Simple Epithelial Tissues

In this video, we're going to begin our lesson on simple epithelial tissues. And so recall from our last lesson video, we said that structurally humans have eight types of epithelial tissues and half of those or four of those tissues are going to be structurally categorized as simple epithelial tissues. And 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. And so 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. Now, moving forward in our course, we're going to talk about each of these four simple epithelial tissues in their own separate videos. And so 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

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 a and so what I really want you to notice is that we're using the number one 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 one 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 memory. 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 three types of simple epithelial tissues, you'll notice that they're going to be numbered and lettered as one B, one C and one D. Where again, the one is indicating this is a simple epithelial tissue with just one layer of cells. And then after we cover all four of the simple epithelial tissues, we'll then transition to talking about the four stratified epithelial tissue. And those will be numbered and lettered as two A, two B, two C and two D. Where again, the number two is indicating that these stratified tissues are made of two 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 that helps 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 and 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 our 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, uh 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 the lungs. And of course, in the air sacs of the lungs, gas exchange or the diffusion of gasses is going to be critical oxygen gas needs to be able to diffuse rapidly from the lungs into the bloodstream. And carbon dioxide gas from the blood needs to diffuse rapidly into the lungs, the air sacs of the lungs so that we can exhale that carbon dioxide gap. Also a simple squamous epithelial tissue is found lining capillaries and forming capillaries which are the thinnest or smallest blood vessels. And so this is also going to allow for the exchange of nutrients, allowing nutrients such as glucose to diffuse out of the capillaries and into the neighboring tissues. And it also allows for the quick and efficient exchange of gasses between the bloodstream and the tissue. And also simple squamous epithelial tissue is found forming the filtration membranes found in the kidneys that are called the Bowman's capsule of the kidney. And so this is going to allow for the filtration of blood to create urine. And this is a process that we'll get to talk more about later in our course, in a different video. Now, in terms of the function, simple squamous epithelia is also important for covering and lining. In fact, we'll see that simple squamous epithelial tissue uh makes up the epithelial tissue that lines the body cavities. For example, the Sears forming the sear membranes of the ventral body cavities that we talked about back in chapter one and this simple squamous epithelial tissue is going to be important for producing that serious fluid, which is the fluid inside of the Sears cavity. And that's going to be important for lubrication and again, helping to reduce friction between these organs. Now, uh in terms of an ID tip, which you'll notice is that most of the time the images of the simple squamous epithelia are often going to be from the lungs, the air sacs of the lung. And this is simply because the other locations where simple squamous epithelial tissue is found. Uh those simple squamous epithelial tissue cells are a little bit harder to see um the cells in those other locations. And so again, usually it's going to be from the air sacs of the lungs. And so notice here in our image, we're showing you the lungs and we're showing you a micrograph of the air sacs of the lungs. And you can see all of the open space here being highlighted and the epithelial tissue, the simple squamous epithelial tissue is lining these open spaces. As you see here and so notice that over here, what we have is just a zoom in of this particular region and it is a sketched diagram so that you can see the cells a little bit easier. Now, what you'll notice is that we are looking kind of a a AAA bird's eye view of the tissue. And so it may appear to be multiple cell layers, but again, we're looking at it straight on from the top. And so uh is creating just one single layer of cell. And again, the basement membrane is going to be so thin that in typical light micro graphs like the ones that you see here. And here, the basement membrane is going to be almost impossible to see without the proper staining techniques or without a more advanced microscope like an electron microscope, but the basement membrane is still there. And so uh one other helpful ID tip here is that when you're looking at simple squamous epithelia from the air sacs of the lungs, it kind of looks like ribbons in open space. And so notice down below, we've got these ribbons to remind you that these ribbons that are going through open space like this kind of look like these simple squamous epithelial tissue going through the open space here creating the air sacs of the lung. And so this year concludes our lesson on simple squamous epithelial tissue. And as we move forward, we'll be able to talk about the other types of simple epithelial tissues and we'll be able to get some practice applying these concepts as well. So I'll see you all in our next video.

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 boxlike. 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 boxlike 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 squish 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 shaped, 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 more 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 uh 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 uh 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.

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 a capillary. And notice down below what we have is that missing interactive blink 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 blink to the cells of the capillary wall. And so our job is to again identify the correct tissue type that of the cells that are forming that capillary wall and then to fill in that tissue type here in this point. 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 gass 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 tiss. And we have carbon dioxide gass 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.

In this video, we're going to talk about the third 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 can 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 organ elves. 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 micro vili on the surface on the apical surface of the tissue. And these micro villi help to increase surface area, ultimately helping to maximize the absorption capability. And so whenever you see micro villa on the apical surface, that's an indication that absorption is going to be essential. And again, not all simple columnar epithelia have micro villa, 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 villa, which are these folds that again help to increase surface area. And if we zoom into the villa here, the epithelial tissue that are forming the villa, 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 in the open space inside the intestine of um 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 micro villa labeled again, these structures on the apical surface that are going to help uh 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 uh 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 the that mucus formation can be found in the uh 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 micro villa on the apical surface, they actually have CIA and those CIA are re recall are little tiny hair like structures that move like ores and help to move substances through the open space. And so the uterine tubes are going to have CIA which help to move the oo site 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 uh 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 micro villa may appear as a border along the apical surface. And so you can tend to see these micro villa again on the apical surface as you see here again, not all of the simple columnar epithelial tissue is going to have micro villa, sometimes they have SIA instead of micro villa and other times they may not have either. And so uh 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.

In this video, we're going to talk about the fourth 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 of 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 and pseudo stratified 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 of the cells come into direct contact with the underlying basement membrane. And so it recalled 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 columna 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 colum 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 we 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, 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, uh because pseudostratified columnar epithelia cells, uh many of them are going to be tall and narrow, this means that there's going to be plenty 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, uh or a simple columnar epithelial tissue, it's going to be sprinkled with these goblet cells which recall our unicellular glands that secrete a product that ends up forming mucus. And so these goblet cells once again, are going to be uh unicellular glands and we'll talk more about them later in our course. Uh But because they end up releasing a product that forms mucus, we know that the mucus can help to lubricate the lining of the tissue. And it can also help to protect the tissue because uh dust particles and pathogens can actually get trapped in the mucus. And then once it's trapped in the mucus, the tissue can actually move the mucus using CIA. And so the CIA recall are little tiny hair like structures that move like oars and can actually move substances through the open space that it's lining. And so the CIA can actually move the mucus along the surface and can move, move the pathogens and the dust particles that are trapped into the mucus into areas of our body where we can eliminate the mucus, for example, into areas of our body that we can cough it up or spit it up or swallow it into our digestive system where it can be eliminated through our digestive system. Now, it's important to note that these CIA are often going to be present, but they are not always going to be present. Now, in terms of the locations or some example, locations of where you can find pseudostratified columnar epithelia. It is actually going to be lining most of the upper respiratory passages, including our trachea. And it can also be found in portions of our uh the male reproductive tracts. And so in the upper respiratory tracts, those pseudostratified columnar epithelia are going to be ciliated because they're going to be moving the mucus uh through our uh respiratory passages. Again, to help eliminate uh microbes and uh pathogens and things of that nature. But in the portions of the reproductive tracts, uh the pseudostratified columnar epithelia is not necessarily going to be ciliated and it's going to function more in absorption and secretion to help with activating and maturing the sperm cells in the male reproductive tracts. Now, down below, we do have an ID tip for you here. And it says that often pseudostratified columnar epithelia is going to have CIA. But again, this is not gonna always be the case. And although pseudostratified columnar epithelia may look like a stratified tissue, it is not a stratified tissue. And so you may think, oh, wait a second, this could look like uh stratified columnar epithelia because uh you have these columnar cells and it appears to be multiple layers. But uh what we'll find out moving forward in our course, when we cover stratified columnar epithelia is that stratified Columbia, epithelia is relatively rare. And so that's what we're indicating here. Stratified columnar epithelia is relatively rare and because it's uh relatively rare in the body, that means that the tissue is more likely going to be a pseudo stratified columnar epithelial tissue. But also in uh the stratified columnar epithelial tissue. What we're going to learn moving forward is that the nuclei tend to form more clear and more distinct layers that are more clearly visible. But again, we'll talk about that tissue later in our course when we're talking about stratified tissue. Um and another ID tip here is that again, multiple layers of nuclei is most likely going to be pseudostratified columnar epithelial tissue. And so in this image over here, notice, we're showing you the upper respiratory passages, specifically the trachea here and we know pseudostratified columnar epithelia is going to be lining the upper respiratory passages and the pseudostratified columnar epithelia lining, the upper respiratory passages are going to be ciliated as you can see here. And you can also see the goblet cell, which again, it's called a goblet cell because it's shaped like a goblet or a wine glass if you will. And this is the cell that's going to be secreting a product that ends up forming mucus. And that mucus again is going to help lubricate and protect the tissue. And so this year concludes our lesson on pseudostratified 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.

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, uh over here on this side, we could, we can see something similar. Again, the connective tissue is here and you can see the uh 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, that 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 a 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 epithelia 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 year 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.