Histology Slide Identification Guide

In this video I've got questions about approximately 60 different histology slides. The first set of questions is a series of side-by-side comparisons going family by family, category by category, and that's going to help you see can you differentiate members of the same group. So can you differentiate all of the simple epithelium from each other, all the stratified epithelium from each other, and so on and so forth. The second set of questions is going to be one tissue at a time. to help you see can you still identify the tissues without having other tissues to compare them to. And because this video is going to be kind of long, I'm going to put time stamps in to make it easier for you to navigate. So to find them you can click here, which will bring up this. So if you want to jump to the answer for the question you're on, without hearing my explanation of what you should be looking for to arrive at the correct answer, just click the timestamp for the next question because I'm going to put that timestamp about five seconds before I actually switch to the next question which will allow you to see the answer. And if for whatever reason you are not seeing any of this you can also just look in the description because the timestamps are there as well. Also in the description I will have links to my related playlists, related videos, and also I'm in the process of making some handouts and mini courses related to histology and when I finish them, I will put them in the description as well. Okay, so moving on to our first set of practice, I'm going to give you 10 seconds of silence and then I'll start explaining what we're looking at. Alright, so you can recognize this group as epithelium because as a family, epithelium is always a sheet of cells which are creating a barrier between an open space and deeper tissues. And in all these slides, we are seeing sheets of cells next to an open space, because remember white on a slide means empty, because all that white is is just the light from the microscope. So in this first slide, we are seeing three separate open spaces. Each open space is lined with a single sheet of square-shaped cells. So this is simple cuboidal epithelium. Remember, simple tells us it's one layer of cells. Cuboidal tells us that the cells are square. So here, it is hard to tell the shape of the individual cells. but we can definitely see that they are flat. If by nothing else you could look at those flat little squish nuclei to know that the cells are flat, which is why this is simple squamous epithelium. Down here we have a single row of tall rectangular shaped cells which tells us it is simple columnar, There's these little fuzzies on top, which are cilia. So this is a ciliated simple columnar epithelium. That's very rare. You do not often see cilia on simple columnar, but it is possible. Then this last one, you would think that you are seeing multiple rows of cells because you're seeing multiple rows of nuclei. But what you're actually seeing is you've got short cells with their nuclei down here, and then you've got taller cells with the nuclei higher up, but because they're all touching the basement membrane, it is only a single layer of cells. And the way that you can tell that this is an illusion that you're not really seeing multiple layers of cells is the fact that we're seeing cilia on top. You do not see cilia in epithelium. that are stratified, and that's how you can identify this as ciliated pseudostratified columnar epithelium. Pseudo means fake, stratified means layers. These are fake layers of columnar cells. So we're still looking at epithelium. But now we're seeing multiple layers of cells lining open spaces. And in this example, we cannot really see the shape of the individual cells, but when we see these multiple rows of nuclei, we know that we must have multiple layers of cells. And even though we cannot see the shape of the cells surrounding the nuclei, the fact that the nuclei are circle tells us that they are cuboidal cells, which is how we can recognize this as stratified cuboidal epithelium. Here we are seeing multiple layers of squashed pancake cells. As you get towards the bottom, they start to look cuboidal, but those are the immature cells. These cells are dividing in the bottom most layer and they're getting pushed towards the top. As they become mature, they flatten out. So we named this epithelium for the mature cells, which is why we named this. stratified squamous epithelium. Then down here, as soon as you see this very flaky top, you know that you are looking at the keratinized version of stratified squamous epithelium. So basically these uppermost layers of squamous cells In keratinized, as they get filled with keratin, they flatten out completely and they're so flat and so compressed you cannot even see the individual squamous cells anymore. You just kind of have to know if you see that flaky top, those are smooshed, squashed little cells. Also you'll see I noted this as thin keratinized stratified squamous. because it also comes in a thick variety, which is, it's literally the exact same thing. It's just there's more flaky top. And in the last example, so we see multiple rows of nuclei, which is how we know that this is a stratified epithelium. But they didn't use stratified in the name because the cells are not columnar squamous. or cuboidal, if we look at the top they're very bubbly. When you see that bubbly top, you know you're looking at transitional epithelium. So sometimes people get transitional confused with stratified cuboidal. When you're looking at stratified cuboidal though, you do not really see this many rows of nuclei. You definitely don't see a bubbly top. So that's how you can tell those two apart. If you're still confused, I do have a video that's just about transitional epithelium where I do a bunch of side-by-side comparisons that I will have linked in the description. We're no longer looking at epithelium, we are now looking at connective tissue. A pretty good hint that these are connective tissue is the fact that We're not seeing a lot of cells. What we're mostly seeing is non-living fibers. And the fibers is what we have to pay attention to to differentiate these guys from each other. In this one, we are seeing two types of fibers with these very squiggly, dark staining fibers. Those are elastic. When we see that, we know we're looking at elastic connective tissue. Here we are seeing one type of fiber going in one direction. So those are collagen fibers. These things that we're seeing in between them, those are just the living cellular part of the connective tissue. They are fibroblasts. When we see collagen fibers going in one direction, we know we're looking at regular dense connective tissue. Here This hamburger meat type appearance, that is irregular dense connective tissue, because those collagen fibers are now going in many different directions. So we're still looking at connective tissue. The last set those were dense connective tissues because those fibers were really dense and compacted. These are all loose connective tissues. There's a lot more white which means there's a lot more open empty space. So in this one we see two types of fibers. We've got these thinner fibers and then those thicker fibers out of focus in the back. These ones are elastic fibers. The thicker pink ones are collagen fibers. Those little dots are fibroblasts. And all those characteristics is how we know we're looking at a realer connective tissue. In this example, we are seeing a net-like arrangement of fibers, which is how we know this is reticular connective tissue. So we've got collagen fibers, elastic fibers, reticular fibers. Reticular fibers are the finest, smallest fibers. and they have a net-like appearance. And last but not least, we see those very thin little bubbles and we know this is adipose. Alright, so these three plus the last three we saw, those all make up the group of connective tissue proper. These three guys are not part of connective tissue proper. So these are all cartilage and we can tell they're cartilage because we're seeing these spaces which are called lacuna. all cartilage have lacuna and we can differentiate our cartilage by looking at what is in between the lacuna. When we see wavy ramen noodle fibers we know we are looking at fibrocartilage. When we look in between the lacuna and we see threads and little fibers, We know we are looking at elastic cartilage. And when we're seeing a smooth appearance between the lacuna, we know it's highline. So these guys are two different types of bone. This is spongy bone. This is compact bone. Alright, so the fact that this has striations, you should know that it is muscle. because we only see striations in muscle and we can recognize this as skeletal muscle because those nuclei are pushed to the outer edges. Over here, the striations are a little bit more subtle and then also mixed in, you can see there are darker lines going in the same direction as those striations. Those are areas where the muscles are more visible. intercalated discs and we only see them in cardiac muscle. And here we don't see any striations, we don't see any intercalated discs, so we can recognize it as smooth muscle. Alright, so when we see these cells with long extensions on kind of a thready background, we know we're looking at nervous tissue. Now I have gotten so many requests to make videos about nervous tissue, but sadly I just, I don't have a lot to say about it. The only thing I have to say is these ones are neurons. They transmit electrical impulses in the background, those little dots, those are glial cells, those are just little supporting cells that are supporting the neurons. Maybe someday if I learn more I will make a video, but for now that's it, that's all I've got. All right so that wraps up kind of our review of all of the main tissue types. So now I want to do two side-by-side comparisons of tissues people perpetually mix up. So on the left we are looking at smooth muscle, which people always confuse for the thing on the right, which is dense regular connective tissue. So dense regular connective tissue, if you look, the cells that you're seeing are smushed in between thick bands of collagen fibers. In smooth muscle you are seeing it's kind of stringier, less like thick bands, and then you're also seeing the nuclei are inside of the fibers because smooth muscle is a living tissue. And the reason I chose to show you those first in black and white is because I think that when people see these, their brains are just so overwhelmed by pink that they are kind of unable to process the other patterns. Your brain sees pink strands here, it sees pink strands there, and that's all you're seeing. Try not to pay attention to the pink, pay attention to the rest of the pattern. People also always confuse these two, so this is simple squamous epithelium, this is adipose. In simple squamous epithelium, these circular shapes you're seeing, you have many little squamous cells holding hands to make a circle. Here, One of these little circles is a single adipocyte. It's a single fat cell that has been stretched out by a drop of fat. So the edges are much thinner. Now looking at these guys side by side, if you never confused them, you might not even realize how somebody... could confuse them because they I think they look so clearly different when you look at them right next to each other. Definitely remember this if you are mixing any tissues up all you need to do is get a couple examples of each look at them side by side and play a game of spot the difference. Okay so if that was a hard time for you and if a lot of that was new information You're kind of not helping yourself by just like going through these and feeling really confused. What I would advise you to do is go to my playlists, look for the one that's labeled basic histology, and then on that playlist you'll see a bunch of videos that start with the word identifying. Those all have practice questions in them. If you go and just practice one family at a time and then come back to this one. you're going to feel a lot better. But that being said, if you're going to stick with me, we are moving on to the individual practice. So the first thing you should notice is that we're seeing all of these light and dark bands which are called striations. So we know we're looking at muscle. The next thing you want to notice is that there appears to be some darker bands which are called intercalated discs. And that's how we know this is cardiac muscle. So looking at this tissue, we see we have sheets of cells lining an open space, so it's epithelium, and We would assume that we have multiple rows of epithelial cells because we're seeing multiple rows of nuclei, but if we look at the top here we see those little fuzzies which are called cilia, which we do not see in a stratified epithelium. So that's how we know this is ciliated pseudostratified columnar epithelium. Then next to it, In this tissue we can see there's these open spaces, which are called lacuna, which we find in cartilage, and then when we look in between the lacuna we can see it's very smooth and glassy, which is how we know that this is highline cartilage. In this slide we are also seeing lacuna and we can see those little nuclei which are the cells inside the lacuna because this is cartilage those would be chondrocytes and then in between those lacuna and chondrocytes we see it is very thready. Those little threads are elastic fibers, so this is elastic cartilage. So here we're seeing multiple layers of cells which tells us this is probably a stratified epithelium. But once we get to the top we can no longer really see the individual cells because they are so tightly compressed together. So that's how we know that this is keratinized stratified squamous because remember those keratinized cells are so flat you cannot see the individual squamous cells anymore. And then earlier in the first side by sides I'd show you I had shown you the thin variety and when we look at them side by side you can clearly tell them apart. In the thick variety, the compressed squamous cells are the same thickness or more than the whole rest of the tissue. So... In this slide we are seeing all of these pink fibers and we need to decide are they living or nonliving? And when we look here, we can see there's nuclei kind of smushed in between the fibers. So that tells us these are nonliving fibers. This is collagen, which would make those cells fibroblasts. And when we see collagen fibers going all in one direction with fibroblasts smushed in between the fibers, we know we're looking at regular, dense connective tissue. So when some people look at this slide they also think this might be regular dense connective tissue because we're seeing you know bundles of non-living fibers but if we look at these cells there's kind of a clear zone around the cell. You do not see a clear zone in regular dense connective tissue so that cell is living in a lacuna which makes this cartilage. When we see Collagen fibers that kind of look like ramen noodles in between lacuna. We know we are looking at fibrocartilage. In this slide, we're seeing two different types of tissue. Here, we're seeing one single layer of cells surrounding an open space. And even though we might not really see the shape of the cells, we see those circular nuclei, so we can kind of assume the cells are square. So one layer of square-shaped cells makes this simple cuboidal. Then over here, It's kind of hard to see the individual cells, but we can see that squashed nuclei. So you can kind of imagine that going around this circle, there's a single layer of squashed cells. So this is simple squamous. So we're seeing the nuclei of a cell here and then this outer edge is the cell membrane of that cell all stretched out it's filled with fat because this is adipose tissue. So when you're seeing this pattern that kind of looks like a tree trunk of a tree that has been cut down, you know you're looking at compact bone. But what do we call these individual circular units? So those are called osteons and we say that they are the structural unit of compact bone, basically meaning they're the lego piece of compact bone. Many osteons all together creates our compact bone. But then we also have these little black dots that are part of the osteon. What are those? So those are lacunae just like you see in cartilage. Remember lacunae are empty spaces. On most slides empty space would be white but when they stain bone they use this black dye that makes all of the empty spaces appear black. So in this case black means empty. Now if these lacunae were in cartilage, they would contain chondrocytes, but because this is bone, they contain osteocytes. So once again, we're seeing light and dark bands. Those striations tell us it's muscle. When we look around we don't see any intercalated discs and we see quite clearly that the nuclei are pushed to the edges of the cell, which is what we see in skeletal muscle. So when you see this hamburger meat type appearance, that is a bunch of collagen going in all different directions, which tells us this is irregular dense connective tissue. So notice that these black fibers aren't straight, they're kind of in a net, and then in the black fibers you see these little red circles, which are blood cells, and that's how you can recognize this as reticular connective tissue. So here we have a single layer of tall, rectangularly shaped cells lining an open space, which is how we know this is simple columnar. Now some people get confused and they're like, but there's a layer here too. There's two layers, but they are separated by an open space. So they're two separate single layers. So we're seeing a bunch of Pink stuff. So we need to question is this living or non-living? If you look, the nuclei do look like they are inside of these pink fibers, not in between them. And we don't see any striations, which is how we can recognize this as smooth muscle. So we have two different fiber types going in multiple directions here. In the background we have these pink ones that are kind of out of focus, those are collagen. In the foreground we have these finer purple, almost black ones, those are elastic. And then scattered amongst them are these living cells which are fibroblasts, and that's how you can recognize this as a realer connective tissue. So we're seeing a layer of cells lining an open space. There's multiple layers of cells, but when we look at the shapes they don't really look squamous because they have these round nuclei. We wouldn't think that these are cuboidal because in stratified cuboidal we don't see this many layers of cells. And if we look at the top, we can see the individual cells have kind of a bubbly dome-like appearance, which is what we see when we're looking at transitional epithelium. Now also, this slide, I don't know what this Schmutz is at the top of the layer. I could see maybe you thinking that it's keratinized, but if you look at the thin version of keratinized stratified squamous, it looks flakier. It's a little bit thicker than that. Once you see enough examples, I don't think you'll be confused. So in a previous video I had done with this slide, some people thought they were looking at fibrocartilage, which confused me at first. But then I realized that they were seeing, you know, what appeared to be cells in empty spaces and they mistook that for lacuna. But if you look around, you'll notice. that there are these kind of dark dashes and if you keep looking those dark dashes are cutting across these fibers all across the slide. So those dark dashes are intercalated discs which is how we can recognize this as cardiac muscle. So I'm a little confused as to why those nuclei kind of appear like they're hovering outside of the slide. My only thought is that cardiac muscle cells branch. So maybe it's like the two edges of the cardiac muscle cell are being kind of like pulled around the nucleus. Not 100% sure, but it is something I see in cardiac quite a lot. So just kind of expect it and also realize that with cardiac muscle, you cannot always see the striations when you're further away because they're just much more subtle than what you would see in skeletal muscle. So this we are seeing cells with clear zones around them, so we would think that they're lacuna. When we look around the lacuna, we do see ramen noodle-like fibers, which is how we can recognize this as fibrocartilage. And if we compare it side by side to the cardiac muscle, I think you'll agree They really don't look that much alike. When you look at this you certainly do not think ramen noodles and that's kind of your hint. Keep looking because it's not fibrocartilage. So instead of just asking you what tissue this is, I'm asking you what family of tissues is this tissue a part of? So blood is a type of connective tissue and that's because it shares a common embryonic origin with the rest of connective tissue. All connective tissue comes from mesenchyme including blood. So these empty spaces tells us it's cartilage because those are lacunae. In between the lacunae it is very smooth and glassy, which is how we can recognize this as hyaline cartilage. So we're seeing multiple layers of cells, but once we get to the top, we see those little fuzzies, which are cilia, so we know this isn't really layered. They're fake layers because this is ciliated pseudostratified columnar epithelium. You're seeing multiple layers of cells and then at the top you can clearly see the outlines of these squashed pancake-shaped cells which is how you know that this is stratified squamous epithelium. So we're seeing two fiber types including these thick, dark, squiggly fibers which are elastic fibers, which is how you can recognize this as elastic connective tissue. So we see lacuna and they're tightly packed together and in between them little threads, little fibers which are elastic fibers which is how you know that this is elastic cartilage. So you're seeing lots of pink little strands and if you look the nuclei appear to be inside the strands which is how you can recognize this as smooth muscle. So once again we're seeing kind of you know pink fibers going in one direction but this time when we look at them the fibers don't really look stringy they kind of look like thick bundles. And then we look at all these nuclei and it's kind of obvious they're not in the fibers, they are in gaps in between the fibers, which is how you can recognize this as dense, regular connective tissue. So we see multiple layers of cells, kind of hard to see the shape of them. We see circular nuclei, but we would not think that this is stratified cuboidal because there's far too many layers. So that's how we know this is transitional epithelium. Alright, so if we look, we see these little cup-shaped cells, which are goblet cells, and then on the edge of the cells we see this dark border, which is microvilli, so it's rows and rows and rows of little microscopic nub shapes. And then if we look here, You can see we have one layer of column shaped cells because this is simple columnar epithelium. So this one can throw people off because there are parts of the slide like here where you're seeing multiple rows of nuclei so you might think that it's a stratified epithelium. I think What's happening is we're seeing cells that are undergoing mitosis, and then in some case we're seeing nuclei that are behind the layer of cells that we're looking at. But when you see those goblet cells and you see those microvilli, you do not see those in stratified epithelium. That's something you find in simple columnar. Not all simple columnar has goblet cells and microvilli. but in the intestine it does and these examples where you kind of have the illusion of it being stratified, they always seem to be an intestine so looking for those other two things can help prevent some confusion. So this is just a different part of the same slide so when we look at this part of the slide We are seeing these pink fibers with nuclei inside them. So this is smooth muscle. So this is the inside of the intestine with the epithelium and then this is the wall of the intestine with the muscle that's going to kind of help squeeze things along. Alright, so here we're looking at one layer of squashed pancake cells, which is how we know we're looking at simple squamous epithelium. Once again, that hamburger meat appearance is from collagen fibers going in many directions. So this is irregular dense connective tissue. All right, multiple rows of nuclei. There's a definite bubbly dome-like appearance to both the tissue and the cells in the tissue, which tells us this is transitional epithelium. So transitional, I think it messes people up because it can look really really different depending on where the sample was taken from. If you're confused, either screenshot all my examples and put them side by side for yourself, or look in the description for the video I made about transitional epithelium, where I just put them side by side for you. So we're seeing these striations, the cells look very straight, we don't see any intercalated discs, which tells us this is skeletal muscle. All right, that's it, we did it. That was my last example. Um, so if there's anything you're confused about, you can definitely ask me. But if you're having the issue of, you know, there's tissues that you continuously misidentify, like I said, best thing you can do for yourself is just get multiple examples of each and put them side by side and then play a game of compare and contrast. Alright, I hope this was helpful. Have a great day and have fun learning!

And because this video is going to be kind of long, I'm going to put time stamps in to make it easier for you to navigate. So to find them you can click here, which will bring up this. So if you want to jump to the answer for the question you're on, without hearing my explanation of what you should be looking for to arrive at the correct answer, just click the timestamp for the next question because I'm going to put that timestamp about five seconds before I actually switch to the next question which will allow you to see the answer. And if for whatever reason you are not seeing any of this you can also just look in the description because the timestamps are there as well.

Also in the description I will have links to my related playlists, related videos, and also I'm in the process of making some handouts and mini courses related to histology and when I finish them, I will put them in the description as well. Okay, so moving on to our first set of practice, I'm going to give you 10 seconds of silence and then I'll start explaining what we're looking at. Alright, so you can recognize this group as epithelium because as a family, epithelium is always a sheet of cells which are creating a barrier between an open space and deeper tissues. And in all these slides, we are seeing sheets of cells next to an open space, because remember white on a slide means empty, because all that white is is just the light from the microscope. So in this first slide, we are seeing three separate open spaces.

Each open space is lined with a single sheet of square-shaped cells. So this is simple cuboidal epithelium. Remember, simple tells us it's one layer of cells. Cuboidal tells us that the cells are square. So here, it is hard to tell the shape of the individual cells.

but we can definitely see that they are flat. If by nothing else you could look at those flat little squish nuclei to know that the cells are flat, which is why this is simple squamous epithelium. Down here we have a single row of tall rectangular shaped cells which tells us it is simple columnar, There's these little fuzzies on top, which are cilia.

So this is a ciliated simple columnar epithelium. That's very rare. You do not often see cilia on simple columnar, but it is possible.

Then this last one, you would think that you are seeing multiple rows of cells because you're seeing multiple rows of nuclei. But what you're actually seeing is you've got short cells with their nuclei down here, and then you've got taller cells with the nuclei higher up, but because they're all touching the basement membrane, it is only a single layer of cells. And the way that you can tell that this is an illusion that you're not really seeing multiple layers of cells is the fact that we're seeing cilia on top. You do not see cilia in epithelium.

that are stratified, and that's how you can identify this as ciliated pseudostratified columnar epithelium. Pseudo means fake, stratified means layers. These are fake layers of columnar cells. So we're still looking at epithelium.

But now we're seeing multiple layers of cells lining open spaces. And in this example, we cannot really see the shape of the individual cells, but when we see these multiple rows of nuclei, we know that we must have multiple layers of cells. And even though we cannot see the shape of the cells surrounding the nuclei, the fact that the nuclei are circle tells us that they are cuboidal cells, which is how we can recognize this as stratified cuboidal epithelium. Here we are seeing multiple layers of squashed pancake cells.

As you get towards the bottom, they start to look cuboidal, but those are the immature cells. These cells are dividing in the bottom most layer and they're getting pushed towards the top. As they become mature, they flatten out.

So we named this epithelium for the mature cells, which is why we named this. stratified squamous epithelium. Then down here, as soon as you see this very flaky top, you know that you are looking at the keratinized version of stratified squamous epithelium. So basically these uppermost layers of squamous cells In keratinized, as they get filled with keratin, they flatten out completely and they're so flat and so compressed you cannot even see the individual squamous cells anymore. You just kind of have to know if you see that flaky top, those are smooshed, squashed little cells.

Also you'll see I noted this as thin keratinized stratified squamous. because it also comes in a thick variety, which is, it's literally the exact same thing. It's just there's more flaky top. And in the last example, so we see multiple rows of nuclei, which is how we know that this is a stratified epithelium.

But they didn't use stratified in the name because the cells are not columnar squamous. or cuboidal, if we look at the top they're very bubbly. When you see that bubbly top, you know you're looking at transitional epithelium. So sometimes people get transitional confused with stratified cuboidal.

When you're looking at stratified cuboidal though, you do not really see this many rows of nuclei. You definitely don't see a bubbly top. So that's how you can tell those two apart.

If you're still confused, I do have a video that's just about transitional epithelium where I do a bunch of side-by-side comparisons that I will have linked in the description. We're no longer looking at epithelium, we are now looking at connective tissue. A pretty good hint that these are connective tissue is the fact that We're not seeing a lot of cells. What we're mostly seeing is non-living fibers. And the fibers is what we have to pay attention to to differentiate these guys from each other.

In this one, we are seeing two types of fibers with these very squiggly, dark staining fibers. Those are elastic. When we see that, we know we're looking at elastic connective tissue.

Here we are seeing one type of fiber going in one direction. So those are collagen fibers. These things that we're seeing in between them, those are just the living cellular part of the connective tissue.

They are fibroblasts. When we see collagen fibers going in one direction, we know we're looking at regular dense connective tissue. Here This hamburger meat type appearance, that is irregular dense connective tissue, because those collagen fibers are now going in many different directions. So we're still looking at connective tissue. The last set those were dense connective tissues because those fibers were really dense and compacted.

These are all loose connective tissues. There's a lot more white which means there's a lot more open empty space. So in this one we see two types of fibers. We've got these thinner fibers and then those thicker fibers out of focus in the back.

These ones are elastic fibers. The thicker pink ones are collagen fibers. Those little dots are fibroblasts.

And all those characteristics is how we know we're looking at a realer connective tissue. In this example, we are seeing a net-like arrangement of fibers, which is how we know this is reticular connective tissue. So we've got collagen fibers, elastic fibers, reticular fibers.

Reticular fibers are the finest, smallest fibers. and they have a net-like appearance. And last but not least, we see those very thin little bubbles and we know this is adipose. Alright, so these three plus the last three we saw, those all make up the group of connective tissue proper. These three guys are not part of connective tissue proper.

So these are all cartilage and we can tell they're cartilage because we're seeing these spaces which are called lacuna. all cartilage have lacuna and we can differentiate our cartilage by looking at what is in between the lacuna. When we see wavy ramen noodle fibers we know we are looking at fibrocartilage. When we look in between the lacuna and we see threads and little fibers, We know we are looking at elastic cartilage. And when we're seeing a smooth appearance between the lacuna, we know it's highline.

So these guys are two different types of bone. This is spongy bone. This is compact bone.

Alright, so the fact that this has striations, you should know that it is muscle. because we only see striations in muscle and we can recognize this as skeletal muscle because those nuclei are pushed to the outer edges. Over here, the striations are a little bit more subtle and then also mixed in, you can see there are darker lines going in the same direction as those striations.

Those are areas where the muscles are more visible. intercalated discs and we only see them in cardiac muscle. And here we don't see any striations, we don't see any intercalated discs, so we can recognize it as smooth muscle.

Alright, so when we see these cells with long extensions on kind of a thready background, we know we're looking at nervous tissue. Now I have gotten so many requests to make videos about nervous tissue, but sadly I just, I don't have a lot to say about it. The only thing I have to say is these ones are neurons. They transmit electrical impulses in the background, those little dots, those are glial cells, those are just little supporting cells that are supporting the neurons.

Maybe someday if I learn more I will make a video, but for now that's it, that's all I've got. All right so that wraps up kind of our review of all of the main tissue types. So now I want to do two side-by-side comparisons of tissues people perpetually mix up. So on the left we are looking at smooth muscle, which people always confuse for the thing on the right, which is dense regular connective tissue. So dense regular connective tissue, if you look, the cells that you're seeing are smushed in between thick bands of collagen fibers.

In smooth muscle you are seeing it's kind of stringier, less like thick bands, and then you're also seeing the nuclei are inside of the fibers because smooth muscle is a living tissue. And the reason I chose to show you those first in black and white is because I think that when people see these, their brains are just so overwhelmed by pink that they are kind of unable to process the other patterns. Your brain sees pink strands here, it sees pink strands there, and that's all you're seeing.

Try not to pay attention to the pink, pay attention to the rest of the pattern. People also always confuse these two, so this is simple squamous epithelium, this is adipose. In simple squamous epithelium, these circular shapes you're seeing, you have many little squamous cells holding hands to make a circle.

Here, One of these little circles is a single adipocyte. It's a single fat cell that has been stretched out by a drop of fat. So the edges are much thinner. Now looking at these guys side by side, if you never confused them, you might not even realize how somebody...

could confuse them because they I think they look so clearly different when you look at them right next to each other. Definitely remember this if you are mixing any tissues up all you need to do is get a couple examples of each look at them side by side and play a game of spot the difference. Okay so if that was a hard time for you and if a lot of that was new information You're kind of not helping yourself by just like going through these and feeling really confused. What I would advise you to do is go to my playlists, look for the one that's labeled basic histology, and then on that playlist you'll see a bunch of videos that start with the word identifying.

Those all have practice questions in them. If you go and just practice one family at a time and then come back to this one. you're going to feel a lot better.

But that being said, if you're going to stick with me, we are moving on to the individual practice. So the first thing you should notice is that we're seeing all of these light and dark bands which are called striations. So we know we're looking at muscle.

The next thing you want to notice is that there appears to be some darker bands which are called intercalated discs. And that's how we know this is cardiac muscle. So looking at this tissue, we see we have sheets of cells lining an open space, so it's epithelium, and We would assume that we have multiple rows of epithelial cells because we're seeing multiple rows of nuclei, but if we look at the top here we see those little fuzzies which are called cilia, which we do not see in a stratified epithelium. So that's how we know this is ciliated pseudostratified columnar epithelium. Then next to it, In this tissue we can see there's these open spaces, which are called lacuna, which we find in cartilage, and then when we look in between the lacuna we can see it's very smooth and glassy, which is how we know that this is highline cartilage.

In this slide we are also seeing lacuna and we can see those little nuclei which are the cells inside the lacuna because this is cartilage those would be chondrocytes and then in between those lacuna and chondrocytes we see it is very thready. Those little threads are elastic fibers, so this is elastic cartilage. So here we're seeing multiple layers of cells which tells us this is probably a stratified epithelium.

But once we get to the top we can no longer really see the individual cells because they are so tightly compressed together. So that's how we know that this is keratinized stratified squamous because remember those keratinized cells are so flat you cannot see the individual squamous cells anymore. And then earlier in the first side by sides I'd show you I had shown you the thin variety and when we look at them side by side you can clearly tell them apart.

In the thick variety, the compressed squamous cells are the same thickness or more than the whole rest of the tissue. So... In this slide we are seeing all of these pink fibers and we need to decide are they living or nonliving? And when we look here, we can see there's nuclei kind of smushed in between the fibers. So that tells us these are nonliving fibers.

This is collagen, which would make those cells fibroblasts. And when we see collagen fibers going all in one direction with fibroblasts smushed in between the fibers, we know we're looking at regular, dense connective tissue. So when some people look at this slide they also think this might be regular dense connective tissue because we're seeing you know bundles of non-living fibers but if we look at these cells there's kind of a clear zone around the cell. You do not see a clear zone in regular dense connective tissue so that cell is living in a lacuna which makes this cartilage.

When we see Collagen fibers that kind of look like ramen noodles in between lacuna. We know we are looking at fibrocartilage. In this slide, we're seeing two different types of tissue.

Here, we're seeing one single layer of cells surrounding an open space. And even though we might not really see the shape of the cells, we see those circular nuclei, so we can kind of assume the cells are square. So one layer of square-shaped cells makes this simple cuboidal.

Then over here, It's kind of hard to see the individual cells, but we can see that squashed nuclei. So you can kind of imagine that going around this circle, there's a single layer of squashed cells. So this is simple squamous.

So we're seeing the nuclei of a cell here and then this outer edge is the cell membrane of that cell all stretched out it's filled with fat because this is adipose tissue. So when you're seeing this pattern that kind of looks like a tree trunk of a tree that has been cut down, you know you're looking at compact bone. But what do we call these individual circular units? So those are called osteons and we say that they are the structural unit of compact bone, basically meaning they're the lego piece of compact bone. Many osteons all together creates our compact bone.

But then we also have these little black dots that are part of the osteon. What are those? So those are lacunae just like you see in cartilage.

Remember lacunae are empty spaces. On most slides empty space would be white but when they stain bone they use this black dye that makes all of the empty spaces appear black. So in this case black means empty.

Now if these lacunae were in cartilage, they would contain chondrocytes, but because this is bone, they contain osteocytes. So once again, we're seeing light and dark bands. Those striations tell us it's muscle. When we look around we don't see any intercalated discs and we see quite clearly that the nuclei are pushed to the edges of the cell, which is what we see in skeletal muscle. So when you see this hamburger meat type appearance, that is a bunch of collagen going in all different directions, which tells us this is irregular dense connective tissue.

So notice that these black fibers aren't straight, they're kind of in a net, and then in the black fibers you see these little red circles, which are blood cells, and that's how you can recognize this as reticular connective tissue. So here we have a single layer of tall, rectangularly shaped cells lining an open space, which is how we know this is simple columnar. Now some people get confused and they're like, but there's a layer here too. There's two layers, but they are separated by an open space. So they're two separate single layers.

So we're seeing a bunch of Pink stuff. So we need to question is this living or non-living? If you look, the nuclei do look like they are inside of these pink fibers, not in between them. And we don't see any striations, which is how we can recognize this as smooth muscle. So we have two different fiber types going in multiple directions here.

In the background we have these pink ones that are kind of out of focus, those are collagen. In the foreground we have these finer purple, almost black ones, those are elastic. And then scattered amongst them are these living cells which are fibroblasts, and that's how you can recognize this as a realer connective tissue.

So we're seeing a layer of cells lining an open space. There's multiple layers of cells, but when we look at the shapes they don't really look squamous because they have these round nuclei. We wouldn't think that these are cuboidal because in stratified cuboidal we don't see this many layers of cells.

And if we look at the top, we can see the individual cells have kind of a bubbly dome-like appearance, which is what we see when we're looking at transitional epithelium. Now also, this slide, I don't know what this Schmutz is at the top of the layer. I could see maybe you thinking that it's keratinized, but if you look at the thin version of keratinized stratified squamous, it looks flakier. It's a little bit thicker than that. Once you see enough examples, I don't think you'll be confused.

So in a previous video I had done with this slide, some people thought they were looking at fibrocartilage, which confused me at first. But then I realized that they were seeing, you know, what appeared to be cells in empty spaces and they mistook that for lacuna. But if you look around, you'll notice. that there are these kind of dark dashes and if you keep looking those dark dashes are cutting across these fibers all across the slide.

So those dark dashes are intercalated discs which is how we can recognize this as cardiac muscle. So I'm a little confused as to why those nuclei kind of appear like they're hovering outside of the slide. My only thought is that cardiac muscle cells branch.

So maybe it's like the two edges of the cardiac muscle cell are being kind of like pulled around the nucleus. Not 100% sure, but it is something I see in cardiac quite a lot. So just kind of expect it and also realize that with cardiac muscle, you cannot always see the striations when you're further away because they're just much more subtle than what you would see in skeletal muscle. So this we are seeing cells with clear zones around them, so we would think that they're lacuna.

When we look around the lacuna, we do see ramen noodle-like fibers, which is how we can recognize this as fibrocartilage. And if we compare it side by side to the cardiac muscle, I think you'll agree They really don't look that much alike. When you look at this you certainly do not think ramen noodles and that's kind of your hint. Keep looking because it's not fibrocartilage. So instead of just asking you what tissue this is, I'm asking you what family of tissues is this tissue a part of?

So blood is a type of connective tissue and that's because it shares a common embryonic origin with the rest of connective tissue. All connective tissue comes from mesenchyme including blood. So these empty spaces tells us it's cartilage because those are lacunae.

In between the lacunae it is very smooth and glassy, which is how we can recognize this as hyaline cartilage. So we're seeing multiple layers of cells, but once we get to the top, we see those little fuzzies, which are cilia, so we know this isn't really layered. They're fake layers because this is ciliated pseudostratified columnar epithelium.

You're seeing multiple layers of cells and then at the top you can clearly see the outlines of these squashed pancake-shaped cells which is how you know that this is stratified squamous epithelium. So we're seeing two fiber types including these thick, dark, squiggly fibers which are elastic fibers, which is how you can recognize this as elastic connective tissue. So we see lacuna and they're tightly packed together and in between them little threads, little fibers which are elastic fibers which is how you know that this is elastic cartilage.

So you're seeing lots of pink little strands and if you look the nuclei appear to be inside the strands which is how you can recognize this as smooth muscle. So once again we're seeing kind of you know pink fibers going in one direction but this time when we look at them the fibers don't really look stringy they kind of look like thick bundles. And then we look at all these nuclei and it's kind of obvious they're not in the fibers, they are in gaps in between the fibers, which is how you can recognize this as dense, regular connective tissue.

So we see multiple layers of cells, kind of hard to see the shape of them. We see circular nuclei, but we would not think that this is stratified cuboidal because there's far too many layers. So that's how we know this is transitional epithelium. Alright, so if we look, we see these little cup-shaped cells, which are goblet cells, and then on the edge of the cells we see this dark border, which is microvilli, so it's rows and rows and rows of little microscopic nub shapes.

And then if we look here, You can see we have one layer of column shaped cells because this is simple columnar epithelium. So this one can throw people off because there are parts of the slide like here where you're seeing multiple rows of nuclei so you might think that it's a stratified epithelium. I think What's happening is we're seeing cells that are undergoing mitosis, and then in some case we're seeing nuclei that are behind the layer of cells that we're looking at.

But when you see those goblet cells and you see those microvilli, you do not see those in stratified epithelium. That's something you find in simple columnar. Not all simple columnar has goblet cells and microvilli. but in the intestine it does and these examples where you kind of have the illusion of it being stratified, they always seem to be an intestine so looking for those other two things can help prevent some confusion.

So this is just a different part of the same slide so when we look at this part of the slide We are seeing these pink fibers with nuclei inside them. So this is smooth muscle. So this is the inside of the intestine with the epithelium and then this is the wall of the intestine with the muscle that's going to kind of help squeeze things along.

Alright, so here we're looking at one layer of squashed pancake cells, which is how we know we're looking at simple squamous epithelium. Once again, that hamburger meat appearance is from collagen fibers going in many directions. So this is irregular dense connective tissue. All right, multiple rows of nuclei. There's a definite bubbly dome-like appearance to both the tissue and the cells in the tissue, which tells us this is transitional epithelium.

So transitional, I think it messes people up because it can look really really different depending on where the sample was taken from. If you're confused, either screenshot all my examples and put them side by side for yourself, or look in the description for the video I made about transitional epithelium, where I just put them side by side for you. So we're seeing these striations, the cells look very straight, we don't see any intercalated discs, which tells us this is skeletal muscle. All right, that's it, we did it. That was my last example.

Um, so if there's anything you're confused about, you can definitely ask me. But if you're having the issue of, you know, there's tissues that you continuously misidentify, like I said, best thing you can do for yourself is just get multiple examples of each and put them side by side and then play a game of compare and contrast. Alright, I hope this was helpful. Have a great day and have fun learning!

Transcript for:Histology Slide Identification Guide

Transcript for:
Histology Slide Identification Guide