welcome back to an avenue to physiology one laboratory i'm kevin took off and in this video we're gonna go over key concepts from exercise four which pretty much is histology histology is defined as the study of tissues and for the most part we're going to be looking at microscope slides or images of these tissues on microscope slides right so let's go into some of the basics now in general there are four tissue types they're listed here epithelia or epithelial tissue connective tissue muscle tissue and nervous tissue now where we have separate labs where we look at muscles and neurons and the parts of the brain we're going to be looking at these tissues separately in those lessons so in this exercise we're only going to be looking at epithelial tissue and connective tissue okay so we have five epithelial tissues and six connective tissues will look at epithelial first and let's actually look at how we classify epithelial tissue we can classify epithelial tissue in two ways one is based on the number of layers of the cells and the other is by the shape of the cells so let's look at the shape so if the cells individually are flat and irregularly shaped like this but the key is that they're flat we call those squamous cells right if they sort of have a square like appearance because they're really three-dimensional but when you look at them on a micrograph image they're gonna look like a square so they look like this they're not much longer than they are wide they're cuboidal in shape and if you have cells that are a lot longer in one dimension than the other they look like almost like a pill so to speak or a column there are columnar alright now let's look at the layers the number of them and see how we can classify it there if there's one layer of these cells the term for that is simple okay so for example here's squamous cells and there's just one layer of those therefore this type of tissue would be called simple squamous epithelium alright the second way to classify the layers generally is stratified so here we see there are multiple layers of these cells stacked on top of one another and so because each individual cell is flat but there's multiple layers we would call this stratified squamous epithelium and you can follow the same pattern down here here I have cube-like or square-like cells but there's one layer of them so this would be simple cuboidal epithelium whereas in this case the cuboidal cells are stacked in multiple layers so this would be stratified cuboidal down here we have one layer of columnar cells so this would be simple columnar epithelium these are stacked in multiple layers so these would be stratified columnar and in general the ones we're going to be looking at in this class they're gonna be simple squamous stratified squamous simple cuboidal and simple columnar along with one other and that's over here which is pseudo stratified columnar epithelium this one is pseudo stratified because as we'll go over in just a few minutes notice that these cells are not perfectly columnar some of them may look like pizza slices so someone just had a pizza they cut it up into slices and kind of just through the step those slices on top of one another to where it might look like in some cases this cell where my mouse is might be a layer on top of this one but it's not a true second layer so it's pseudo stratified and they're generally approximately columnar shape so we call it pseudo stratified columnar epithelium so this is kind of the exception to the rule but other than that you classify them in these ways in this course we will not be looking at stratified cuboidal or stratified columnar epithelium and additionally instead of using a microscope directly in class as you saw or will see we're actually just gonna be looking at images of these slides just for the purpose of time here's a typical diagram of epithelium and connective tissue here we have epithelial cells and these since they are cuboidal in shape and there's one layer this is probably simple cuboidal epithelium and always with epithelium on one side we have just a physical space usually empty space there could be a number of things in this space but the physical space is called the lumen typically okay the side of the epithelial tissue that faces the lumen is called the apical surface so this side of every one of these cells is to call the apical surface on the other side of the epithelial tissue we have connective tissues all this in here all these squiggly lines these are connective tissues of some kind the side of the epithelial tissue that faces the connective tissue is called the basal surface and associated with the basal surface is the basement membrane which is this solid pink line right here so the basement membrane is sort of an anchor that anchors these epithelial cells or the tissue to the underlying connective tissue so the basement membrane in some ways is like the glue that sticks those two together and the side of the cells that faces the connective tissue is the basal surface in here you have connective tissue itself here's some cells and you'll typically hear me talk about this term when we get to connective tissue the matrix so the matrix is really just everything but the cells so all this stuff and here all this fluid which is actually called ground substance and then these fibers which could be collagen or something like that all of this with the exception of the cells all of this is the matrix all right now let's go into the epithelial tissues and we have five of them and these names right here on this slide which you have these are the names that you would need to put on the exam to get full credit this these full names right here all right first we have simple squamous epithelium so these are micrograph images of that so for simple squamous this is the easiest picture to look at notice that these cells are completely flat these darkened spaces right here these dark parts are the nuclei nuclei tend to stain dark but you see that these cells are flat this is actually in the lungs these are actually the nuclei of the squamous cells for the alveoli which you'll talk about in anatomy and physiology - another common place that you can find simple squamous epithelium is in the lining of blood vessels so if you look at this part right here where the lining as I'm kind of tracing it with my mouse you see that these cells are very flat here's one cell right here denoted by its nucleus here's a second cell again nucleus possibly a third fourth and you can see that these cells line the blood vessel this is actually a longitudinal section of the blood vessel here's a cross sectional view of it and again you can see simple squamous cells lining the surface of that and notice in here in this space that doesn't stain and all this is the lumen okay here's the lumen inside here so the lumen is like we said just usually a space and things can be inside of it for example here blood runs through this lumen and this since this is also a blood vessel blood runs through here as well and so this part of these cells would be the apical surface okay and then the other side could be the basal surface alright so simple squamous make sure you can identify these all right let's move on to simple cuboidal epithelium a very common way at least in this course that you'll see simple cuboidal epithelium is you'll see these cuboidal cells very large nuclei relative to the size of the cell and they sir go around some lumen like this in a circular pattern so notice these simple cuboidal epithelial cells form a circle around this lumen so here's one system right here here's another clear system right here simple cuboidal cells running around this lumen here's another picture right here and again right here so you can see this setup is very common these are cross sectional views of this by the way also notice just some more terminology again here's our lumen so these this side of these cells is the apical surface and not listed here this would be where the basal surface is but also associated with the basement membrane which would be sort of here in these yellow dotted lines alright and also in general locations simple cuboidal epithelial tissue would be found in kidney tubules the ducts of many glands and then glands themselves alright so these are simple cuboidal epithelium alright let's move on to simple columnar epithelium all right so these are literally just columns shaped cells you can see here here's each individual nucleus but notice here we've got these along gated cells like this okay you can see again a picture of this here now these cells are located mainly in the digestive tract and also excretory ducts of glands and since they're located in places like the digestive tract where you need secretions and enzymes and mucus you need specialized cells that are actually able to produce and release this mucus and so forth into traps so notice here we have other types of cells embedded in the simple columnar epithelium and these are called goblet cells and they typically appear as kind of clear space is almost not completely clear but they certainly don't stain as dark as the simple columnar cells so these right here that I have labeled these are very clear and imminent goblet cells so in this type of tissue if you're given this you need to pay close attention to whether or not it says name the tissue or name this cell that I have an arrow pointed to I may have an arrow pointed at the goblet cell itself all right and again here's the lumen up here where my mouse is okay in this picture down here this would be the lumen all right and there's not really super clear goblet cells but I might guess this might here since it didn't stain this might possibly be a goblet cell but these are definitely three right here all right now simple columnar epithelium is not the only tissue to have goblet cells the other one is ciliated pseudostratified columnar epithelia kind of a pain to write that all out but you do need to do that um notice with these these are pseudostratified so these are not perfect columnar cells remember when we went to this picture it looked as if it was very uneven they're not perfect columns and then also it might look like in some cases you know someone took the pieces of the pits and just kind of threw them on to a microscope slide you can tell these are definitely not perfect columns also notice here these also have goblet cells right so here's two right here possibly a couple over here we go in under this picture here's a goblet cell there's a goblet cell you can see labeled as G for goblet there's actually quite a few in this picture down here at the bottom another thing to notice and this is an easy way to distinguish between ciliated pseudostratified columnar epithelium and the previous one is that these are ciliated if you look at the apical surface of these cells there are hairlike projections very dense hair like projections called cilia you can actually see them in all three of these pictures this one over here on the right it's not as clear but you can still see them on this darkened apical surface it's easily visible in both this one right here and this one at the bottom and in fact its label is c4 cilia so if I point it to these structures right here you would need to name those as cilia notice that the previous ones simple columnar does not have these cilia you see this very defined apical surface but no hairlike projections on it and that's how it differs from ciliated pseudostratified columnar epithelium this tissue is generally located in the respiratory tract especially the trachea and these cilia are actually able to beat up and push particles and bacteria out and prevent them from getting deeper into the respiratory tract and and preventing them from getting deep into the lungs alright so these have cilia and goblet cells make sure you watch out for those the last kind of epithelial tissue that we're going to look at in this course is stratified squamous now remember the difference between simple squamous and stratified squamous is the number of layers we still have flat cells but in stratified squamous epithelium these cells are stacked this is a really good image here on the top you can clearly see that these cells are flat and appearance at least at the top and there's definitely multiple layers alright and if you look here on this bottom picture you'll also see we've got a ton of flat cells again in multiple layers usually the distinction between simple and stratified squamous is pretty obvious because there's usually a lot of layers alright and pretty much the stratified squamous epithelium is going to be in any location where you're gonna need protection from abrasion so if you think about the lining of the esophagus we constantly eat food and so the food can scrape off these cells but luckily since they're stratified they can grow back in multiple layers also obviously the mouth the vagina can be a braised obviously and then the epidermis obviously your skin is in constant with lots of things so very important to have stratified squamous tissue in that region all right now we're going to go into the connective tissues I think to some extent these are actually a little bit easier than the epithelial tissues that's just my opinion and in this course we have six of them all right we're first gonna look at the three types of cartilage the first is elastic cartilage now a few things about cartilage that will help you identify it so see these things right here where my mouse says there's a ton of these these are called lacunae or lacunae is the plural and the lacunae are spaces in which you have cells called chondrocytes so actually guessing these little pink regions inside the lacunae those are the chondrocytes but they're in a space called a lacunae all right you do need to be able to recognize those in many cases particularly in elastic and hyaline cartilage I think they kind of look like a bunch of octopus suckers so if you actually look at a real octopuses arms it actually has a ton of suckers on it and they kind of look like that so if you actually recognize those lacunae that tells you it's cartilage now the question is how do you determine what type of cartilage it is well in terms of elastic cartilage there's two kind of general ways to look at it the first way which is kind of a not as good way because there can be some exceptions but in general it's usually true in elastic cartilage these octopus suckers or these lacunae are actually much more dense and more tightly packed if you look how tightly packed they are in this image versus the next one hyaline cartilage and you'll definitely see that an elastic cartilage these octopus suckers or lacunae are a lot more tightly packed more dense alright but the better way to tell the difference between elastic and Highland is that in elastic cartilage this matrix outside of the lacunae so every space here that's not occupied by lacunae is very rough looking in appearance even if you look down here you can tell looks like there's a lot of scratch marks all this stuff so in elastic cartilage the matrix is a lot rougher all right now in terms of the location we have elastic cartilage in both the ear and the epiglottis we won't be looking at the epiglottis until Anatomy ooh - but you can obviously feel your ears you hopefully know your ears are made of cartilage but the specific type is elastic and I think it confused think II for elastic efore ear and epiglottis all right the key with elastic cartilage is we have the lacunae with the chondrocytes and the matrix is rough in Highland cartilage we still have these octopus suckers we have these lacunae which you do need to be able to recognize but notice that the matrix is a lot smoother if you look outside of these this looks like a much smoother matrix than it does an elastic cartilage and that's sort of the giveaway that it's hyaline cartilage all right also in hyaline cartilage generally speaking these lacunae are not as tightly packed together they can be a little bit more sparse but you should still easily be able to see them all right now hyaline cartilage you have in your joint cavities most most joints with the main exception being the spine your vertebral column most joints all the bones that articulate in that joint are covered in a type of cartilage which you will see later is called articular cartilage but it's specific type is Highland cartilage so for example if you look in your knees many of you may know about the meniscus in your knee it's a commonly injured tissue that is actually hyaline cartilage it's part of an articular cartilage deposit in your knees but all your joints have it you also have hyaline cartilage in the ribs the costal cartilage which we'll look at in a couple lectures the nose your nose is cartilage that's hyland and then also whenever you develop in utero you actually don't start out with bone you start out with an embryonic skeleton made of cartilage specifically Highland cartilage and over time it ossified into bone all right the last type of cartilage also has lacunae there not is obvious on they look a little bit different but you can still usually tell they're lacunae here's an example right here in my mouse is on the bottom image you see here a chondrocyte surrounded in kind of a whitish space all of these things are lacunae you can see them appear at the top now fibroids fibrocartilage the lacunae look a little bit different than they did in hyelin and elastic cartilage but in fibrocartilage we kind of have sort of what are called striations so striations are sort of when you have a general appearance of like fibers kind of all going in the same direction okay so notice if you kind of look at it like wisps of a cloud in this top image the fibers or striations appear to go from up here kind of down here if you follow my mouse from up here to kind of down there from up here to kind of down there okay in the bottom picture they seem to be going roughly left to right or like right to left whatever horizontally but in fibrocartilage you do have these striations which is very important to recognize you have both the lacunae with the chondrocytes but also these striations that generally go in one direction all right now fibrocartilage we're gonna see this in two lectures from now but when we look at the pelvis the two halves of it which are called offs coxae are actually joined by a type of fibrocartilage known as the pubic symphysis but the more important area where you have fibrocartilage is actually the intervertebral discs which we'll look at actually in the next lecture in bones each vertebra is actually cushioned from the adjacent one by a fibrocartilage deposit called the intervertebral disc alright so that's the three types of cartilage now we've got three other tissues which I don't think are actually as bad these are actually a little bit easier this is a very easy one to recognize adipose tissue this is body fat all right now if you look at these cells each one of these white blobs is a cell alright and these cells since they're fat cells they hold a tremendous amount of fat so they hold it triglycerides cholesterol all sorts of lipids just lipids in general and this entire the entirety of it this white is all lipid now what's this is a good cell right here in my analysis see this purple dot kind of on the exterior by its membrane see it's surrounded by the membrane which is in purple but this really dark spot that's its nucleus without a post tissue there's so much fat inside the cell that's store so much lipid that literally all the organelles including this nucleus are all pushed to the periphery of the cell so you can't see the other organelles because most of them are too small but they would all be pushed to the membrane the nucleus you can see here and again it's pushed to the periphery to the cell membrane because the lipid droplet inside is so massive all right now individually each cell here is called an adipocyte but this whole thing is adipose tissue all right so again these are really easy to recognize I like to put this on the test because it's one of my favorite tissues to study so make sure to watch out for these and pretty much this is just going to be anywhere where you have fat tissue all right this type of tissue is called loose connective tissue although I actually learned it as areolar which is another name it's areolar tissue you can use either one of these terms Ariel or tissue or loose connective tissue I think in class most people actually use loose connective tissue maybe it was easier to remember but in general areolar tissue or loose connective tissue looks like a spider web I include a little image down here from Return of the King Lord of the Rings this character gets tied up in a giant spider's web and that's kind of what areolar tissue looks like notice you have all this web like fibers and they go in all sorts of directions there's another image down here now areolar tissue is one of these tissues kind of like where we looked at goblet cells and cilia or these lacunae right so areolar tissue you have some things you need to know first of all these very thick pink fibers like right where my mouse has that pink fiber that's kind of going like this they're much thicker in appearance actually in this one but these thick pink fibers those are called collagen fibers so they are collagen your textbook calls them college enos fibers you can use whatever term you want either one it's correct I always call them collagen that's how I learned it also you see these much thinner purple fibers let's see if I can find a good one here's one right here they're kind of going up and down like this this thin purple fiber again there's some down here looks like here's a good one right there and my mouse is in the bottom right corner those are elastic fibers although the usual scientific term is elastin but you can use elastin or elastic fibers all right again the whole thing just looks like a spiderweb you also have cells in here here's a mast cell that's a type of immune cell we also have other white blood cells but in general all these cells collectively your book calls interstitial cells so there's actually a few things to know from this obviously that it's areolar tissue or loose connective tissue but also being able to recognize collagen fibers elastic fibers and then the interstitial cells which are pretty much is all these cells in the tissue all right and you're typically gonna find loose connective tissue under many kinds of epithelial tissue underneath it very similar to the picture we saw here okay let's go down and look at the last one dense regular connective tissue this is the last one we're gonna look at in this particular course dense regular connective tissue looks very similar to fibrocartilage okay now in fibrocartilage we do have striations and we also have them in dense regular connective tissue all of these striations go in the same general direction you can see here in this one on the bottom left they're kind of going like this in this one on the right they're going left to right or horizontally in this picture on the top they're going kind of like this but there's striations the you may see some cells here but these are not gone these are not chondrocytes in lacunae all right these are just simple fibroblasts alright notice that they don't usually have this white surrounding you'll typically just see them as purple blobs they won't be surrounded by this kind of white or lightish region around them so these are not lacunae these are just simple fibroblasts all right and because there's no lacunae that's how you recognize these as dense regular connective tissue all right now dense regular connective tissue one of the common places that you find this is in tendons and ligaments which we're gonna talk about briefly when we do muscle tissue after the first practical all right you typically are gonna find this tissue where things need to be very very strong alright so again that's all of the tissues that we're going to look at in this course until we get a muscle and nervous tissue later on but for now you need to know these eleven tissues again I'm gonna say this one more time when you put the names of these tissue on tissues on the exam these lists right here these are what you need to write okay even if it's a pain these four words written out dense regular connective tissue or in this case ciliated pseudostratified columnar epithelium you need to write all of those out okay another important thing to make sure that you do when you're studying these is don't memorize these tissues by their color because the color that you see in the slide depends on the scientist who stained it there there are different stains that you can use for the same tissue and so the colors may look very different an obvious example of this is usually seen with the cartilages here the cartilage matrix looks kind of pinkish but here it's very dark another example where it's typically observed is that actually fibrocartilage here they're both kind of pinkish but this one's much darker but I remember look when we looked at this in class we had one where the matrix was blue so don't memorize these based on the colors memorize these based on the features that each one of these has alright so this has been a lecture over histology the study of tissues hopefully this video helped I will see you in class