Fundamentals of Histology and Tissues

Okay, in this tutorial I'm going to cover an introduction to histology. Now this really is just an introduction. If you want 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. Alright, 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. When 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 and nervous. That's what we're going to focus on. And it's a 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 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? They're 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 and 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, glanular 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 body is covered in epithelium. And then what about lining organs like that in orange? There's your visceral pleura. It's 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 avascular, without blood supply. So 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 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 the overall tissue, but there's different flavors of epithelium. And so we do it by describing the layers of cells, the shape of the cells, 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 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 epithelium. 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 cilia 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 of arms, lots of cells of cilia. Yeah, okay, I'm just explaining that analogy a little bit more. So if this epithelial tissue has cilia, we call that tissue ciliated. 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 the specialization they're so close together these microvilli often the term that's used in light microscopy is a brush border. There's a nucleus, there's one cell, and so it looks like a brush on the top. So the microvilli I described is having a brush 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's 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, simple squamous epithelium. Let's look at a couple of examples. This is a greenle 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. The apical surface, in this case, faces the filtrate and 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 in cuboidal cells, the nuclei are centrally located and they're kind of oval, okay? And it's epithelium. Okay, so now the functions of simple cuboidal 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 it's summer break. This distal tubule and cross-section is ideal for reabsorption or secretion, or a sweat gland, which is ideal for secreting sweat and salts into the lumen for you 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. 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. 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 brush border of microvilli. where the lumen and the food would be. This is the G-genome, 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 they're 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 of 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 cell stays intact, or the rest of the pencil. stays intact. So I just got Invisalign and because my teeth are really crooked, 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 going to spit all the time. I kind of feel like I'm going to spit all the time. Now the location, that was 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, 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. So there's no nuclei. Whereas in the esophagus or the vagina, this is non-keratinized stratified squamous epithelium. So you'll see nuclei all the way to the apical surface. So here is the epithelium. Stratified squamous keratinized 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. The apical layer are dome-shaped or festoon-shaped. And the functions for stretch and per... 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's the multiple layer of cells with the loose connective tissue deep to the basement membrane, the basal layer of cells and the apical layer of 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 it looks like there's more than one layer of cells, but every cell is anchored to the basement membrane. Therefore, it is falsely stratified, pseudo-stratified, and that many of these cells have cilia, so we use that specialization ciliated. They're tall, thin cells, so we use the word columnar, and it's epithelium. Hence, pseudo-stratified 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 it's simply called respiratory epithelium, which 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 is 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 that we have in a nutshell. We now go to connective tissue. So connective tissue, there are four different types of connective tissue. There are, 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. Talk about an eclectic group of different tissues, eh? 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 in bone and red and white blood cells in the blood. And they're surrounded by an extracellular matrix. All of them have space surrounding these cells. So let's talk about connective tissue proper. 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. Whoops. 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 phagocytize and destroy microorganisms and damaged tissues. Macro means big, phage means eater. So there's a macrophage, and in red there's a bacterium or a germ. And so what it does is it surrounds it 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. Mass cells as well, they're the inflammatory cells. They secrete histamine. promote vascular leakiness. So there's a mass cell and you notice all of those granulars of histamines so that when they become activated, 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 is what allows 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 collagen and all the rest of the space is filled with jello that's the ground substance okay connective tissue proper so here's 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 at a tissue that is strong in all directions, like in the dermis and the submucosal 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 collagenous connective tissue is strong in one direction, like in a tendon, because the collagen fibers are lying 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. 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 avascular, 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 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's actually the arrows technically pointing to a lacuna, a black space. And 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 they're 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 right, 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 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 yours. bones in your skeleton. Now blood, this seems like the odd one where you could hit someone over the head with 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 urethrocytes. Oh, I did have a slide for that. Okay. White blood cells, or WBCs, they're for immune defense. Those are like lymphocytes, neutrophils, eosinophils, and so forth. And then platelets or thrombocytes. Yeah, so platelets, when we see in this blood smear, these are for helping to clot blood. All right, now the extracellular matrix of blood is plasma. Plasma is water and 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. Shing. Now, let's talk about muscle tissue. Now, 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, and the muscle fibers are long. They're striated and multinucleated. So here we have an example of muscle tissue. We zoom in. There are the nuclei, and there's more than one. in each muscle fiber. There are striations that look like there's these stripes, and that's myosin and actin proteins that are end-on-end, and it gives a striped appearance. And muscle tissue, skeletal muscle tissue, is 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 in 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 name is perimysium. The histology, the type of tissue, is 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 skeletal muscle. And the primary location, it's anywhere you've got muscles that attach to bones. So anywhere you've got muscle tissue that's attaching 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 striated and it has something called intercalated discs. 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. We call it myocardium. So cardiac muscle tissue or myocardium are synonymous. Anywhere you find heart muscle on 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 in the bottom and this is non striated you 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. 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 neural glial 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 a 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 is one oligodendrocyte with numerous branches, or I should say a few, because the prefix oligo means a few, more than one. And so there is a central nervous system axon, and those are the other ones. And so notice that oligodendrocyte 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. 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 oligodendrocytes 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 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, as 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 just got lazy. You could just continue all the way down its lining, and it's got these cilia to move the CSF throughout the ventricles. Now the microgliae, 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.

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.

Alright, 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. When 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 and nervous.

That's what we're going to focus on. And it's a 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 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? They're 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 and 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, glanular 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 body is covered in epithelium. And then what about lining organs like that in orange?

There's your visceral pleura. It's 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 avascular, without blood supply.

So 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 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 the overall tissue, but there's different flavors of epithelium.

And so we do it by describing the layers of cells, the shape of the cells, 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 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 epithelium. 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 cilia 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 of arms, lots of cells of cilia. Yeah, okay, I'm just explaining that analogy a little bit more.

So if this epithelial tissue has cilia, we call that tissue ciliated. 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 the specialization they're so close together these microvilli often the term that's used in light microscopy is a brush border. There's a nucleus, there's one cell, and so it looks like a brush on the top.

So the microvilli I described is having a brush 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's 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, simple squamous epithelium. Let's look at a couple of examples.

This is a greenle 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. The apical surface, in this case, faces the filtrate and 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 in cuboidal cells, the nuclei are centrally located and they're kind of oval, okay? And it's epithelium. Okay, so now the functions of simple cuboidal 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 it's summer break. This distal tubule and cross-section is ideal for reabsorption or secretion, or a sweat gland, which is ideal for secreting sweat and salts into the lumen for you 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. 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.

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 brush border of microvilli. where the lumen and the food would be. This is the G-genome, 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 they're 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 of 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 cell stays intact, or the rest of the pencil. stays intact.

So I just got Invisalign and because my teeth are really crooked, 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 going to spit all the time. I kind of feel like I'm going to spit all the time. Now the location, that was 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, 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.

So there's no nuclei. Whereas in the esophagus or the vagina, this is non-keratinized stratified squamous epithelium. So you'll see nuclei all the way to the apical surface.

So here is the epithelium. Stratified squamous keratinized 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. The apical layer are dome-shaped or festoon-shaped. And the functions for stretch and per...

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's the multiple layer of cells with the loose connective tissue deep to the basement membrane, the basal layer of cells and the apical layer of 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 it looks like there's more than one layer of cells, but every cell is anchored to the basement membrane. Therefore, it is falsely stratified, pseudo-stratified, and that many of these cells have cilia, so we use that specialization ciliated.

They're tall, thin cells, so we use the word columnar, and it's epithelium. Hence, pseudo-stratified 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 it's simply called respiratory epithelium, which 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 is 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 that we have in a nutshell. We now go to connective tissue.

So connective tissue, there are four different types of connective tissue. There are, 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. Talk about an eclectic group of different tissues, eh? 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 in bone and red and white blood cells in the blood. And they're surrounded by an extracellular matrix. All of them have space surrounding these cells.

So let's talk about connective tissue proper. 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. Whoops. 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 phagocytize and destroy microorganisms and damaged tissues. Macro means big, phage means eater.

So there's a macrophage, and in red there's a bacterium or a germ. And so what it does is it surrounds it 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. Mass cells as well, they're the inflammatory cells. They secrete histamine.

promote vascular leakiness. So there's a mass cell and you notice all of those granulars of histamines so that when they become activated, 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 is what allows 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 collagen and all the rest of the space is filled with jello that's the ground substance okay connective tissue proper so here's 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 at a tissue that is strong in all directions, like in the dermis and the submucosal 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 collagenous connective tissue is strong in one direction, like in a tendon, because the collagen fibers are lying 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. 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 avascular, 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 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's actually the arrows technically pointing to a lacuna, a black space.

And 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 they're 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 right, 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 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 yours.

bones in your skeleton. Now blood, this seems like the odd one where you could hit someone over the head with 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 urethrocytes. Oh, I did have a slide for that. Okay.

White blood cells, or WBCs, they're for immune defense. Those are like lymphocytes, neutrophils, eosinophils, and so forth. And then platelets or thrombocytes. Yeah, so platelets, when we see in this blood smear, these are for helping to clot blood.

All right, now the extracellular matrix of blood is plasma. Plasma is water and 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. Shing. Now, let's talk about muscle tissue. Now, 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, and the muscle fibers are long. They're striated and multinucleated. So here we have an example of muscle tissue. We zoom in.

There are the nuclei, and there's more than one. in each muscle fiber. There are striations that look like there's these stripes, and that's myosin and actin proteins that are end-on-end, and it gives a striped appearance. And muscle tissue, skeletal muscle tissue, is 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 in 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 name is perimysium.

The histology, the type of tissue, is 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 skeletal muscle. And the primary location, it's anywhere you've got muscles that attach to bones.

So anywhere you've got muscle tissue that's attaching 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 striated and it has something called intercalated discs.

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. We call it myocardium.

So cardiac muscle tissue or myocardium are synonymous. Anywhere you find heart muscle on 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 in the bottom and this is non striated you 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. 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 neural glial 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 a 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 is one oligodendrocyte with numerous branches, or I should say a few, because the prefix oligo means a few, more than one.

And so there is a central nervous system axon, and those are the other ones. And so notice that oligodendrocyte 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. 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 oligodendrocytes 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 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, as 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 just got lazy. You could just continue all the way down its lining, and it's got these cilia to move the CSF throughout the ventricles. Now the microgliae, 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.

Transcript for:Fundamentals of Histology and Tissues

Transcript for:
Fundamentals of Histology and Tissues