with cube-like cells, is involved in absorption and secretion, located in kidney tubules and glands. Simple columnar epithelium, characterized by tall cells, aids in absorption and secretion, often featuring microvilli or goblet cells, and is found in the digestive tract. Pseudostratified columnar epithelium appears layered but is a single layer, primarily found in the respiratory tract, and functions in secretion and protection.

How does the structure of simple squamous epithelium relate to its function?

Simple squamous epithelium consists of a single layer of flat, squished cells that come into direct contact with the basement membrane. This thin structure allows for rapid diffusion of molecules across the tissue, making it ideal for locations where quick exchange of substances is necessary. For example, it lines the air sacs of the lungs, facilitating gas exchange, and forms the walls of capillaries, allowing for efficient nutrient and gas exchange between the bloodstream and tissues. Its thinness also means it is not suited for protective roles, which are better served by thicker, stratified tissues.

What are the distinguishing features of simple cuboidal epithelium?

Simple cuboidal epithelium consists of a single layer of cube-shaped cells with centrally located, round nuclei. These cells have more cytoplasm than simple squamous cells, allowing for more organelles and thus supporting their functions in absorption and secretion. Simple cuboidal epithelium is commonly found in kidney tubules, where it aids in filtration and absorption, and in the ducts of glands such as salivary and mammary glands, where it is involved in secretion. Under a microscope, it often appears as a ring or tube-like structure due to its role in forming ducts and tubules.

Where is simple columnar epithelium typically found and what are its functions?

Simple columnar epithelium is typically found lining the digestive tract, including the stomach and intestines, as well as the uterine tubes and gallbladder. It consists of a single layer of tall, narrow cells with oval-shaped nuclei located near the basal surface. This tissue is specialized for absorption and secretion. In the intestines, it often features microvilli on the apical surface to increase surface area for nutrient absorption. Goblet cells, which secrete mucus, are also commonly found within this tissue, aiding in lubrication and protection of the lining.

What makes pseudostratified columnar epithelium unique among simple epithelial tissues?

Pseudostratified columnar epithelium is unique because, despite appearing to have multiple layers, it is actually a single layer of cells where all cells contact the basement membrane. The term 'pseudostratified' means 'falsely stratified.' This tissue consists of mostly tall, narrow cells, but some cells are shorter and do not reach the apical surface, creating the illusion of stratification. It is primarily found in the respiratory tract, where it often features cilia and goblet cells. The cilia help move mucus and trapped particles out of the respiratory passages, providing a protective function.