Hi, this is the recording to accompany the slides for the tissue level of organization lecture. My name is Dr. Alita Partasadarsu and I'll be walking you through these slides. So the reason for including this diagram in this first slide is to actually show you the differences between what's normal and what's abnormal.
So this is a section of the cervical epithelium and what you can see here is in the normal epithelium the cells are very organized and structured in a fixed format whereas in the abnormal epithelium where it there is an arrangement of cancerous cells you can see that it's not very well organized There's an irregular arrangement of these cells and so you can see that they're very different this section from the section of normal epithelium. So this is the study of histology, the study of tissues, as we've covered in a previous lecture. So let's go on.
So the second slide in this lecture, as well as all other lectures, is to actually give you an overview of the slides that are found within this. So what you can see over here is we're going to cover the different types of tissues that are found in the human body. So there are four different types of tissue.
For the purposes of this lecture, we are going to cover the first two in great detail and I'm going to briefly talk about the muscle and nervous tissue. As you can see here in the diagram on the right, what you can see here is that the nervous tissue consists of brain, spinal cord and nerves, epithelial tissue, are covering and protective tissue. You've got muscle tissues. There's three different types of muscle tissues in the human body.
And then there's a whole bunch of different types of connective tissue. And as I said previously, what we're going to do in this lecture is focus on epithelial tissue, as well as the general maladies of connective tissue. So let's start off by talking about tissue membrane.
So a membrane is a thin layer that covers something. So in this case, a tissue membrane is a thin layer or sheet of cells that covers the external body surfaces, that covers organs, that covers internal passages, and that covers cavities in the human body. There are two different types of epithelium. The first type is, sorry, there's two different types.
type of membranes. The first one is made out of epithelial tissue and then the second type is made out of connective tissue. When we look at epithelial membranes, there are three different types of epithelial membranes that are listed over here.
So you've got the mucous membrane that line the hollow openings of the digestive, respiratory, urinary, and reproductive tracts. They are called mucus membranes because they contain mucus glands. And the purpose of mucus glands is to secrete mucus.
And mucus is secreted in order to help with the transport of different items through these different tracts, systemic tracts in the body. The second type of epithelial membrane are the serous membrane. So the serous membranes line body cavity. They're closed off to the exterior of the body. So it lines the abdominal cavity, the peritoneum.
It lines the lungs, the pleural cavity, and it lines the opening that the heart is located in, the pericardial cavity. And again, it produces fluid and the fluid here helps to reduce friction and to minimize heat production as the different types of organs contained within the serous membranes and contained within these body cavities move around. And then the third type of epithelial membrane is the cutaneous membrane, also known as the skin.
We're going to cover that in the next lecture. And the skin, as you know, covers the body surface. Thank you. And it's got a whole different layers.
It's got multiple layers to help to protect the body from desiccation or dehydration and from different pathogens, virus, parasites, bacteria from actually entering into the body. So those are the three different types of epithelial membrane. When we go and look at the connective tissue membrane, there is one type and that's the synovial membrane. So the synovial membrane lines most of the joints found in the body.
It lines the synovial joint and it produces fluid within the synovial joint in order to actually help most of the joints in our body actually. move around freely. So let's go on and talk about the first tissue type, that is the epithelial tissue. So I've got over here just an overview of the epithelial tissue in terms of its properties. So you can see here this is a typical section of a type of epithelial tissue.
You can see here that the cells are located fairly closely together. There's very little space in between the cells. The epithelial tissue is avascular, so that means there are no blood vessels found within it.
So what happens is you've got blood vessels that run just underneath the epithelial tissue, and that then the blood vessels will transport. the nutrients to actually nourish the epithelial tissue and will also carry waste that are produced by the epithelial tissue. Because the epithelial tissue is avascular, it limits how thick and how many layers are found in the epithelial tissue.
The epithelial tissue, because it's often the covering tissue of an organ, it undergoes wear and tear. So when we think about the skin, the epithelial tissue of the skin is constantly being replaced. And so we can say that the epithelial tissue is capable of reproduction because it needs to be replaced frequently because when we walk around and live our lives, we're constantly bumping into stuff and um, We may actually have a scratch or a graze on our skin, and that will mean that the epithelial needs to be replaced quite frequently.
Function of the epithelial tissue are listed over here. So the main four functions are to protect us, our bodies from mechanical and chemical injury and from entry of foreign pathogens such as virus, fungi, bacteria from entering into our body. And you know that our skin or another epithelial tissue protects our deeper tissues from mechanical and chemical injury because it stops a lot of chemicals from entering into our body and it also helps to prevent mechanical injury of the structures underneath it. Our epithelial tissue also has a sensory function, so it can sense changes. what's going on in the environment.
So when we think about the skin, our nose, our eyes, our ears, we can actually if we can sense with our skin if there is hot water being touching our skin or cold water or ice or we can change we can sense if there are there are mosquitoes or flies landing on our skin and so all that sensory all is All of that is included in the sensory functions. The epithelial tissue also produces secretion. So some types of secretion that different types of epithelial tissue produce include hormones, include mucus, include juices from the digestive tract, as well as sweat.
And our epithelial tissue also acts as a barrier to control movement of gases, solutes, and fluids across it. And if we want easy movement of gases across the epithelial tissue, for example, in our lungs, it means that the epithelial tissue in the smallest unit of our lungs is only one layer thick in order for gas exchange to occur. In our digestive tract, in our small intestine, again, the epithelial tissue there is only one layer thick.
one layer thick in order for nutrients to be absorbed. But if you think about the epithelial tissue of our skin, it has to be multiple layers thick so that things can't go through, right? So that chemicals can't go through, so that foreign pathogens can't go through.
So again, the level of barrier protection depends on the location of the epithelial tissue. As you can see in the diagram in the top right, the epithelial tissue is organized into layers. So in this example, You've got an epithelial tissue that contains many layers, right?
So you've got all the different layers over here. And then you've got two different sides. You've got the apical surface, which interacts with the external environment. And then you've got the basement membrane that helps the epithelial tissue actually connect to the underlying tissue, to the connective tissue.
Right, so you've got the basement membrane and then below the basement membrane you've got the connective tissue. In the diagram at the bottom what you can see here is you've got the epithelial tissue up above and then the basement membrane over here and then deeper to the epithelial tissue. Below it you've got the connective tissue and so the basement membrane then connects the epithelial tissue to the connective tissue down below. There are two main types of epithelial tissue. One is a covering type, so the membranous epithelium, like I talked about in the previous slide.
And then the second type is glandular epithelium. So glandular epithelium produce secretions, and glandular epithelium are split up into whether those secretions are released into the body, in which case they would be called endocrine glands, or whether... those secretions are released outside the bodies, in which case they would be called exocrine glands, right? So endo refers to inside, exo refers to outside. And so you can see whether you can actually tell whether the glands release their secretions into the body, in which case it would be endocrine glands, or they release the secretions out of the body, outside the body, in which case it would be an exocrine gland.
As I said before, epithelial tissue are connected by cell junctions. And so what I'm going to do in the next slide. So when we go and talk about cell to cell junctions that are found in epithelial tissues, what happens, as I said, is that epithelial cells, cells of the epithelial tissue are connected very closely to each other. And they're connected together by these cell junctions.
And they don't have cell. material in between those cells. And so the most common type of cell to cell junctions are called anchoring junctions. So you can see here that there are three different types of anchoring junctions, depending on where they're located.
These anchoring junctions provide strong and flexible connections. So the most common type are these desmosomes. So you can see here this is the cell membrane of cell one. This is the cell membrane of cell two.
And what happens is you've got the system called a desmosome that actually glue or connect these two cells together. The second type of anchoring junction is called a hemidesmosome. And so if you look at the location of these hemidesmosomes, they anchor the bottom layer of...
the epithelial tissue to the basement membrane. And then the third type of anchoring junction is called the adherence and what they do is they form a belt so you can see here instead of being of ending over here they form a belt around the inside of the cell and so they basically encircle the tissue with this type of anchoring junction. A second type of junction that's not an anchoring junction is called the tight junctions. So in the tight junctions there's really really no space at all between the cells.
So you've got the intercellular space and you can see here the tight junctions are like super glue. They don't allow really any space in between. And these tight junctions are found in locations such as the stomach or in the blood-brain barrier to stop substances from going across it. The third type of junction is called the gap junction.
So you can see here, you've got the plasma membrane of one cell and the plasma membrane of another cell. And in between the two, you've got these gaps, which are like these channels or these pores that allow material to go in from one cell to another quite freely. So what this... gap junction, a location of the gap junction is found in cardiac muscles, in muscles of the heart, and that they allow, as I said, ions and other substances to flow directly from one cell to another, and that allows the function of the heart to be coordinated quite well. When we talk about the different types of epithelial tissue, again, we can actually say that epithelial tissue can be organized based on both the number of cells found in the epithelial tissue, as well as the shape of the cells at the top layer of the epithelial tissue.
So an epithelial tissue that is a simple epithelial tissue only has one layer. So out of this seven or eight diagrams over here, you can see that this one only has one layer, this one also only has one layer, and the one right below it also has one layer. Epithelial tissue can contain two or more layers.
So in the diagrams, if you look over here, you can say that the top picture on the right-hand side contains two or more layers, so does the picture beneath it. and the picture beneath that. And then we've got pseudostratified, which is a type of epithelial layer that is really one layer thick, but it looks like it has more than one layer. And the reason why it has it and an example of a pseudostratified epithelial layer is the picture on the bottom right hand corner.
And the reason why it looks like it has them. more than one layer is that the cells are different shape and the nuclei are at different heights, right? And so it looks like it's got more than one layer, but it really only has one layer. And then the fourth type of epithelial tissue that is based on the number of layers is the transitional epithelium, which can stretch.
and it changes the shape. So you can see here, this is a transitional epithelial, and it looks like this when it's not stretched, whereas when it's stretched, it looks elongated. And so the location of transitional epithelia is within the urinary tract in the bladder and in other places within the urinary system. So... Number of layers describe epithelial tissue.
Another way of describing an epithelial tissue is the shape of the cells at the top layer. And so the first shape that I'm going to talk about is squamous. So the diagrams on the top left is you've got the flat and thin shape of the tissue, as is the diagram on the top right.
The second shape of cells of epithelial cell is cuboidal, which is boxy. So it's as wide as it is tall. And so the second one down in the left column is an example of an cuboidal epithelium, as well as a second one down on the right hand side.
And then you've got columnar epithelium. which is rectangular. It's taller than it is wide.
So an example of columnar epithelium is the one on the third, one's down on both sides. So this one is rectangular, so it's columnar, as well as this one is also rectangular, so that it's columnar over there. And so when we put these two different naming types based on number of layers and shape of cells, what we get is we get this.
So we have the simple squamous epithelium that is involved in absorption and secretion. So it's found in the, it lines the alveoli of the lungs, it lines the hearts, it lines the blood vessels. and it lines the lymphatic vessels.
Stratified squamous epithelium is second, so you've got lots of layers, and the top layer is flat, and that offers protection, and they're found in these different parts of the body. Next one is the simple cuboidal, so simple means one layer. Cuboidal means that it's boxy in shape, and so you've got here... It's used for absorption and secretion, and you've got here where it's found. The fourth one is stratified, more than one layer cuboidal, so it's boxy at the top.
And again, any stratified epithelium is good for protection, and so they're found in these locations. You've got simple columnar epithelium, so one layer taller than it is. wide found in these locations. And then you've got stratified columnar epithelium.
So stratified more than one layer. The top layer is rectangular, taller than it is wide, and it's found in this layer. And you can see again, one of the functions of the stratified epithelium, columnar epithelium is protection. And then the seventh one, is the pseudostratified columnar epithelium.
Again, the location, what it's used for, and then you've got the transitional epithelium that's found in the urinary tract. So it's also called the urothelium, and it allows the urinary organs to expand and stretch depending on the volume of urine that's located within these spaces. As I said, when you look at the overview of what...
each of this stratified epithelium do. You can see that protection is the top function of these epithelium, whereas with simple epithelium, it's involved in absorption secretion over there. So there are some commonalities within these different types of epithelial tissue.
And again, as we go through the course, we will actually examine each of these different types of epithelium as we go through the multiple organ systems. So this describes membranous epithelium. We're going to go and talk about glandular epithelium next.
So the way that we can um Categorized glandular epithelium is where they actually release their secretions. So if the secretions are released to the external environment, they are called exocrine secretions. Whereas those glandular epithelium that release their secretions directly into surrounding tissues and flutes, are referred to as endocrine secretions.
Over here, what you can see is you can see the example of exocrine glands, so goblet cells that produce mucus, sweat glands that produce sweat, salivary glands that produce saliva, and mammary glands that produce breast milk are all examples of exocrine glands. Whereas endocrine glands are... Some examples are the anterior pituitary, thymus, thyroid, sorry, adrenal cortex, and the gonads.
And each of this produces hormones. They release it into the bloodstream, as you can see over here. And then the hormones then travel until it reaches the target's tissue and can have an effect on the target tissue.
In terms of exocrine gland, there are three different ways that the exocrine secretions are released into the external environment. So the first way is through merocrine secretion, and this is the most common type. And so what you can see here is that in the merocrine exocrine glands, What you can see here is those exocrine secretions are packaged into the secretory vesicles.
You can see over here the secretory vesicles are transported towards the plasma membrane. And then what happens is the vesicles fuse with the plasma membrane and then the exocrine secretions are then released. And this type of... of exocrine gland, there is very little damage to the cell. The second type of exocrine gland is called the apocrine secretion.
And so in this, what happens is, again, the exocrine secretions are packaged in these vesicles. But instead of the vesicles actually connecting with a plasma membrane, what happens is that that part of the cell that contains the secretory vesicles is pinched off and then the secretions are released and it also causes relatively little damage to the cell. And so these are some examples of apocrine secretions. The third type are holocrine secretions. So again they are released, the secretions are packaged in the secretory vesicles.
But what happens is that those secretory vesicles are not released until and unless the cell becomes mature, dies, and ruptures. And so when the cell ruptures or explodes, then the entire cell is destroyed, right? So some examples of holocrine secretions are sebaceous gland on the skin and the hair. So we've got the different types of epithelial tissue. Here we've described the various different types in terms of shape and number of layers, as well as whether or not they're glandular epithelium.
And so what I'm going to do is leave the epithelial tissue now and move on to the second tissue type. That is the connective tissue. When we go and look at the connective tissue, which is the second type of tissue that's found in the body, what we find out is that all connective tissues in the body help to support and connect with other tissues. The diagram up above is an example of a typical connective tissue and so most connective tissues have fibroblasts and fibrocytes. So when you look at the name fibroblast and fibrocytes, what you can see is that there is a common prefix.
So fibro, and that refers to the fibers that they produce. And then the suffix, which is the second part of the name, you've got blast versus cyte. So when you've got something blast, it usually means that it's the active younger version of the cell.
So active in that it's actively either growing or actively producing things. So fibroblasts produces polysaccharides and proteins, including fibers. And then when the active younger fibroblasts become more mature, then they become fibrocytes and they kind of settle down and they just maintain the structure of the connective tissue. Adipocytes are also found part of connective tissue and adipocyte, so the word, the second half of this site refers to cell, adipo refers to adipose. tissue which is fat.
So adipocytes stores lipids in the cytoplasm. The second, another type of cell is called the mesenchymal cells. And these are multipotent adult stem cells. So they can differentiate and produce more of the same type of cells.
And we've also got macrophages as well as mast cells. So both macrophages and mast cells are part of the immune system. A macrophage is a type of phagocyte which destroys foreign pathogens, whereas a mast cell contains these granules that are filled with this chemical called histamine and heparin, and mast cells are involved with the inflammatory response. So you can see here that unlike the epithelial tissue, The connective tissue contains a whole bunch of different cells, right? And they have a different type of function.
Within the connective tissue, connective tissues are not, unlike epithelial cells, they're not joined closely with each other because they're different types of cells. And also because they are found within what we call the... extracellular matrix over here. So the cells are kind of floating around and depending on the type of connective tissue and the type of cells that are found within it, the connective tissue can either be fluid or can be solid, right?
So when we look at the fibers that are produced by the fibroblasts, there are three different types of fibers, right? that are produced by the fibroblasts. So the first one is collagen fiber and collagen fibers are thick and long and straight so they give the connective tissue flexibility with great strength. So it resists, it allows the connective tissue to resist stretching so it doesn't become overstretched or floppy and it's very strong, it's very resilient.
The second type of fiber is called elastic fiber, which as its name suggests, allows the tissue to return to the original shape after it's either stretched, elongated, or compressed. So the elastic fiber has got different characteristics compared to the collagen fiber. The third fiber is called...
the reticular fiber. And if you can see here on the diagram, reticular fibers are fine strands. And so again, very similar in composition to collagen fibers, except they are finer.
And so again, flexible with great tensile strength, resist stretching, resilient, exactly the same properties as collagen fibers. But again, because they're thinner, they help to actually form a mesh around organs. And then in between the cells and the fibers, you've got the ECM or the extracellular matrix.
And you can see over here that the extracellular matrix can contain water, but also can contain proteins, polysaccharides, and other substances, right? So they So the type of extracellular fluid that are found in different connective tissue depends on which connective tissue it's found in. So on that note, let's look at the different types of connective tissue.
So you can see here, connective tissues can be classified into three different categories. Connective tissue proper, supportive connective tissue, and fluid connective tissue. depends on the amount of extracellular fluid and ground substance as well as the amount and type of fibers that are found within it.
So we're going to go through each of these different types of connective tissue in the next few slides. So the first type of connective tissue is the loose connective tissue. Two different types, or three different types, adipose, areolar, and reticular connective tissue.
So adipose refers to fat, right? So you can see here in the adipose tissue, it's made largely of adipocytes, right? And remember, sites refers to cells, adipose refers to lipids. So adipocytes are found in adipose tissue, and the purpose of adipose tissue, fat tissue, is to store lipids. Second type of loose connective tissue is areolar tissue and areolar tissues are organized in a random web like fashion to fill spaces between different types of tissues, right?
So it forms kind of like a mesh and it fills different spaces. So very similar to the reticular tissue. So you can see here the reticular tissue contains a lot of reticular fibers. So those are those fine, strong, resilient fibers. And they again provide a mesh-like supportive framework for some of the soft organs in our body.
The second type of connective tissue is the dense connective tissue. So as the name suggests, The dense connective tissue contains a lot of collagen fibers compared to loose connective tissue and these collagen fibers provide greater resistance to stretching, right? And so some of these dense connective tissue can also contain some proportion of elastic fibers to help to retain its shape after stretching or compression.
So in terms of dense connective tissue, we have dense regular connective tissue. And I've just realized they are actually the opposite way around in here. So dense regular connective tissue, what you can see here is that the fibers are arranged in neat little rows, right? So what happens is these little arrangements allows great strength in one direction. So a couple of examples of dense connective tissue are ligaments and tendons.
The second type of dense connective tissue is dense irregular connective tissue. So same type of composition and everything. The only difference between dense regular and dense irregular. is that in dense irregular, the fibers are arranged every which way.
So you can see here the fibers are arranged every which way. And so what happens is it provides great strength in all directions, right? In all directions.
So some examples of dense connective tissue in our body is the underlying dermis in our skin. and the walls of our arteries. And if you can think about your arteries, they have to stretch to accommodate blood flowing through it and then relax when blood actually leaves it.
And so they require these fibers to be organized in, to be arranged in all different types of, in all different directions. So another kind of connective tissue is cartilage tissue. Cartilage tissue, like epithelial tissue, is also avascular.
So it's got no blood vessels through it, which means that if you injure cartilage tissue, it takes a long time for it to heal because there's no blood vessels. And so what happens is the nutrients have to diffuse slowly from other connective tissue around the cartilage in order to reach the chondrocytes. In terms of the different components of cartilage, you've got these two different cells.
So chondrocytes and chondroblasts are cells that are found within the cartilage tissue and what you can see here is chondro refers to cartilage. Whereas similar to fibroblasts and fibrocytes, chondroblasts are the more active, developing, growing type of cartilage cells, whereas chondrocytes are the less active, more mature, more maintenance type of cartilage cells. You can also see here that the cells in the cartilage are surrounded by...
are located within lacunae. So lacunae is a space that surrounds the chondrocytes and it contains fluid for exchange of nutrients and waste. Around the cartilage, we've got a protective layer, and this is called the perichondrium. Peri means around, chondri refers to cartilage, right? And we've also got the extracellular matrix that consists of polysaccharides together with fibers.
When we look at the types of cartilage, cartilage there are three main types. So the first one, the hyaline cartilage, is the most common. You can see here is that they've got some short dispersed collagen fibers. They've got a lot of ground substances.
They're strong and flexible. So these are the locations that they're found, some of the locations that they're found in our body. The second type of cartilage is called the elastic cartilage. So it also contains those collagen and proteoglycans that are found in hyaline cartilage, but it also has some elastic fibers. And so the elastic fibers provided some elasticity so that it can regain its previous shape after it's been stretched or compressed or bent out of shape.
So an example of elastic cartilage is found in our external ear. The third type of cartilage is called fibrocartilage. And so in this type of cartilage, what happens is the collagen fibers are organized into thick, thick bundles. And so it means that the fibrocartilage is the toughest and most resistant to damage out of the three different types of cartilage.
And fibrocartilage is found as part of our knee joint, as well as in between the vertebrae in our... back and this actually helps our body support our weight. Next type of connective tissue is the bone. I'm going to talk about it very briefly here because we have a whole lecture on bone tissue. So as you know the bone is the hardest connective tissue in our body and the function of bone is to support the body as well as to protect internal internal organs are the extracellular matrix that's found in bone is made is rigid is hard is solid and it's made out of organic compounds collagen fibers embedded in a mineralized ground substance containing inorganic compounds and the inorganic compounds that are found in bone are these hydroxyapatite, which are a form of calcium phosphate, right?
So again, this is why calcium intake is so important for good, strong, healthy bones. Like chondrocytes in cells, bone cells are called osteocytes, and the younger version of these bone cells are called osteoblasts. And these bone cells are located within a lacunae, similar to the chondroblasts and chondrocytes of the cartilage. Bone is a highly vascularized tissue.
Bone is a highly vascularized tissue. And so when you break your bone, it's... relatively quick to actually recover from injuries compared to a vascular tissue such as cartilage.
That's all I'm going to say on bone tissue because like I said, we're going to talk about it in another lecture soon. The last type of connective tissue that I'm going to talk about is fluid connective tissue. So we've got two different types of fluid connective tissue in our body, blood and lymph fluid.
So blood flows within blood vessels, within arteries, within veins, within capillaries, whereas lymph... lymphatic fluid is found within our lymphatic system and what you can see here in the diagram in the right is that the The vascular system, which contains blood, and the lymphatic system, which contains fluid, are very interwoven. So you can see here you've got lymphatic capillaries located in the same general region as blood capillaries.
So again, that's all I'm going to talk about in terms of fluid connective tissue, because we're going to talk about it more when we actually come to the relevant sections of this course. The third type of tissue that is found in our body is our muscle tissue. So again, just one slide just to give you a brief overview.
So the muscle tissue in our body allows us and our body parts to move. They respond to stimuli, so they are excitable and they can contract and relax in order to move stuff around. Either our body, our body parts or things contained within.
the various tissue types. There are three different types of muscle tissue. The first type is skeletal, so associated with bones.
Skeletal tissue is voluntary. It produces heat, it protects organs, it moves our body and our body parts. The second type of tissue is cardiac tissue, which is found in the heart. Luckily for us, we don't have to force our heart to move.
Our heart beats involuntarily without any conscious control on our part. And the purpose of the cardiac tissue is to pump blood through our heart and through our vascular system. And then the third type of muscle is a smooth muscle. So you can see here it's short, spindle-shaped. It's got no evidence striation, so it's not arranged in bands of light and dark.
And this is also controlled involuntarily, right? So we have smooth muscle in a lot of our internal organs, in our esophagus, in our stomach, in our bronchi in the respiratory system, throughout the body. And... So it's good that it's involuntary. Again, we're going to talk about muscles when we come to that part of this course.
And then the fourth type of tissue in our body is the nervous tissue. And so the nervous tissue, like muscle, is excitable. It can send and receive electrical signals that provide the body with information. It communicates.
It allows communications between different... parts of our body and it's vital for our body to actually work together as a whole. In terms of the different cells that are found within nervous tissue, it can be separated out into two main categories, neurons that are the working part of the nervous system and neuroglia, which are the supporting part of our nervous system.
So you've got the neurons over here. So signal comes in here from the dendrites, processed over here, and then sent down through the axon to cause release of neurotransmitters at the axon terminal. And then in the second diagram over here, you've got four different types of neuroglia, or support cells that are found in the central nervous system. So I hope that you've learned something from this lecture and I'll see you again soon.