Okay, let's get started with our conversation about chapter 4. This is the first of two presentation lectures that will cover chapter 4. Chapter 4 is all about hisystologology and will largely align with lab two in the course. Uh lab two recall is also all about hisystologology. Before I begin, let me just say some of you will listen to this presentation first and then we'll follow up with your prelab 2 and your lab uh video. Others of you will watch the lab first and then watch this. Regardless, you will be hearing many of the same ideas between the two presentations. I'll also say now that as we start moving through the hisytologology tissues, you are responsible for 20 different tissues in lab. Those same 20 tissues will be covered here in this presentation. For completeness, I may quickly mention a couple of the other tissues, but you will not be responsible for recognizing or knowing anything about those those tissues above the 20 that you're already seeing in lab. So, let's get into uh this today. Right now, I'm going to talk about 4.1 types of tissues and 4.2 epithelial tissues. A second presentation will then cover connective tissue, muscle tissue, nervous tissue, and a little bit about um aging and tissue repair. So you learned in the first chapter that the human body is highly organized and if we think about the atom to atom continuum you know that cells combine to make tissues. There are in your body at least 200 some books would say up to 220 different cell types in your body. Recall each of those cells has the same DNA, but it is the transcriptional regulation or the gene expression that is turned on or turned off across the genome that causes cells to be quite different in function one from another. Also recall that there are four types of tissue. So let's review that and your job will be to one know the main features of epithelial tissues versus connective tissues. You'll also be responsible for recognizing a number of these tissues, knowing their locations in the body, knowing the special cells and some of the special features that are a part of those cells and tissues to allow them to do their job. So the four types of tissues are epithelial tissues. You'll hear epithelium or epithelia plural. And epithelial tissues are found in a few very basic places. Number one, they cover the external surfaces of your body from head to toe. The outer layer of your skin is referred to as the epidermis. And that epidermis is composed of epithelial tissue. Secondly, epithelial tissues are lining all of your body cavities. Remember in chapter one, we learned about the thoracic cavity and the abdominal pelvic cavity. And all of those spaces are lined by epithelial tissue. Also, all of your tubes, all of your passageways, blood vessels, lymph vessels, the esophagus, uh the windpipe, the trachea, all of your passageways are also lined by epithelial tissues. And finally, most of your glands such as the liver, the pancreas, the salivary glands, the sweat glands. When you hear the word gland, uh just know that that tissue is not exclusively but is also largely made up of epithelial tissues. The second group of tissues are the connective tissues and as you'll see in lab, this is a very broad group of tissues. They are made up of cells and are working in multiple ways in your body to protect, to support, to do all sorts of amazing jobs. And you will be learning quite a few different connective tissues this semester. Muscle tissue is the third type of tissue. And one of the cool things about muscle tissue is that it is excitable. meaning that when it gets activated or excited, it is going to respond. And muscle tissue always responds by shortening, by contracting, and by moving things. And so, we'll see that there are three major types of muscle. And then finally, there's nervous tissue. And nervous tissue is also excitable. But here it's not that the tissue moves like muscle, but instead nervous tissue sends electrical signals along structures within that tissue in order to affect change somewhere else. So recall that cells come together to make tissues and that tissues then come together to make organs. Let's take a look again briefly at this image. just gives us another review of this. So in your body, epithelial tissues, I'll go in the same order. Epithelial tissues are covering your surface of your body, the epidermis, and are lining all of your body cavities, also lining all of your tube like structures, and also I didn't say it a moment ago, but also are covering all of your internal organs as well. connective tissues, things like bone, tendon, ligament, fat, the dermis of your skin, all of those connective tissues um found all over the body, very distinctive. I think when you start looking at these, you will see that connective tissues look quite different from each other under the microscope and the identification of these tissues will not be as challenging as the epithelial tissues are. Thirdly, muscle tissue. Three flavors. We have the most common, the skeletal muscle. This is the muscle that you have making up the muscles of your body. The voluntary muscles, the ones that you have control over. Then there is smooth muscle. Smooth muscle is found lining your internal organs. Found lining your intestines, your bladder. And smooth muscle also lines a bit of your blood vessels. So smooth muscle when it contracts is moving things. It's moving blood. It's moving digestive structures etc. digestive uh food things etc. And finally cardiac muscle is found exclusively in the heart. Again all these muscles tissues move as their basic general characterization. And then finally nervous tissue uh is found all over the body but highly found in the brain and the spinal cord. And again, it is tissue that sends electrical signals very quickly to other places in the body. So, make sure you know the four groups of tissues: epithelial, connective, muscle, and nervous. Now, where do these tissues come from? Let's remind ourselves of a little bit of the end of chapter three. Recall that we all were once a zygote. The fertilized egg or when egg and sperm come together. That first cell recall we referred to as being totally potent. Total potential to become any and all cells of the body. But very early on those cells begin to specialize. They begin to undergo differentiation. And the first thing that happens in the in the embryo is that that ball of cells after a short while starts to divide into three distinct layers. Those layers are referred to as the germ layers. And all of your tissues and all of your organs are eventually formed by one of those three germ layers. Let me introduce them to you here. Then I'm going to go back to an image that we saw at the end of chapter 3 to pull this together and then we'll continue on with this image. So the three layers are as follows. There is the ectoderm. Now ecto means outer. So that's the outer layer. The middle layer of the early embryo is the misoderm. Miso refers to middle. And finally there is endoderm. And endoderm endo means inner or within. So that's the layer on the inside. Let me just flip back really quick to an image at the very end of 3.6 and remind you of this image and pull this together for you. The very very end. This is under stem cell research. And in this image, you're reminded that the early cell of the body, the zygote, is to potent. The first ball of cells, oops, the first ball of cells are also toad potent. But early early on in the embryological development, that ball of cells begins to form three distinct layers. The endoderm, the misoderm and the ectoerm. And those layers are no longer totent, but they are now plur potent. Remember plur potency means that the cells have begun to differentiate and they can still become a plurality, right? Many many cells, but they can no longer become all of the cells at this point. They're beginning to specialize. And those layers then go on to form multi-potent stem cells. And we saw an example of a multi-otent stem cell in the bone marrow story where there is one cell, the hemocytoblast in the adult bone marrow that has the ability to go on and form all of your different types of blood cells. We also see these kinds of stem cells in your skin. Why is it if you cut yourself that your skin is able to so quickly heal? It's because there are multi-potent stem cells in your skin that can then differentiate and become any cell that you need in repairing your skin. Your bones also have these cells. Uh teeth have these cells. You may have heard of people who save their kids umbilical cord blood. Again, those cells are multi- potent and could be in the future used is as our ability to use these cells increases. And then those multipotent cells remember go on to be oligopotent. That's not shown in this diagram. And eventually the cells in your body become uniotent as is shown here on the bottom where these cells are highly specialized. And if a uh lung cell divides, it can only make another lung cell. So once you are uniotent, you don't have the ability to make other types of cells. When a uni- potent cell divides, it is only going to have the ability to make that same exact kind of cell. So that is at the very end of your chapter 3, section six. And now let's continue back to chapter 4 and look at this diagram a little more completely. So we have these three layers. And here is what I want you to know. The ectoerm, the outer layer of the early embryo will go on, my computer has its own mind, will go on and form the epidermis. Well, that should make sense that the outer layer of the early embryo goes on to form the outer layer of your entire body from head to toe. What m what might not make sense is that the ectoerm also goes on to form your nervous system. So your brain and your spinal cord are also formed from the outer layer of the early embryo. So I want you to know notice there are other things in here but I want you to know that the end ectoerm goes on to form the outer layer of your body the epidermis as well as your nervous system. The other things you can skip, not worry about. The middle layer of the early embryo, the misoderm, goes on to make the vast majority, I'm going to say all of your connective tissues, bone, cartilage, blood, all of that is made by your misoderm. So that middle layer is going to continue to differentiate, become more specialized to form all of your connective tissues. Also, your misoderm is going to form all of your muscle tissue. So all of your connective tissues, all of your muscle tissues, and lastly, it also forms your cirrus membranes. Recall the cirrus membranes, the plura, the paritonyium, and the paricardium. They also are formed from this middle layer. The novial membranes, we'll be talking about those in a few minutes. They're also formed by the misoderm. And then finally, the endoderm, the inside layer, the inner layer of that early embryo, goes on to form what I think of as your inner organ systems. So goes on to form your respiratory system. all of the tube, the trachea going down from your nose down into your lungs and all of your digestive system going down the esophagus through the stomach and the intestine. Okay, so that is a cool thing to be thinking about that the early layers of the embryo then go on to form very distinctive organ systems in your body. From a developmental standpoint, this is important. Um if a child is born with some sort of significant birth defect, they can oftentimes figure out where did development go wrong, where did things not go right uh in that early development such that the child was born without certain organs or certain structures. And knowing this kind of information helps to I guess as a detective figure out where things may have gone wrong in development. If one of these layers does not form right and all the organs from it do not form properly. In addition to getting an understanding of the four tissue types and understanding of where those tissues are coming from in the early embryo, we also want to look at tissue membranes. So membranes, there's four different types of membranes in the body that I'm going to present to you. um some of them are connective tissue and some of these membranes are epithelial uh types. So let's take a look now. One of these you already know. You already know about your cirrus membranes, right? Your cirrus membranes, the paritinium, the plura and the paricardium. Those you are already familiar with. Remember that those membranes are surrounding your internal organs and internal body cavities and they are completely contained within the body. You are not able to touch any of your cirrus membranes unless there's some sort of trauma. Now, oops. Now, the second one that I want you to know about are the mucous membranes. You're you're going to hear a little bit more about these. Mucous membranes are the membranes that lead out of the body. So, the inside of your mouth, the inside of your down your esophagus, uh down your um u trachea, uh the urethra and the anus. All of those areas in and out of your body are mucus membranes. As the name suggests, they produce mucus, a thick sort of protective uh substance. And the way I remember mucous membranes, these are the membranes that wherever you put Tabasco sauce, it's going to burn, right? So in your nose, in your mouth, and I'll let you imagine the rest of them, but Tabasco sauce is going to burn on mucous membranes. And the other thing about mucous membranes is that you can touch all of them with your finger. May not be comfortable, but they all open to the outside world. The third type of membrane you already know by a different name and we'll be learning more about and that is cutaneous membrane. That's just a fancy name for your skin. So your cutaneous membrane aka your integment aka your skin an important part of your integimementaryary system and covers your body from head to toe. And you're learning that the cutaneous membrane is uh both epidermis and dermis. And so it's both epithelial and connective. And then finally there's synenovial membranes. We'll pick this story up again in the joint chapter later on, but synovial membranes are lining and covering most of the joints in your body. They are pro producing a fluid that is both uh lubricating and protective to your joint spaces. We will see them again in the future. So know your four different types of membranes. Cirrus, mucus, cutaneous and synenovial. Again, the synenovial membrane maybe I didn't say just a moment ago. The synenovial membrane is a connective tissue membrane. Whereas the epithelial membranes include the mucous membranes and your cirrus membranes. Make sure you are watching these animations for a deeper and better understanding, a great visual way of seeing this information. You'll also be seeing much of this in the laboratory under the microscope. For some students, they enjoy the microscope. Others more enjoy these animations. Regardless, you have got to be able to identify and um understand the role, the purpose of these structures in the body. And then lastly, right, the skin, the cutaneous membrane, it is an epithelial membrane. And we'll come back and learn about the skin in chapter five. So that's the end of section 4.1 relatively short introduction to tissues. Make sure as always that you are entertaining these questions and coming to lecture or lab or study group with questions from anything from these questions or from the presentation that I can restate or clarify for you and for your classmates. Moving on to 4.2, we'll spend the rest of our time learning about epithelial tissues. First of all, and this will be reiterated in lab as well, epithelial tissues are largely or most of the time large sheets of cells. Now, these are epithelial cells that make up epithelial tissues. We'll see that there are some extra special cells that appear in some of the epithelial tissues, but by and large the cells in epithelial tissues are epithelial cells. And those sheets of cells are covering the surfaces of the body. Think epidermis. And lining the outside of your organs. Think visceral paritinium, visceral paricardium, visceral plural that are shrink wrapped to the surface of your organs. Also lining the inside of your body cavities. Again, your glands are largely made up of epithelial cells. the lining of your airways, trachea and the lungs, the lining of your intestines, the linings of your bladder and your urethra, the lining of your um vagina. Again, all of these are lined by epithelium. Now, where do epithelial cells come from? Think back to the three layers of the early embryo. The ectoderm, the misoderm, and the endoderm. If you look closely back at that list, you'll see that epithelial cells are actually derived from all three layers of the early embryo. And let me just tell you about which ones come from where. The name actually tells you. So the ectoerm, right? The ectoerm, the outer layer. we've already said forms the outer layer of your skin. That's your epidermis. That one's easy to remember. The lining of your airways and your digestive system are endoderm, right? That makes sense. They're with on the inside layers. And then we also have the the um misoderm. And from the misoderm you're going to make your cirrus membranes as I mentioned your misothelia. So again the epithelial tissues come from all three layers of the early embryo. That's different than the other tissue types. The other tissue types all come from one or the other primarily but epithelia are made from all three. So if epithelial tissues are composed of sheets of cells, it should make sense that these cells are held together very tightly in order to do their job. And because these cells are held tightly together, that also suggests that there's very very little if any space in between the cells. So another way of saying that is that epithelial tissues have little or no extracellular matrix right there's very little extracellular protein or stuff outside of the cells and that also suggests that these cells are held together by particular certain structures. So let's go through that a little bit. Also epithelial cells exhibit a polarity. In other words, they know their top from their bottom. The top of a cell is referred to as an apical surface and the bottom of the cell is referred to as the basil surface. Now, when we talk about epithelial tissues, another feature of epithelial tissues is they always sit on top of an underlying connective tissue. And where an epithelial tissue and a connective tissue meet is called the basement membrane. Now the basement membrane is actually formed by both layers. So the basil lamina right think about it. Basil the bottom lamina means a layer. Think laminated countertop right? So if you have a laminated countertop you know that it's a very thin layer. So basil lamina just means the bottom layer. So the very very bottom layer is made up of the basil lamina and then the very very top layer of connective tissues is called the reticular lamina and these two pieces the basil lamina and the reticular lamina form together the basement membrane. So again where epithelial tissues come down and interact with connective tissues beneath beneath them is actually made by both of the layers. The epithelial and the connective layers both make a portion of that basement membrane. Another feature of epithelial tissues is that they are nearly completely avascular. Rarely rarely rarely do you see blood vessels coming up through the basement membrane into the epithelial tissues. It's very very rare. So for the purposes of the lab and for the purposes of the learning I always say that epithelial tissues are indeed avascular. When there are blood vessels coming all the way up to the surface of the skin that is abnormal. Okay. So in normal anatomy we can say quite convincingly that epithelial tissues are avascular and you know from your vocabular means without any blood vessels. Finally epithelial tissues are capable of dividing very very quickly replacing damaged cells replacing dead cells. Another way of saying this is that epithelial tissues are highly mitoic. They are dividing very very quickly. This is true of epithelial cells. All of the dust in your house is mostly you right sloing off the outer layers of your skin. Your cells inside your mouth down your esophagus down through your intestines. Those cells are also being constantly sloed off and are constantly being replaced. And so epithelial cells are some of the fastest, most mitoic cells in your body. So what do epithelial tissues do in general? Pretty obvious. They protect, right? They protect from the outside. They protect our organs from each other and basically the epithelium acts as a gatekeeper to our body. So whereby the cell membrane acts as a gatekeeper for the cell itself, the epithelial layers, especially those on the outside of our body, the epithelium is acting as a gatekeeper into our body altogether. And if you're thinking about food traveling through your intestines, it's the epithelium that line your intestines that are acting as a barrier about what will or will not be absorbed into your body. So let's take a look at different types of tissues as well as epithelial cells. Again, epithelial cells are u they have a polarity. They have an upside and a downside. And there's a couple of other things that we're going to see on some epithelial cells. In some epithelial cells, we are going to see psyia, not all, but some. And psyia are long extensions that help to move things. And we'll see psyia in the airways. We'll see celia in the nasal passages. And there are also psyia for example in the fallopian tubes. And they are helping to move things along air or sperm or the early embryo. We'll also see that in some of your epithelial cells that we're going to have and there's a nice video on psyia. We're also going to have microbilli. And microbilli are microscopic little ripples in the surface of the cells to increase the surface area. So let's take a look at the different types of connections between these epithelial cells. Let's take a look first and these are all just simply called um junctions, okay, of some sort. So, let's first look at tight junctions. And what are we looking at here? Look at this inset here. We're looking at two. Here's one cell, a second epithelial cell, a third epithelial cell. So, we're looking at three epithelial cells. And the box here tells us what we're looking at. This is a blowup of that box. And so, we're looking at a connector that's up toward the top, up toward the apical surface of the cell. And so what we're looking at here, here's one cell on the left. Here's another cell on the right. This is the cell membrane of each of those two cells. And we see that tight junctions basically knit these two cells together again more up toward the apical surface. And to me, this kind of looks like uh Charmin toilet paper, right? We're kind of knitting it together and holding this together. Now, what this does is that these two epithelial cells because they're being held together tightly, it doesn't allow molecules to squiggle down between the cells. Right? These tight junctions are basically creating more barriers so that the molecules that pass through this sheet of epithelial cells are not sliding through randomly between the cells but instead are having to come into the cell in a regulated way. Now another type of junction are gap junctions. Gap junctions look again at the inset. They're a little bit more toward the basil surface of the cell. They're in the lateral sides, right? They're in the sides of the cell. And gap junctions are composed of these proteins called conexens. Conexens. And as the name suggests, they are connecting the cells one to another. And oh, look, these conexens actually are tunnels. Tunnels. These are not only holding the cells together, but they're also creating a way by which molecules are able to travel from one cell to the next. Remember, these are epithelial cells. Epithelial cells and epithelial tissues don't have a direct blood supply. Remember, they're avascular. And so, these cells need to share their nutrients with their neighbors. And so that's one way of thinking about these gap junctions. Not only are they holding the cells together, but they're also creating a channel through which molecules can be transferred from one cell to the next. Thirdly, there are some really cool structures called desmosomes. Now, desmosomes again, you see them, they're connecting two epithelial cells together. Desmosomes though are like rivets or buttons between two pieces of fabric. Where do we have rivets in our jeans? Right? Look down at your jeans. Look at your pockets. Usually, your front pockets of your jeans have a little rivet. Why did Levis start putting little rivets on the pocket? Well, the reason is if it didn't have that extra reinforcement, your pockets would tear off over time from the extra stress. And so these desmosomes are like buttons and both cells create half of the button or half of the rivet and basically they plug together. Again, they are reinforcing. Now these desmosomes will be present in tissues that are under higher stress. The heart has desmosomes uh the heart muscle. So as the heart contracts right 50 60 120 140 times a minute when you're exercising there's a lot of stress on those muscle cells and these desmosomes help to hold those cells together under that stress. You'll also find desmosomes in large number in the vagina for example or in the anus places where tissues are under stress um or in the esophagus. I'm going to skip the adherence and I'm going to go down now to the hemisesmosomes and as the name suggests these are like half a button or half a snap. The hemesomes are found on the basil surface. So if we're looking at this cell here on the inset, here is the epithelial cell. Here is the connective tissue down below. And this hemisesmosome is a half of a button or half of a snap. And these uh connectors are not so much about holding the cells, the epithelial cells, one to another, but they're helping to hold the epithelial layer down to that basement membrane below. You ever thought about this for a moment? But when you slide your hand along your arm, your skin cells are not coming off in large number. When you slide your butt across a backseat of a car, you're not losing layers of cells as you scoot across the seat. So again, we have these connectors that keep our epithelial layers connected down to the connective tissue layer below. So just know these different types of cell junctions and you'll hear about them a couple of more times. Make sure you also are watching the animations to make sense of all this. And all everything I just said is said here in the words and there's a question for you as well. So let's now get into classifying epithelial tissues. You might hear the word classify, name, describe. But if you're asked to classify, name, or describe an epithelial tissue, it's asking you what type is it, right? Name this type of epithelial tissue. And as you'll see in lab in even more detail, epithelial tissues have epithelial cells of different shapes. First of all, there is squamus. Squamus cells are flat, squishy, squashy cells. Cubuidal cells, as the name suggests, look like little ice cubes. They are cubic in shape. And then there are simple columnar or columnar cells. These are taller cells than they are wide. They look like tall rectangular prisms. And so we have squamas cells, cubuidal cells and columnarshaped cells. Additionally, epithelial cells come in different layers. If a tissue is composed of only one layer of cells, it's referred to as simple. So one layer of squamus, simple squamus. One layer of cubuidal, simple cuboidal. One layer of columnar, simple columnar. or tissues can be composed of two or more layers. Stratified squamus, many many layers of cells. The top layer, notice here, are very flat, very squamus. When we're naming a stratified epithelium, we do not look at the shape down in the deeper layers. We instead only look at the shape up at the surface. And so we will see stratified squamus in the lab. In fact, we'll have two different versions of stratified squamus epithelium. Now, in your body, there are also stratified cubuidal and there are also stratified columnar. Notice that in the stratified columnar, we're only looking at the superficial layer for the size. Right? If we looked at the deeper layers, we would call this cuboidal. But we always look at the more superficial layers to get the name of the cell shape, stratified columnar. Now while those two examples do exist in the body, we will not be learning any particular examples of stratified cuboidal or stratified columnar this semester. So let's first talk about the simple epithelium. We're going to be looking at four of them. We're going to be looking at simple squamus, simple cubuidal, simple columnar, and we'll also look at another one called pseudoratified columnar here in a moment. Remember, we're looking at a single layer of flat cells. Man, that doesn't sound like much, does it? Right, simple squamus epithelium. And there are two places specifically where we're going to see this. One is the endothelium. Endothelium. It actually tells you where it's coming from. It's made by the endoderm, right? That endothelium is made by the endoderm. That inner layer of your early embryo. And what where we find endothelial cells is lining blood vessels, your lymphatic vessels, and your blood vessels. We also see simple squamus in your alvoli down in your lungs. The little air sacks also have simple squamus. So again blood vessels lining your blood vessels and making up the air sacks of the lung. Another place where we find simple squamus is your misothelia. Right? Your misothelia code word for your cirrus membranes. So your paricardium, your paritinium and your plura are actually simple squamus epithelia collectively called misothelium. And this also reminds you that they are coming from that middle layer the misoderm of the early embryo. Again, watch these videos for a quick but also very effective way to remember this. Let's move on to the simple cuboidal epithelium. These are going to be a one layer of cells. They're going to be cubic or box like in their shape. And these uh layers are found oftentimes in the kidney tubules. And we'll see them in glands. In the lab, you'll see examples of kidney uh tubules. You'll also see some thyroid glands that are also used to show you simple cubuidal epithelium. One of your major jobs here and in lab is to not only learn what these different tissues look like under the microscope and identify them, but to know where they are found. And so make sure you are keeping track of these specific characteristics and their locations. There are tables coming up. There's also lovely tables in your lab manual. And then simple columnar. The one layer of cells that are taller than they are wide. One layer of column-like cells. These are famously found in the digestive system specifically lining your intestines, your small intestines. It will be the primary place where we will see examples of a simple columnar epithelium. One of the other things about these cells is that in the intestines, these cells have microbilli on their apical surface. And microbilli are basically little ruffles that increase the surface area so that as food is traveling through your intestines, it can be quickly absorbed into your body. Now there are simple columnar epithelial cells lining the fallopian t tubes fallopian tubes as well and in those situations those cells have psyia. We will not be seeing that in lab this semester. We will only be looking at simple columnar epithelium lining the intestine and contain microbiali. The fourth and final type of simple epithelium is a mouthful. It is pseudoratified columnar epithelium. This is the epithelium that is lining your respiratory system. Specifically, it's going to be found in your nose. It's also going to be found down your trachea. And this tissue will always have associated with it cyia. So put cyia as highly associated with pseudoratified columnar. Some books even call it pseudoratified columnar siliated epithelium. These psyia are there to catch and sweep away particullet, smoke, other things, pollutants that would try to come down your respiratory system down deeper into your lungs. When we look at this tissue, let's figure out why it's called pseudoratified. And we look at this tissue here in this cartoon, it almost appears that there's here's one layer of cells, right? Kind of short, stocky cells, and then here are taller cells next to it. It almost looks like there's a couple of layers of cells, doesn't it? But if you were to take a deep dive into this tissue and where I'm scanning now, this brown represents the basement membrane, you would note that every one of these cells does indeed have direct contact with the basement membrane. And so while it appears that it's a couple different layers of cells, it's really just one layer of cells that are jumbled together, hence the term pseudoratified. They are not truly stratified, right? Pseudo falsely stratified. It is an example of a simple epithelium. And we see here in the in the representation here the long psyia that are coming off these cells. Again, this is found going down the trachea and up also in the nasal passages. Also in this tissue in this pseudoratified columnar epithelium there are additional cells called goblet cells. We'll also see these same cells in the simple columnar epithelium of the small intestine. And these goblet cells are producing mucus. So here's a cartoon representation of these goblet cells. You kind of see why they're called this. They sort of have a a tall base. You can almost imagine sort of a goblet kind of shape, a goblet, a wine goblet or something. And these cells are making all of these mucousy vesicles. And these vesicles are released from the surface of the cell, the apical surface. And this green represents the mucus that is released. Note in a moment that mucus, the stuff, the slimy stuff that you release is mucus, mucus. But mucus is produced and released on mucous membranes. and mucous membranes. It's m u cou. So mucus and mucus two different spellings. Uh different reasons, right? So the mucous membrane spelled this way, mucus. And the actual stuff that's slimy is mucus. Okay, without the O. So those are the simple epithelium. Now let's take a look at the stratified epithelium. There is stratified squamus epithelium. This tells us that it's many layers of cells that at the surface are flat. Now we'll see that there's two flavors of this. There's keratinized and non-caratenized. More about that in lab for sure. On the outside of your body, your epidermis is a dry keratinized stratified squamus epithelium. This dry, scaly skin is what's flaking off from you all the time and is being picked up in your vacuum cleaner. Also, as you walk around all day, you are breathing in the dead floating cells of you and your neighbors. And what's happening to those cells, right? Those cells as you breathe them in are getting caught up on the psyia in your nose and down your respiratory tract. And then your respiratory tract is also making mucus by those goblet cells. And those psyia are also beating only in an upward way. And so as you are breathing in smoke and particulates and your own epithelial cells and the epithelial cells of all of your classmates and your family members, your body is largely lifting those cells up and out of your respiratory tract so they don't collect down in your deeper tissues. There's also stratified cubuidal stratified columnar. As I said, these exist, but we will not be looking at them in the course or in the lab. So, don't worry about those particular types. The last of the stratified epithelia is transitional epithelium. Transitional epithelium, as the name suggests, transitions. It changes its shape. And this tissue is found in the urinary system specifically uh in the bladder lining the bladder the inside of the bladder as well as the uriters. The urers are the tubes that carry urine from your kidneys down to your bladder. And as your bladder fills those cells are and the bladder is going to expand those cells are going to get thinner. And then as you release the urine and the bladder shrinks back, those cells are kind of going to get thicker again or a little bit uh bigger in diameter. So because these cells are changing their shape multiple times a day, they are referred to as transitional, you can recognize them a couple different ways. One though, and you'll see this in lab, is that most of the cells are cuboidal on the apical surface and there are these umbrellashaped cells at the surface and they are in fact the telltale indicator that you're looking at transitional epithelium. So to recap, here's a nice little table. Uh this table is going to uh break down the simple versus the stratified epithelium. I think we've got the shapes down. Let me just point out one thing that simple epithelium I don't care if it's simple squamus simple cubuidal simple columnar it's all about materials moving absorbing absorbing right so very thin layers uh you know one layer of cells these epithelia are are lining and coating but things are able to absorb or move across these thin this thin layer Okay? Or things are secreted. Now, when we get down to the stratified epithelium, what you see, you no longer see anything about uh absorption. You now see protecting. So, stratified squamus epithelium is all about protecting against abrasion. When you scratch the surface of your skin, you don't bleed because you have multiple layers of cells. Some of those layers are are sloing off, but you have many more layers down below that protect you. Likewise, when you eat something, the inside of your mouth is stratified, squamus, non-caratinized. And as you swallow something, uh, cells are definitely being scraped off your oral cavity, your tongue, and your esophagus, and down your uh, to your digestive system. And when you defecate, you're definitely losing cells lining the anus, but again, they are protecting you against the abrasion. And again, they would have lots of those tight junctions to help hold those cells together as well. And the transitional, as we said, lining the bladder and the urethra, and it's all about stretching and expanding multiple times a day. So your job again is to recognize those different tissues, know where they're located, know any of the special features like psyia or microbilli or goblet cells that I presented in that section. Now in addition to those tissues I said that glands are largely made up of epithelial tissues. Glands come in two basic flavors. We have exocrine glands and we have endocrine glands. Don't make this difficult. You know the endocrine system is a bunch of glands that release hormones. Same thing here endo within trying to secrete. So endocrine glands are glands that release or secrete hormones substances into the body. Whereas exocrine glands are going to secrete or release things out of the body to exit the body. We're not going to spend any extra time here talking about endocrine glands. We will talk about the endocrine system later on. What we will be discussing though in this section are exocrine glands. Now exocrine glands again are releasing substances out of the body to an epithelial surface. Think like sweat, right? When you sweat, you're releasing substances outside of the body to the surface of your epidermis. Uh tears are exocrine. Spit is exocrine, your saliva. When you uh make saliva, either you can spit it out, it exits, or you can swallow it. And that um those substances would then find their way out of the body through the digestive system. Breast milk is also another example of exocrine glands. Breast tissues are glandular producing milk that exits the body. So that's what we're going to be talking about here for the next couple minutes. And I am not going to get super excited about this first section. And that is glands come in multiple shapes and sizes. Whoopdedoo. I'm not going to ask you to know as tubular versus simple versus compound different glands. What I want you to see is that no matter what kind of exocrine gland we're looking at, let's zoom in here. No matter what we're looking at here, we're looking at a group of in this image purple cells. These are the epithelial cells. They are releasing some sort of substance and that substance as you can see is then going to lead up a duct and go to the surface. So exocrine glands all have epithelial cells releasing a product and that product goes up a duct up a tube and eventually goes to the surface of an epithelial layer. Now this could be the outside of the body or this could also be the inside of your mouth. That's an epithelial layer. It could be the inside of your stomach. Your stomach is lined by epithelial cells. It could be uh uh it could be your liver again releasing substances that end up in your gut and in your digestive system. So don't worry about the different shapes. Just recognize that we are looking at epithelial cells in the gland releasing their products into a duct. What I do also though want you to focus on for a moment though is the way by which these glands release their material. And there's three different methods or modes of secretion and these are important. Number one, meocrine. Let's look at what we've got here. We've got three epithelial cells. Those three epithelial cells are sitting here on a basement membrane. They are releasing things. Here is the endopplasmic reticulum and the Golgi apparatus. Right here's the Golgi. And we see that it has produced these little vesicles. These little vesicles are releasing substances and this should give you nightmares of remember exocytosis where we're releasing substances from the inside of the cell to the outside of the cell. Think of this as like spit, right? You're releasing something out of the body. Fine, that's meran. I'll come back to that in a moment. A second type of secretion is apocrine. Remember crime means to secrete. And remember that epithelial cells are made up of an apical surface toward the surface and a basil surface at the bottom. So an apocrine secretion as the cell is releasing its products it doesn't just simply release the products like exocytosis like we see in meran but instead the entire apical portion of the cell is pinched off. Now this is the way that breast milk is produced. Breast milk is produced through apocrine secretion. So a portion of the cell pinches off those cells and regenerate that apical portion of the cell. We'll also see that your stinky sweat glands in your armpit also release sweat by apocrine secretion. And then finally there is holocrine secretion. And what is unique about this type of secretion is that when the cell releases its products, it doesn't just release them, the whole cell dies and releases everything. So the cell dies in the process and all of that cellular junk is released with it. Now holocrine secretion is the kind of secretion for your facial glands, your uh sebaceous oily glands. And so it makes sense that those glands and those ducts leading that stuff out to the body surface gets clogged up because of all of the cellular debris that also travels up those ducts. So the way I remember this is that in holocrine secretion the whole cell wh the whole cell is dying and is releasing its entire product. In apocrine again the apical portion is released and in meacrine the way I remember this is that the cell stays merry. It stays happy. It's still alive and well. Right? So the meocrine secretion is not uh dying or pinching off. It is quote merry happy and is doing its job. One more thing that I want you to appreciate about this. Um here is a sebaceous gland. We'll look at skin more carefully in chapter five, but here is a hair gland. Here's a hair. You see the hair coming up and poking out of the surface. Uh little sebaceous glands are oily like glands that are always releasing their product up along a hair shaft. And these sebaceous glands release their products again via holocrine. So when these cells are releasing that oily substance, it very easily clogs up these pores leading to acne and boils and other lovely things that most of us have unfortunately experienced. More about that in chapter five. Lastly, when glands secrete, they secrete basically two different kinds of stuff. Glands either release cirrus stuff. Cirrus secretions would be watery. Uh this would be your um spit. This would be your tears. This would be your uh regular old sweat. This would be also um when you're about to eat a meal, right? You're you get watery uh saliva as you prepare to digest your food with those extra enzymes in your saliva. Or glands can be mucus. Mucousy glands are thick, right? They're going to be more oily. They're gonna be more sebaceious, right? More more uh oily. Now, the one kind of gland that is mixed are your salivary glands. Think about it for a moment. Uh when you are about to eat, as I just mentioned, your saliva increases, your salivary glands are releasing that uh fluid and it's very watery as you anticipate the digestive process. But tell me about your saliva when you're nervous. Tell me about your saliva when you're about to do public speaking and you go cotton mouth, right? You go dry and your uh saliva becomes very thick, right? Very mucousy. And so salivary glands can depending upon the situation release either watery cirrus secretions or can release thick mucousy viscous products. So we say the salivary glands are mixed glands. And that brings us to the end of 4.2 and everything about epithelial tissues. Again, check out these questions. Uh come to lab and come to lecture with questions. Label these things down here to really help you with your understanding. The second lecture in this uh series for chapter 4 uh will cover connective tissues, muscle tissues, nervous tissue, and a little bit on tissue injury and aging. That'll be in the second posted video on chapter 4.