okay for histology today we're going to talk about epithelium and answer the what questions what is epithelium what are the different classifications functions and locations of epithelium and what are cilia and microvilli hello everyone my name is dr morton and i'm the noted anatomist so first thing is what is epithelium well epithelium is one of the four basic tissue types in the body which is along with connective tissue muscle and nervous tissue which are the other three and epithelium also known as epithelial tissue form glands and lines the outside and inside of the body so glands so any glandular tissue in the body like your liver and pancreas there's your liver if we take a little section all of those red things you see in there are epithelial cells what about the pancreas shing we take a picture of that all those are epithelial cell epithelium forms glands and also is lining it lines the inside of the body like the luminous tubular organs so there's our stomach we take in section we're going to blow up and take a little square all of those cells are epithelial cells that form the inside lining of the stomach and other tubular organs in the body and also lines the outside cavities of the body so if we like in the thoracic cavity if we take a look at this internal surface of um in blue that's a serous membrane that lines the inside body cavities of your thorax and abdomen pelvic cavities and also does a covering externally to the body like your skin so there's a skin and that yellow arrow showing that's the epidermis is the outside of your skin okay and outside of organs and so then orange that's the outside lining of your lung but also does your heart and other organs of the body so epithelium consists of epithelial cells anchored to a basement membrane so there are epithelial cells and there is a basement membrane right there and those epithelial cells are anchored much like legos thunk on that basement membrane and epithelial cells and epithelial tissue have apical and basal surfaces apical surface means to apical means towards the surface and basal means towards the base in other words the part that's anchored to the basement membrane epithelial tissue has no extracellular matrix so if you look in there there's really no space or very little space between these epithelial cells much like bricks that you see anchored together and as a result epithelial tissue is a vascular without a vessels and so to get vessels you're going to need something up to get blood to the epithelial tissue you're going to need loose connective tissue that are deep to the basement membrane so there is a loose connective tissue and within the loose connective tissue are capillaries and the capillaries then are what's providing nutrients and gas exchange with the epithelial tissue there is one that you can see in basically longitudinal section often what you're going to see is in cross-section like that one all right there's epithelium so basement membrane no extracellular matrix all right so classifications of epithelium now and so here are all the different types of epithelial tissue we're going to talk about now as we go through this to try to help make sense of the mumbo jumbo the way the histologists name epithelial tissues they say all right how many cell layers are there and what is the shape of the cells and are there any cell specializations if any and then we're going to add the word epithelium so we're going to add one two three four shin and that gives us the name of the epithelium so keep that in mind as we go through each one of them let's start with simple squamous epithelium so simple squamous epithelium gets its name because the word simple means one layer and one layer of cells anchored to that brown basement membrane squamous gets its name because it means flat or scale-like because the cells look like a frisbee and there's the word epithelium so let's add all that together we get simple squamous epithelium which is a bunch of one layer flat cells now simple same as some simple squamous epithelium has the following functions one is diffusion and diffusion means where you get gas or water that can diffuse through that plasma membrane and basement membrane from a from a concentration gradient filtration is when fluid and solutes filter through openings between adjacent epithelial cells like the holes in a colander and then lubrication is when you've got two membranes that secrete fluid that are right on top of each other and that secretive fluid and allow for this movement that you'll see in mesothelia lining of like serosal cavities like your heart and lungs that was our cat ramses now the locations of simple squamous epithelium there are a number of places one common place is the alveolus where there's a simple squamous cells for gas exchange with the air in the blood and then there's our glomerulus where in part of your kidney where you've got uh flat cells hold on i gotta get my cat because he's making too much so that that's the parietal layer of cells in the glomerulus and they're flat and then you also have these flat cells that line blood vessels those endothelial cells which most pathologists don't like to call endothelial cells simple squamous epithelium but they look like it all right so let's do an example here's a hematoxylin and eosin abbreviated h and e stain of the renal corpuscles basically taking a section of the kidney and that picture we saw previously in here we have it in a very zoomed up picture now there is a nucleus now the reason why i know that's a nucleus is it's dark and purple hematoxylin in eosin stains hematoxylin stains nucleic acids dark and purple so nuclei just go and they pop out so it's easy to see that purple dot now the problem is you can see the purple dot you just can't see the fence you can see the house but not the fence and what they mean by that is the nucleus like the house you can see but the fence the plasma membrane plasma membranes do not stain so now you superimpose your knowledge around that nucleus like that is it really that big i'm guessing but you know that all epithelial cells are anchored to a basement membrane so now we superimpose our basement membrane on top of that and deep to all basement membranes are loose connective tissue in pink because hematoxylin eosin eosin stains proteins pink and that's why that loose connective tissue which is basically collagenous protein is stained pink so every cell has a basal surface which is anchored to the basement membrane and the apical surface towards the surface okay all right there is simple squamous epithelium as description function and location in a nutshell now let's go to simple cuboidal epithelium simple cuboidal epithelium here gets its name because the word simple means one layer anchored to the basement membrane cuboidal because the cells look cube shape like a rubik's cube in a sheet that kind of looks like this the cube shaped and the the nuclei are oval shaped as opposed to flat like a pancake and squamous these are oval or round and epithelium because they're a bunch of epithelial cells so simple cuboidal epithelium right there its functions are absorption which means something that the cell is absorbing into it and secretion is something the cell is secreting out and so the locations of simple cuboidal epithelium are as follows the functions are i'm sorry locations are as follows nephron is one of them where you have these tubules where you have a lot of absorption of the filtrate that happens one big location another one is basically glands like the sweat gland so there you have a long duct which are secreting things into the duct and so a lot of glandular every time sweat glands liver pancreas all those you'll find cuboidal epithelium and so here's a kidney so we zoom in on that and there is a nucleus and so a nucleus we know that's a cell because there's a nucleus so we superimpose the fence the plasma membrane which there's always a basement membrane so that means that deep to the basement membranes loose connective tissue which means that's the basal surface and that's the apical surface which is close to the lumen of this tube this is a straw in cross section so their simple cuboidal epithelium in a nutshell now let's talk about simple columnar epithelium it gets its name because the word simple means one layer anchored to the brown basement membrane well the basement membrane in this picture is brown columnar because these are tall thin cells much like a skyscraper and so the nucleus is either thin and narrow or round and circular often you'll see it round and narrow and then it's epithelial tissue because you've got a bunch of cells together making epithelium now the functions are as follows absorption which something going into the cell secretion something coming out of the cell and another function is sometimes one of the cellular modifications is they have a thing called cilia these projection finger-like projections that stick up and move fluid across the apical surface of the tissue and so in this more three-dimensional view those are cilia that's a ciliated version on the right and there's no cilia of that tissue on the left now location gi tract from the stomach to the anus is a big part and then also in glands and airways and in the uterus and uterine tube so here's the gi tract so there is simple columnar cells with cilia and here's the base of a gland whereas often you see simple kilometer at the base of the gland simple cuboidal along the duct all right let's take a look at a h and e stain of one little section of the jejunum part of our small intestine there you can see a nucleus so we superimpose the cell membrane around the outside of that nucleus and so then you then have must have must be anchored to a basement membrane like that and so deep to all basement membranes is loose connective tissue which means that's the basal surface and then that's the apical surface and you're going to notice the brush border the microvilli i'll talk about brush border in a minute on the apical surface and that's where the food would be located and being absorbed into those simple columnar cells there is simple cuboidal epithelium in a nutshell okay so now let's talk about stratified squamous epithelium and so stratified squamous epithelium gets its name because the word stratified means more than one layer so there's more than one layer of cells and i mean only one layer cells is anchored to the basement membrane a bunch on top of it squamous because it gets its name not because the basal cells because those are cuboidal it's because of the apical cells or squamous so a stratified epithelium is often uh classified by the shape of the apical cells and then you've got a bunch of cells so it's epithelium that was rude of miyani in my sorry it's saturday morning i don't know what the deal is okay stratified squamous epithelium functions well they protect underlying tissue from abrasion and so how does that work well all these cells here their main purpose is to be sloughed off when that tissue comes up against something for example a good example analogy is like an eraser so when you rub an eraser you're abrasio that you're causing friction and you got these little pieces of rubber that come off the skins the same way as we get flakes of dust from your skin that come off all the time now locations are two pulled one in the epidermis and the other one's the esophagus and the vagina those are the main places and so for the skin and the this is showing the esophagus okay and so keratinized when you add keratin to this keratin is a very tough protein it's the same type of protein classification you get in your fingernails and in your hair and keratin in the epidermis helps to protect the water and you'll notice that there's no nuclei that's how you tell carotinized stratified squamous epithelium the apical cells have no nuclei whereas in the esophagus and vagina it's non-cratinized you don't have the keratin but you see nuclei and that's how you can tell the difference when you're looking under a microscope so let's look at stratified squamous keratinized epithelium in the epidermis so there is a whole bunch of layers of cells look at those layers of cells there's probably about 50 layers of cells there and so that means that all these cells the bottom layer is anchored to that basement membrane that we just drew on and if that's the basement membrane then deep to the basement membrane is loose connective tissue because that's how you get blood to supply the this stratified epithelium and the part of the bottom layer cells they call the basal cells and the top layer cells or the apical cells but let's take a little square of this basal cell and go bing and blow it up and you'll notice that those basal cells have nuclei now let's take a look at the apical cells and do a little section and blow that up you notice that those apical cells have no nuclei you notice how it's almost like scraping off that's like the eraser okay and that's the outside environment okay now that stratified squamous epithelium overview we move on to transitional or urinary epithelium so urinary transitional epithelium is here there's more than one layer of epithelial cells so it's a stratified epithelium we just don't call it that because the only place you find it is in the urinary system and those very apical layers are dome-shaped shaped just as it shows there and its function is it permits stretching and distension of the urinary system empty bladder full bladder empty bladder full bladder beginning of the movie into the movie and so the locations are basically urinary system the ureter the bladder and the proximal urethral distal urethra will be stratified squamous so here we have a section of the bladder okay and there is our basement membrane that we just drew on and so one of the things i'll mention now is that epithelial tissue remember how i said that it's like that there's no extra cellular matrix they're bricks they're right together where loose connective tissue there's space between those cells so epithelial tissue basically does not practice social distancing connective tissue does practice social distancing so there we've got multiple layer of these cells and those epithelial cells are close together now how do you know they're the cells well all those purple dots represent nuclei and those nuclei beside each other even though you don't see the plasma membrane barriers between each adjacent cell you superimpose that knowledge so deep to all basement membranes is loose connective tissue so there's the basal layer cells there's the apical layer and notice the apical era cells are dome-shaped and that's where the urine would be in this so there is urinary or transitional epithelium in a nutshell so let's talk about pseudostratified ciliated columnar epithelium whoa that's a mouthful pseudostratified ciliated columnar epithelium shown here gets its name because the word pseudo stratified huh what does that mean well there's a cell and there's a cell and there's a cell they kind of look like the two those some cells are on top of each other just like here here and here it looks like those cells are kind of crowding each other but what we notice is that it looks like more than one layer of cells but every cell is actually anchored to the basement membrane so histologist said we're going to call it falsely stratified because it looks stratified but it's not so that term pseudo like pseudoscience false science pseudostratified is falsely stratified all the cells are anchored to the basement membrane but they look like they're layered ciliated because there is this uh uh the cilia project from it and then columnar because the cells are tall and thin and epithelium because you got a bunch of different cells here okay and all those different cells make even though you see various cells like green and brown and blue and purple cells all those different cells you add a bunch of cells together what do you get a tissue those are epithelial cells and they make epithelium or epithelial tissue now the function is secretion mainly mucous and propulsion by cilia so there these goblet cells uh secrete mucus and then the cilia are going to then move the mucus on top so those are the two functions and i'll talk about both of those a little bit later now locations is mostly the respiratory system trachea and proximal bronchi so let's take a section of the trachea and we'll look at it now this is why i actually prefer respiratory epithelium but you see this really long name still in a lot of literature primarily because i think science people and doctors like to use really big words but respiratory epithelium is one that i like to use mostly so here's the section of the trachea and let's zoom in a little bit on it and so there's where the basement membrane would be how do i know that lots of purple dots above fewer purple dots below really dark purple above that line pink down below so h hematoxylin stains nucleic acid dark purple eosin stains proteins pink down below so there is our loose connective tissue below and so there's the basal layer and there's the apical layer of this respiratory epithelium and so it looks like there's multiple layers of cells so let's take a look at that cell and then that cell that cell that cell and that cell looks like they're all on top of each other but each cell is actually anchored to the basement membrane so it's not really stratified it's pseudostratified there's the cilia projecting looks like grass at the top and that's where the air would be in this trachea all right so there is pseudostratified ciliated columnar epithelium also known as respiratory epithelium in an overview of its description function and location now let's talk about cilia and microvilli for a second so cilia are located on the apical surface of anchored cells and they move it moves liquid over the surface of the cell so here is ciliated columnar cells and there's the cilia projecting from the top and there's a goblet cell and goblet cells make mucus and what does mucus do it goes blue and then goes over and then notice the cilia see how the cilia are moving the cilia are moving all of that mucus along the top well cilia are kind of like what you see at a concert for crowd surfing okay so here's a concert and you're like hey there's lots of people with arms sticking right up hey look there's lots of cells with cilia sticking right up hey look the person being transported on top by the crowd by their arms they're moving along hey look fluids being transported on top by the cells by cilia in a very similar way no i'm not saying people who go to concert and crowdsource are like snot but the analogy works so here we have a section of respiratory epithelium and they're ciliated columnar cells and look there's that cilia like grass projecting from the top and there's a goblet cell that makes mucus and you can tell it's a goblet cell there because it looks frothy in appearance all right now what about microvilli well michael varela are also located on the apical surface of anchored cells and by anchored cells i mean to the basement membrane and their purpose is to increase surface area for absorption all right so here is one epithelial cell but there's no microvilli so now let's look at the apical surface and then measure the surface area that's that could be responsible for absorption so let's take that line and blow it up and then just go shing like that that is the amount of surface area that that cell could absorb stuff now let's look at a cell with microvilli and now let's measure all of the the length of those microvilli for their surface area for absorption bring that up now let's stretch that out look at that the surface area for absorption is about 25 times the amount of area that is available for absorption that really sounded like an infomercial i'm sorry i didn't mean to do i got a little excited there so that surface area there's 25 times more for each cell and so we take a look at this from the jejunum look at every single cell as we go over this villus is what it's called notice those microvilli holy cow it totally increases surface area for absorption and so there you can see the cells microvilli and plus the microvilli kind of look like barb simpson's head don't they all right now there we have a nucleus okay you see that nucleus right there which then we superimpose our knowledge and there's a cell and so there is a drawn in cell beside it and there's the microvilli now we call it a brush border because those microvilli are so close together that it kind of looks fuzzy almost like a hairbrush and like the hairs from a hair brush and that's why they call it a brush border that's what increases surface area for absorption in this case the jejunum that's how you get your your amino acids and simple sugars and fats absorbed from well leave fats out of that for a second my apologies that's how you get like your nutrients like amino acids and simple sugars absorbed into the cells let's do a little practice shall we so here what i want you to do is take a look on the left hand side is a bunch of the tissues we just covered in order and the right hand side and different and mixed up are a bunch of different tissues i want you now to pause this video and to match them and when you're ready to go press play again i'm going to continue so it's there's simple squamous epithelium it is because it's one layer of fat cell flat flat cells that's bowman's capsule from the glomerulus and then symbol cuboidal epithelium that's one layer of cubed cells and they're cubed because even though you can't see the actual cell the nucleus is round and then here is simple columnar cells how can you tell well one layer of cells and the nuclei are tall and thin that's the jejunum and then there is pseudostratified ciliated columnar epithelium it looks stratified but it's not and one of the things is the cilia projecting at the top help me know that's respiratory epithelium there are stratified squamous keratinized epithelium because there's more than one layer of cells the top layer of cells are flat and there's no nuclei and then here is stratified stratified squamous non-cratinized epithelium because there's more than one layer and the top horizontal arrow is showing a nucleus which means you can see the nuclei so it's non-cratinized and so that my friends is epithelium in a nutshell [Music] down ah you