the tissue level of organization chapter 4 okay so if you have noticed we've been going up the hierarchy of life we started in chapter 2 with the atom and the molecule then in chapter 3 we went into the organelle and the cell and when we group cells together we make tissues which is what this chapter is about and then we'll go on from there to talk about individual organs and organ systems that make up the organism so tissues are defined as collections of specialized cells and their products that will perform very specific functions or jobs tissues that group together will form organs like the heart or liver or lungs histology is the study of tissues so there are four main types of tissues in the human body and we can fit just about everything into one of these four they are epithelial tissue connective tissue muscle tissue and finally nervous tissue we are going to focus mainly on the first two in this chapter we will make a reference to muscle and then later we'll go much more in depth in muscle when we get into the muscle chapter and we will get in detail with nervous tissue as well a little further on in the course so epithelial tissue just in general we're going to go into it in great detail after we give a little overview this is what we're gonna find covering exposed body surfaces as well as internal passageways so epithelial tissue lines or covers the human body and it can also form Glen's connective tissue is going to fill spaces inside your body it supports other tissues transport Minh transports materials and also stores energy and mostly in the form of fat muscle tissue is specialized to contract and does include three main types of muscle skeletal heart or cardiac and smooth muscle which is what we find lining hollow organs nervous tissue is going to carry electrical signals from one part of the body to another so again we'll revisit those a little bit at the end of the chapter but in great detail when we get into their individual chapters so this chart is a nice overview of the four tissue types this would be a good screenshot if you want to refer to it later so again looking at our hierarchy of life we have the individual cell which secretes extracellular material so that would be the material outside of the cell and fluid this material in fluid is what helps the cells stick to each other in combination to form tissues tissues can be divided up into four categories epithelial which we talked about is going to cover and line body surfaces connective which is found filling internal spaces giving support and storing energy mainly in the form of fat muscle tissue for contraction and nervous tissue to carry information and send signals if we combine all four of those tissues we create organs which interact with accessories or other organs to form organ systems so let's focus in on the first type epithelial tissue so epithelial tissue is the one we talked about that lines and covers all body surfaces so the one that you can see really easily would be your skin the part of your skin that you can touch that's considered a type of epithelial tissue and then if you think of specific organs inside the body like the lining of the intestines or the lining of the stomach or esophagus those would all be lined with epithelia as well so it's going to also include epithelial tissue will also include glands and depending on where we are in the body those glands are going to change for example if we're talking about the epithelia in the skin then the glands we would think of maybe would be oil glands or sweat glands if we're thinking of the epithelia that lines the intestines then those glands might be mucous glands okay so epithelia again layers of cells that cover internal or external surfaces they are also going to help make glands which are structures that produce fluids again that's going to vary depending on what gland we're talking about so if we think about the fact that epithelial lines and covers body surfaces one of the first functions of epithelial we might think of would be protection especially when we're talking about the skin that top layer of skin is definitely going to physically protect us from our environment it also can control permeability now this can be internal and external but it's going to help keep what's in in and what's out out and have more control over what passes back and forth it can also provide sensation so again if we go back to the skin we can certainly feel through the top layers of our and produce specialized secretions we talked about how that could be sweat or mucus again depending on where the epithelia is so we said that epithelia was going to line and cover surfaces and that tissues are made up of collections of cells but those cells have to be able to stick to each other so we're going to look at how these cells stick together to form sheets like they do in epithelia and also some other main characteristics that we're going to see in epithelia that helps us to identify it apart from other tissue types so epithelia is going to exhibit polarity by having an apical and basal surface and what that means in English is a top and a bottom essentially and we'll also see an uneven distribution of organelles so let's take a look at that in an image to help us better understand what the heck that means so this is a representative of a clump of epithelia and really it's just two cells that are stuck together in the epithelial sheet and what you can see here is that there's definitely what looks like a top and a bottom now of course that's going to be you might look at that differently what's top and bottom if we're talking about internally but the apical surface is the surface that we see up here if this were for example in the intestines then the apical surface would face the hollow inside of the intestine if this were from the skin which it isn't the apical surface would be what you touch if you're touching your own skin so apical surface here and then talk about that a little bit more in a few minutes and then down at the bottom we have the basal surface or basement which kind of makes sense right so the basement of a house is underneath at the bottom so here's the basal surface also we said that epithelia in polarity has in addition an uneven distribution of organelles do you notice how we can see that almost all the mitochondria in this picture almost all the mitochondria are down in the bottom of the cell they're not spread evenly throughout the cell they're found mostly at the bottom we've also got a lot of open cytoplasm up here at the top so the organelles are not equally distributed they're kind of packed to one area in the cell so that's something that we often see in epithelial tissue so in addition we're gonna see cellularity which means cell junctions so in epithelial tissue it's made up of a bunch of cells all connected to each other they're not separate individual cells they're all connected to each other and well we will show how they do that and some upcoming slides the epithelia also attaches to a basement membrane and the basement membrane we actually saw this is it down here a basement membrane this is what epithelia sticks to and epithelia can regenerate it is continuously replaced so epithelia can also become specialized and is able to move fluid over itself so when we see epithelia with cilia for example we know that that cilia are for movement they move fluids across the cell so we would expect when we caecilia to think of movement right away and epithelia can also move fluids through itself which is called a permeability it can produce secretions we talked about how those secretions will differ depending on where the epithelia is found and repeating here polarity so we talked about the apical surface we looked at it again this is where the cell is exposed to an external or internal environment we talked about at the top of the skin would be the apical or if we were discussing the lining of the intestine the apical surface would be facing the hollow inside of the intestine we talked about how cilia can move fluid across the cells and micro villi we talked about those in chapter 3 their job is to increase surface area for absorption so we're going to see micro villi in places where we're absorbing nutrients perhaps like in the small intestine and we talked about the basal surface which was the the bottom or where the epithelia sticks to the basement membrane but there's also a basal lateral surface so this would be the bottom side where the cells connect their neighbors so this here is the basal surface and then if we include the side that's bays OH lateral that's where these cells would connect their neighbors and here is some micro villi up here so this again would these are short little projections that don't move and they're responsible for absorption so the integrity of epithelia is maintained by some connections between cells which we call inter cellular connections the epithelia is also attached to its basement membrane which we looked at the previous image and the epithelia is able to maintain and repair itself now this is not true for all tissues necessarily or certainly not as easy for every tissue type and epithelia is pretty great at repairing and maintaining itself so how do those cells actually stick to one another to make sheets like we see in skin they do it by inter cellular connections and these connections can either be for support or they can be for communication and we'll see the difference as we go through the types they are created by cell adhesion molecules or cams which are a type of protein that connect the cells at their membranes proteoglycan acts as an intercellular cement so this is kind of like a glue that holds the cells together sticky substance so the inter cellular connections there are three main ones we'll talk about and I'll add a fourth on probably gap junctions we'll start with those so gap junctions are openings between neighboring cells that will allow for rapid communication these gap junctions are created by transmembrane proteins so these are proteins that interlock to neighboring cells and allow these proteins allow for a little portal where molecules and ions can pass back and forth so this allows the cells to communicate with one another so this is what it would look like up close so on the left here we have one cell membrane and then this is a neighboring cell membrane and in between you can see these little openings little hallways that lead from one so over to the neighboring cell so again this allows the cells to communicate or talk back and forth and also share ions and molecules so that again is a gap Junction next on the list is the tight junctions and tight junctions are between two plasma membranes as well and we'll see in the tight Junction what's called an adhesion belt an adhesion belt is a protein belt that attaches to what's called a terminal web and it'll certainly be easier for you to understand if I show you a picture of that so hold that thought for one second these tight junctions are going to help really pull tightly two cells together and that's going to prevent the passage of water and solutes solutes between cells this will keep enzymes acids and wastes in the lumen of the digestive tract okay so that's just an example but what that means is if you think about your stomach I'm how your stomach actually has in it a very strong acid called hydrochloric acid and hydrochloric acid is going to give your stomach a pH of about 1.5 to 2 which is highly highly acidic so that could burn through the your tissues so these tight junctions are so snug that the acid that is managed in the hollow inside of the stomach which is called the lumen is unable to seep in between the cells and get into deeper tissues where it could actually destroy those tissues okay so in this picture reviewing here are some gap junctions right here these guys allow for communication between neighboring cells and then here are tight junctions so tight junctions and we're gonna look at them up close this would be a tight Junction right here and underneath it is the adhesion belt which is a web of proteins that attach to the terminal web which is this again more protein so adhesion belt connected to terminal web and this interlocks and links up all these proteins to keep the cell tightly together above that or the cells tightly together above that is the tight Junction so let's look at that up close so here's the tight Junction so it's fused it's formed by the fusion of two plasma membranes so here's one on the left and one on the right and to me it almost looks like they've been bolted together nice and tightly and then below we have the adhesion belt and this belt adhesion belt is tied to the terminal web which again is a network of proteins and this just gives further reinforcement okay so next we have desmosomes cams and proteoglycans link opposing plasma membranes there are two kinds of desmosomes spot and hemi desmosomes spot desmosomes ty skin skin cell or ty cells together like in the skin cells as an example and this is why when you get a sunburn and you get blistered your skin peels off in flakes or sheets because those individual cells are all connected by these desmosomes so they come off as a group instead of individuals these desmosomes are so nice and tight that it also allows for tissues to bend and twist without tearing Hemme desmosomes that was my that was really the fourth one I wanted to add to the three that I initially gave you gap junctions tight junctions and desmosomes but we can technically stick it under the desmosomes category hemi desmosomes attached cells to the basement membrane so I like to think of those has more of a root system so here is the spot desmosomes so the first type of the two types and it looks a bit like to me that the two cells were zipped up like maybe this is a little bit similar to a zipper so on the Left we have a plasma membrane and on the right we have a plasma membrane and these cams are interlocked tying the two cells together and this would be at the bottom or the basal surface of the cell these are the Hemi desmosomes that anchor or route the cell down into the basement membrane so that's what's going to keep the epithelia down and not slipping away from the underlying tissue so the basement membrane is made up of two parts the basal lamina which is the topmost part that's closest to the epithelium and the reticular lamina which is the deeper portion of the basement membrane that gives it strength so if we go back we can take a look at that so here's this whole thing is the basement membrane and at the top basal lamina and at the bottom reticular lamina epithelial cells again are great at maintenance and repair they are replaced by a continual division of stem cells these stem cells are located deep near the basement membrane now to shift a little bit we can classify epithelia based on its shape so when we say classify we mean named the epithelia and the naming of epithelia is a two-step process we're gonna name it based on the cell shapes and we're going to name it based on how many layers we find in that particular epithelia so let's start with shapes so the shapes are here's our three choices we have squamous or squamous these are thin flat and flaky these cells are typically irregular so one is going to look very different from another but they're they're a bit like some people describe them as like a fried egg nice and thin where the yolk will be where the nucleus is the yolk is a little swollen where the nucleus is cuboidal is square or box shape like a cube and columnar are tall slender rectangles like columns we also have the layering there's only two to remember simple which is one layer of cells that's easy enough and stratified which would be two or more layers of cells so this would be when the cells are stacked on top of one another so let's look at some examples of this so first we've got simple squamous or squamous and what we want to do first or what I always tell myself is find the basement membrane which is going to be right here so when we find the basement membrane that's where the epithelia begins so anything on top of that is considered epithelial tissue now first we can say is it simple or is it stratified one layer two layers three or twenty so it's clearly one layer thick so this is a simple epithelia and the next thing we want to do is determine shape of the cells well that definitely doesn't look like a column or rectangle definitely doesn't look like a cube or box so it must be squamous and it is so we would name this simple squamous epithelium now looking over on the right again locate the basement membrane which is here anything above it is considered epithelial tissue okay so is it simple or stratified well there's definitely more than one layer there so it has to be stratified so stratified we got that and then the next thing we're gonna do is determine shape well that seems a little scary because there's a lot of shapes there so what do you do when you have stratified epithelia well the rule is we name the tissue by the apical surface so we're only gonna look at the top surface to determine what type of epithelia we have so the top surface shows that that's not a cube and it is in a column it's a pretty thin so that must be squamous or squamous so we would call this stratified squamous epithelium so it doesn't matter that there are some cubes down here it doesn't matter if we even see some that are shaped a bit like columns we only for the apical layer so why would we have areas of the body that have one cell layer thick simple or multiple layers thick stratified so it's really a simple common-sense answer anywhere on our bodies that could come into contact with something abrasive or close to or any part of our body that comes in contact or close to the outside world needs to be stratified so if it's on the outside or close to the outside it's almost always going to be stratified so some examples skin it's very likely you could bump scratch nick or burn your skin so it needs to be thick to withstand all of those possibilities if our skin was only one cell layer thick or simple we could bump into a pillow and bleed to death so clearly that's not going to work for our survival but it isn't just the outside what about the lining of the nasal cavity can you reach it yeah you could so that needs to be stratified what about the ear canal or the surface of the tone stratified same thing with the urethra that would also need to be stratified it's close to the outside so anything that opens up or communicates with the outside world or is on the outside is going to be stratified anything deep inside the body and well protected can be simple so the lining of the stomach or the lining of the alveolar sacs in the lungs very deep very well protected definitely can be simple another reason we might want to have simple epithelia is because of absorption or diffusion so if you want to absorb nutrients like in the small intestine you don't want to have to absorb nutrients across 50 layers of cells that would be extremely difficult cult so by having simple epithelia we can absorb very quickly and get those nutrients on in same thing in the alveolar sacs of the lungs which are simple epithelia we want to be able to get oxygen and co2 across that thin layer as quickly as possible so simple is very helpful in that situation so looking at some more examples so here we're gonna look for the basement membrane what's above it one layer definitely simple looking at the shape clearly box or cube shaped so this would be simple cuboidal epithelium here basement membrane two layers so we know this is stratified and then when we look at the shape we're gonna look at the apical surface because we've got more than one layer those are definitely cubes so stratified cuboidal epithelium next we have columnar so if we find the basement membrane and look above it definitely simple definitely column shaped so this would be simple columnar epithelium basement membrane looking above we can see multiple layers so that's stratified remember we always go to the apical surface to determine this shape those are definitely columns stratified columnar epithelium okay so as we move on to the next reviewing squamous or squamous epithelia simple squamous is good for absorption and diffusion stratified squamous will protect against mechanical stresses so anything that's close to the outside or on the outside will be stratified okay so here are some actual body real body examples not just drawings of the different types so this is an example of simple squamous epithelium you can see the irregular flakey thin shape and in the cross-section we can see that it is only one layer thick here's the actual light microscope picture and because this is simple we know it's going to be deep inside the body and well protected and it is this is actually taken from the lining of the peritoneal cavity in the abdomen so here is another image if we start at the basement membrane we can see that that is clearly stratified and we look at the top surface to determine what the shape is and it is definitely squamous or squamous so we would call that stratified squamous epithelium because it is so thick we would expect to find this somewhere close to the outside of the body and if you look it is in fact taken from the surface of the tongue so that makes sense cuboidal simple cuboidal epithelium is for secretion and absorption same rule as the simple squamous we can find it in glands and portions of the kidney stratified cuboidal is more rare but we do see it in the ducts of sweat glands and also mammary glands so here's a real-life image of simple cuboidal again you can see it's only one cell layer thick and the cells are cube or box shaped so simple cuboidal because it is simple we would expect to find it deep inside the body and do we find it in the kidney here is a stratified cuboidal epithelium so we find the basement membrane here's the hollow inside known as the lumen of the gland and we can see multiple layers so that's easy to tell it's stratified and then we locate the apical surface remember apical means that it faces an internal or external environment if it's on the outside it would be the top layer of skin if it's the inside it faces the lumen so here's the lumen and these are cube shape they're a little squished but they're cube shaped so this is stratified cuboidal epithelium and this is from a sweat gland which is in the skin so we could bump or scratch that so it makes sense that it needs to have more than one layer now this one's kind of a wild card we have two of those this one doesn't really fit into any other category as far as shape this one's just special so kind of considerate its own little thing transitional epithelium so transitional epithelium is going to tolerate stretching without tearing and it looks different as it stretches the cells will flatten out when we stretch it and a really great place to find this is in the bladder and if you think about it that makes a whole lot of sense because the bladder has to stretch a lot multiple times a day over your lifetime so this is an empty bladder and the lining of the bladder is transitional epithelium which is this and you can see that it's nice and tall very very stacked up this is a full bladder and when the bladder fills it stretches so you can see that the transitional epithelium has kind of thinned out because it's being stretched so again transitional epithelium can stretch without tearing and it's it's own little category all right so our last group are the columnar and the columnar epithelia can be of course simple or stratified like we talked about but then we've got a weird one in there called pseudo stratified so we'll come back to that one let's go first with the two obvious ones so simple columnar is when we have one cell layer thick and simple columnar is going to be found in lining the stomach small intestine and large intestine and it's really great for absorption and secretion stratified columnar epithelia means multiple layers of columns and it is relatively rare and you'll find it in the pharynx anus and urethra so let's take a look at what those look like so here's simple columnar we find the basement membrane and look above it you can see it's only one cell layer thick so that would be simple and the shape is clearly column so simple columnar epithelia because it is simple we know it's going to be found deep inside the body where it can't get bumped nicked or scratched and this is taken from the lining of the small intestine another little hint it might might have been in the intestine is the micro villi micro villi are for absorption and that the intestines is where we absorb 90% of our nutrients okay so this is our stratified columnar so let's take a look we'll find the basement membrane right there and we can see there are multiple layers so that's definitely stratified and then we look at Shay so we're always gonna look at the apical surface which is clearly columnar so this would be stratified columnar epithelia and this one is taken from the salivary gland duct which is close to the surface so here's our other weird one it's own little wild card as well it's called pseudo stratified columnar epithelia because at first when you look at it we find the basement membrane it looks like it stratified looks like you can see some small cells at the bottom and some larger cells on top but it really isn't stratified it's actually simple if you look closely every one of these cells is in contact with the basement membrane now it's a little difficult to see in this particular image but like this little guy right here is blocking our view but this cell behind is actually touching the basement membrane too so every cell we see in this image they're all squeezed and kind of distorted but every one of them is in touch with the basement membrane which means they are not stacked they are one layer it's again a little difficult to see in this image but that's the definition of pseudo stratified it looks stratified but it really isn't it's not true stratification all the cells are touching the basement membrane which means we have one layer and we're going to find this in parts of the respiratory system okay so moving on to finish up epithelia epithelia can also have glands and when we say that they can have glands it means that depending on where the epithelia is the and lands are going to be present and they're going to be different as far as what they produce this is one of the hallmarks of epithelia epithelia is also what we call a vascular a vascular in that it does not have any blood supply any direct blood supply so epithelial tissue must get all nutrients by way of diffusion of nutrients into it and diffusion of waste out of it because it does not have any of its own vascular ization so if you were to cut the very tip top layer of your skin it would not bleed because it does not have any blood vessels now if we cut down a little further we bleed because we've cut into connective tissue but the very top is a vascular so epithelial tissue again a vascular that's one of its hallmarks that makes it different from the other types of tissues okay so glands are collections of epithelial cells that produce secretions endocrine glands release hormones that enter the bloodstream there are no ducts involved with endocrine glands and we'll talk about the endocrine system when we get to chapter 18 which is part of anatomy to material exocrine glands produce exocrine secretions through a duct so that's what we're going to focus on now because those are part of epithelia so there are three methods of secretion marroquin apocrine and holocron merocrine secretion is when a gland secretes a product by way of exocytosis now that word should be familiar we talked about it in chapter 3 that is when we use a secretory vesicle to expel a product out of the cell and an example of a gland like this would be a salivary gland or a merocrine sweat gland so this is what it would look like so in the celebrate gland for example here are the epithelial cells that would line the gland and saliva is being produced and packaged into these secretory vesicles which will head to the membrane and then the saliva will be ejected by way of exocytosis next we have apocrine secretion and apocrine secretion is when we release a product but we also shed cytoplasm with the product and an example of that would be a mammary gland so looking here this is from the mammary gland and these are the cells that line the mammary gland so we have a cell here with secretory vesicles filled with milk and instead of just ejecting the milk the whole top part of the cell pinches off and cytoplasm is released with the product which in this case is milk the cell regenerates and produces more milk and then begins to pinch off again and we will begin the cycle again so we release the product with cytoplasm that's an apocrine secretion holocron is the last and holocron secretion is released by cells bursting which kills the cells the cells will be replaced by stem cells so they'll make new ones right after these are killed and an example of this is a sebaceous gland which is also known as an oil gland so let's take a look at that Poliquin so here is the lining of an oil gland and here are the cells that would be found in the oil gland you can see the cells at the bottom are undergoing mitosis we're making new cells because we know the ones on top are going to die so we're regenerating the cells on top have secretory vesicles filled with oil which is what we're making in this gland and when the oil is ready to be released the whole cell bursts open and dumps out its contents which is a mixture of oil and also all the cell guts or innards of the cell but that's okay these cells are dying as they release their oil because we've got new ones being produced that will push right on up and then they will burst and the cycle will continue again and again and again so the types of secretions produced by exocrine glands remember exocrine glands have ducts we have serous glands that produce watery secretions mucus glands which produce mucus mucus secretions and mixed exocrine glands that produce both serous and mucus okay so the next tissue after epithelial that we're going to spend some time talking about is connective tissue and connective tissue is what it sounds like it connects the epithelia to underlying tissues connective tissue is highly highly vascular so if you remember an epithelial tissue it was a vascular no blood supply no direct blood supply in connective tissue there is a ton of blood vessels so connective tissues a little different it is not completely cells just like we said epithelia was made up of cells connected to one another connective tissue is made with three things specialized cells and I'll give you some examples of which ones we're talking about extracellular protein fibers I'll give you some examples of that as well and then those two things will be suspended in what's called the ground substance matrix is is the last two items protein fibers and the ground substance so if we combine those two we can refer to that as the matrix so the matrix made up of ground substance and protein fibers the matrix makes up the majority of the tissue volume and will also help to determine the specialized function of the tissue so let's take a look at that a little bit deeper so this is another illustration taken from my book and I feel that this is a helpful illustration because it gives you an everyday example of how the matrix and the cells work so you know those awful in my opinion molded jell-o salads that people make sometimes where you've got jello and you've got fruit mixed into the jello well this is similar to how connective tissue works so in this drawing the jello in the background all of this space here that represents the matrix the matrix remember is made up of ground substance that's the can be fluid or it can be gelatinous like this and it could also be hard depending on what tissue we're talking about so this would be the matrix the jello and then these are the individual pieces of fruit these the cells so if you notice in the jello the cells are suspended in the matrix so an epithelial tissue it was a bunch of cells but in connective tissue we have cells or fruit in our example floating around in a matrix that again is what the cells are suspended in which in this example would be like the jello so very different from epithelial tissue which is just cells now we're going to go through some examples of connective tissue and the connective tissue remember there are many kinds so in each kind we're going to talk about the jello or the matrix and what its consistency is so it can be liquid it can be gelatinous like this or it could be rubbery or hard and then the fruit will also change the cells so in some tissues we'll have certain kinds of cells and other tissues will have other kinds of cells so we're gonna be specific about that as we go through our examples so in general if we're not getting specific about a particular type of tissue connective tissue has multiple important functions it can give us structure for the body it can be used to transport fluids and other dissolved materials it can protect your organs support surround and interconnect other types of tissue that's one of the reasons it's named connective it can store energy especially triglycerides which is a type of lipid and can defend the body from invading microorganisms like bacteria so we can divide connective tissue into three big groups we have the first called connective tissue proper this one can be used to connect and protect we'll talk about some examples we then have fluid connective tissue which is going to be used for transport and supporting connective tissue which is used for structure and strength so here's another quick chart from the study guide and this is basically showing the three categories that we're going to find in connective tissue so again on the far left connective tissue proper and we're going to talk about that one first and there are two types loose and dense we then have fluid connective tissue there are two types blood and lymph and then third we have supporting connective tissue there are two types cartilage and bone so let's go back to connective tissue proper and focus in on that one all by itself so connective tissue proper again can either be loose or dense loose connective tissue has more ground substance and fewer fibers so I like to think of it as a little bit squishy so as it says there's more ground substance not as many fibers so it is going to be very loose and squishy an example of this would be fat tissue or adipose which we certainly know feels quite squishy unfortunately and then dense connective tissue is going to have more fibers so more long stringy fibers running through it we're going to talk about what those fibers are as we get a little further there's less ground substance in this so it is going to be a little bit more sturdy an example would be a tendon tendons being the tough tissue that connects muscle to bone so in connective tissue proper remember the rule so the rule is that all connective tissues must have three items one specialized cells two fibers and three ground substance remember that fibers and ground substance are what we call the matrix collectively so this is a list of the main specialized cells that we will see in connective tissue proper so depending on the tissue you may see some of these all of these or even just one type in the tissue but we're going to go ahead and get acquainted with all of these so that we recognize when we hear a specific tissue we recognize the cells that are in that specific tissue so first we have fibroblasts fibroblasts are the most abundant cell type so we're going to see a lot of those in connective tissue proper and they are helpful in secreting protein to keep the ground substance thick or viscous so when we hear the word viscous we should think of syrupy syrupy sort of like the consistency of honey or maple syrups are nice and thick but still pourable fibrocytes are the second most abundant type of cell and they help to maintain the connective tissue fibers of connective tissue proper adipocytes these are just fat cells mesenchymal cells are stem cells that respond to injury or infection and they're going to do that by dividing melanocytes are going to produce the brown pigment melanin macrophages are large that's what the macro part means faj is from the word phagocytic phagocytic means to engulf or eat so these are large phagocytic cells they're part of the immune system and their job is to eat pathogens and damaged cells mast cells will stimulate inflammation after injury or infection and inflammation has just increased blood flow to an area and this happens because of the release of histamine which will enhance inflammation and also heparin so heparin is an anticoagulant in other words it helps prevent blood from clotting to enhance blood flow so this is important when we're trying to repair an area lymphocytes can develop into plasma cells which produce antibodies so these defend against infection microphages are small blood cells that are phagocytic so they to engulf pathogens and other things that can enter the tissue so those were our specialized cells and remember that all connective tissues must have again number one specialized cells number two they've got to have fibers so this is our list of fibers the three main fibers we're going to see in connective tissue are collagen reticular and elastic fibers so looking first at collagen is the most common fiber and connective tissue proper it is long straight and unbranched they look like strands and I'll show you some pictures of these things it's very strong and very flexible so you're gonna find collagen in the skin that's what gives our skin bounce and elasticity but as we get older that starts to break down and our skin gets a bit less bouncy and can begin to sag or wrinkle it can resist force well in one direction so collagen can be torn if we stretch an area too far and we do see a lot of it we mentioned the skin but we see a lot of it in tendons and also ligaments so they're going to be able to withstand quite a bit of pulling and stretching reticular fibers form a network of interwoven fibers so these guys look a bit more like a net when you see them in the tissue they're strong and flexible and they can actually resist force in many directions because they are interwoven we find reticular fibers in sheaths that surround organs elastic fibers contain the protein elastin they are branched not quite as branched as reticular not particularly looks more like a wet eye web or a net because it's inter woven but elastin has branches but doesn't quite look like a net it returns to original length after you stretch it and some examples would be the elastic ligaments of vertebrae which are very tough so that was the second thing we're gonna see in connective tissue proper but we also are going to have that ground substance which is remember the jello and the example of the jello salad that's what the cells and fibers are suspended in and like we mentioned ground substance depending on where we are in the body is going to vary from liquid to gel too rubbery too hard and so in this image this is an example of connective tissue proper and you can see several of the things we talked about in the last few slides so for one thing we can see some of the specialized cells we spoke of so we've got the Milano site here that's the one that makes the brown pigment melon here's our plasma cell macro Fache mast cell lymphocyte mesenchymal cell adipocyte fibro site those are all examples of things we might see in connective tissue proper we see all of those that we just went over in this one tissue we've also got our fibers so that's the second thing we find in connective tissue here's the reticular fibers it looks like a knit then we have long branched elastic fibers and these yellow stripe ones those are collagen so what do you think that would mean the pink stuff is in the background what the cells are suspended in that would be the ground substance so ground substance again is a clear colorless and viscous viscous again means surbhi and it's going to fill the space between cells and slow pathogen movement loose connective tissues we gave examples are we said that there was four connective tissue proper loose and dense loose connective tissue can act as a packing material filling space between organs cushioning cells and supporting epithelia so let's take a look at some examples of loose connective tissue proper so remember we said this is going to be a little bit squishy and texture so one example of loose connective tissue proper would be embryonic connective tissue which is very soft so this is going to be found in the embryo not in adults the Mezen chyme is an embryonic connective tissue that is the first tissue to appear in the embryo the first connective issue two appear in the embryo and it's going to give rise to all the other connective tissues mucus connective tissue is also a loose embryonic connective tissue and can be found in the umbilical cord a very soft tissue so here's a picture of embryonic mesenchyme and what we can see here is these mesenchymal cells so those are the specialized cells in embryonic mesenchyme and then in the background we have ground substance which because this is loose connective tissue we can expect that it will be very syrupy and not at all hard this is a picture of mucous connective tissue which is also referred to as Wharton's jelly and it can be found in the umbilical cord we see again mesenchymal cells and in the background a very soft gelatinous ground substance so some connective tissue we find in adults would be areolar at a post and reticular areolar tissue is the least specialized has an open framework and a very syrupy ground substance there are elastic fibers in it that's one of the fibers we're gonna see mainly and it will help to hold capillary beds so in adults we find this or not necessarily adults but not an embryo we find this under the skin so the areolar tissue separates the skin from the muscle so when you pinch your skin you are not also pinching the muscle the areolar tissue separates the two so here's a picture of areolar tissue and we set an example you can find it in other places but an example would be under the skin and what we can see in it is it does very much look like a connective tissue it's not all cells we see some specialized cells here scattered about some collagen and in the background we have our ground substance adipose tissue or fat contains many adipocytes so that's going to be its main specialized cell adipocytes and adults do not divide so when we gain weight adipocytes expand to store fat so they become more swollen which makes us look a little thicker and then if we lose some weight the adipocytes shrink as fat is released so here's a picture of adipose tissue and it is going to be filled with large adipocytes here are the individual cells and then if you look in between we see what we also should expect ground substance and we're still in loose connective tissue so the ground substance will be viscous reticular tissue provides support and contains a lot of reticular fibers which is why it's named reticular tissue these reticular fibers will form a complex three-dimensional stroma which means a net and this will support cells of organs so here's a picture of reticular tissue and this can be taken for example from around the liver and you can see in it there are some specialized cells some lavender colored ground substance which would still be viscous but a lot of dark purple reticular fibers creating a web or a net so this will help this tissue to provide a supporting framework so that concludes loose connective tissue proper and brings us to dense connective tissue proper so dense connective tissue proper is going to be what it sounds like dense there's going to be a lot more fibers in it which is going to make it a little tougher and a little less squishy it can also be called collagenous tissue so because it has a lot of collagen there are three types of dense connective tissue dense regular dense irregular and elastic dense regular connective tissue is tightly packed and all of the collagen is parallel so that means nice and neat and every collagen fiber runs in the same direction so it's a regular pattern which is why we call it regular we're going to find this in tendons that attach muscle to bone we're going to find it in ligaments that connect one bone to another and help to stabilize organs and we'll also find it in aponeurosis which are tendons but they are big tenderness sheets that will attach a broad flat muscle to another structure and we're going to find one of those right on top of the skull so if you take a look at a picture of a muscular view of the head and neck you will see a nice big flat aponeurosis going across the top of the skull so here's a great view of why we call it regular dense regular connective tissue so if you see here we can see some specialized cells in there these little dark nuclei of the fibroblast but mainly what we see is a ton of fibers you can't even see the ground substance here because there's so many fibers these are collagen and if you notice they're all running in the exact same direction parallel which is why it's called regular because it has a nice neat or nice pattern so next we have dips irregular connective tissue and this is going to have collagen fibers running in every which direction so not organized instead its interwoven and forms a network this kind of tissue dense irregular is much tougher than dense regular because of the interweaving pattern of collagen it provides strength to the dermis which is part of your skin this is why you can pull on your skin and kind of yank on it in every which way and let go of it and it bounces right back that is partially because of that collagen it gives the dermis lots of strength and stretchiness it will also form the protective sheaths that we find around cartilage and bone which we'll talk about more when we get to those chapters and forms capsules around certain organs like the liver kidneys and spleen they all have capsules around them to protect them dense irregular connective tissue is a large proponent of those capsules so here's a picture of dips irregular and again an example taken from the dermis of the skin which is the second big layer down and you can see that the collagen runs in every which direction there is no parallel running of fibers it is not organized it forms an interwoven network so that's why we call it irregular elastic tissue is made of elastic fibers and an example would be the elastic ligaments of the vertebrae so it's very organized you can see that it it's mostly parallel here but what's different about this then dense regular is that it's made of elastic fibers not collagen so remember elastic fibers are branched and they are a little bit stretchy ER this is going to give them a good stretchy toughness that is a great support for the spinal vertebrae all right so that ends connective tissue proper and brings us straight into our next one which is fluid connective tissue and fluid connective tissue is what it sounds like it's going to be a liquid which is kind of weird because most of the time we think tissues probably were thinking of something solid but fluid connective tissue is going to be a fluid just like it sounds like and there are two examples blood and lymph blood contains a watery matrix so the ground substance in blood is going to be liquid and there are some dissolved proteins in the blood so that watery matrix of plasma is going to contain ground substance and dissolved proteins but in this example that matrix is going to be liquidy or watery so we're not no longer a gel like we were in loose connective tissue a gel or a viscous solution we are now watery and it contains cells and cell fragments collectively known as formed elements so the main cells we're going to find in blood so these would be our specialized cells that are suspended in the matrix called plasma we have red blood cells which are also known as erythrocytes and white blood cells which are known as leukocytes so red blood cells are what's going to carry oxygen around the body white blood cells help to fight infection and platelets are used for clotting so here are red blood cells and again they're called erythrocytes and they make up about half the volume of blood and they or what gives blood it's red color length is the second type of fluid connective tissue and it forms as an interstitial fluid which is a tissue fluid that enters the lymphatic vessels and so the lymphatic vessels are vessels that go all around the body similar to your blood vessels and they carry lymphatic fluid and lymphatic fluid is a watery fluid so a watery matrix and it contains specialized cells like white blood cells that help to fight infection so it is monitored and part of the immune system so that ends fluid connective tissue and brings us into supporting connective tissue supporting connective tissue includes cartilage and bone those are the two groups cartilage provides shock absorption and protection so we're going to see it in between the bones at the joints we also see it in between the discs of the vertebrae and we see it in the tip of the nose and in the ears for example cartilage has a matrix that is a firm gel so cartilage is a little bit more sturdy so we're gonna have a gel a firm gel here not viscous not watery but a firm gel and that gel contains a polysaccharide derivative called chondroitin sulfate and that's going to help to give the matrix its firmness the cells specialized cells that are suspended in that matrix are called chondrocytes which is a cartilage cell there are three main types of cartilage hyaline elastic and fibrocartilage so looking at Highline first it is the most common type of cartilage it's tough and flexible sort of it helps to reduce friction between bones and is found in the synovial joints so those would be the joints we often think of things like the shoulder hip elbow knee in addition we also find it on the tips of the ribs the sternum and helping to make up the trachea elastic cartilage is supportive but it bends really well it's probably the the most bendable type of cartilage we have and this is what's found in the tip of the nose and in the ear so you can ball your ear up and let it go and it bounces right back fibrocartilage is very durable and tough it limits movement but prevents bone to bone contact and we're going to find this in certain joints between the pubic bones and also between the vertebrae making up the discs so taking a look at some examples we have hyaline cartilage first this is the one that's very common and we find it lining synovial joints so this would be the shoulder and here you can see what it would look like under a microscope there's a lot of gel matrix firm gel remember not liquidy and then the chondrocytes are the specialized cells elastic cartilage like in the ear is going to be similar we're still going to have a matrix and we're still gonna have chondrocytes but what we've added here are elastic fibers which is what makes this cartilage a lot more bendable fibrocartilage is very tough because it has interwoven collagen we can see chondrocytes here and then we can see the matrix is filled with lots and lots of fibers which makes this very tough and it can withstand compression so we find this in between the vertebrae making up the vertebral intervertebral discs okay and supporting connective tissue also includes bone we are not going to talk a lot about bone yet we are going to do that in great detail in Chapter six so right now we're just going to give a little information but not too much yet so bone is also known as osseous tissue and it is great for weight support and also protection of vital organs it is very hard so the matrix of bone is rigid which makes sense because bones are rigid and it's made rigid by calcium salt it also has in it in addition to the calcium salt in the matrix we will find flexible collagen fibers and that makes bone resistant to shattering so we've got calcium and collagen making up the matrix and then we've got the specialized cells which in this instance would be bone cells called osteocytes okay so here's a picture of what bone would look like and we'll talk a lot more about this in chapter 6 but we can see that it this matrix looks very rigid it looks very hard made up of calcium salt and collagen and then we can see some little cells that are kind of pinkish those are the specialized cells osteocytes suspended in that matrix all right so that ends connective tissue three categories connective tissue proper fluid connective tissue and supporting connective tissue and brings us into membranes so membranes are physical barriers that line or cover body surfaces they are made of epithelia supported by connective tissue so now we know what both of those are so we can talk about membranes there are four types of membranes mucus Cirrus cutaneous and synovial so we'll start first with mucous membranes these are going to line passageways that communicate with the outside of your body so they'll be found in the digestive respiratory urinary and reproductive tracts so for example anything that communicates with the outside world your nose your mouth your urethra all communicate with the outside world these epithelial surfaces must be moist to reduce friction or to help with absorption or secretion depending on where we are which mucous tissue we're talking about and so of course they are going to produce mucus so mucous membranes are coated with the secretion of mucus glands and these membranes are going to be found again in the digestive respiratory urinary and reproductive tracts and what you're looking at here just to practice in this particular tissue here's our basement membrane so anything above that is epithelia anything below it would be connective tissue which we just talked about so this would be simple columnar wouldn't it one layer thick column shaped there's kind of a weird-looking cell here in this picture and that's called a goblet cell goblet cells produce mucus which is what this delicious-looking stuff is right here that mucus is ejected and moves across the surface of the tissue because of these little hairlike thingies which are probably called cilia serous membranes line cavities that do not open to the outside so they're going to be found in sealed internal body cavities they're thin and they produce fluid to reduce friction so we call it serous fluid that reduces friction so this is gonna keep all the more the organs all slippery so that as they move and and flex inside there's no friction so here's what a serous membrane would look like in cross-section so again basement membrane so all of this would be connective tissue below the basement above the basement we have epithelia and this would be simple squamous right nice thin flaky and we're producing serous fluid which lubricates the surface of the serous membrane and reduces friction so we'll find this lining body cavities like the in the abdomen which is where the peritoneal cavity is in the lung cavities which is called the plural and the pericardial cavity which is where we would find the heart cutaneous membrane also known as skin that covers your body is thick relatively water resistant and usually pretty dry synovial membranes line synovial joint cavities and when we move this will stimulate production of synovial or joint fluid to lubricate the joint so here's a visual of the skin basement membrane so that would mean this is connective tissue and anything above the basement membrane would be epithelial taking a look at it I think it's clear that it is definitely stratified and remember when we have stratification we name the tissue by looking at the top surface only which we call the apical surface that is clearly squamous so we would call this stratified squamous epithelium and we would find this close to the surface because of all the stratification and we do because this is the skin so it certainly would be on the surface and need lots of protection okay so here is a synovial membrane and this represents a joint here's one bone here's another bone and this is the joint capsule and lining the joint capsule in red is the synovial membrane synovial membrane produces synovial or joint fluid which would be found all in here and that is also going to reduce friction in the joint okay so finally we have muscle tissue and muscle tissue is specialized for contraction so again we are not going to talk a lot about muscle tissue now because we do have a chapter on it coming up in chapter 10 so we're just going to give some bullet points on muscle tissue as an introduction its specialized for contraction and there are three main types skeletal cardiac and smooth skeletal muscle tissue consists of long thin fibers which we call muscle fibers and the cells do not divide we also refer to them as striated which means they have a striped appearance and they are voluntary which means you choose when you would like to use your skeletal muscles so here's a picture of skeletal muscle cells and you can see they are long and thin and they have a striped appearance which we call striations they are voluntary which means you choose when you would like to use them and they are found on the skeleton hence the name skeletal so a bicep would be a good example of a skeletal muscle cardiac muscle tissue is regulated by pacemaker cells and which means that it is involuntary so you do not control when your heart beats the cells look branched and they also are striated so they do have a striped appearance as well and again involuntary we do not choose when our heart beats so here is cardiac muscle tissue found only in the heart hence the name cardiac the cells are branched and striped and we can also remember hopefully that they are run by a pacemaker so next we have smooth muscle tissue which is found lining hollow organs so that would mean things like the stomach the intestines the esophagus the platter the uterus these cells are small and spindle shaped they can divide and regenerate and they are non striated so no stripes which makes them look nice and smooth and they too are involuntary so we do not control when our stomach intestines or bladder spasm or contract so this is a picture of smooth muscle short little squished spindle shape no stripes and they too are involuntary so we do not control and are found lining hollow organs so finally we have nervous tissue and again we're not going to say much about this yet either because we have a chapter chapter 12 that will go over nervous tissue in great detail nervous tissue is specialized for conducting electrical impulses it's concentrated in the brain and the spinal cord we have nerves as well and the two main types of cells we're gonna see in nervous tissue are neurons which send and receive signals and neuroglia which are supporting or helper cells tissues can respond to injury in two stages inflammation so that's when we increase blood flow to an area and regeneration to restore normal function as we age the speed and effectiveness of tissue regeneration decreases with age and that is because of the slowing of repair and maintenance activities that comes with age hormonal alterations and reduced physical activity the chemical and structural tissue changes can cause thinner epithelia as we age fragile connective tissue increased bruising brittle bones cardiovascular disease and also mental deterioration this concludes chapter 4 a study of tissues and we will begin next in chapter 5 which will go over the integumentary system [Music]