Transcript for:
Overview of Animal Tissue Types

hi everybody and welcome back today we're going to be looking at the different kinds of animal tissues and going through this topic the most important thing to keep in mind is that every tissue has a specific function and its function is linked to its shape now there are four main types of tissues that we are going to cover and that's connective tissues epithelial muscle and nervous tissue now there are subdivisions of each of these tissues we're going to go through their specifics what they look like how to identify them i'm also going to look at some micrograph pictures and some ways in which these can be asked in tests or exams so to begin looking at our tissues we need to start off with looking at epithelial tissue one of the simplest tissues in the body and we need to look at its structure so we can understand how we use it and its function and why do we find it in these specific locations so our basic structure of our epithelial tissue is very simple the cells are often one layer thick as we can see in this example however they can also be multi-layered in other words they can also be what we call stratified in other words you get like layers of them on top of each other and they're fairly simple cells but some of the most important things we need to remember is that these cells are our protective layer and in order to hold them close together we need something called a basement membrane a basement membrane effectively is a thin membrane that sort of acts as like a sticky surface for our cells to be attached to and you'll notice that if you look very carefully there are very few intercellular spaces in epithelial tissue and that's because if we look at the function you'll notice that it is there for protection and lining the internal and external surfaces of the body and you don't want any openings into the body if that's the function you'll also notice that there is a thin layer of connective tissue sitting under the base membrane and that's simply because we need to connect the epithelial tissue to the tissue that is sitting underneath this epithelial tissue which is sometimes fat or muscle another very defining feature of epithelial tissues are their nuclei now when we look at some of the examples i'm going to tell you how to tell the difference between them in pictures but you want to keep an eye out for the shape of the nucleus some epithelial tissues they have a circular nucleus like the one we can see alongside and then others have a more elongated nucleus almost like a teardrop shape so keep your eyes out for those nucleus shapes and varieties the last thing that we're going to familiarize ourselves with with basic basic epithelial tissues is their overall shape and epithelial tissues are mostly geometric in shape which means that if we look at these cells these have a very square-like shape to them you will notice that a lot of epithelial tissues follow a very similar pattern they seem to have a square or a rectangular shape to them now let's look at the three most basic shapes that we find epithelial tissue in and that is a squamous collection of cells a columnar and a cuboidal now as you can already imagine and you can see by the pictures these tissues are largely based off of their shape and that's where they get their name from and we're going to look at their functions and how best to identify them let's start off with squamous epithelium so what we're going to be looking for is we want to look for a thin irregularly shaped cell and if we have a look at these you'll notice that it seems as though they don't have a very definite shape to them sometimes they look like flattened squares sometimes they look like a flattened diamond shape but essentially what you're looking for is very flat tightly compacted cells and you'll notice that a very defining feature when you are looking out for them and how to identify them other than their flattened appearance is you are also looking for the flattened nucleus and the nucleus seems to be squashed in this lower area in the cell and so it's almost as though you've taken a circle and you sort of squashed it in the middle so it's bulged out on either side where do we find the squamous epithelium we find it in the lining of our mouth alveoli and in the surface of our skin and many other places generally i like to remember squamous as the tissue that we often actually lose every single day think about all of the lining of your mouth how it renews itself every day the skin on the surface of your skin that renews itself every day so squamous tissue is something that you are maybe very familiar with and you'll notice that this tissue actually heals very quickly and it needs to because remember epithelial tissues are there to protect so you need to renew that layer very quickly now when it comes to columnar epithelium we're looking for these elongated cells essentially you're looking for a very long thin rectangular cell and often the way we look for them and how we identify them is we're going to look for an oval shaped nucleus if we have a look at the photograph just above here you'll notice that they're mostly positioned pointing upwards and they're not very circular the nuclei so you're looking for that oval shape now they can also be ciliated now this columnar in this photograph is not ciliated but effectively what cilia look like are these tiny hair-like structures that grow off the surface of our columnar epithelium and essentially all you would call them is ciliated columnar epithelium and basically what they do is all of these little cilia these little hair-like structures they increase the surface area of the columnar epithelium making a lot more surface area which means that there's a lot more absorption it's more efficient now generally columnar cells are associated with secreting mucus and so that's why it's important to have a larger surface area because generally mucus is also there for protection but also for absorption and the more surface area there is the better you can do those jobs another thing that columnar is associated with as i mentioned is digesting food often this is the site of absorption it's where food is diet when it's digested in the um digestive system in your stomach and then when it moves into the small intestines that needs to be absorbed and it's the columnar's job to do that and so popular places that we find our columnar epithelium is in your intestines and also in your gall bladder as well last but not least is our cuboidal cells and their name also gives it away they look like squares and so we're often looking for these defined square shapes um and they also have a very very very spherical nucleus and that is something that really sets them apart from the other epithelial tissues is how circular their nuclei can be um you'll notice that generally when we look at cuboidal cells you'll see that often you're given what looks like a tube made out of them and that's to signify generally the um orientation the way in which they're all they're way in which they're set inside um of our structures it's generally lining tubes and that then makes sense because if we look at its function it's therefore absorption and secretion so a lot of these cuboidal cells main job is to absorb substances or to secrete them and that secretion of substances can be a variety of things it can be hormones it can be sweat it can be excess salts and potassium there's a variety of things that these cells can do and we often find them in our sweat glands in the thyroid gland and also lining the tubes of the kidney now if we move on to our next type of tissue we're going to look at the nervous tissue and the nervous tissue is responsible for conducting electrochemical signals between the organs of the body and the brain essentially these are our message pathways it's where all the instructions are sent between the brain and the auger organs of the body the effectors the muscles and essentially we have to get the message from one location to the next and we have three different kinds of nervous cell tissues that you'll be able to identify you must be able to label these as well um and it's really important to know what they look like because the slight differences between them tell us not just what message they carry but also where and how do they connect to other nerve cells so let's start off with um actually i'm going to begin with this sensory neuron over here i'm going to start with the sensory neuron because it is the neuron that would be responsible for sensing in other words the information is coming in to you from this cell and generally things associated with sentry neurons are your senses so sight hearing smell etc and so what will happen is if we break down the overall structure of a nerve cell all nerve cells have four basic components they have dendrites they have a cell body they have an axon and axon terminals and these are the basics of what every single one of these nerve cells have now what's important to notice is the difference in the structure so our sensory neuron and how we tell what it looks like is its cell body which is this structure over here sits off to the side almost separate it's got a little extension and essentially what happens is this the flow of the impulse always enters through from the dendrites so that means we're going to receive a message from your receptors maybe like your eyes or your skin you're going to sense the stimulus that's going to move through the dendrites it's going to go past the cell body the reason why it needs to go through it and passed it is because the cell body will determine where that message needs to go next and then it moves into the axon and then finally out of the axon terminals where does it go past there well i'll get to that soon what's really important is the naming of these regions and so this is the important part i want everybody to know the area before your cell body is the dendrites the whole area the area after the cell body is known as the axon and you're going to notice that this label moves slightly depending on which one we're looking at let's look at the motor neuron so a motor neuron is a neuron responsible for movement particularly with your muscles and this is where you're going to carry out your function so let's say for example the sensory neuron has picked up that you've put your hand on a hot plate the stove is still on now you need to move your hand away from that hot stimulus and so the only way to do that is for the motor neurons to contract your muscles and to move your hand away from the hot object so yet again you will notice that this structure of the motor neuron is slightly different you'll see that the cell body is sitting right in the center of our dendrites and you'll notice that the axon label is a little sooner and so this is what i want to clarify with everybody because the cell body sits inside of the dendrites that means just this upper area is our dendrite area whereas everything beyond that all this lower part here is the axon and so essentially wherever the cell body is will determine where the axon is versus where the dendrites are and so what happens in our motor neuron is yet again the message will come from the dendrites it will go down towards the axon terminal and then into the next neuron that's next door and motor neurons um are multi-polar it means that they have lots of these little um dendrite branches as you can imagine and that's because they need to be able to send the message to multiple locations last but not least we have relay neurons or we also call them interneurons um and basically an interneuron is like the name says like an in-between neuron and these are the neurons that we find mostly in the spinal cord and in the brain and interneurons literally relay information between the sensory neuron and the motor neurons so if i were to draw in arrows what happens is information will come in from the sensory neuron it will go to the relay neuron or the interneuron a decision will be made and then that decision will be sent out of the interneuron to our motor neurons to tell the motor neurons what to do and how to move yet again if we break down the structure of the interneuron which is very important i want you to notice that the entire area before the cell body is the dendrite the area after the cell body is the axon and how do we tell that this is an interneuron well the cell body sits inside of the center of our nerve cell and so when you compare the three side by side they have a lot of similarities but the key difference is where the cell body sits moving on to connective tissues now there are six major types of connective tissues and essentially a connective tissue is there to support and stabilize and protect your body's organs and to be a connective tissue you are have to have a certain structure to be called a connective tissue and that is you often need to be a group of cells surrounded by either a fluid or a matrix and this fluid or matrix can be a liquid but it can also be a semi-liquid or a solid and like the name gives away connective tissues connect one tissue to another some of them we're very familiar with and some of them are a little bit new to us as well so we're going to start off looking at our tissues um and we're going to cover um the basics of what they all look like how to identify them and what are their functions now looking at our first type of connective tissue we are going to look at areolar tissue and areolar tissue is a very basic tissue and what it does is it actually binds epithelium it often sits below the epithelial tissue it's what we saw a little bit earlier on in the video when we did a basic structure of epithelium and we looked at the cells in the basement membrane you need to stick those epithelial cells to the next tissue and the best way to do that is to use areolar tissue and in order for it to be a connective tissue it must be cells suspended in a matrix now this matrix is mostly made out of collagen and elastic fibers and we can see that if we have a look at the diagram the elastin fibers are the really thin stretchy fibers whereas the collagen fibers are much thicker and they're not as stretchy they give strength to this particular connective tissue and we often find areolar tissue in between our organs it actually attaches our organs very loosely to each other so they sort of stay in place and it's also found like i said under the surface of your skin the next connective tissue is our fibrous connective tissue and this tissue is a little bit more neatly arranged than its areolar chasm and you'll notice that it's a dense network of non-elastic collagen in other words we don't want this substance to be stretchy we want it to be strong and it needs to be flexible so it needs to be able to bend and twist but not stretch the problem with stretching is that sometimes it doesn't go back into its original shape now the easiest way to identify fibrous tissue is you're going to look for these elongated rows of fibers so if we look up at the picture you'll see what i mean by you're going to look for these long elongated fibers that are all going in the same direction and these little fibroblasts are the cells remember we're always looking for cells that are suspended in a matrix which in this instance the fibroblasts are the cells suspended in the collagen fibers now where do we find these well we mostly find fibrous tissue in our tendons and our ligaments remember that tendons attach muscles to bones and in ligaments you're going to join a bone to a bone last but not least is cartilage now our cartilage there are many different types and i'm just going to do the very basic idea of what cartilage is but cartilage is a connective tissue that provides a lot of prevention of friction and often yet again it follows the same principle we have cells suspended in a matrix in this instance we have what we call chondrocytes and they are found in their sort of semi semi-fluid semi-solid matrix and often cartilage has a very smooth glossy appearance if you have a look at the diagram you'll see what i mean in that each of these little purple individuals is the cell it's sitting in a little empty space which we call the lacuna or lucunai depending on how you want to pronounce it it's this little empty space and these chondrocytes actually secrete out the fluid or the semi fluid that sits around them that's this light blue substance that's the actual matrix and the purpose of cartilage is to absorb shock so we often find this in between bones and at our joints in our ear in our nose it's important to know that there is more than one type of cartilage and depending on what the cartilage needs to do the next type of connected tissue is blood and blood is actually the only liquid connective tissue all the other connective tissues are either a semi-solid or completely solid and when we look at blood there are three major types of cells that we're going to be looking at we're going to be looking at the lymphocytes which are the white blood cells we're going to look at the erythrocytes which are your red blood cells and then you get something called platelets platelets are technically cell fragments they're not whole cells each one of these cells has a different job lymphocytes are for your immunity and your red blood cells are for carrying around gases and platelets are there for blood clotting and so the most common functions of blood is that we're going to transport waste nutrients and also hormones now blood carries chemical messages around the body um often in a liquid form whereas if we mentioned previously in the nervous system the nervous system transports electrical messages and where do we find blood well we find it in the circulatory system within all the blood vessels the veins arteries and capillaries remember it's important to know that blood shouldn't be outside of the arteries or the veins and that might lead to internal bleeding so you want to keep them inside the circulatory system next we have is the adipose tissue now adipose tissue is largely made out of fat cells interestingly enough you're born with a certain amount of fat cells and and if you gain fat the cells just get bigger you don't actually grow more fat cells and the purpose of adipose tissue is to store excess energy so this is when you don't use all your carbohydrates up and you need to store it for later but it also provides insulation for heat retention but also to keep the body cool depending on what needs to happen from the external environment and where did we find adipose tissue well we found it around our organs it gives it a nice insulation keeps your organs warm but also cushioned and it's also under your skin and it allows your skin to insulate your heat it allows your skin to be a bit more supple and softer and flexible last but not least is our bone tissue and we'll go into bone in a more detailed video later because it requires a lot more explanation but the basic idea is that bone is made up of a network of systems and what i mean by that is you'll notice if you look at the diagram there seems to be a circular structures stacked next to each other they're called have vision systems and essentially what that means is these cylindrical or circular concentric circular structures give your bone their ultimate structure and their function and in yet again a connective tissue style our osteocytes are these cells that make up your bone and they secrete the solid matrix that sits around them so the osteocytes in this picture here are represented by these little purple cells and those long sort of outgrowths are how they secrete out your solid bone matrix it provides a framework for your body in other words it's ultimately the structure of your body because it makes your bones and it also allows for muscle attachment where do we find bone well we find it in the skeletal system finally we can look at muscle tissue and muscle falls into three categories we have skeletal muscle smooth muscle and cardiac muscle and um often the name that is given to them is representative of actually what they do and i'm going to tell you exactly how to tell the difference between the three starting off with skeletal muscle so when we're looking at skeletal muscle what we're looking for is striations and it's one of the most defining qualities of skeletal muscle and striations are these things little stripes that run down um the muscle fibers so you're looking for those striations it's one of the most important qualities and the reason why the striations are there is those are the little components that actually contract and then relax which makes the muscle actually move another defining identifier for skeletal muscle besides their stripiness is that they have lots of nuclei so they're multi-nucleated and what that means is one muscle cell will have multiple nuclei embedded in it and you can see that in the diagram above all those dark little flattened circular structures are the multiple nuclei now skeletal muscle is involved with voluntary movement which means that's the movement you choose to do that's like running walking lifting up a glass and those are things that are actively happening within your brain and you you think about doing them where do we find the skeletal muscle well it's attached to our bones and it allows us to move so when looking at smooth muscle we're looking for muscle that is not striated and that is really its defining characteristic there are no stripes and you need to look very carefully because when you look at the picture above it sort of looks like those are stripes but don't be fooled those are the muscle fibers but if you look at the individual fibers you will notice that there are no stripy appearances and what you're actually looking at are these thin spindle shaped fibers now spindle literally means if we look at the cell shape you'll notice that it is quite swollen in the middle and then it gets skinnier at the end that is what spindle means it means it's quite big in the middle and then it tapers off and it gets thinner and thinner near the edges of the cell now in terms of its function smooth muscle is responsible for involuntary movement these are movements you don't have to think about they just happen like blinking or coughing or breathing and so often we find these um muscle tissue types in the digestive system and in our blood vessels these are systems that we don't have to think about moving they just move for us finally we're going to look at the cardiac muscle now the cardiac muscle is a tricky one because we often confuse this with skeletal muscle when we look at some of the diagrams and what you're going to look for is its most defining feature which is it's that it's a network of branch muscle fibers and if you look at the diagram above you'll notice what they mean you have a muscle fiber and another muscle fiber and they are connected with these branch branch-like structures that run through them they're almost interconnected so you're looking for those branches to tell you if this is cardiac muscle or not something else that can help you look for and identify cardiac muscle is it does have striations so that might help you tell that it's not smooth muscle because it has striations but if you're going to tell the difference between skeletal and cardiac muscle the striations are a little bit fainter they're a little bit fuzzier in this diagram in the micrograph they're very difficult to see so what we are looking for here is this branchiness this almost fibrous look to it and that's what we're looking for that's what's the most defining feature in terms of its movement it's responsible yet again for involuntary movement but very very specific involuntary movement because it's only found in the heart that's the only place it's found hence the name cardiac interestingly enough the heart is made up of a muscle the cardiac muscle which is the only muscle in the body that can move on its own in other words it requires no instructions from the brain in order to function in this video we have covered an enormous amount of content with a lot of terminology and these are the most basic terminology words that you need to have known from this topic first of all we need to know that we have four types of tissues we have the epithelial tissue which lines the internal instrumental surfaces provides protection the nerve tissues which transport electrochemical signals the connective tissue which holds all the tissues together and our muscle tissue which allows movement we looked at squamous epithelium which is the squashed squares we have the columnar the elongated longer cells they secrete things and the cuboidal cells are square like cells that line the tubes they also secrete some substances we looked at the sensory neuron which is how you sense your surroundings how you see hear touch taste motor neurons which is how you move it's the neurons responsible for telling your muscles to move and interneurons these are the neurons that make all the decisions within the spinal cord and the brain we then looked at the connective tissues areolar is loose it sits just under the surface of the skin and basically attaches epithelium to other tissues fibrous which is what we see in our tendons and ligaments it's not very stretchy we've got blood the only liquid connective tissue bone our solid connective tissue which provides the framework for our body adipose which is where we have our fat cells for insulation and also for cushioning and then we looked at muscle we have skeletal muscle which is striated it can move on its um when given instructions which means it's voluntary and it's attached to our bones smooth muscle is involuntary it moves without us telling it it's responsible things like breathing for digestion we find it in the digestive system we find it in your esophagus and lastly we looked at your cardiac muscle this is the muscle that the heart is made out of it's also involuntary muscle it moves on its own and it's very special because it's the only muscle in the body that can move without being told to move by the brain i hope you've enjoyed this lesson and that has been very useful to you and i will see you all again soon bye