all right moving on to chapter three in chapter three we're going to look at tissues and that's going to be histology histology is the study of those tissues so now tissue by definition is a group of cells similar in structure that perform a common or related function so they're all going to look pretty much the same and they're going to be set apart when we start to look at other different types of tissues as we go through this if you take the time just to pick out one characteristic maybe two characteristics about that slide or image that you're going to look at you're going to be able to identify all the tissues that i'm going to go through and histology of course is the study of tissues first a little bit about how they make the slides and eventually get those pictures tissue preparation it is from once living organism first it has to be fixed so it doesn't decompose so we're going to preserve it then it has to be sectioned section is a very thin slice of that tissue and it can be in longitudinal which is the length of something it could be a cross section it's literally a slice and then an oblique is always going to be in an angle between the cross transverse section and the longitudinal once they do that they're going to stain it most tissues are very bland and so the colorful stains that you're going to see on the pictures and slides are to allow you to see the different structures and then of course your your part is observation another way of producing some slides is by smears and spreads where they literally take tissue and they will spread it across the slide kind of like butter on toast if you will or in a case of liquid tissues like blood they just simply put a couple drops on there we're going to break this chapter down into four primary types we have epithelia epi for superficial connective it's going to do just that it's going to connect other things it's basically what binds us together muscle tissue is going to produce movement and then nervous tissue is for control we're going to start with that epithelial tissue now as we go through this this chapter i want you to realize that most of the tissues we're going to talk about are widespread through the body even though i'm going to give you one or two examples they can be found in lots of different different regions for example if we just look at the top bullet here the nervous tissue is your brain spinal cord but then literally these nerves are going to go down innervate every portion of the body right down to your toes and so we're not going to just have one lord or two locations most of these are widespread with just a few exceptions so epithelial tissue overall functions protection it lies on the surface absorption you have epithelial tissues that are internal so sometimes we need to absorb things like in our digestive tract filtration filtration is an important component of the urinary system excretion secretion now excretion are things that are produced that um we don't necessarily need and secretion are things that the body needs and that's going to happen across these epithelium linings and then since epithelia is on the surface it's really important with sensory reception from external and internal changes now some things about epithelial tissue that makes it unique it has something called polarity this means it has a top and a bottom surface specialized context most of the epithelia that you're going to look at has cell to cell to cell there's not going to be any gaps between them and so they're going to be really structurally sound underneath there's always connective tissue another important part that sets epithelial tissue apart from several others is its avascular that means there is no direct blood supply all the blood that goes into this lining has to diffuse in but because it's involved with sensory perception it is highly innervative there's lots of nerve endings and most epithelium can regenerate if it is lost so back to that polarity it has a top it has a lower surface that top surface is called an apical surface and this always is going to be exposed to a cavity or to the outside of the body it's always going to be the top edge that's one thing you can always count on with epithelia it's always going to have an edge to it basal surface is underneath of that and then it's going to be attached to more connective tissue now the surface of epithelial tissues are generally smooth and slick we want to reduce friction some of the epithelial tissues especially inside the body are for movement of things through these tubes and we don't want any hang-ups some have microvilli microvilli are for absorption and then some have cilia cilia are for movement now underneath episodic tissue we're always going to have a basal lamina this is what's known as an extracellular product it's out of the cell it's made up of a molecule called a glycoprotein which is for binding and then collagen fibers which is going to give strength to the above tissues it's going to act as a adhesive sheet it's literally going to help stick that tissue to the character tissue below it's going to be involved in a couple different filters that we're going to look at in different chapters as we go through and it's also a starting point for wound repair now some of those specialties contacts include tight junctions and what those do is they allow the epithelia to be literally a continuous sheet that covers everything and again that's one of the things with epithelia it's going to be cell on cell with no gaps between them now all the epithelial tissues are supported by a couple additional layers called the reticular lamina and the basement membrane now the reticular lamina is just underneath that basal lamina remember that's the glue it's an adhesive sheet and this is full of collagen fibers collagen fibers are very strong so it's going to give some strength now the base membrane is characterized as the basal lamina and the reticular lamina this again is going to reinforce the above epithelial sheet it's going to help reduce it over stretching and damaging itself regeneration this is an important component of epithelia because most epithelia is on the outside or inside of a cavity and it is exposed to lots of friction and this only works as long as we're healthy and so as long as you're a healthy individual most of the epithelia including your skin will replace itself now when studying tissues especially epithelium tissues you want to look at a couple things first cell shape cell shape can vary from squamous which is flat squamous thinks squished cuboidal which is kind of a blocky form cuboidal think cube that cube does not have to be four-sided it can be six-sided or eight-sided or in some cases even round um the thing with cuboidal is you just want to make sure it's the same dimension no matter how you measure it or similar dimensions now columnar is just that it's a column that is taller than it is wide so this is the first thing i would look at if you're when you're starting to decide what you're looking at now the different classes come in simple pseudostratified and stratified so simple is one cell layer thick and it could be any of the cell shapes pseudostratified looks like it has lots of layers but in this case it's just some of these cells have not grown to this to the surface so pseudo false stratified now stratified is just that it has different layers some cases there's a few layers in some cases there are dozens of layers the rest of this chapter we're going to start looking at the different types of epithelium and there's lots in the name right there are the titles you see simple squamous epithelium simple tells us it's one layer squamous tells us we're looking for a flat cell epithelium tells us that we're looking at a surface so again the cells are pretty flat there's not a lot of room for cytoplasm and you're going to find this where you need diffusion or absorption quickly for example in the kidneys and the lungs kidneys we're filtering the blood we're going to make a filtrate so we want to move things across that membrane in the lungs the whole idea there is to get oxygen into the bloodstream and then co2 back out so it's pretty quick we're going to find these in areas like the endothelium endothelium is the lining of lymphatic vessels and blood vessels and in the inside of the heart and the mesothelium this is the serous membrane that we talked about in chapter one so let's look at this cartoon first nice thin sheet squamous cells purple nuclei adhered to that basement membrane this is a section this is a section from a lung and you could see these flat cells making the individual walls inside of the air sacs for the lungs the location here is the lung itself but we can also find them inside of the kidney the lining of the heart and then the linings of all the cavities the ventral body cavities simple cuboidal again everything's right through the name we're looking for one layer cuboidal cell on a surface because it's still one cell we can secrete we can absorb and these are going to be found in some of the smaller ducts which are passageway and inside of the kidney tubules so here's this cartoon we're looking at a single sheet of cubed like cells all uniform this is a cross section of a kidney this is the simple cuboidal epithelium this is a kidney tubule and this is only found inside of the kidneys this structure it is located this tissue is located in other areas but this particular one because of this rounded shape of this tubule this gives it away as the kidney but look at the cells this one's almost completely square but we can have triangular cells and if you look around here you might see oval cells or other sides but the thing is it's all about the same dimension no matter how you measure it simple columnar same thing we're looking for columnar cells this time and again just because it's a little taller we can still absorb and secrete here's a cartoon nice tall cells this particular example is from the digestive system this is an individual cell it makes that columnar shape other things notable here are the goblet cell this is a gland that's going to secrete mucus into the digestive tract and the digestive tract is characterized by these microvilli that are right on the surface so simple columnar epithelium now pseudostratified is false stratified so the cells are going to look like they're layered but the cells in actuality they're just some are shorter and then some are much taller so here's our pseudostratified cartoon you can see cells not quite making it to the top and then you can see these cells that do indeed make it to that apical surface the particular example here is from the trachea you can see this stratified looking appearance to it but these columnar cells at the surface give it away as pseudostratified columnar now this is the trachea and so the distinguishing factor from this slide is that the cilia with pseudostratified columnar this is the only combination you're going to have and so that's going to give you the location remember cilia are for movement now stratified we're looking for layers and this is defined as two or more cell layers now on the free surface we're always going to have flatter cells and that's what you want to look at when you're looking at a stratified epithelium you want to look at the surface cells that's going to give you the type now the deeper cells since the younger can be cuboidal or even columnar but you always want to go to that apical surface this can also regenerate it's going to do that from the basal cells that are right at the bottom and then those cells are going to push upward like a conveyor belt all the way to the surface you're going to find this in areas where you need protection so this is stratified squamous epithelium we are looking for multiple layers and this whole darker region is that stratified squamous epithelium these cells have different shapes they're kind of blocky this one's a little bit taller but once you get to that free edge these are all stratified so that's what you want to look at this is also another example of stratified squamous epithelium all the way up all the way to the top you can see all these little flat cells up here now you are going to have to be able to tell the difference between keratinized and non-keratinized when cells are keratinized this means they have a protein in them that's going to give them some waterproofing and a little more structure and what happens as as these living cells which are located here move closer to the surface that keratin becomes so concentrated we can't get nutrients in here anymore and so all the cells above this line are dead so that's why they're all flat the other thing you don't see here are nuclei the nuclei are non-existent in this upper apical surface that's what gives away keratinized if we look at non-keratinized nutrients are able to move all the way up to the apical surface and we can still see the individual nuclei that's what's going to give this one away as non-keratinized nuclei on this side no nuclei over here now stratified cuboidal and stratified columnar do exist i'm not going to show you any particular examples of that because they're pretty rare cuboidal can be found in some sweat glands some mammalian glands and usually a couple cells thick now stratified columnar also exists it's a little bit in the pharynx a little bit in the male urethra and um again columnar cells usually two or three cells thick at the most here's a cartoon though of a stratified cuboidal epithelium you can see these kind of blocky cells in here and two cell stick this would be from a sweat gland transitional epithelium this is found in the urinary system this is going to give you a little bit of trouble it's going to look stratified it's going to look pseudostratified but i'm going to tell you i'm going to show you in a minute just how to tell these apart now transitional epithelium is designed to stretch especially in the urinary system so as the bladder fills up with urine it's allowed to stretch and so that epithelium could stretch with it without being damaged and as the urine goes through the ureters we have that same thing we can have stretch in there without any damage here is a slide of transitional epithelium it runs from this border all the way up to the top so again at first glance this could be pseudo stratified you might get tricked into thinking this is stratified columnar but what gives this away is the cells on top tend to be longer than they are high and so that's the distinguishing factor right here now one component of epithelia is there are glands embedded in it for secretion onto a surface and most of these secretions are going to be aqueous they're going to have a water component to them we can classify these by the site of the product release is it endocrine or exocrine endocrine is for release into a tissue this is involved with the hormones on the endocrine system and then exocrine this is a secretion onto a surface relative number of cells we can have unicellular these are the goblet cells that i mentioned earlier or multicellular now in unicellular we're only going to be concerned with those goblet cells these are found in the epithelium we can find these in the intestinal and respiratory tract and they produce a protein called mucin that mucin when we add water becomes mucus and this provides a nice slick surface to reduce friction here's a cartoon of a goblet cell this is a complete cell we have the nucleus you remember this is for dna rough er has those ribosomes on it mucin is a protein so this is for protein production golgi apparatus you should remember this is for packaging and shipping we're going to package all of that mucin into these vesicles they're going to slowly work their way to the surface to be turned into mucus now endocrine glands these are what are considered to be ductless everything that goes out of these glands is secreted through the cell wall into tissues this again is for hormone production and those hormones when they're secreted in the tissues get picked up by the lymphatic systems or the bloodstream and then can travel through the body so endo internal secretion exo external secretion this always goes on to a surface lots more of these than the endocrine glands all of your sweat glands all the oil glands on the surface of your skin are an example they're going to make the products those products are going to be secreted into ducts and then again we're going to a surface again mucous glands sweat glands oil glands salivary glands inside of your mouth are all examples here's a couple cartoons we have an endocrine gland usually associated with a nice rich blood supply so that as those hormones are produced they can be picked up and then transferred out exocrine gland is a series of cells it's going to secrete the product into this duct system and then eventually this duct system is going to go on to the surface either internally or externally different types of those glands include serous glands these secrete thin watery fluids like the serous fluid we talked about previously mucous glands they secrete mucin that becomes mucus in your digestive system you have mixed glands that secrete a whole host of different things and then cytogenic glands are glands that release whole cells and this is going to be for the ovaries and sperm cells in the testes now exocrine secretion is different depending on the type of gland american glands do it by exocytosis so little pockets are going to be released slowly the american gland cell continues to be healthy apricorn glands sit right in between between the top and the bottom one that i'm going to talk about in a second these generally fill up with more product and then release a lot of it at one time but they still live on these cells aren't completely damaged holocrine glands are the cell is going to fill up with product and the entire cell ruptures then and then that cell is completely lost now this cartoon shows you the different types of excretion so the merocrine cell we're going to fill up these vesicles those vesicles are going to go to that cell surface and release this would be the example of what happens inside a portion of the mammillary glands now apricorn also involved with mammalia ground secretions these are larger vesicles so this is a larger amount going out at any one time but the cell continues to function just like the american cell now the holocron gland is made up of cells that produce products until literally they are full and then once they're full they're making their way to the surface and they literally just rupture and then spill onto the surface these are secretions like oil glands and and things like that