let's start our discussion of connective tissue the same way we started our discussion of epithelial tissue that is to say we will talk about the general functions of this tissue type and then we'll talk about the characteristics of this tissue type that sent the tissue apart from the other tissue types so for connective tissue some of the general functions are providing a structural framework meaning like bone and cartilage kind of make your body shape and shapes of some of your other bodily structures transportation for example blood moves things throughout your body protection bone and cartilage can both protect organs but you also have immune protection from white blood cells supporting surrounding connecting other tissues may be ligaments and tendons would be a good example of support in connecting different tissue types in insulation and energy story and that's really specific to fat which is a type of connective tissue so these are really diverse functions for connective tissue and it may not seem like blood and bone and a tendon will have very much in common but where we will see some similarities in these tissues is when we talk about these characteristics remember an epithelial tissue the characteristics we looked at were like polarity a vascularity cells being close together regeneration very rapid regeneration connective tissue is all related by different characteristics so throughout the body will find connective tissue all the connective tissue comes from mesenchyme which is an embryonic tissue that can then diversify to form all these connective tissue types but structurally all of these connective tissues will share two main components specialized cells and a matrix so just at these two examples of connective tissue we have elastic cartilage we can see all these kind of white you know cell shaped structures those are specialized cells they're special cartilage cells that means that everything else all the purple goop in between those cells that's called the matrix or if you were to look at blood you would see a bunch of red blood cells and some white blood cells and some platelets everything else in between those cells is the matrix so let's talk about specialized cells first we start with this mesenchyme this embryonic tissue and so there are special cells in the mesenchyme just called mesenchymal cells but of course if we make it past the embryo stage these mesenchymal cells and tissue start to differentiate and then we have things like cartilage so we just saw a picture of the histology of cartilage and we said there were special cartilage cells but obviously that's not the official name the official name of a special cartilage cell is a chondrocyte and anytime you see this term Kandra you should be thinking about cartilage that rate means cartilage so cartilage cells if we were to look at a slide of bone tissue we would see some osteocytes an osteo means bone for example osteoporosis is a bone disease there are other osteo cells to osteoblasts osteo class we're going to talk about those when we get into the bone so for now just as one example an osteocyte is a specialized bone cell in fat we have adipocytes in fact we're going to replace this word fat tissue with adipose tissue in a few minutes so adipose tissue is full of adipose sites there is a type of tissue called lymph and lymph we will find many lymphocytes and in the blood we already saw red blood cells white blood cells and platelets we can be more detailed and say erythrocytes is the official name of red blood cells leukocytes are white blood cells and then you have platelets sometimes are called Strom both sites but we can stick with platelets so then we have a few other types of connective tissue cells these big eater immune cells well big is macro just like small is micro and eater well remember we talked already in this unit about phagocytes and how they do endocytosis to bring things into the cell so if you combine those two routes you get macrophages that's big eaters so their immune cells wandering around eating up things that shouldn't be there there are also some histamine producing immune cells called mast cells mast cells are part of this inflammation response that you'll have in in events when you have some injury or infection and finally the most common cell and connective tissue these are responsible for making and maintaining the fibers within the matrix so we'll talk about this a bit more later but these are called fibroblasts so they're going to be making a bunch of fibers eventually they mature and become fibrous sites that's when they just take care of the fibers that they've made but much of the time we will see and be discussing fibroblasts so we'll be using these terms again you know as we get to bone we'll revisit the term osteo site as we get to fat we'll revisit adipocytes but this is just the first peek at some of the specialized cells that are characteristic of connective tissue but remember connective tissue is not just the cells but also the matrix those are the two things you'll find in all connective tissues so what is the matrix well it's made of two different things ground substance and protein fibers so think of it like this in these connective tissues the cells are not typically sometimes they are but not typically very close together so what separates those is the matrix but there will be some liquid or gel or some solid substance in between the cells and then also within that substance that ground substance there will be protein fibers running this way in that way you'll be practicing in lab at identifying the different types of fibers and looking for ground meat ground substance the matrix will do a little of that here as well but you'll have more time to practice this than just seeing these pictures quickly in the lecture but there is a ground substance some type of fluid gel or solid with protein fibers criss-crossing throughout and there are different types of protein fibers collagen fibers are wound around each other to form very thick and strong fibers so you'll find those in places that really just need that extra strength like in tendons you know muscles are pulling on tendons a lot so they need to be strong and in your skin your skin has a lot of collagen if you're a female your skin has even more in different types of collagen to make it extra strong elastic fibers are more wavy meaning if you're looking at in a microscope at some tissue and you see some wavy line that's probably an elastic fiber and these are made of elastin proteins and they have the ability to stretch and recoil so you'll find more elastic fibers in places that need some ability to stretch and recoil like in your aorta as that pressurized wave of blood hits the aorta it has to be able to stretch and snap back to size your outer ear can stretch and snap back to size and there are other areas in your body that do that as well the last kind of protein fiber is called reticular fibers those are made from collagen although they're a different type of collagen and they form thin strands that get interwoven into more of a net-like structure and this will help more with stabilizing certain organs two important note here notes here is that number one multiple types of fibers can be found in a connective tissue it's not only one or the other or the other a second important note is that blood is typically considered a connective tissue lymph another fluid is typically considered a connective tissue so is there fibers running through your blood no but you do have the proteins in your blood that could come together to form fibers but they're suspended in the ground substance or they're floating in the plasma so there are no strands of fibers but there are the ability to build fibers in your blood if you need them for example when your blood is clotting okay so you all the connective tissues we'll talk about Plus briefly the mesenchyme and what you'll see here is that we can separate them into three categories connective tissue proper fluid connective tissue and supporting connective tissue so before we start our first category just to quickly revisit this concept of mesenchyme or mesenchymal tissue that is that Embree embryonic tissue there are these roughly star-shaped cells with very very fine protein filaments but really appear we just want to acknowledge that this tissue type will give rise to other tissues other connective tissues so then we get into our connective tissue proper some of these are going to be very loose connective tissues some will be more dense really what we're talking about here is how are the fibers arranged or the fibers kind of loose like as you see in the image here with lots of space in between the fibers or the fibers pack together so our first official connective tissue areolar connective tissue you will find this in the dermis of your skin so below the stratified squamous epithelial epidermis between muscles around blood vessels and other structures in fact it's in many many many places in your body what it has is all the different fiber types like in this image we can see some big fat collagen fibers and we can see some thinner glue elastic fibers and there are lots of specialized cells present so here we've got labeled fibrocytes macrophages and mast cells but there are other specialized cells wandering around in the areolar tissue so what is it that aerial or tissue does that makes it so important and so common in the body well it's cushioning it can bind things together it can hold fluids it has an immune function because there's a bunch of different immune cells so it does a whole bunch of stuff the way that I best remember areolar connective tissue is by thinking about its role in the dermis basically your skin is made of two layers officially the epidermis and the dermis so the aerial or connective tissue is in the dermis but it's at the very top and it's gonna help glue or bind the dermis to the epidermis just like here it says the areolar tissue can bind things together and your skin needs a lot of cushioning so it kind of makes sense that that will also be a slightly cushioning layer in the skin and if ever have like a small cut or injury to the skin that open up your skin to pathogens so the good thing about the aerial or connective tissue is there's lots of different types of immune cells that can wander around through this nice loose connective tissue so in between the epidermis and dermis or I should say at the top of the dermis is this areolar connective tissue with a bunch of immune cells just patrolling so helping defend against infection so if you learn about the skin and areolar connective tissues role in the skin you'll have a good understanding of the functions of areolar tissue adipose tissue this is fat so you probably could list places where you would find it but in your hypodermis around the kidneys to cushion them in your butt in your abdomen breast etc it's function well there's really three major functions of adipose tissue it's cushioning it insulates the body from heat loss and it stores energy long-term energy storage the description is that the matrix is an areolar connective tissue yeah so you have some fibers found in adipose tissue but you just see them sparsely distributed there you don't see much of the fibers the main thing you want to know about identifying adipose tissue is that the cells store the fat so they have these fat vacuoles that fill with that and it pushes the nuclei to the very edge of the cells we call that a peripheral nucleus so when you see these big empty looking cells with the little dots off on the edge to kind of look like a diamond ring shape or something that's at a post issue our last loose connective tissue is reticular and of course this will have reticular fibers in it making that interwoven net-like pattern and you'll find this tissue in organs that have a lot of blood cells like the liver the spleen lymph nodes and bone marrow the reticular tissue is going to support those organs you don't want them to goopy that the organs will fall apart or something so the tissues will inner interweave to support the organ providing a supportive skeleton not a bone but of fibers okay so now we have the dense tissues starting with dense regular connective tissue this is what you'll find in tendons and ligaments so it's going to allow for a very firm attachment because tendons attach muscle to bone ligaments attach bone to bone and they need to be able to resist stress in one direction meaning if you think about the action the movement of some of your muscles you know like my bicep is pulling on my arm in only one direction it's not getting pulled out in from above or below or anything like that so tendons and ligaments are typically just dealing with stress in one direction so all the fibers are parallel they're all just running in the same exact direction usually a kind of a wavy line those are all of these collagen fibers and you'll see some cells here and they're sprinkled throughout fibroblasts help make all these fibers and then fibrocytes stick around and maintain the fibers after they're made dense regular is very different in appearance from dense irregular dense irregular it's still a bunch of collagen fibers but instead of them all being perfectly parallel and kind of wavy lines you get a mess of fibers that are running all different directions or all interwoven twisting around each other curving and this is going to provide the ability to resist stress in multi-dimensions this is found like in the dermis of the skin that's your thickest layer of your skin is the dermis and it's full of all these collagen fibers running every which way that gives your skin the ability to be strong even if pressure comes let's say from like dislocating a finger and there's all this pressure on the skin and this is a true story from a ski accident I had yeah so my finger is dislocated my skin was so tight you know it looked like if I hooked it with a pin it would just rip open but it wouldn't of course that collagen is very strong and it allowed the skin to stretch you know in this direction and in this direction at the same time to accommodate that dislocated bone that's dense irregular and our last connective tissue proper is elastic tissue as the name suggests we will find elastic fibers here but don't forget it doesn't mean there's only elastic fiber here it's just one of the one of the fibers so where would we find elastic tissue between the vertebrae is one example I'm not talking about the pads of cartilage in between the bodies of the vertebrae I'm talking about there's little bands of elastic tissue that hold the vertebrae together so these disks are that's something different elastic tissue pulls the vertebrae together from above and below you'll also find elastic tissue in the walls of very large blood vessels especially in arteries as we mentioned before when we talked about elastic fibers being found in the aorta they allow for expansion and recoil did you do yeah matrix is mostly collagen fibers but then with a lot of elastic fibers as well okay so before we move on what I want to acknowledge is that in many places in the body you will be seeing many many many types of tissue all at once so if you find a piece of hypodermis and you zoomed in very very closely you would just see the fat the adipose tissue would be all you would see but if you take an entire skin slide like I have here and you look at this skin slide there are many tissues here in fact there are five that we've already talked about but there are at least five more that are present just in this little piece of skin so for example know that you're looking at skin and you can usually do that by looking for this kind of wavy line tell you you're looking at skin you can start to just name the layers from the apical surface the top down to the bottom like I know that my outer skin is made of stratified squamous epithelium stratified squamous epithelium is this top layer here I can also see these little flakes of kind of transparent substance that is keratin or keratinized cells so this is keratinized stratified squamous epithelium the next layer skin is the dermis but remember we said that the dermis is mostly dense irregular connective tissue that's irregular but at the top of the dermis there's a little bit of a tissue that will bind the dermis and epidermis together and provide for some cushioning and provide for some areas for immune cells to wander around so right up in here this kind of lighter colored region in here this is areolar connective tissue in the dermis the hypodermis not officially part of the skin this is all adipose tissue and then finally for the five tissue types we've talked about I see labeled here sweat glands so I know that sweat glands are stratified cuboidal epithelium from the previous video in lab you'll have more practice looking at slides like this and getting used to telling apart the different types of tissues because sometimes if you were to be tested on understanding tissues you might give a slide and all you see is just adipose tissue everywhere and then that's pretty straightforward but other times you'll really want to know oh this is skin and then you work through everything you know about all the types of tissues in the skin to get to your answer but like I said there are five other types of tissue at least found in the skin so we haven't officially talked about these yet but I think it will make sense if I were to tell you that somewhere in here not easily visible at this magnification but somewhere in here is blood blood is a type of connective tissue if you have blood it's traveling in blood vessels and I know blood vessels are lined with simple squamous epithelium so somewhere in here is that as well I all so no from studying my organ systems that the lymphatic system one of its jobs is fluid balance meaning that our blood vessels are very leaky so anywhere you have blood and blood vessels you have lymphatic vessels and lymph that's sucking up blood that leaks out of our blood vessels so that's another type of connective tissue in here I know that my skin has sensation so there must be nervous tissue in here and I know that if I watch a spooky movie that my hair will stand up on my arm so there's muscle that contracts to pull on the hairs on my arm so that's five other types of tissues I might have forgotten some many types of tissues all get blended to make our organs in this case our skin okay so let's move on fluid connective tissues include blood and lymph although sometimes you'll see people arguing that they shouldn't be included as connective tissues because they don't have fibers proper you know they don't have fibrous strands built within these tissues but we'll we'll keep them as connective tissues blood is just found in the cardiovascular system it can transport stuff around in your body like oxygen nutrients and waste but you also have white blood cells helping with immunity and platelets helping with clotting so here's red blood cells with the official name white blood cells with their official name and platelets sometimes called thrombocytes are these little cell fragments that help with clotting and they're all floating about in a fluid called plasma business fluid found in a lymphatic system and so depending on how much you studied up on the lymphatic system basics well the lymphatic system is involved in fluid balance and immunity and like we just mentioned that in these capillaries these tiny blood vessels fluids are going to leak out of these vessels what you don't want is that fluid just to constantly leak out and leak out and leak out and then just drain down to your feet and cause all this swelling or something in your body you need to suck that fluid back up so anytime you have these little capillaries you'll also have these lymphatic vessels and these will suck up the fluid that escaped clean it in your lymph nodes and dump it back into the heart so the lymph is the fluid inside these lymphatic vessels and that's it for the fluids we finish with supporting connective tissue which is just means cartilage and bone and we have three kinds of cartilage to talk about hyaline cartilage is found between the tips of your ribs and your sternum at the ends of your bones in your trachea and nose so let's do those again so in your nose this is hyaline cartilage you can feel it it's a little bit flexible but it's pretty stiff in your trachea there are rings of cartilage I can feel them as little bumps on my airway those are little rings of Highland cartilage at the ends of my bones like seen in the image there's pieces of hyaline cartilage and between tips of ribs and bones of sternum what does that mean that's this this is the sternum these are the ribs but there's cartilage between the tips of the ribs and the bones that make up your sternum the ribs don't go all the way to the sternum so if you palpate your body if you try to feel next to your sternum boy that cartilage is very stiff if you push hard enough I feel a little bit of flex but it's quite stiff quite a stiff type of cartilage and it typically has kind of a glassy appearance you can see that these are the cells the chondrocytes and they live in these little pockets or bubbles called lacunae and the cells can divide in there so you might see just one cell in there you might see up there like four cells inside one little lacunae one little lacunae means a lake like a small pool or a lake what these chondrocytes do is secrete this gel like matrix so that's what gives this cartilage a little bit of flex is this flexible gel like ground substance found within the matrix and their collagen fibers within this matrix to provide the strength of hyaline cartilage compare that to elastic cartilage it's found in very different places the Oracle of your external ear and your epiglottis well what's the epiglottis if you can look far enough down somebody's throat this is the epiglottis it's a little flap of elastic cartilage and when you swallow it blocks your airway to keep food out we're gonna learn more about it later but that's what it is so this type of cartilage is very flexible it can be bent and bounced back to shape and it looks kind of similar to Highland cartilage except all these cells these chondrocytes inside the lacunae are separated with a very dark purple color that is all the elastic fibers so comparing that to this the cells have a very gray or light purple or clearish matrix between them here that matrix is very dark purple and our last cartilages fibrocartilage found in the pads and your knee joint your menisci between the pubic bones and in your intervertebral discs so in this picture we can see the disks in between the vertebrae that's fibrocartilage hopefully you can picture your knee joint but when I say between Cupid bones of pelvis this is what I mean right here this is the pubic symphysis that's a chunk of cartilage separating your two pelvic bones and when you walk or run especially you don't want the pubic bone smashing into each other this is a pubic bone here's a pubic bone so this cartilage helps cushion this articulation this location and your body where bone meets bone if you have been pregnant had a couple kids maybe you may have experienced a lot of pain in your pubic region because this cartilage starts to break down before you have children it loosens up so that this space can widen and allow birth to take place my wife had a hella sore pubic symphysis during all those pregnancies okay so its goal is to resist compression and cushion wear bone meets bone and there are little chondrocytes in lacunae it's not quite as clear perhaps the lacunae here gotten lots of collagen for strength so let's finish with bone we'll just do a little bit it's found in the skeletal system it gives your body structure helps protect organs like your rib cage is protecting your organs and it stores minerals calcium for one but others as well it's made out of a matrix that has hard calcium salts and collagen fibers basically these calcium salts are very very hard they are what make makes bone hard the collagen fibers are what give bone strength but still a little bit of flexibility in spongy bone like at the ends of your long bones you'll see these crazy net like patterns that's called trabeculae that means bridges or branches so they're like branches of bone that's what spongy bone looks like if you look at compact bone like much of your skeleton it's compact bone you will see these circular structures called osteons and all these little black dots here those are the osteocytes specialized bone cells living in little pools called lacunae if that term sounds familiar it's because cartilage also has its special cells living in lacunae and bone and cartilage are very closely related but we'll save that for another day okay so that's connective tissue we'll finish next time with very quick looks at muscle and nervous tissue and we'll introduce a few more concepts we need to understand to really fully comprehend the magic of connective tissues