so today we are going to talk about the basic concepts related with the epithelium epi helium or epithelial tissue or epithelium right now human body consists of primarily four basic tissues what are those four basic tissue just plays what are those four basic tissue which made our body yes of course number one there is epithelia number two number two is connective tissue number three is muscles very good and number four is neuronal tissue right nervous tissue on neuronal tissue tissue so body basically consists of four tissues epithelial tissue connective tissue muscles which include cardiac muscle smooth muscles and skeletal muscles and neuronal tissue now today lecture is about the epithelium so who will define epithelium for me any idea Appaji liam is made of made of epithelium is made of tightly packed tightly opposed cells number one thing about epithelium is that it consists of tightly opposed cells cells which are very much the membranes are very near to each other and there is no vascular tissue in between this epithelium is a vascular there is no vascular tissue in between what are the petheram epithelium is collections of cells which are opposed together with very little material in between right and apathy neural tissue restaurant basement membrane which separates the epithelial tissue from other tissues for example underlying connective tissue is there right so what is epithelium epithelium is basically made of cells which are very much opposed with each other without much tissue in between without much material in between and without any vascular tissue in between right and now these epithelial cells are arrayed basically in two fashion that epithelial cells are arranged as long sheets of cells cells are arranged in sheets so we can say membranous epithelium what does that membranous epithelium or in some parts of the body epithelial tissue makes the Landler tissue epithelial tissue makes yes glandular glands right black blood sugar glands right in glands would happen that epithelial cells look these are different epithelial cells again they are very much attached with each other and they're in this in between this cell and the other cell there is no vascular tissue there's no other tissue is that right there again tightly packed cells but they can act as glands that produce different kind of secretions so we can say either epithelial cells are as shields right they are as membranes or shields or their folded epithelial cells are arranged in glandular pattern now when epithelium is present as membranes these membranes are number one covering the external surface of the body epithelial tissue or epithelia cover external surface of body of course that is epidermis secondly epithelial tissue also line all the internal closed cavities number two it also lines internal closed yes cavities for example it is lining the cardiac cavity pericardial cavity pericardial cavity plural cavity an abdominal cavity is also called peritoneal cavity very tonyia cavity right around the heart there is pericardial cavity around the lungs there is pleural cavity and in the abdomen there is peritoneal cavity so these cavities are alkaline by epithelial membranes or epithelial cells or epithelial tissue and of course your cardiovascular system in which blood is circulating cardiovascular system all arteries and veins and capillaries and cardiac chambers all the cardiovascular system is also closed cavity so cardiovascular system is also lined by epithelium very good so cardiovascular system is also lined by epithelial tissue this is that right then we come to third component is that epithelium also lines all the body tubes epithelium also lines the body tubes body tubes which communicate to the exterior for example tubes of respiratory system tubes of gastrointestinal system tubes of your genital system so it means all the body tubes which are communicating to the external right exterior they are also lined by different type of epithelium for example yes respiratory system respiratory system gastro intestinal system and uro genital system so let me repeat it what is epithelium epithelia or epithelium is special specialized a special type of tissue in which cells are very much in proximity with each other there is no much material in between the cells right and epithelial tissue rest on the basement membrane which separate the epithelial tissue from the underlying connective tissue epithelial tissue can be arranged as or can be arraigned as glens is the right when it is arranged as membranes right then it is lining the body surface external surface as well as it is lining the internal cavities of the body as well as it lines the tubes in the body which are communicating with that exterior this is that right so this is about the basic now what are the functions of epithelial tissue what are the basic functions of epithelial tissue yes who'll tell me what are the basic function of course number one is protection skin is protective so when we talk about function of epithelial tissue number one there is yes protective function for example epithelium on the skin which is epidermis would protect you from abrasion right or injury second is secretions epithelial cells also produce secretions for example in the gastrointestinal system let's suppose that here are epithelial cells now these epithelial cells right which are lining the gastrointestinal tube these epithelial cells they can produce different types of secretions then they also play a role in absorption that when you are taking the food when proteins are broken down into amino acid or carbohydrates are broken down into glucose this is taken from lumen of the gastrointestinal system through that within yourself to the connective tissue and circulatory system and going to the circulatory system so what is this function number one it can secrete different type of secretions number two it can absorb also material so it's functions are protective it's functions are secretions it's functions are yes what is this absorption right epithelial cells can absorb the substances they can secrete Sansa's they act as protective layer on the external surface of the body or even within the body organs then I am more function of epithelial tissue yes any idea there's one more function of epithelial tissue very easy function look Parlin they talk to each other they communicate to each other that is not the function of that is the feature of epithelial tissue I'm talking about one special function that epithelial tissue can produce very good that is sensory function some cells in epithelial tissue some cells in some specialized epithelia can detect the stimuli for example the olfactory epithelium in the nose and that can sense the smell order or there is epithelium related with the tongue which is making taste buds and that can work as taste detection system and the same in the internal ear there are special sensory epithelium in the internal ear which help you - yes here and they also help you to keep your balance so what we can say that some specialized epithelial lining play an important role in yes detecting the different type of stimuli right all factory stimulus is sensed by olfactory epithelium in the same bed for the taste stimulus is detected by gaspari epithelium on the tongue and then there are some sensory epithelium in the internal ear which can detect the yes movement to keep the balance as well as they can detect the sound this is the right so basic function that protection the secretion absorption and detection of sensation right now now we come to the different types of epitheliums epithelial tissue can be classified I will go in detail of membranous epithelium now right I was going to detail off membranous epithelia and when we talk about membranous epithelia how are they classified membranous okay now the membranous and blur blur we classify them together rather right so just we talked about we are classifying epithelia now classify epithelium basically it is on two basic criteria number one number one what is the shape of cells shape of epithelial cells right shape of cells for example some cells in epithelial lining they are flat cells with the central nucleus this is the right now this cell is a flat cell and in this cell if you look yes that the central nucleus but it is like a fried egg right height of the cell is very little and width of the cell is very wide is the right these type of cells are called yes these type of cells are on sequoias cells so those epithelia which are having flat cells we call them sequoias epithelium then there are other epithelial cells and though the pith in your cells have equal yes equal height and width and depth right now such cells which have these features right these are these has that like a cube because these cells are like a cube so such epithelial tissue which is having cells like cubes they are called cuboidal epithelium cuboidal epithelium then they're in some other epithelia cells are very tall cell they're very tall and in these epithelia nucleuses near the basal area this is the apex of the cells this is the base of the cell right and nucleus is pushed near the base and when any epithelial tissue has cells which are linked tall their height of the cell is too much but width of the cell is less right we say these cells are like a column and because these cells are like columns we call them columnar cells and such a within ear card yes please which epithelia yes phenomena epithelium so there is supremacy with helium when they are flat cells there's cuboidal epithelium and there is cells with equal almost equal height and width and then there are a Virginia which we call it columnar epithelia in which fundamentally cells height is too much and which is less right so this is columnar epithelia am i clear now so this is one way to talk about epithelium according to the cell and then another way to talk about epithelia is according to that how many layers of cells are there according to the layers of cells layers of epithelial cells right now when we talk about layers of epithelial cell there may be single layer ah epithelial tissue may have multiple layers of cells multiple layers whenever this single layer such epithelium is called simple epithelium and if there are multiple layers we call this is having stratification so when the multiple layers recall is stratified epithelium stratified epithelium now simple epithelium if it has only yes now you have to tell me it has only one layer with flat cells what is this kind of epithelium yes simple sequoia Mesopotamia what is that simple sequoias epithelium but if there is single layer of cells but they are cuboidal what is this simple yes cuboidal epithelium and if cells are columnar but there is only one layer of cells what we call it what kind of epithelium is this yes simple columnar epithelium important point here is and simple epithelium all the cells which are participating in epithelial lining all of them are attached with what basement membrane all the cells are resting on the basement membrane right and simple epithelium cells have single layer and all the cells are attacked with the basement or resting on the basement membrane is that right but when we talk about stratified epithelium right what really happens in stratified epithelium there there multiple layers right if there are multiple layers then all cells are not resting on basement membrane for example there is a basement membrane here right and this is multi-layer epithelium and let's pause these aren't cells over here right and sell them a slightly vary in shape from layer to layer now this is not simple epithelium it is multi-layered epithelium in which only the basal cell are resting on the basement membrane and other upper layer cells are not resting on the basement membrane so such epithelium is called stratified epithelium now stratified epithelium is named according to the cells which are present at the top now the cells which are present from the top layer they are sacrum of self so this should be called what kind of epithelium stratified squamous epithelium what is it this is stratified rate t5 yes sequoias epithelium right now look at another type of epithelium that here the cells are again multi-layered right cells are multi layered or epithelial tissue is multi-layered and again we have to look what is the features of cells at the top now in the top layer if you look at these cells are these famous cells or cuboidal or columnar yes these are cooked cuboidal cells and because all cells are not resting on the basement membrane and it is multi-layered so it is stratified epithelium and as the top layers cuboidal but we will call this type of epithelium yes stratified very good stratified yes cuboidal epithelium because you have to look at the top cuboidal epithelium is there right then you may come across another type of epithelium again it is multi-layered so we can say that this is also stratified but here the top cells are not so famous and top cells are not cuboidal rather they are yes columnar so how you will name this epithelium very good this is called stratified columnar epithelium this is stratified columnar epithelium then there is another type of epithelium which is specially founded urogenital system and injury genital system that epithelium you know for example the epithelium which is lining the urinary bladder right it is four or five layers of cells but it has some special feature that when Jordan Airy bladder is full of urine and urinary bladder stretch out the layers become more or less layers become less and when you pass the urine out and urinary bladder become smaller then the same number of cells are accommodating into smaller area so number of cells in a layer will be in a tissue the layer of cells will become more this is the right so such type of epithelium in which when it is splashed when it is stretched there are less layers and when it is this is when it is stretched and when it is not stretch right this is making more layer right this type of epithelium that when it is stretched right as urinary bladder is full of urine and it is spread it is less layer and when urinary bladder is empty and whole epithelial cells layers become more as it gets smaller such apathy liam is called transitional epithelium transitional epithelium right as the transitional epithelium is only found in euro urinary system right and the ureter and calluses will drain the kidney minor calyce's which are draining the kidney ureter urinary bladder and urethra now what we have seen that they are simple epithelium and there are stratified epithelia now we'll go into a little more detail of every epithelium simple squamous epithelium where it is found screamer's simple squamous epithelium is lined lining the cardiovascular system right for example it is the your blood vessel system cardiovascular system the epithelium which lines here the simple thermos epithelium is called endothelium endothelium right in the same way simple epithelium also lines the respiratory system in the respiratory system when air reaches to gas exchange area there is simple epithelium lining here in the oil villi this help in gas exchange that oxygen will go from the alveolar area from air in airbags to the blood and carbon dioxide will come from blood to the airbags alveoli so this is also simple squamous epithelium and endothelial cells and also simple squamous epithelium in the same way in the kidneys also in the kidney there are special tubes there are tubes which are called nephrons in one kidney you have 1.2 million nephrons and in the nephron specially in this area which are filtration unit the add cells and these are also called yes simple thermos epithelium right simple squamous epithelium is for filtration purpose here for gas exchanges here and for metabolite exchanging there for example glucose or amino acid from the blood go to the tissues and maybe metabolic wastes come back to the blood right so therefore usually exchange epithelium simple cuboidal epithelium simple cuboidal epithelium is normally present in which tissue yes simple cuboidal epithelium is normally present number one in the nephron in some areas of the nephron this is nephron nephrons are special tubes in the kidney which make the urine right so nephrons have in the filtration unit simple squamous epithelium but here they have cuboidal cells so nephrons may have simple cuboidal cells then in the same way in the glandular ducts many glands the ducts are lined by simple cuboidal epithelium and females surface of the ovaries is also lined by simple cuboidal epithelium then we come to simple columnar epithelium classically this epithelium is present in gastrointestinal system right simple columnar is president yes here gastro intestinal lining stomach small intestine large intestine and simple columnar is also present what is this tissue gallbladder so simple columnar is also present in the gall bladder after discussing this simple epithelium right i want to talk about some very special type of epithelium look here there is a basement membrane here right some cells are tall other cell that not as fall now this is an epithelium in which every cell is just reaching up to the basement membrane but because cell they're different heights right because cells are different height some cells nuclear with cells which are top nuclear have gone at upper level and cells which are basal area the nuclear at lower level so when you make a section under microscope due to the presence of nuclei at different level it looks as if this is stratified epithelium but actually it is not stratified because every cell is resting on that what is this this one membrane right so apparently it looks stratified epithelium but the car why it looks stratified epithelium because some cells are tall and some are not tall and nuclear presented variable height this is that right so it it is not truly stratified so what we call it what we call this type of epithelium yes which looks like which looks like stratified but it is not stratified we call it pseudo stratified epithelium what is this pseudo pseudo mean false it is stratified but false stratified not a - stratified pseudo certainty fight epithelium write pseudo stratified epithelium is found in prey Kea right and respiratory conducting pathway in respiratory system at the end that exchange area there is simple squamous but an upper part this is true dose pseudostratified epithelium which is having usually Celia also which is having cena also and they have some cells which release mucus mucus secreting cells right these are the special features of pseudo stratified epithelium president airways and respiratory system then pseudostratified epithelium is also present the epididymis epididymis and the males right epididymis do you have any question up to this okay we come back now to this stratified squamous epithelium listen stratified squamous epithelium has two types of two variants this is post basement membrane this is stratified squamous but some of the stratified squamous even though flat top cells are flat even though top top cells are flat but the uppermost layer cells you know these are flat but the most layer cells do not have nuclei these cells are very flat and they do not have nuclei they are just full of keratin they're full of keratin so this type of stratified squamous epithelium which has at the top cells without nuclei and full of keratin protein this type of stratified squamous epithelium is called keratinized stratified squamous epithelium what you will call it keratinized keratinized stratified squamous epithelium now classically this keratinized stratified squamous epithelium is present on your skin right this characterization help you to resist the injury or abrasions or mechanical pressure on the skin right so there is stratified squamous epithelium which is keratinized we also call it stratified squamous epithelium which is characterized and dry usually the skin is dry until you don't make it wet right and we also call it stratified squamous epithelium which is called knee fide so cornified or keratinized there is one in the same world right cornified cor and IFI Edie but look if you compare these two epithelia both of them are stratified squamous epithelia this is cornified oh this is keratinized but that is not characterized because here the top cells that having nuclei and they are not having the flat cells without nuclei with keratin so top cells are even though flat but they are having nuclei so we call it what stratified squamous epithelium non-keratinized or stratified squamous epithelium non cornified this is cretinous that is non-keratinized this type of epithelium is found where in the body this is found in your oral cavity and this is found in the vagina stratified squamous epithelium which is non-keratinized right and then an esophagus esophagus right so oral cavity esophagus and vagina has stratified squamous epithelium non cornified skin has stratified squamous epithelium cornified and then we come to stratified cuboidal epithelium this is presently ducts of some gland some ducts or some glands that is having stratified cuboidal epithelium and stratified columnar epithelium is also present in large ducts of the gland right and in the end what is their transitional epithelium right which is multi-layered epithelium but when it is stretched layers become relatively less when it is not stretch layers of the cells become relatively more this kind of epithelium is urine proof it does not allow the urine to escape from your nervous system and to reabsorb in the body and this is called transitional epithelium which is lining the calluses ureter and urinary bladder with derasa any question here there is no questions now we come to the real business that is about the specialization of epithelial cells look as we look at these epithelial cells okay specific and just look now as you know one side of the cells epithelial cells one side of the cell is resting on the basement membrane other side of the cell is yes free side of the self right so this side of the cell this side of the cell this is called basal domain basal domain of the epithelial cells right and this side of the cell which is at the top of the cell this is called apical side of the cell or apical surface of the cell or apical domain of the cell right this is epical domain of the cells this is the adult domain of the cell and this side of the cell epithelial cell which is adjacent to the next epithelial cell this is called yes lateral domain of epithelial cell or we call it natural surface of a particular cell so classically epithelial cells of is apical domain which is the free side and they are having lateral domains where epithelial cells are in contact with each other and the basal domain where epithelial cells here are in touch with the basement membrane any question up to this now we will talk about that different areas of these epithelial cells different domains are structurally and functionally and even biochemically specialized for example apical domain may have different functions and whether domain may have different functions right so I will talk now about the epithelial cells different domains with special specialized specialized features right because different surfaces of the epithelial cell have different type of features so we call that epithelial cells on all sides are not the same if I'm a pitching yourself from one epithelial cell the features here are different epical features are different if you are standing with me lateral features are different and down when I touch the floor that is my basal feature may be different because different surfaces of different specialization so we can say that as far as structure function and biochemical characteristics of epithelial cell is concerned they have different polar I mean different polarities because there's some other Seldon body which are not a path in yourself all sides of the membrane may have same features this is the right now we're going to detail off that what are the different features of different domains of epithelial cell and why we need such kind of domains let me make let's suppose here is the kidney