hi everyone for chapter 4 we will be discussing the next level in the hierarchy of structural organization the tissues level we already went through the first two levels at the chemical and cell levels in the last two chapters so now we will talk about how can those cells connect with each other and what different types of tissues arise from those cells now bear in mind that this is one of them I would say the longest chapter of the entire semester and usually for my two our 40 minute classes I actually need the entire time so for you know incline faced if this was a face-to-face lecture I usually need to cut into the lab time so but this is the only you know lecture or chapter that will need and require that much time with that much time just because it's a long chapter so bear with me I will separate the this chapter into parts of one hour so at one hour I'll give you a break and then it will go to part two alright so let's get started okay remember we mentioned that cells work together to form tissues and that the study of tissues is called histology there are four basic types of tissues we will talk about in this chapter first type is called epithelial tissue okay which ourselves that cover and protect exposed surfaces line internal passages or hallow spaces and some of them even release a specific types of secretions for example for lubrication purposes as we have mentioned with the serous membrane in the last and the very first chapter so I would say a key term for epithelial tissue is covering okay covers so any covering of any sort surfaces covering of external or internal areas that's a type of epithelial tissue most likely second type of tissue is called connective tissues okay so that's a second and call connective tissue and this is the most diverse group of tissues we have and hence is the longest section of the chapter which is another reason why this chapter is so long because we have to talk about every single one of those specific kind of tissue within the connective tissue category they serve usually as purpose of filling internal spaces kind of like I like to describe them as styrofoam nuggets in a shipment package if you've ever received online orders in your mail you see all those bubble wraps those little styrofoam nuggets you know those kind of like the package material that stabilizes your important product so in our body we have our important organs so these connective tissue is kind of like serving as those package material to stabilize our important organs and tissue other tissues okay so other than packaging and filling the internal spaces it serves to provide structural support and even other functions like storing energy so that's why this is the most diverse group of tissues is because some of them are structural some of them are packaged some of them are even just for distributing nutrients so we'll talk about all those different type of connective tissue alright and then the third type of tissue is called the muscle tissue which is very straightforward there are three different types of muscles in our body and of course it functions to help with movement and then the last type of tissue the simplest of the four is the nervous tissue and their main job is to carry electrical signals okay excuse me not crossing it out but circling it is to carry sensory and motor information in form of electrical signals even though in this chapter in terms of the types of cells they have is not very complex it is one of the most complex chapter when we do get to the nervous tissue and explaining how does an electrical signal go from one end of the neuron to the other end of the neuron there's a whole long process and pretty complicated that we will go over when we get to chapter 12 and also mention it in chapter 10 in talking about how nervous tissue activates muscle muscular tissue so be looking forward to those things so all four of these tissues will combine in different ways to make different organs and organ system okay so let's start by talking about the epithelial tissue the very first type of tissue we have in the body the epithelial tissue contains of course the epithelial layer which are cells that cover your external like your skin for example or internal surfaces like the interior wall of your airway your stomach your intestine etc now the epithelial layer may associate with glands that produces secretions that are either attached or derived from the epithelia itself so we'll talk about those accessory glands as well when we get to towards the end of the epithelial tissue part portion okay so the epithelial tissue has four main function one is one of course is to provide that physical protection that I said is important physical protection you know again especially against things like you know rubbing abrasions so this is you know for example in areas that is more consistent that is you know consistently prone or exposed to rubbing or things are passing by all the time all day long there will be several layers of these epithelial tissues as protection so they won't change or damage the connective tissue or the muscular tissue or other features that's underneath your epithelial tissue remember that the epithelial tissue is serves as a surface okay whether it aligns exterior or interior things if things are constantly rubbing against it you know cells will be torn off okay so that this is why we need to have that epithelial layer to protect those tissues underneath okay now they also protect against dehydration so that's what we have dehydration listed here you know this is why we have glands in the epithelial tissue that secrete mucus this is - you know in case that we have you know we're not walking around I like it like i usually say we're not walking around like a little slime man we are we try on our surface and the ability of our cells to have mucous membrane in some areas is what keeps us hydrated now for the skin we have special features that we'll talk about such as keratinization that prevents ourselves from drying out or it needs to dry out before it becomes keratinized for surfaces of our skin but if you think about interior surfaces like the lining of your esophagus lining of your airway trachea lining of your stomach all those are kind of mucus see slimy and that's all for the purpose of keeping your body you know those surfaces hydrated so that when things are constantly rubbing against it food is moving past by your esophagus they're not you know they're not they're not having a hard time passing by those tissues or squeezing those food down because it's too dry so that's why you need those mucous membranes there we'll talk about a mucus on your mucous membranes and mucus glands we'll talk about those in a bit now the epithelial tissues also protects us against chemicals or biological agents okay we'll talk about how our skin is the first line of defense against microorganism so pathogens that try to come into our body they need to get by our skin first unless they come through our mouth or our eyes or other openings of our body but other than that our skin is pro doing a lot for us against pathogens second they can help with controlling permeability of that particular organ for example when we talk about the urinary system there's a lot of different types of permeability within different areas of what's called the nephron in the kidney some areas are only permeable to water and some areas are only permeable to sodium chloride or salts and it is because of this differences in permeability that enables the kidney to filter our blood absorbing what's necessary and secreting what's unnecessary or even harmful or concentrate our urine to manage our body water content okay so either we're absorbing what's beneficial or we are releasing what's harmful to our body or we are concentrating our urine down so that we make sure we don't lose too much water if our body is in need of water at the moment okay all of these things we'll talk about in a and P 2 for the urinary system but the ability of the urinary system within the kidney that they can do that is because they have that selective selectively permeable membrane as designed by the epithelial tissues of the nephrons within the kidney so every organ we will be talking about we will mention what type of epithelia it has and why they have those epithelia a lot of times there's a function and the reason why that area of the body have this type of epithelia and we'll talk about the different types of epithelia in a moment so in addition our body can control permeability of epithelial tissues with hormones okay so these are some stimuli some soon a lot of times those are in forms of hormones if we go back to the kidney as our example there are specific hormones called ADH an antidiuretic hormone if you have heard of that hormone before it is what tells your nephrons to either conserve more water or excrete more water in urine so again going back to what I talked about previously in Chapter one that our body needs hormones as means of communication to achieve homeostasis so we'll go talk about all that those things in detail in the second semester and like I said a little bit about calcium regulate calcium ion regulation in the blood with our skeletal system in this chat in this semester but most of the homeostasis stuff will come in the second semester now some epithelial tissue will provide sensations okay the ability ability for us to feel different degrees of temperature for example pressure pain etc we'll talk about some of this in the integumentary system when we get to chapter 5 lastly some epithelial tissue will produce unique secretions like I was talking about with their gland cells to protect surfaces like for example cerebrospinal fluid we'll talk about when we get to the brain chapter that protects the brain and the spinal cord against you know mechanical shock excetera you know just because you're hit in the head with a ball it doesn't give you a coma every time you're hit in the head with a ball because there's that cerebrospinal fluid in addition to your skull protecting your brain there will be mucus along large intestine for example that's another type of unique secretion is because as your feces is moving along your intestine it's also getting dehydrated as well that's the main job of your large intestine is to reabsorb as much water as possible from the food that you ingest so as your feces is drying up it'll get tougher and tougher to move along those the intestinal lining and that's why the large intestine compared to the small intestine have a lot of mucous membrane okay well excuse me mucus glands we'll talk about that in anp2 again and kind of see it through this chapter as well some epithelial tissue can regulate temperature like sweating on our skin that's part of cool our body down as we've mentioned in Chapter one or as means of communication through interstitial fluid or blood so those secretion can do a multiple number of things for us in the body okay so even though there can be different types of epithelial tissues covering different organs or parts of the body they do share some general characteristics and these are going to what we're going to be talking about here for sure first they have what's called polarity polarity meaning what's that meaning that what's on top or the exposed surface of the cell is structurally different from the bottom or attached surface of the cell the superior portion and the inferior portion of the epithelial cells is not necessarily symmetrical again a lot of times they are not symmetrical because one is exposed to the outside surface or your hollow space within your stomach or hollow space within your intestines while the bottom part of the cell is attached to the connective tissue that's underneath or the muscular layer tissue that's underneath okay so that's why there is always polarity with epithelial cells the exposed surface is referred to as the apical surface while the attached surface is referred to as the basal surface so the easy way to remember phase overs is apical phase Oh sounds like base okay so that must be the bottom okay of the cell and then apical starts with an A okay it a comes before B so a is on top first before you get to the basal surface and a lot of time that's a good Anatomy word to remember because you will we will refer to apical surface of something or apical region of an organ which means the top portion of that organ as I have talked about in the cell chapter the apical surface of these cells often have either micro villi or cilia okay remember the difference between these two microvilli is for absorption or secretion purposes they are smaller and looks like that tinier and probably more dense a lot of times cilia is for movement of fluid around the cells so either you're moving mucus along or you're moving an egg cell along etc you're moving something along alright so the basal surface of the cell is attached to what's called the basement membrane okay so this is the basement membrane right here this layer this gray area right there so this is a thin non-cellular layer and it is you know it is serving as means of connection to the next layer below and resisting over stretching of the cell because these epithelial cells a lot of times it's serving as a purpose of protection or maintaining fluid within a hollow organ so you can't have these cells falling apart whenever they want then that's why this basement membrane is kind of serving like a little layer of glue then make sure all the cells stays together okay epithelial cells usually don't have blood vessel or what we call a vascular okay a vascular means a without vascular vessels okay so that's why they lack blood vessels hence in order for epithelial cells to receive nutrients for oxygen you know nutrients or oxygen and it was what I mean everything has to happen through the diffusion process okay there's no duct or only scuse me there's no blood vessels that deliver certain things to epithelial cells specifically a lot of times things need to travel into the plasma membrane via diffusion or specific channel proteins and carrier proteins we talked about in the last chapter and lastly most epithelial cells have the capacity to regenerate which means you know the ability the ability to sell divide okay we mentioned that one of its main function for epithelial cell is to protect against abrasion now that doesn't mean they're like cells of Steel like metal sheets they are prone to damage okay they do tear and fall off but they have the capacity to regenerate and so areas like the skin or the esophagus where it is constantly exposed to things rubbing against the surface will have many layers of cells to replenish and that's what you will see when we talk about the integumentary system in the next chapter for chapter 5 in addition to those general characteristics individual epithelial cells may have additional features that enable them to move fluids over surfaces through epithelium and produce secretion so these are the specializations I've already mentioned them before so again as I've mentioned micro villi is what's up usually abundant in areas where there's a lot of absorption or secretions involved and those curvatures you see these micro villi here these curvatures right here can actually provide 20 times more surface area to the cell compared to if it was completely flat okay so curvature versus flat makes a big difference now imagine if you took a piece of flat sheet of paper and you crumble it into a ball this is what I usually will demonstrate in class if this was a face-to-face class lecture well on that surface area you can feel free to do it on your only if you want but you can imagine you know crumble a piece of paper now all that surface area of that entire sheet of paper is now hidden in that ball of paper okay so it not only conserved space but it also is able to provide all that surface area to allow for exchange of important materials like nutrients and gases like oxygen and carbon dioxide so that piece of paper is just like microvilli so in a sense you have tons of little crumpled pieces of paper all over that top of the cell to provide the cell with extra surface area now the other special feature we talked about being on the apical side of the cell is cilia okay and when epithelium is has cilia on it sometimes we call it a ciliated type of epithelium and one cell can actually have about 250 cilia that beats in one direction okay note that one direction let me erase that curvature so I don't end up covering up stuff okay all right so note that something is important about something important for cilia beating is that it must be coordinated and also always in one direction okay imagine a little swish wipe okay those swishy wipe in a bus is not serving the purpose of moving things in one direction so if you're trying to move things in one direction if the silly is just swishing however they want whenever they want asynchronously sometimes then your your whatever you're trying to push is not gonna get anywhere the cilia has to beat in that one direction so they will be able to sweep something in that one direction so here's a good video you know a short clip that will show you how cilia works and why pushing or sort of moving in that one direction isn't as important in moving for example a piece of this gunk right here you'll see this piece of gunk right here move from the bottom of here of the cell to the top of that organ or tissue with these ciliated epithelium so here's that gunk you see how I move from that location slowly slowly moving upwards towards this area you can ends up being here so that's how silly is able to work if it's swish swash whoa you know back and forth back and forth you know that piece of gunk is gonna stay there but because they're all moving sweeping in that one direction it's gonna move that piece of gunk in you know in the direction we want it to be and if this was the airway for instance then it will be towards our oral cavity so we can spit that piece of mucus out and that piece of mucus can contain pathogens or dust particles pollen particles etc so that's why we you know you have to blow our nose we have to hack off some mucus from our throat etc in you know different times of the day is because to get rid of those things from our important Airways now interestingly the cilia that lines our Airways can be damaged by nicotine and carbon monoxide okay in cigarette smoke so this is why they say you know people that chronically smoke now I'm not saying that you smoke one one or two cigarettes and then there goes your cilia you know this is a gradual process so if someone has been smoking for years a lot of their cilia will become damaged and what they've seen on epithelial cells between comparing epithelial cells of a nonsmoker compared to a smoker they see a lot less number of psyllium that's why a lot of times you will see chronic smokers needing to cough a lot and they have a much harder time to cough up their mucus and it's because you know technically speaking the cilia supposed to do some of the work for you in moving mucus away from your Airways but if you don't have them then you have to rely on that burst of air coming out from your lungs to move the cilia along but how do these epithelial cells connect with each other so that for example your red blood cells won't try to seep through between two adjacent epithelial cells that line your blood vessels for example or if a scarier situation in a in a scarier situation is how can epithelial cells of the stomach lining ensure that the stomach acid which has pH of one we have learned in the chemistry chapter make sure that those stomach acid won't leak through between the cells of your stomach so we don't burn other tissue layers of the stomach or even other organs nearby okay there's no other organ in our body that can withstand such a low pH of liquid so it is very critical that we contain liquid like that so there are specialized inter cellular connections cause cell junctions that exists between epithelial cells that are adjacent to each other there are two main types to mention one is called gap junctions and which contains channels that allow small molecules and ions to pass between cells so it's kind of named after the name itself speaks for what it does they contain gaps so gaps like this okay gaps like this that can allow stuff to go through between the cells from one cell to another now for example we just gone through the cilia movement that have to be coordinated so they can't be waving around whenever they want and in that coordinated manner how are they able to coordinate is they are able to pass ions from one cell to the next in signaling the next cell when to beat in that particular manner same with heart muscle cells okay they know when to beat in a coordinated manner due to existence of these gap junctions that allow little messages in form of ions to pass from one cardiac muscle cell to another so that's why gap junctions are very critical for function purposes as well of those cells now these channels that is these holes you're seeing here are created with a protein called connexin okay connexin sounds like connecting okay so if you see something sounds like connecting connexin that means it joins two cells together by forming some sort of silly with a central opening kind of like a long donut okay that allows things to move through just like this okay within the between two cells for example this is epithelial cell and this is another epithelial cells and there's that gap junctions that allow things to move through a second type of cell Junction is called tight junctions which binds to cells with interlocking membrane proteins kind of like staples okay I won't require you to know the name of these proteins okay there's a lot of information and I know it will be information overload already so I try to stick with what what's important for that chapter so this type of tight Junction is supported with an addition in addition what's called adhesion belts that further reinforced the connection between the two cells this is how we can prevent fluids from leaking out of tissues and organs using these tight seals between epithelial cells of you look you know zoom in to this area right here between two cells here's those staples like tight junctions I was talking about and that adhesion belt that further supports the connection between the two cells so other than the basement membrane here serving as glue to keep the cells together you have these staples all along between two cells and make sure there's you know sticking pretty close together so you don't have things leaking out or things falling apart tissues falling apart when you don't want them to so on the basal side of the epithelial cells we have already mentioned the existence of a basement remembering like I was saying okay so we have the basement membrane itself is what keeps the cells together and make sure that the epithelial layer is firmly attached to the rest of the body so epithelial cells don't have blood vessels so they need the support of the other layer of cells and tissues like connective tissue muscular tissues to keep them alive okay especially connective issue because a lot of the blood vessels resides within the connective tissue layer and once an epithelial cell detached from other cells they will die just like how dead skin cells are able to fall off and that's why it doesn't hurt when we you know sort of lose some of our skin cells by rubbing on the table right now in front of you it's because they are technically dead cells and we'll talk about that in the next chapter five okay so again if we want to review tight gap Junction is what allows ions to go through allows chemicals to go through okay tight Junction is what keeps fluids from leaking out of tissues and organs using those staples and adhesion belt that keep things fluids from you know we keep fluids contained okay and then you have that attachment to the basement membrane now the basement membrane is made up of two layers the basal lamina and the reticular lamina so here's the basal lamina being this layer right here and the reticular lamina being the bottom inferior layer or deep layer of the basement membrane the basal lamina is just as layer that's close to the epithelial cell the functions as a filter of some sort to prevent large molecules from escaping into next layer of tissues like proteins or red blood cells whatever it is that tries to go through it will prevent it from going through reticular lamina on the other layer contains fibers that give the membrane strength and some flexibility okay so it's for strength and flexibility okay strength and flexibility and basil lemon and lamina is the main filter that prevents big molecules important molecules for example amino acids glucose all that good stuff from trying to get across and stay contained so how our apathy leo cell classified by name this is the one type of tissue where we do have systematic way to classify them by the cell shapes okay and the number of cell layers it has so it is pretty you know straightforward in remembering how to name epithelial cells specifically so for cell shapes there are three types in case you have your squamous cells okay then now all of these here different views of the three types of cell shape we're talking about a sectional view where we're cutting the across epithelial cells or the organ to see and look at how they look like okay so for squamous there they tend to appear more thin and flat and they look a little bit like scales so sometimes they look like this sometimes they you would see something like this okay so when they're in many layers sometimes it would look like tons of scales are attached and stacked on top of each other like that cuboidal is a second type of cell shape and you know it kind of shaped like the way it sounds like little cubes or boxes like this okay and then you have columnar which shapes again like the way it sounds as well like columns where you have tall slender rectangles as a cell okay so columnar cells cuboidal cells and squamous cells just and you can see you know how you name that piece of tissue by how they shape like now for number of cell layers is either you have one layer or many layers very simple there are two ways to name them epithelial tissue that is made up of only one cell layer is cost simple epithelium where though while those that is made up of two or more layer is cost stratified epithelium so because simple epithelium is made up of only one cell layer they're usually very thin and usually function two-line internal compartments or passageways where a lot of things need to go through and diffuse through okay for example those serious membrane we learned about in Chapter one and also those that line the respiratory passageway excuse me your respiratory air sacs like your alveoli they are usually very thin because they need that efficient gas exchange between your lungs and the blood vessels so that's why those would usually have simple epithelium okay and because serious membrane like pleura pericardium and peritoneum all of those are for reducing friction so you can have a really thick piece of rubber between tissues that defeats the purpose of lubrication so that's why those tend to be very thin in a simple one cell layer stratified epithelium on the other hand can be made up of several cell layers so they're usually functioning as a mechanical or chemical protection of some sort for the cells for example the surface of our skin we will learn in the next chapter that the most outer surface of our skin the layer called epidermis is actually made up of tens of layers of cells so that you know every time we accidentally scratch ourselves on our skin or rub against something we're not cutting down to the connect necessarily down to the connective tissue layer we'll just probably have removes our epidermal tissues so stratified epithelium is for that mechanical mechanical and chemical protection okay simple epithelium for lubrication okay or for areas where there's there needs to be fast exchange between two areas of the organ so to complete the nomenclature of epithelial tissue we just need to combine cell shape and cell layer together so let's go over the different types of epithelial tissue we can have in the body we will start with simple squamous epithelium simple means one layer okay and squamous we just said means they are flat and scale like shaped epithelium so out of all different types of epithelium this is the most delicate one and be kept because they have only one layer and since they are thin it is very efficient like I was talking about for allowing diffusion or absorption of materials where things need to get across a membrane very quickly okay now this is not talking about intestines we're talking about for example surfaces of your lungs alveoli where we're constantly doing gas exchange of oxygen and carbon dioxide and their exchange all the time at a rapid rate our cells are always in need of oxygen and they're always producing the byproduct of carbon dioxide that we need to get rid of so that's why those areas will have this simple squamous epithelium or you know like I was talking about this type of epithelial tissue can be used as a surface to reduce friction for example like those of serious membranes okay linings okay serious membranes that lines your body cavities such as your lungs or your heart so okay lungs or your heart or your abdominal cavity so blood vessels okay are also lined with simple squamous epithelium for easy diffusion of nutrients and gases okay so three areas okay one is where we need quick exchange of diffusion okay by diffusion second is where we need to reduce friction like the body cavities that lines that those aligns our body cavities those that line your lungs your heart and then thirdly those that you know need quick exchanging your blood vessels that's another area where we have simple squamous epithelium okay a general term for epithelial tissues that line body body cavities is called mesothelium remember those pleura pericardium peritoneum we talked about in the chapter one there is generally referred as the mesothelium while those that line the inner surface of blood vessels or the heart are called endothelium remember what I talked about in terms of prefixes and to remember so endo okay means in there so if you see endo as a prefix it means it's lining or something that's on the inside or something that lines the inner layer of the organ or tissue so for the lab on classification of tissues you will have to be able to identify different types and kinds of tissue by histology pictures and what organs they are from so for example the type of tissue for all of these three pictures here is epithelial tissue okay so this here refers to as the type of tissue so make sure you pay attention on lecture exam or lab practical purposes whether I'm asking for the type of tissue or specific kind of tissue okay so type of tissue is epithelial tissue and the specific kind of tissue we're talking about here is simple squamous epithelium okay so all of these three are different different parts of the body so here in this case we have alveoli of the lungs that I keep mentioning and this is the stat simple squamous layer between those alveoli if you look at models of the alveoli you'll see that your lungs are filled with these little balloon like structures and they're kind of like this okay they tend to look like your little grapes okay you have these great like structures within the lungs okay so these are your alveoli and when you take a cross-section slice it through that's what we see is those curvatures of where every one of those little curvatures or spheres you're seeing on those balloons so every one of those simple squamous epithelium is for diffusion of gases between the capillaries of the surrounding your lungs and your lungs okay it's for oxygen exchange okay oxygen and carbon dioxide movement so this second picture here is talking is looking at an example of the mesothelium specifically the peritoneum that those that line your abdominal cavity and you can see this layer right here and it kind of even extends out and kind of goes off okay so that is a mesothelium layer and this is just part of that in internal organ in your abdomen okay and that layer here is the peritoneum or what we call this serious membrane okay then make sure our abdominal organs are not rubbing against each other and there's lubrication and then lastly you have your blood vessel and this right here is that simple squamous epithelium I was talking on me see how there's a cell here a cell there and a cell there they're usually you can tell that there are cells by that purple dot because that's the nucleus I of the epithelial tissues okay so that's why you see these dots here because there's those multiple nuclei nuclei of the different types of cells that's formed that layer okay okay so make sure you know specific type of tissue epithelial tissue specific kind of tissue is simple squamous epithelium this is from lungs alveoli of the lungs this is from peritoneum of your abdominal cavity this is a blood vessel in your within your circulatory system okay be able to identify these by pictures in case I do end up asking them on exams or lab practical will you will have another set of pictures in lab exercise okay so the next type or excuse me next kind of specifics epithelial tissue we will classify is stratified squamous epithelium stratified here means that there are two or more epithelial layers of epithelial cells that make up this epithelium and in areas where it is more prone to a lot of mechanical stress there will be multiple layers of cells so here are some examples where there will be stratified squamous epithelium for example surfaces of your skin like I've talked about lining of your mouth esophagus anus those are areas of the body where things are moving past those tissues consistently so if you this is the particular example on the surface of the tongue and you will see your squamous stratified squamous epithelium the up here there will be more obvious pictures in a bit that I will show you on examples of these cells this is not the book the one from the book is actually not that great but I will show you other pictures that give you a better idea of what stratified squamous epithelium looks like alright so those stratified squamous epithelium that lines the exterior sir is usually has a protein called keratin that's what I was talking about in terms of keratinization of your skin cells so that protein keratin is what provide water resistance so that our skin does not need to be slimy and lying with mucus like a frog or a slug this is what I was talking about how we don't need to be walking around like a slime man because our surfaces of our skin is made up of skin cells or epithelial cells that have went through the process of keratinization I'll talk about that process in detail in chapter 5 integumentary system now those that line our interior surfaces like the oral cavity thro esophagus anus and vagina are non-keratinized meaning that they do not have that that ability to resist sort of not not be mucusy okay they have they don't they have to be hydrated all the time so this is why those particular surfaces need to be continuously have that secretion of mucus to keep them moist and not dry out okay so it keeps them from drying out okay if they do dry out they will deteriorate so that's why though these areas will be need the purpose cells that we'll talk about what those are in a bit because they are non-keratinized okay so these are the more specific pictures that you can see the stratified squamous epithelium so for example these two pictures are all both of the esophagus this is the esophagus as well it's just that this is more of a zoom out view this is more of a zoom in view so zoom out feel farther away and you can see the esophagus as a bigger tube if you take a cross-section across your esophagus this is that opening of the esophagus right here okay so this is the whole thing as the esophagus right here and this is the opening where food will move through and he's right here is that stratified squamous epithelium I was talking about you see how there are many many layers of flat like scale like tissues and cells that are stacked on top of each other one after another so either in this view or this view you have tons of layers of cells that you're seeing to show you what stratified squamous epithelium is like okay and this is in the case of the vagina and again you will see that same stratified squamous epithelium those dots represent the nuclei of the epithelial cells and you see many of these epithelial cells line up against each other okay you don't have to know you don't have to identify blood vessels or lamina propria okay just know that this is the stratified squamous epithelium if it's a picture like this it will be the esophagus if as curvatures big curvatures like that that will be your vagina okay alright so moving on to the next specific kind of epithelial tissue the simple cuboidal epithelium which are one layer of box shaped cells simple one layer cuboidal box shape stuff okay so again since they are only one layer thick they can only provide limited amount of protection and but they're better than simple squamous at least because they're a little thicker and but they tend to be around areas where secretion and absorption is taking place slowly now this is not where we need fast gas exchange so we don't need that squamous epithelium but this is where we need time okay we need time to absorb a lot of things like water ions nutrients etc so like the kidney tubules call the nephrons I think I'm gonna write that word here nephron so kidney tubules are called nephrons we'll have the simple cuboidal epithelium so this is how a kidney looks like and within there they're a gazillion of these nephrons within it and if we take a cross-section of that particular kidney to be oh you will see that they are made up of that simple layer of simple squamous a simple cuboidal epithelium or the thyroid gland also has simple cuboidal epithelium I'll show you that in a bit and in the later it's in another slide here is a good picture of histology picture cuz you know your book always shows you these beautiful to picture-perfect microscopic views of tissues but a lot of times a week ago a lot of these histology pictures they're not as perfect and you can't tell what's what and that's what's hard about the tissue lab is because there are so many tissues you have to look at identify and and at least you know for online purposes it's easier because I show you where things are but you know in person what's hard about the tissue chapter is that sometimes you have to look all over the place for the tissue that you're looking for so in this case this is still showing the kidney but it has this huge structure that is not a nephron this is actually called the glomerulus that you will learn about in the next chapter and around the glomerulus is not simple cuboidal epithelium it's actually simple squamous epithelium that surrounds that glomerulus which is equivalent to this structure right here okay that structure right there is equivalent to this so this is not the area where we have simple squamous epithelium these are the areas where we have simple cuboidal epithelium so these are those kidney tubules I was talking about all of these okay you see how it has the square like shape cells all around the epithelium of those tubules whereas those that surround the glomerulus they are a lot flatter okay so you see this flat cell right there for example okay so make sure you don't miss identify what part of the histology picture you're looking at okay so stratified cuboidal epithelium is when you have multiple layers of those box-like cells okay so stratified many layers cuboidal box shape these are usually rare in the body just like but just like simple cuboidal cells they also function as secretion and absorption along with some protection okay so secretion and some protection for the stratified cuboidal epithelium there's only a few places where we have this type of epithelium like ducts of sweat glands and memory glands and in this particular example these are sweat gland ducts okay so here's a sweat gland underneath our skin and they're talking about taking a cross-section right there and that's what we will see within the microscope slide of a sweat gland of that particular section now these are other representation of other glands such as your memory glands okay so memory glands this is a zoomed out view of memory glands this is the stratified cuboidal epithelium that makes up the memory gland and inside here is the milk if we zoom in to the memory gland we'll see that it is indeed because here you're like oh I don't know that's really two layers or one layer but if you zoom in you will see that there are two layers of kube looking cells all along the memory Glan okay now there are two in-between special kinds of epithelial tissues that we will mention the first is called transitional epithelium the words speaks for itself in what it does it transitions between squamous and cuboidal shapes okay so between these two shape it changes depending on the state of the organ this allows for the flexibility in an organ that can go through repeated cycles of stretching without damaging the tissues again there's not a lot of places in the body that has this type of epithelium transitional epithelium is usually in the urinary bladder renal pelvis and ureters everything that has to do with the urinary system kind of has this this transitional epithelium so this is for example the bladder this right here is actually you have your kidney kidney and then there's these tubes it goes down to the bladder okay so this here is the bladder this here is the ureter and something right here it kind of shapes like a funnel within the kidney to collect urine is the renal pelvis again you'll know these parts in the next chapter when we talk I may excuse me next semester when we talk about a urinary system but this is got a good glimpse of it so when the bladder is empty its epithelial cells will appear more plumpie like cuboidal cells right here so you see this plumpie i like to call it pump because it looks plumpie on the head on the microscope again you'll see a lot of these cube-like structures of cells and resembles more of cuboidal epithelial cells but when the bladder is full its epithelial cells especially the more top layers of that of that epithelium will appear more flat like squamous cells in case it's like squamous cells to accomodate for the pressure the amount of urine exerting on the bladder because your your bladder is now filled with fluid all over the place so it's pushing against those epithelium lining of the bladder and that's why they will appear more flat and stretch versus plumpie like in an empty bladder again this is another representation that is not as picture perfect like those in your book from the internet where you have your plumpie cells okay serving as you or empty bladder because there's no fluid that will be pushing against this epithelial tissue and with a distended or full bladder then you have these squamous like T cells especially that top layer right there because the urine fluid is pushing pressure against and smooshing your epithelial layer in a sense okay alright so then moving on to simple columnar epithelium so this is when you have a single layer of tall rectangular cells like this just one layer of them these are usually in location where there are lots of secretions and absorption wherever those happen and again this is usually a slow progress okay and it needs to be slow to maximize the amount of secretion and absorption involved like your digestive tract and their columnar shape you know as means of protecting against chemical stress so this is why the cells itself is so thick it's because there there's probably some chemical stress involved within that organ and that's why you can't have simple squamous epithelium in these particular tissues so these are used the stratified excuse me the simple columnar epithelium is usually found in linings of the stomach your small in large intestines or even the gallbladder and other stuff but mainly I want you to remember stomach and intestine okay because those are areas where we have chemical stress for example your stomach acid coming from your stomach cells and then you have feces within the large intestine that can Harbor pathogens and you know bacteria and stuff like that so that's why those areas will have a thicker type of epithelial cells like Cola simple columnar now this is an example of the small intestine cells specifically where we have microvilli remember microvilli are in areas where we have lots of absorption going on so you would see that in this drawing right here but on the microscope you actually have a hard time locating the microvilli as you can see it's just a layer of really mushy stuff all on top you can't tell individual microvilli with the power of our light microscope but you can see cilia so that's how we can tell the difference between ciliated epithelium versus just epithelium that has micro villi micro villi you can't tell there's little lines on there but cilia you can okay micro villas are just too small and too close and densely packed together for us to see individual little finger-like structures so this is an example from your stomach okay example histology pictures and that's why you see all these columnar cells along that forms that lining of the stomach that goes around okay all right so here is it the other in-between special kind of epithelium I was talking about earlier so the other one was transitional epithelium within the bladder this one is called pseudo stratified columnar epithelium this is due to the fact that its appearance looks as if they have multiple layers of cells but they are in fact a single layer of cells that every cell have some sign of kind of contact with the basement membrane even though it doesn't really look like that here it doesn't appear that way but it is in reality in contact with the basement membrane so if I were to give a you know sort of pictorial drawing of this so maybe something looks like dads themselves it looks like themselves it looks like that it looks like that so every one of those cells are in contact with that basement membrane but they're just not all columnar looking some looks squamous I'm looking scoubidou okay so that's what we caught it pseudo stratified columnar epithelium now these tend to vary in shapes like I was saying you know most of them appear you know but most of them do you appear like tall rectangular cells and that's what we call them columnar epithelium in addition the epithelium oftentimes have cilia at the apical side of the cells because they're located in areas where some fluid or mucus movement is involved so examples in the body where we have this type of pseudo stratified columnar epithelium are those that line your nasal cavity trachea your bronchi which is these regions right here and parts of the male reproductive system tract as well so this is the trachea these are your bronchi and those alveoli was talking about earlier are at the ends of those little branches so that's what I was saying even with the same or within the same or again you can have different types of epithelial tissues for different purposes so here is what I was talking about you can see those cilia lining you see those little hair looking things those are the cilia lining on top of pseudostratified columnar epithelium so that's another good way to remember or identify cells as pseudo stratified columnar epithelium is if you can see little hairs on it because other all the other cell types don't have cilia on it not the ones we show you anyway there can be exceptions in other organs and areas of the body but the ones we show you the tissues that you have to know this is the only type that has cilia on it alright so I was talking about where they line at and this is another good example of what the trachea epithelial cells look like now you have a better view of these so-called columnar cells but you also have smooshy cells like this and then there's these interesting clear looking cells like these these are called goblet cells so make sure you remember what goblet cells are goblet cells are what secretes mucus along this pseudo far pseudostratified call Lemar epithelium our airway needs to be lubricated in order to do its function you know your cilia needs to sweep something some fluid along some mucus along and cave it's dry then we can't get rid of dust particles or pollen particles as easily so that's why your trachea has a lot of these goblet cells right here for secretion of mucus and then the other area where you have pseudostratified columnar epithelium without the goblet cells is for example seminal vesicle which is a gland an accessory gland within the male reproductive system for secretion of the fluid that surrounds your sperm cells ok the semen ok the semen the majority of the volume of semen is made from seminal vesicles within the male reproductive system but you can see how it looks like simple columnar but you see these tiny little cells underneath here these here as well so that's why is pseudo stratified columnar epithelium and lastly for the epithelial cells we have glandular epithelium which are those that mix up your secretory glands there are two main types of glands endocrine glands and exocrine glands endocrine glands are those that produce hormones and release them into the bloodstream directly there are no duck okay that's the fee keyword therefore endocrine glands is that they don't have ducts that connect the gland to the circulatory system they just release the hormone and the hormone diffused through into the circulatory system some examples are your thyroid gland thymus okay and pituitary gland and this is a picture for example the thyroid gland and here's those simple cuboidal epithelium I was talking about earlier when I was talking about simple cuboidal epithelium thymus is another gland within the sits on top of your heart and at the apical side of your heart and they are 40 Sal mature pituitary gland will talk about immensely in the next semester for endocrine system the other type of glands like I was saying it's caught exocrine glands which are those that release secretions into surf onto surfaces or into the blood your circulatory system with a duct of some sort so that's the main difference between endocrine and exocrine gland endocrine glands are ductless exocrine glands have ducts in them okay so for example sweat glands in our skin have ducts that arrives at the external surfaces of the skin like the picture we've seen when I was talking about um stratified cuboidal epithelium so here's your section of our skin here's some hair that sticks out of your skins and a lot of time you see this duct and then some curl curvature of coils of tubes so this can be a sweat gland and then you see that there is a duct here that releases sweat onto the surface of your integumentary system skin cells okay so there's a duct that leads from the gland onto the surface okay tears through tear ducts okay also is another good example of exocrine glands exocrine glands so they're called lacrimal excuse me they're called lacrimal ducts we'll talk about these in the last chapter of this semester in chapter 17 milk releases milk milk also releases from memory glands through lactiferous okay ducts through you know before excreting around the nipple area so all of these exocrine glands have some kind of ducts and their name with different names of course but they have ducts that lead to their destination okay so the difference between endocrine and exocrine cells is most obvious in the pancreas the pancreas is a special organ where it has both and Dornan and exocrine functions and lokrum function is performed by pancreatic islets for production of insulin and glucagon for example to regulate blood glucose and they have no ducts connected to them the hormones just gets released directly into the bloodstream on the other hand there's another type of cells in the pancreas caught acinar cells that perform exocrine function where they produce digestive enzymes release into the intestine to help with the digestive process so these digestive enzymes have to go through a duct called the pancreatic duct and there's a duct that leads to the secretion to their destination in the small intestine so if I were to draw this out you know usually the pancreas is kind of shaped like this like little fish and then you see that there's a central duct okay and all of these are divided into lobes lobules what we call so there are specific areas within the pancreas where is for endocrine function which is insulin and glucagon and these hormones just travels out into the bloodstream and usually there's a blood vessel nearby where they can travel into the bloodstream and into the circulatory system and go to their destinations for regulating blood glucose now there are areas within the pancreas that is caught acinar cells and those release for example i'm just gonna call it digestive enzymes for now but there's proteases that is for bread digesting proteins nucleases for digesting nucleic acid but just know them as digestive enzymes for now you don't need to know the specifics and they will get released into this pancreatic duct right there this whole thing is the pancreatic duct and then it goes into your small intestines okay small intestines and release into the small intestine for digest digestion of the food that you're eating through your digestive tract okay so this is for endocrine function and asuna cell as in our cells is for exocrine function one has ducts okay and one doesn't involve ducts okay all right I think that's all for epithelial cells and now is a good time for a break because one hour is up so I'll give you a break here for part 1 of chapter four don't be surprised if I have to divide this chapter into three parts because of its length okay so I will come back in part two to talk about connective tissue