hi welcome back to educator.com this is the lesson on tissues now of course when we say tissues we're not talking about blowing your nose kind of tissues we're talking about a bunch of cells together with some common purpose some some functional goal in terms of what they're doing for your body so it is cells organized into groups for a specific set of functions or purposes sometimes it's just one purpose a lot of times it's many epithelial tissue is the first one we're going to talk about and EP thelium that's the other way to put it is always cells that are on the outermost part the most superficial layer of an organ or the innermost part uh the deepest parts of an organ uh so if they're in the innermost parts that organ has some kind of passageway or or Hollow area it's called Lumen and the cells on the innermost part those epithelial cells are probably helping to move something through absorbing chemicals secreting chemicals it could be a variety of things so epithelium very plentiful in your body extremely important connective tissue the most abundant tissue in your body uh because connective tissue is a lot of different kinds of cells functioning together uh it really does connect your body parts to each other and help bind organs to neighboring tissues muscle tissue and neural tissue are technically a type of connective tissue uh but these are major tissues in the human body you're going to find muscle tissue all throughout the body uh even in part Parts where you don't realize it's there because some of your muscles are doing involuntary actions that you don't directly control consciously um so muscles are actually in your dermis you actually have muscles in your skin that you don't consciously move but they do contract and relax uh Without You realizing it neural tissue also all throughout the body it's not just the brain not just the spinal cord uh we're talking every single nerve all the neurons um billions and billions of cells hystology very important kind of Branch or study related to an anatomy and physiology that's the study of tissues and to be more specific it's it's really looking up close at a tissue to see what the cells look like and how they're oriented related to each other so that's why it's typically with a microscope that you're going to be looking at some kind of histological picture and actually later on in this lesson I will show you a hystology slide so the first kind of um tissue we're going to talk about is EP eal tissue also called epithelium the purpose of epithelium is to cover every external and internal surface of the body not just on the outside but internal organs as well these epithelial tissues are always attached to a basil lamina uh also known as a basement membrane that's the other kind of synonym for this term here's what's meant by that uh you're going to see on pictures I'm going to either draw for you or or have displayed on the slide later on in this lesson that it's always cells bound to what looks like just a line looks like a kind of like cement like a cement line that the cells are attached to and anchored to that basement membrane or basil lamina isn't actually made of cells uh it's kind of like think of it as an organic protein glue that's anchoring all those uh cells to that surface and then that basement membrane is connected to whatever tissue is immediately uh below it or deep to it so basement membrane you're going to find associated with every epithelium also epithelium is a vascular it gets nutrients and gases from diffusion and or osmosis so what does a vascular mean specifically um vascular let's take the cardiovascular system always has to do with transporting fluids so for instance a vascular plant like a tree is called that because the tree is able to suck water up and and get it up through osmosis to the tippy tops of its leaves that's a vascular uh plant we are vascular because we're able to move fluids Against Gravity all throughout our body but this specific tissue is avascular because when you look at blood vessels and the transport of fluids related to this the blood vessels don't actually go right up into it um so you're not seeing capillaries those tiny blood vessels of your body feeding this directly with oxygen and nutrients the oxygen and nutrients the the gases that are going to be given to these tissues get there from whatever tissue is right next to it so it's diffusion in osmosis that's getting the nutrients and gases to the epithelial tissues and because we're talking about parts that are on the very outside of your body on the passageways that that you're swallowing stuff into or or inhaling uh air into they're consistently damaged by a wide variety of environmental factors regenerated with stem cells you're getting pretty much constant regeneration of these epithelial tissues depending on where they are in the body so let's take the epithelium on the surface of the tongue that needs to be regenerated a lot because every time that um tongue cells get rubbed up against by something you're chewing or or you know eating you're going to need to replace those same with the epidermis the outer parts of your skin I'm getting rid of thousands right now by doing this so yeah you do need to regenerate them as they get damaged so those are some characteristics of epithelial tissues in general so now the types of epithelium uh they are named based on cell structure and shape and I'll give you some examples momentarily and is it one layer two layers many layers so let's let's look at an example simple squamous epithelium why is it simple why is it squamous well simple has to do with how many layers it is this means one layer that's as simple as it gets later on you're going to see uh a stratified as a word so stratified is the opposite of one layer we're talking many many layers on top of one another uh squamous this means round or uh dislike yeah so they just they look like that that's a squamous cell so one layer of round or dislike cells that's what simple squamous epithelium is and you're going to see more detail about that later on in this lesson here it is simple squamous epithelium one layer of plate shaped I said dis shaped but same thing plate-shaped cells they just look like this meant for areas that need a high rate of diffusion and osmosis through the cells so think about inhaling air or transporting nutrients through blood vessels you want to get the oxygen to your cells as quickly as possible you want to get nutrients like sugars and proteins and fats as quickly to cells as possible you don't want to have having them drift through layers and layers of cells it would take longer and be harder to get that stuff around the body so two examples are the Alvar walls and capillary walls let's see here's here's a good picture of how they look so let's say we were to take a capillary which is the tiniest blood vessel type in the human body and if we were to cut that capillary down the middle because it's a tube let's say we cut it and we could look down it with a microscope the walls would be one cell thick simple and squamous because if you looked from the outside of it you would see all these dislike uh cells that make up these right here so I'm also going to draw a little nucleus and since it's one cell Fick what a capillary does is it gets oxygen to the tissues around it so you get a very quick diffusion uh passive natural movement of um gases and nutrients out of the capillary into the tissue and vice versa with CO2 and waste and you'll take those back to the lung so you can breathe out the CO2 molecules so having one cell thick great for quick diffusion in osmosis and Alvar walls if you wonder wonder what are those well if we look at the capillaries in the lungs you want to get the CO2 out of the capillaries and into the pass of your lungs for exhaling and vice versa with the oxygen well the little they're kind of like microscopic bubbles that make up the alveoli of your lungs you have hundreds of millions of these little air sacks they are also one cell thick so here's a alveolar bundle if we were to like take a cross-section through the alveolar bundle guess what also one cell thick and so it's brilliant in terms of like getting oxygen that you've inhaled into your lungs into the capillaries quickly and efficiently and so that's ideal for diffusion in osmosis simple squamous epithelium now stratified squamous epithelium we still have those round plate looking cells but a stack of them many layers of these plate shaped cells meant for areas that have to deal with or do with a lot of friction or rubbing like I mentioned earlier the epidermis of the skin being touched rubbed you need to regenerate those cells because you're going to lose them the surface of the tongue uh the esophagus that's the tube that takes food from your throat area down into your stomach every time you swallow a chunk of food it's rubbing against the inner part uh of that uh esophagus it's called the mucosa and you're losing those cells you need to be able to regenerate that epithelial tissue the vagina or the anus you're going to have friction in those areas too depending on um what AC it you're engaged in so you got to be able to regenerate these epithelial tissues uh because of those environmental um sources of friction here's a little image of what they would look like you could see that they're still you know roundish and then as you get towards the surface here's the superficial part of it this could be the epidermis of the skin it makes sense that these flattened cells here are worn away from the top and down here cell division of these in a sense stem cells are going to be providing the new cells that gradually move away from from the blood supply down here and look this black line right down here that's the basil lamina or basement membrane so this is stratified squamous Epi epithelium ideal for friction or protection here's a histological slide of part of the esophagus and stomach connection so I can show you some actual micrographs which means a photograph taken with a microscope so this is zoomed in really close and this passageway right here this is the Lumen of the lower part of the esophagus the most inferior part of the esophagus and here is the beginning of the stomach and here's the Lumen of the stomach so you're going to have mucosa lining that inner part of the stomach and you're actually going to have some um mucus glands that are going to be on the esophagus but what you also need to have stacked on the innermost uh part of the esophagus is lots of this stratifi squamous epithelium so you can see that there's Stacks and stacks of those round cells because every time food rubs against it it's going to damage parts of it and so the mitosis down here is bringing up um new epithelium here you're going to see all kinds of epithelial tissues in the stomach uh for instance right here you've got some glandular epithelium you're going to hear more about that later uh these are secreting gastric juice and all those little um chemicals and molecules inside the stomach to help with digestion process another kind of epithelium simple columnar this is one layer because it's simple of column shaped cells like the name says meant for absorption and secretion typically so it just depends on what specific organ we're in sometimes they are uh absorbing something they're they're taking something in from the passageway or they're secreting something into that passageway or Lumin sometimes they have what are called microvilli and I'll actually draw some microvilli for you right here they look like little hairs on the surface and actually um epithelial cells are known as uh cells with polarity meaning that one end of the cell uh usually functions a little bit differently than the other end in terms of the look of it and the structure and you could see that with simple columber down here this is the anchored part of the cell that's going to be adjacent to the Bas membrane and up at this end um you know if we're talking about a space or Lumin this is the end that's actually doing the absorbing or secreting and these little microvilli are going to be going like this for instance in the lining of the stomach and intestines you definitely have to be absorbing stuff and secreting stuff like if we take the small intestine uh you definitely need to have the ability to um further the process of digestion and the small intestine very long tube in your body that's doing a lot of absorption so these cells are perfect for that stratified keter is very similar to the previous picture but you're actually going to see stacks of these cells and yeah I could add a nucleus or nuclei to all of these but just for the sake of time that's that's good enough and here's that basement membrane uh and sometimes these also have um cyia on the top not necessarily though um so stratified Coler epithelium many layers column shaped cells that could even be more than this meant for protection similar function to that stratified squamous epithelium but the cells are just shaped differently locations the epiglottis the epig glotus is actually a flap that comes down on the entrance to your Airway to your trachea every time you swallow because often times when a human being is swallowing they're getting food or liquid down into their dig digestive tract and uh you don't want it going down into the lungs so the epiglottis is a nice flap that uh protects us from aspirating on something other than air uh the anus and the urethra also need protection uh based on what's going through uh those areas pseudo stratified ciner epithelium pseudo meaning like fake or false uh stratified meaning many layers and columnar shapes so kind of a false stratification and that's because it appears to be layered but it is one layer of column shaped cells and the reason why it appears to be layered is the varying Heights of nuclei give it the illusion of being many layers um so let me draw you a picture sometimes you get one of them being smashed in like that I'll do another one that's kind of smashed in but you can see that this is one layer of epithelium of column shaped cells but you'll see this so because you have varying Heights of nuclei at first glance you might think oh yeah it's two layers it's more than one layer but it isn't so it just appears that way sometimes these have pilia actually times it just depends on where so cyia I mentioned cyia in the previous slide but um let me explain more here um similar to microvilli the difference is that cyia usually are helping brush something along rather than um the absorb absorbing kind of process or secreting so think about the lining of the trachea and bronchi these are tubes associated with breathing in air and exhaling you generate mucus in your lungs and if it wasn't for the swe sweeping up brushing up of uh mucus so that you can hakal Lugi you would actually end up drowning in your own fluids especially when you're sick so the brushing up of that mucus that's generated in the passageway of the lungs very important so in the trachea and bronchite you're going to see lots of pelia um brushing up mucus almost constantly simple cuboidal epithelium one layer of cube shaped cells meant mainly for secretion and absorption secretion absorption protection sap sap those are the uh that's the way I remember it uh those are the three major functions of epithelium those are the big three you're going to see a lot secretion absorption Protection One or the other or some combination of the three when we look at kidney tubules the little tubes that help make urine that's going to eventually go to the urinary bladder you're going to see these and the thyroid gland which has a lot to do with regulating your metabolic rate um this SEC secretes hormones into the bloodstream um these two definitely have simple cuboidal so if we looked at one of the passageways through which um urine would eventually become urine or um thyroid gland secretions are found you're going to see Cube shape so not quite round kind of the the squared off edges and here's the nuclei this is your average looking uh kidney tubule epithelium so you can see that pretty good for secreting and ab absorbing stuff you know easily things are going to go in and out so same as uh simple squamous epithelium except for the cell structure so it makes sense that you can easily have um secretions uh going in and absorbing um you know through this as well stratified cuboidal um similar to what I just drew for you except instead of just one layer you're going to see additional layers of these Cube shaped cells um so I'm not going to draw all of them but you're going to have stacks of them and so on and so forth so seeing Stacks next to some kind of tubular structure or Lumen as this is called yeah that's stratified cuboidal uh meant for protection secretion and absorption like I said earlier sap or PSA what whatever you want to remember not as is some of the others I've already told you about in this lesson but you can find them so the lining of sweat glands like in the dermis of your skin uh often times if you cut through sweat gland and you were look at it under a microscope that histological view is going to show you U stacks of cube shaped cells transitional epithelium meant for stretching and recoil you have certain structures in the human body certain organs where you need it to expand and then go back once whatever was inside of it has left so when relaxed next it looks a lot like columnar so here's uh your relaxed transitional epithelium like the lining of the urinary bladder or the uterus and yes you'd have the nuclei of course so when relaxed when there's not much in it they look like that but then when it is stretched let's say Ur urinary bladder has close to a liter of urine in it that's is the max um that means that person is going to really have to urinate it stretched quite significantly so when you stretch out those cube-shaped cells they they don't look cubed or sorry not Cube shape the column shaped cells they don't look columnar anymore uh because they are stretched yeah so definitely a big difference between this and this so think about any organ that's meant to expand um even the stomach is one so urinary bladder has urine in it got to stretch it uterus a baby got to stretch it now I'm going to tell you about glandular epithelium it's meant for producing and releasing secretions so anytime that you have a gland whether it's releasing a secretion outside of the body into a body cavity it's made of glandular epithelium in terms of the production of what's being secreted in the actual Act of secreting it so there are three main types of gland epithelium the first one is marrine then apocrine and then holocrine and I remember uh this pneumonic device ma ma like you're calling your mom you're saying Ma and the reason for that is because the order will help you remember what does what and you'll see why so the marrine type an example is salivary glands and here we have um the different types of salivary glands there's actually three pairs total of salary glands in humans um you've got the pared sublingual submandibular um and all of these have the glander epithelium that is the marrine type and marrine actually secretes just little bits of substances from the cells so the cells in epithelium are actually not leaving just bits of the substance for example let's say this is the gland and here's the opening in which the secretion actually comes into your mouth along the edge of it you have cells that are responsible for producing saliva and secreting it into the cavity or the Lumen and so secretions into here will then exit into the opening of the mouth to help you you know dissolve things you're eating what actually happens is if we were to zoom into one of these cells there are little sacks or vesicles is a better name for and inside you have water and enzymes these little sacks will fuse with the edge of the cell and then you end up getting let me erase it here water and these little enzyme packets exiting and that's really saliva so if you remember that merocrine is the smallest bits of secretions you'll see that with apocrine it's a little bit more when we look at apocrine glands your epithelium an example is mamory glands the glands that actually release milk um when we look at a mamory gland you'll see it's it's a little bit different so here are the cells that are lining that actual Lumin or opening instead of it just being little packets that are released they're actually parts of cells not the whole cell but parts and here's what it would look like you would actually have here's the cell with you know it's little organel and parts leaving you see that I'm drawing these arrows to show that it's actually getting rid of a section of the cell and all these little cell parts together make up the milk all those carbohydrates proteins lipids hormones Etc that are in breast milk and so apocrine a little bit more is released not just little packets but parts of cells then we look at holocrine let me use a different color uh sebaceous glands when we look at hairs so there's a hair shaft there are glands adjacent to the base of the hair shaft near the follicle and they release an oily substance to help coat and protect your hairs and they're associated with the hairs all over your body holocrine the way that I remember it it it being more of a secretion in terms of the amount that's released whole H is kind of like saying w h o e like a whole cell and so the the mo thing I told you about before marrine releases little bits apocrine releases parts of cells holocrine releases whole cells so if this was actually the lining of the gland here this sebaceous gland and this sebaceous gland you would actually see the whole cell being released as part of that oily glandular secretion and so those are the three different main types of glandular epithelium when we look at connective tissues this is an important tissue in the body it is the most abundant tissue it's all over the place it's connecting the body parts to each other stabilizing your body giving it structure and stability and it is meant to connect and bind together all the organs and organ systems to form a cohesive Cooperative body as a whole and you have different skeletons here of course on the far right that's a human skeleton uh we've got gorilla uh chimpanzee um gibin orangutan and whether you're looking at a primate or we are a primate but whether you're looking at uh a monkey an ape or a human the skeleton is made of connective tissue um so when we look at connective tissue anything that is found throughout the body helping to bind organs to each other um helping to to let the body communicate with itself it's probably connective tissue and if you think about it bones really do connect body parts to each other via joints and if it wasn't for your bones well you wouldn't be alive so connective tissue is made up of connective tissue fibers and cells so first we're going to talk about the fibers the fibers are made of protein protein the most abundant solid substance in the body if you were to remove all the water from a body uh protein is your next most abund abant substance collagen fibers collagen one of the most abundant proteins in the body it is a bundle of protein units that are slightly flexible or that is slightly flexible but very strong and typically arranged in One Direction a good example of that would be tendons so tendons help connect muscle to Bone ligaments would help connect bone to bone so a tendon like let's take the calal tendon for example or the Achilles tendon as it's better known if you think about how it connects your calf muscle or gastrus to your heel which is called the calenus bone that's why it's the calanus tendon that Achilles tendon is a band that's in One Direction it's very tough it's very strong and of course it is slightly flexible because anytime that you you know contract that muscle that gastrus uh you're going to be pulling up on your heel and when you relax it the opposite is going to happen and all of those aligned in One Direction help keep keep it stable connect that muscle effectively to that bone and it is very strong and anyone who has snapped that tendon um knows it's very painful and they realize how important uh that tendon is and typically when it snaps away from the bone surgeries required to reconnect it uh so collagen fibers is not just tendons and ligaments collagen's found all throughout your skin it's in your bones it's all over the body very important elastic fibers is another example of a connected tissue fiber this is not quite as strong but a lot more flexible a bundle of protein units that are very flexible elastic I mean it says it right there but it's still strong of course just not quite as strong as as collagen an example is invertible discs so intervertebral discs if you look at the vertebrae this is a side view so what you're looking at here is this side is the anterior side towards the front of your spine bones and this is the posterior or um dorsal side this would be uh that little bony extension that makes up those bumps you see on someone's back when they when they bend over they're more obvious and this is a a little process that connects to uh the ribs for instance and also uh muscles can connect there but anyways this bone on the top and bottom of it you're going to see a disc and that's why they're called intervertebral discs because they're in between uh the vertebrae and these have to be flexible they have to have some give and elasticity because think about when someone jumps off of a ledge or jumps off of U something that's pretty high the amount of force of the bones coming together when you when you hit the ground you want to have that cushioning and a little bit of give um so you do have slight elasticity there as time goes on um the Integrity of these and the um thick can drop a bit and that's why some older people sometimes the older they get they actually can be a little bit shorter U My grandmother used to be very close to 5 feet now she's more like 410 and we can blame um some of those invertible discs for that little drop in height but yeah they're made of these elastic fibers and a good example of elastic fibers is the name elastin that's the most common elastic fiber and you're going to find it in those invertible discs and finally retic fibers same subunits as collagen but not in One Direction so remember with tendons we have the collagen lined up you know in One Direction because that's how the muscle contracts it contracts along one plane back and forth but with reticular fibers retic means net and if you took biology you remember that the endoplasmic reticulum that organel in a Cell um kind of looks like a little net next to the nucleus so reticular fibers they're netlike and a good example is inside the liver uh these net-like fibers are found throughout the liver to help keep it together and keep it stable you wouldn't want U collagen fibers just lined up along One Direction of the liver you want them kind of spread out and and you know kind of all throughout the tissue to help give it uh stability and keep it together so those are connective tissue fibers connective tissue cells are another important part of connective tissue fibroblasts um for instance when you get a a cut in your skin fibro blasts are what are helping heal that cut and and and remake those those proteins and secrete those proteins to help bind it back together so you know if if it's not a thick cut you won't need uh or thicker deep cut you won't need uh stitches if it's you know a thin cut your body takes care of it and often times it won't scar so you can thank fiber blasts for uh secreting uh these connected tisue fibers to help rebind those parts of the skin that have been separated macr fages that literally means big eater and macras are these giant cells they kind of look like Pac-Man they will engulf uh foreign bodies so let's say you've got a bacterium here uh a bacterial cell that is potentially harmful to your body uh here's a nucleus inside of your macro Fage and there's all these little usually lomes little organel that have enzymes that are meant for uh breaking down foreign bodies so once the maccrage swallows up remember it's a big eater uh that foreign body little enzymes inside these lomes will fuse with the packet that has now engulfed this uh this bacterial cell and those enzymes will break it down and get rid of it so macras some of them are fixed they're kind of like a permanent resident of organs or tissues in the body others are free uh where they migrate in and out and the amazing thing is these macras can flatten themselves and squeeze in between U the cells of tissues and and the ones that are free migrators it's amazing how they will go and Target uh foreign bodies and get that immune response going masted cells mass cells secrete a couple different things they secrete histamine and heparin so those mass cells cells histamine is one of the main things they secrete and histamine uh if you've ever taken an anti-histamine you're familiar with the opposite of what this does an anti-histamine is going to get rid of the swelling especially in your nasal cavity uh so if you have a a stuffy nose it's very uncomfortable and that's your body's natural response to U getting some kind of infection or or irritation in your upper respiratory tract to um you know get inflammation in that area is to get more blood flow and try to get rid of that problem uh that foreign Invader that's causing the problem but it's very uncomfortable so you take an anti-histamine to reduce the swelling so that tells you that histamine is the cause of inflammation so this is released to um make blood vessels get dilated and that results in swelling Heparin is pretty much an anti-coagulant and that means that this will prevent or get rid of blood clots sometimes blood clots are a very good thing uh a clot prevents more blood from exiting out of a wound um from out of blood vessels but once the the healing has happened and you've repaired the wall of that blood vessel you want to get rid of that clot you don't want it to stay there if it gets dislodged that that clump of um of a clot could get lodged somewhere where it doesn't belong and that could cause problems so heparin will actually um thin the blood or get rid of those clots lymphocytes an important cell of the lymphatic system and lymphatic tissue is all throughout the body that is connecting body parts to each other and lymphocytes are responsible for um uh making antibodies so th this can actually give rise to what's called a plasmo site and a plasmo site um helps uh to get antibodies to areas where you have a certain kind of foreign Invader and anti bodies are part of that immune response which you'll hear more about in the lymphatic system lessons atpo sites atpo sites look like giant yellowish cells and in the corner kind of shoved over to the side you'll see a nucleus and some people say that a cross-section of adipocytes looks like a class ring because this yellow um well the plasma membrane can often times look a little different than yellow but inside you're going to see lots of lots of yellow um but their point is that it looks like a class ring because you have that that edge and then this little nucleus off to the side kind of squeezed to one corner and that looks like the jewel of a class ring so I'm drawing this all yellow because lipids or fats in the body are stored in atpo sites and this literally means a cell that contains fat uh so you have all this fat jam-packed inside of the plasma braan in in the cytoplasm of this cell and the nucleus is just squeezed over to the side because of all that fat uh so that's a typical look for an osy and then finally melanocytes so melanocytes uh they make melanin so melanin is that pigment that gives your skin hair and Iris within the eye it's color and so these cells um found all throughout your skin they are stimulated to make melanin and there are genetic factors associated with that and of course environmental factors like UV radiation and finally connected tissue examples so when you get combinations of those fibers that I told you about and cells that makes up different types of connective tissues adipose tissue like I mentioned before you're going to have atopos sites storing uh that fat in the body the the most abundant um sight for adapost tissue is going to be uh the deepest parts of your integumentary system so the lowest parts or deepest parts of your skin called the hypodermis is a site where you have lots of atpo sites and of course the amount of fat storage varies from person to person and it varies in different parts of the body right your uh your buttock area typically has a lot more atap storage than um in your hands for instance tendons and ligaments um definitely tendons and ligaments made of a lot of connective tissue fibers but you also have cells in the neighborhood like fiberblast that can reinforce or make little repairs if need be now if you tear your ACL in your knee the anterior cruet ligament if you completely tear it you're probably going to need surgery to get a new strong ligament in there but if you have microscopic tears you know that cause a little bit of pain after you you do make that injury happen you're going to have cells that can actually reinforce and and remake parts of those fibers and sometimes people don't need surgery with those tiny little uh tears your body can um compensate for that blood uh blood is definitely a connective tissue um there are lots of uh blood proteins associated with this this particular tissue and of course there's all kinds of blood cells um macras um is just the tip of the iceberg in terms of um cells that are uh assisting in terms of blood flow around your body cartilage uh soft bone uh cartilage uh found in every uh movable joint in your body uh found in the nose the ears Etc um very important you not only have a lot of fibers associated with cartilage but cells that can um produce those fibers and and release them to make that cartilage and then bone of course it's a lot harder than cartilage uh collagen fibers very very abundant in bone um and of course cells without cells in the bone you're not going to be able to uh produce that collagen and and maintain the Integrity of your bones and muscle um muscles of course uh made of muscle fibers and those fibers individual muscle cells are jam-packed with proteins so these are just several examples of connected tissue types in the human body and thanks for watching educator.com