okay in this tutorial i'm going to cover an introduction to histology now this really is just an introduction if you want a the deeper view into histology please go to the histology wizard my friend and colleague dr kathy moore her youtube channel for much more in depth this is kind of think of like histology for basic tissues light and in this i'm going to answer the questions what is the hierarchical organizational living matter what are the four basic tissues in the body and what are the descriptions and functions hello everyone my name is dr morton and i'm the noted anatomist all right so first what's this hierarchical organizational living matter that looks like a bunch of steps well first cells are the smallest unit of living matter and there's about a trillion of them or so give or take a few inside the human body things like red blood cells brain cells muscle bone cells and so forth now if you take cells and put them together you get tissues so the definition of a tissue a group of common cells organized for a common purpose and there are four basic tissues in the body epithelium connective muscle and nervous i'm coming back to this now you take the tissues and put them together you get an organ an organ is a group of tissues organized for a common purpose organs like your heart lungs stomach kidneys and so forth and then you take organs and put them together you get organ systems which are a group of organs organized for a common purpose like your cardiovascular respiratory nervous endocrine systems you put all those organ systems together what do you get you get an organism you get you okay so there is this hierarchical organization of living matter now that is histology the study of tissues the study of epithelium connective muscle nervous that's we're going to focus on and it's miraculous thing because these are the materials that everything in the body is made from just those four tissues now another way i've kind of heard histology is histology oh that's looking at slides with purple dots and pink stuff because you get a slide that looks something like this you're like oh purple and pink this is called a hematoxylin and eosin stain in short an h and e stain it's the most widely used stain in histology and in pathology in in medicine hematoxylin stains the nuclei purple because it stains nucleic acid purple and eosin stains proteins pink and so when you look at something like this and you zoom in you're like well there's something dark purple that's a nucleus here's some pink stuff probably proteins and we zoom on this one and go what's this purple dot that's a nucleus what's this pink stuff the proteins and it helps us to get an idea of the parts of a cell and in the case we're going to talk about the parts of tissues so here are h e stains for the most part there's a couple of differences in here of these four basic tissues epithelium connective muscle and nervous and we're going to start with epithelium now epithelium forms glandular tissue and it lines the lumen the hollow part of tubular organs and body cavities it also externally covers the body and organs so here's a liver and that's epithelial tissue because the liver is a gland here's the pancreas both exocrine and endocrine glands you see all those purple dots all those are epithelial cells and what about this the inside lumen of your stomach there is a bunch of epithelial cells like that it's lining the lumen of tubular glands in this case so glandular tissue liver and that this is lining tubular glands now what about body cavities so here that blue there is a serous membrane lining the inside of the thoracic cavity and same for abdominal and what about externally covering the body well there's your skin and that's showing the epidermis the epidermis the entire outside of our bodies covered in epithelium and then what about lining organs like that in orange those are visceral chlorides lining the outside of many of our organs now epithelium consists of cells that are anchored to a basement membrane and the cells have apical and basal surfaces so there's epithelial cells there's a basement membrane and there's an apical and basal surface basal means it's anchored to the basement membrane apical means it's towards the surface and in epithelium there's no extracellular matrix or ecm and that the tissue the epithelial tissue is a vascular without blood supply so there's there's very little if any space between cells and as a result there's no blood vessels so epithelium is avascular so epithelial tissue is like bricks cell right beside each other now the basement membrane not bowel movement anchors epithelium to the underlying connective tissue where the capillaries reside so there's the basement membrane and there's the loose connective tissue and there's a capillary and that capillary is allowing the oxygen and nutrients to diffuse into the epithelial cells to supply it so there's a capillary and there's a capillary and cross section that second arrow is what it looks like often in an h e stain there's epithelium all right now how do you classify or name each of these types of epithelial so there's epithelium is overall tissue but there's different flavors of epithelium and so we do it by describing the layers of cells the shape of the cell specialization and that gives us the type of epithelium all right so let's first talk about layers of cells the word simple is used if there's one layer of epithelial cells anchored to a basement membrane so there's in each of these cases there's one layer of cells touching the basement membrane now the term stratified is used for more than one layer of epithelial cells and only one layer touching the basement membrane so notice many layers not touching the basement membrane in both these examples now let's talk about the shape of cells if a cell is flat with a nucleus that is flat we use the word squamous which means scale-like and in a side profile view it looks like an egg on a side or from a bird's eye view like that the next is square or cube shaped cells where the nucleus is round and centrally located we call that cuboidal tissue and if it's tall and thin with a basally located nucleus we call that columnar tissue now specializations of epithelial cells if the cells have cilia which are the movers here we have ciliated columnar cells and the cilia move and so for example if that's a goblet cell that's making mucus watch what happens is that the cilia is moving that mucus along the apical surface and so silly are kind of like what you see at a concert for crowd surfing so they got a bunch of people you know how they're on top and someone jumps in and everyone's arms move and the person floats on top that's what cilia does except with stuff like mucus lots of people with arms lots of cells of cilia um yeah okay now just explaining that analogy a little bit more so if this epithelial tissue has cilia we call that tissue ciliated um oh here's an example of it so there's ciliated columnar cells where that's the cilia shown on the apical surface and there's a goblet cell that's making that mucus okay like that now another specialization is called microvilli and it increases surface area for absorption so there is a cell with no microvilli and notice the amount of space on that apical surface so the surface area for absorption is limited now take a look at this cell with microvilli and take a look at how much space now if we the surface area for absorption we pull that out and go shing it's got far more surface area for absorption this is why we find in kidney and gi tract cells with microvilli 25 times more space surface area for absorption here's one example and it kind of looks like bart simpson's head is when you see a cell with microvilli in histology because those uh that the specialization they're so close together these microvilli often the terms is used in light microscopy is a brushed border there's a nucleus there's one cell and so it looks like a brush on the top so the microvilli described as having a brushed border now another specialization is keratin which is a structural protein that protects epithelial cells from damage and stress and it's water insoluble so the epidermis is a good example of a primary place we find keratin or your hair or your fingernails all have this structural protein keratin all right now that we have that in mind let's name and go through these different flavors of epithelial tissue let's start with simple squamous epithelium simple because there's one layer of flat or scale like cells and it's epithelium notice that that nucleus is flat and it's epithelial tissue so there we have simple squamous epithelium now the functions of this because it's so flat and thin is it's ideal for diffusion and filtration and lubrication so here are some simple squamous epithelial cells so notice that gases like oxygen and co2 go through very thin cells to allow for more facilitated diffusion this is why you find simple squamous epithelium in the alveoli of your lungs when you breathe or capillaries when gases are exchanging systemically another is filtration when things like water or electrolytes like sodium chloride are diffusing between cells and you find these often in capillaries the glomerulus of your kidney and the liver and then lubrication where you've got these thin layer of cells like you have in serous membranes and they make this serous fluid you'll find it in the pleura in your lungs pericardial sac in your heart and peritoneal cavity in your abdomen those are the serous membranes i just mentioned so there's the function functions a simple squamous epithelium let's look at a couple of examples this is a green corpuscle so you see that one flat cell there's the nucleus there's i just you don't really see the cell membrane in an h e stain so i imposed a membrane is what i just drew in the black line and there's where the basement membrane would be where the other simple squamous cells are anchoring and deep to that is loose connective tissue and the basal and apical surface the basal surface faces the loose connective tissue where the capillaries are at the apical surface in this case faces the filtrate in the glomerulus simple squamous epithelium all right what about simple cuboidal epithelium one layer of cube shaped cells that make epithelium and you'll notice that the the the in cuboidal cells the nuclei are centrally located and they're kind of oval okay um and it's epithelium okay so now the functions of simple chloride epithelium are absorption bringing stuff into the epithelial tissue through the basement membrane and into the capillaries or secreting substances from the cuboidal cells into the apical surface the locations are like the nephron is a key place like the tubules and cross section can you hear that those are my boys because of summer break this distal tubulin cross section is ideal for reabsorption or secretion or a sweat gland which is ideally for a deal for secreting sweat and salts into the lumen free to sweat out so here when we zoom in there is a nucleus of a cuboidal cell with the basement membrane there with the loose connective tissue deep to the basement membrane on the basal surface and the apical surface facing the lumen of this tube all right simple cuboidal epithelium now simple columnar epithelium are one layer of tall thin cells with the nuclei either being round at the base or a narrow nucleus and it's an epithelial tissue so simple columnar epithelium and it's also ideal for reabsorption or absorption like you'd have in the intestine or secretion like you'd have in also the intestines or your airways of the bronchi and often simple columnar epithelium are lined with microvilli and cilia more on that later all right and this is why we find simple columnar epithelium lining the gi tract from the stomach to the anus glands airways uterus uterine tube and so forth there's a gi tract and there we have simple columnar tissue okay here again is a nucleus and there's one cell with the basement membrane shown with the loose connective tissue by the basal surface and the apical surface near with a brushed border of microvilli where the lumen and the food would be this is the jejunum so your small intestine simple columnar epithelium all right now stratified squamous epithelium the term stratified for more than one layer more than one layer of cells like that and only one layer touching the basement membrane squamous because of cells that are flat you're like wait those cells aren't flat those are square stratified epithelium is named for the apical surface of apical layer cells and you'll notice those are flat and this is epithelium so stratified squamous epithelium stratified squamous epithelium is ideal for protecting underlying tissue from abrasion and often these cells or some of these cells have keratin and so you notice that these cells up here are good for abrasion it's kind of like an eraser and you rub it things come off but the rest of the tissue and the rest of the cell stays intact or rest of the pencil stays intact so i just got invisalign and because my teeth are really quick and my dentist says i need to get it i thought i'd share that with everyone it's really weird to talk with this so sorry if i sound like i'm gonna spit all the time i kind of feel like i'm gonna spit all the time now the location is a tangent for stratified squamous epithelium is any place you need protection from abrasion like the epidermis the outside layer of skin or the esophagus and the vagina now these three things the epidermis is keratinized and so when you see the skin those apical layers are keratinized with which means all of the cells are filled with keratin and they're dead and they get rid of the nucleus and organelles to make room for keratin and that's your epidermis whereas the um so there's no nuclei whereas in the esophagus or vagina this is non-keratinized stratified squamous epithelium so you'll see nuclei all the way to the apical surface so is the epithelium stratified squamous cratinized epithelium multiple layer of cells there's the basement membrane there's the loose connective tissue deep to the basement or basal layer and if we take a zoom in on that there you can see the nuclei and then we take a look at the apical layer like this there are no nuclei there okay and there's the environment like the air all right now transitional epithelium or urinary epithelium has more than one layer of epithelial cells uh the the apical layer are dome shaped or festoon shaped and the functions for stretch and pur uh it stretches and permits dissension of a urinary organ empty bladder full bladder empty bladder full bladder and why it's called transitional epithelium but urinary is better because the only place we find it is in the urinary system like the ureter the bladder and the proximal urethra so here's an h e stain where there's the basement membrane right there and there is the multiple layer of cells with the loose connective tissue deep to the basement membrane the basal layer cells and the apical layer cells and they're dome-shaped and that's where the urine is okay transitional epithelium pseudostratified ciliated columnar epithelium now this prefix pseudo it says it's pseudostratified what does that mean well if you look at all these different cells it looks like some cells are lying on top of each other like there's more than one layer so looks like there's more than one layer of cells but every cell is anchored to the basement membrane therefore it is falsely stratified pseudostratified and that many of these cells has cilia so we use that specialization ciliated they're tall thin cells so we use the word columnar and it's epithelium hence pseudostratified ciliated columnar epithelium now epithelium is a tissue and a tissue is a collection of cells that's why you'll notice that there are different colors of cells that have different functions different epithelial cells make this pseudostratified ciliated columnar epithelium now the function is secretion mainly mucus and the propulsion of mucus by the cilia to the outside of the body so the goblet cells secrete mucus and the cilia propel that mucus to the top of your throat and you spit it out okay the locations are primarily the trachea and bronchi the bronchial tree and this is why often is simply called respiratory epithelium which is i far prefer so here is an h e stain of respiratory epithelium there is the basement membrane now i keep adding it because you cannot see in an h e stain the basement membrane but you can see the difference between the proteins in pink and the dark purple for the cells so you impose where the basement membrane is and there's the loose connective tissue deep to it the basal layer and there's the apical layer and there's looks like there's multiple layers of cells but they all actually touch the basement membrane there's one cell and there's another cell and there's another cell and there's another cell and there's another cell okay each cell's anchored to the basement membrane and there's the cilia that brush border okay and there's the air all right now there is all the epithelium then we have in a nutshell we now go to connective tissue so connective tissue there are four different types of connective tissue they're all derived from the same embryonic tissue called mesenchyme that derives from the mesodermal layer of a developing embryo and the four different types are connective tissue proper cartilage bone and blood if there's talk about an eclectic group of different cell tissues a where but they all possess the same structure a small number of cells surrounded by an extracellular matrix so there are connective tissue cells and there is lots of extracellular matrix or space between the cells epithelial cells in contrast are like bricks right by each other connective tissue there's lots of space between cells okay epithelium has no space so all of these have a small number of cells fibroblasts and connective tissue chondrocytes and chondroblasts and cartilage osteocytes and osteoblasts and bone and red and white blood cells in the blood and they're surrounded by an extracellular matrix all of them have a space surrounding these cells so let's talk about connective tissue proper those the primary cells are fibroblasts and they're the primary connective tissue cell they synthesize the extracellular matrix the collagen and elastin fibers in the ground substance so there's a fibroblast and it produces or synthesizes collagen and elastin here is a fibroblast and there are the protein fibers in this case primarily collagen now connective tissue proper also has adipocytes which are fat cells that store lipid in a single droplet here's an adipocyte a lipid droplet and a peripherally located nucleus and that's with the whole thing together that's adipose tissue so we zoom in there's one adipocyte a lipid droplet with a peripherally located nucleus oops and all of those different cells have that it looks like white space because when you do an h e stain it actually takes out the fat so the white space is where the lipid droplet would be another cell in connective tissue is a macrophage which is which phagocytize and destroy microorganisms and damaged tissues macro means big phage means eater so there's a macrophage in a red there's a bacterium or a germ and so what it does is it surrounds and goes and it breaks it up through all these different lysosomes and that's what a macrophage does whether it's a microorganism like a bacterium or damaged tissue mast cells as well there are the inflammatory cells they secrete histamine that promote vascular leakiness so there's a vat mast cell and you notice all of those granulars of histamine so that when they become activated these they secrete these histamines all throughout the area and makes blood vessels leaky connective tissue proper also has so those were the cells now we have the extracellular matrix the material surrounding cells there's a ground substance this is amorphous material that fills the space between cells and then there's the fibers the main ones are collagen and elastin so here is that example the ground substance of the extracellular matrix is surrounding it and it is basically all this amorphous material that's surrounding the space between cells but it's not the fibers the ground substance holds fluid whenever we talk about interstitial fluid or extracellular fluid that's the fluid within the ground substance and it functions as a sieve through which water and solutes diffuse between the capillaries and the cells it's the medium in which this diffusion occurs and also in the extracellular matrix are fibers like collagen this really strong structural protein it's a tough structural protein it provides tensile strength there's more than 15 types of collagen in the body it's the most abundant body protein we have and then in yellow is elastin which allows stretch and recoil like this and this would allow things like your skin to stretch and then go back to its normal shape okay all right connective tissue it's kind of like a jello salad so here we've got a bowl of jello salad there's pineapple pineapple and little strands of carrot and then there's jello well connective tissue is like a jello salad we have pineapple things like cells surrounded by carrot strands like proteins elastin and collagen and all the rest of the space is filled with jello that's the ground substance okay connective tissue proper so these are the different types loose connective tissue or areolar connective tissue this is the tissue that's deep to all epithelial basement membranes then there's dense irregular collagenous connective tissue this is which a tissue that has strong in all directions like in the dermis and the submucose of organs this is where it's got a really high concentration of collagen except the collagen is just in a bundle like a pile of hay where those fibers go in all different directions in contrast dense regular collogenous connective tissue is strong in one direction like in a tendon because the collagen fibers are lined side by side with each other just like you'd imagine wheat growing in a field and then finally adipose tissue which is basically adipose cells together it stores energy padding and insulation and primary place you find this is a hypodermis all right so connective tissue proper connects attaches and packages cartilage there are three different types of cartilage hyaline cartilage which we find in the ribs your costal cartilage or the articular cartilage the bumpers you find at the end of every long bone like in synovial joints that's where you find hyaline cartilage elastic cartilage as its name implies has high concentration of elastin and we find this in the ear and the epiglottis because it's firm but it goes right back to its original shape now fibrocartilage has a greatest concentration of fibers of collagen we find that in the intervertebral discs the pubic symphysis and the menisci in your knees so it also gives some flexibility but it is very strong so cartilage that's one of the things is it's strong yet flexible the cells in cartilage are called chondroblasts that maintain the cartilage and then mature chondroblasts become chondrocytes cartilage is strong yet flexible it absorbs shock and technically i don't know if it's technically considered a vascular but it's got very little blood supply so it takes a really long time to heal if it ever heals if it's really damaged now bone tissue bone tissue as all connective tissues has cells like osteoblasts that secrete bone matrix and build new bone so here's bone tissue and those yellow cells are bone are osteoblasts and they're building the bone tissue osteocytes are mature osteoblasts that reside in lacunae these little caves they monitor and maintain the extracellular matrix so there's an osteocyte there that that's actually the arrows technically pointing to a lacuna a black space in in that black space is where we'd find an osteocyte so here we've got now those mature osteocytes in pink that are surrounded by bone matrix now osteoclasts secrete enzymes that catalyze the breakdown of bone matrix and bone matrix is calcium and phosphate so there are those things that with the multinucleated cells are often multinucleated they're then breaking down the calcium and dumping the calcium into the blood all alright so to review osteoblasts build bone tissue osteocytes maintain bone tissue and osteoclasts break down bone tissue now the extracellular matrix of bone is calcium and phosphate so all those black dots and the bone in that tissue slide represent osteocytes and all that space around it is filled with calcium and phosphate and that's why the location of bone tissue it's all your bones and your skeleton now blood this seems like the odd one where you could hit someone over the head with a a bone or like a tendon and they'd feel that blood's liquid it's a liquid connective tissue but it has the same features it has cells surrounded by an extracellular matrix or cells or red blood cells that transport oxygen red blood cells or rbcs or urethra sites oh i did have a slide for that okay white blood cells or wbcs they're for immune defense there's like lymphocytes neutrophils eosinophils and so forth um and then platelets or thrombocytes uh thrombo yeah so platelets we see in this blood smear these are for helping to clot blood all right now the extracellular matrix of blood is plasma plasmas water and you know clotting factors and so forth and so basically where do you find blood anywhere there's blood the heart lumen of the heart arteries veins capillaries and so forth all right so there we have all the different connective tissues all it kind of looks like the brady bunch or something like that where there's the different types of connective tissue proper there are the three types of cartilage and then bone and blood all right connective tissue [Music] now let's talk about muscle tissue now muscle this muscle tissue is comprised of contractile type cells and there are three types of muscle tissue skeletal cardiac and smooth now muscle tissue one skeletal muscle is so meaning let's talk about skeletal muscle tissue first it's voluntary means and the muscle fibers are long they're striated and multinucleated so here we have example of muscle tissue we zoom in there are the nuclei and there's more than one in each muscle fiber there are striations it looks like there's these stripes and that's myosin and actin proteins that are and on and it gives a striped appearance and to muscle tissue skeletal muscle tissues compartmentalized by connective tissue sleeves so here's a cross section of a skeletal muscle and there in cross section is one muscle fiber that's like if you're looking at a straw and cross section and there's one muscle fiber and it's surrounded by connective loose connective tissue and we call it endomysium within the muscle and then a bunch of muscle cells put together is called a muscle fascicle and it's surrounded by dense connective tissue and we call that perimysium so the anatomical names pyramicium the histology the type of tissue is a dense connective tissue and then all the muscle fascicles that make a muscle is surrounded by epimysium like that okay so there is the connective tissue bundling of skull to muscle and the primary location is anywhere you've got muscles that attach to bones so anywhere you've got muscle tissue that's attached to bones that's why we call it skeletal muscle and it's voluntary because you control it consciously now the second type of muscle tissue is called cardiac muscle tissue and this is involuntary but it's also stride and it has something called intercalated disks so there's the nucleus and the intercalated discs are these junctions between adjacent cardiac muscle cells that anchor them together and they have gap junctions to allow an action potential to spread and they're striations because you have that regular arrangement of myosin and actin and its location hence the name cardiac muscle tissue is in the wall of the heart call it myocardium so cardiac muscle tissue or myocardium are synonymous anywhere you find heart muscle in the wall that's all cardiac muscle tissue so the anatomy name is myocardium the histology name is cardiac muscle tissue all right now smooth muscle is involuntary and it's non-striated so we zoom in on this and we see a nucleus and often the nuclei in smooth muscle they look in longitudinal section they look like a corkscrew and cross section they're centrally located like the one on the bottom and this is non-striated i can hear my puppy barking it's non-striated because the myosin and actin are in there to allow contraction but it is not in a regular arrangement so you don't see the stripes so they say it's non-striated or smooth in appearance and this is located in the wall of almost all of our hollow organs sink stomach small and large intestines your bladder blood vessels uterus uterine tube urethra and so forth like stomach smooth muscle bladder smooth muscle there's a cross-section of an artery smooth muscle okay there are three different types of muscle tissue striated and skeletal and cardiac because the myosin and actin are regularly arranged non-striated and smooth because it has myosin and actin but in a non-regular arrangement voluntary skeletal muscle you control moving your bones because of these muscles but the cardiac and smooth is involuntary because you do not have to think for your heart to contract or your arteries to constrict now let's conclude with nervous tissue nervous tissue is comprised of cells neurons are the functional part and glial cells or neuroglial cells are the supporting cells let's start with neurons and a neuron consists of the following parts dendrites that conduct an action potential towards the cell body or the soma and then axons that conduct that are surrounded by schwann cells to insulate that conduct the action potential towards the terminal axon and that's where a synapse occurs and the synapse is the space between that neuron and an adjacent neuron or functional tissue so neurons send and receive messages via neurotransmitters and neurons are separated by synapses so there's one neuron on the left and another neuron on the right and the synapse is both a noun and a verb it's a noun because it's the space between these neurons but it's also a verb because you say it synapses where the one neuron secretes a neurotransmitter that then binds to a receptor on the adjacent neuron or that postsynaptic membrane which then causes an action potential to continue so here's an example a neurotransmitter secreted by one neuron binds to receptor in this case the lacrimal gland which makes tears and it waters your eye all right neurons are classified based on their function sensory neurons conduct an action potential towards the central nervous system motor neurons conduct an action potential away from the central nervous system and an interneuron connects sensory motor neurons now neuroglia these are the non-neuronal cells in the central and peripheral nervous system they provide physical and metabolic support to neurons examples are like oligodendrocytes where they produce myelin surrounding axons in the central nervous system there's one oligodendrocyte with numerous branches or i should say a few because the prefix oligo means a few more than one and so there's a central nervous system axon and those are the other ones and so notice that a lego dendrocyte surrounds a part of one axon but it surrounds parts of numerous axons in contrast schwann cells produce myelin surrounding axons in the peripheral nervous system here's one uh peripheral neuron and you'll notice numerous schwann cells that are surrounding only one axon an axon of one neuron but it's only part of it and you know this myelin other lego dendrocytes or schwann cells they increase the speed of conduction of an action potential and there we have in cross section you can see the axon in the middle and the yellow around the outside is the myelin from the schwann cells astrocytes are star-shaped glial cells that regulate the transmission of electrical impulses in neurons and they support the blood-brain barrier so there's an astrocyte and there's a brain capillary we zoom in a bit more you'll notice that the the those red endothelial cells are of a capillary in the brain that's where the blood-brain barrier is there's tight junctions between to regulate the distribution of substances between the blood and the brain tissue astrocytes support that blood-brain barrier that's shown in that illustration ependymal cells line the ventricular system of the brain so here's lateral and coronal view of the brain and we zoom in on that and there's one ependymal cell and then you just see and i would i just got lazy you could just continue all the way down it's lining and it's got these cilia to move the csf throughout the ventricles now the microglia micro for small glial cells these are immune cells they're the macrophages of the central nervous system and there's one microglia cell with lots of these plasma or you know like cellular extensions they serve as macrophages so they are all the neuroglia of the nervous system and that my friends is the histology introduction in a nutshell um [Music] [Music] you