In this video, we're going to introduce introduce to some of the connective tissues that we're going to be learning about in lab. Connective tissue is a really diverse tissue type, things ranging from blood to bone to cartilage to fat. It seems like those tissues are very different, but the truth is that they all share one sort of set of common features. That is that connective tissue will have typically loosely arranged cells surrounded by an extracellular matrix. All the space outside and between these cells is referred to as this extracellular matrix. It's within that matrix you're going to be finding various fibers, as well as this stuff called ground substance, that we'll talk about more in lecture. It's really the types of cells, the types of fibers, the components of the ground substance that really determines the type of connective tissue. Bone and blood, very different in their overall features, and that's because of these differences in types of fibers and types of ground substance material. For today, we're going to be focusing on six, which are referred to as these connective tissue propers ... these fibrous connective tissue: cartilage and bone and blood will hold off and do when we do with the respective systems later. All of these today, we're going to be trying to identify the appropriate irrelevant cell type as well as the types of fibers that you'll find spread throughout. In this first example here, this is referred to as loose areolar CT. This is really thought of as a very generic connective tissue. It's the packing. It's the supportive tissue that often surrounds organs or is actually underneath the epithelial tissue we learned about. One of the features of areolar CT is it's loosely packed cells with very loosely sort of randomly arranged fibers. It typically contains multiple cell types and all the fibers that you'd find in CT. If we start to look around, we'll notice there's a bunch of nuclei. Most of these nuclei represent what are called fibroblasts, and fibroblasts are the most common type of cell associated with connective tissue. Some of the features, they have very prominent nuclei. The cytoplasm doesn't really show up very well, you just really see nuclei. The other thing is you'll notice in a lot of these there's a nice dark black dot inside the nucleus, and that's the nucleolus. That's a feature that you were asked to learn as it associated with cells in general. This is a cell type where it's really prominent and easy to see. The fibroblasts are the cells that are actually maintaining this extracellular matrix. They're producing the fibers. They're producing the ground substance. They happen to be nice loosely packed in this view. The other cell type that we can see here, you'll notice this cell down here and this one and then there's a few up top. These are called mast cells. They're pretty large cells. You tend to be able to see the nucleus as well as the cytoplasm. Really the feature that should be most apparent are all these small little granules. It's these small granules that actually contain things like histamines and heparin, and these are compounds associated with inflammation. Mast cells are our cells associated with allergies and inflammation. It's because of their ability to release these compounds that will induce this localized inflammation. They're commonly associated with this loose areolar CT. This is the type of connective tissue that we typically find directly below the epidermis on the surface of our skin. The types of fibers we see here. You'll notice there are two different types of fibers. There are these very thin black stringy fibers, these are elastic fibers. Elastic fibers, as the name suggests, are quite elastic. They can stretch and snap back. Pretty important when you think about the layer of tissue supporting our skin. The other type of fiber here are these thicker kind of wavier, kind of a lighter purple, these thicker fiber. This is collagen, probably arguably the most common protein we have in our body. The collagen fibers in this field of view are also pretty loosely packed. It turns out there is a third type of fiber that would be present in areolar CT, it's called reticular fibers. We typically can't see those because they require a special stain. Normally, if you can see collagen and you can see elastic you're not going to see the reticular fibers very well but we'll see a slide here in a moment of those. Loose areolar CT is just this very loose kind of nice packing supportive CT. It's typically dominated by fibroblasts. You're often going to find a lot of mast cells and all of the different types of fibers will be present. In this next slide, this is one that may be set up as a demonstration for you. There is a third common cell type that you'll find in loose areolar CT and those are referred to as plasma cells. Plasma cells are the ones that synthesize and release antibodies associated with our immune system. The difficult thing about these is they're hard to find. We're actually not going to ask you to find them ... we will set up a demonstration slide. One of the features that is often used to identify them, here's one right here, is the nucleus is very prominent. It tends to have a lot of these little stained things that maybe represent a clock face or kind of a cartwheel-shape thing. The other thing that is used is this shadow right here or this negative shadow, essentially. Just outside the nucleus, there's a space that seems to be non-pigmented and this is called the Golgi shadow. The Golgi apparatus occupies the space, and they tend to have a very large Golgi apparatus. When stained that actually leaves behind this kind of negative shadowy area. Again, these are plasma cells. They're associated with our immune system antibodies, but we won't ask you to find them but you should be able to identify them. We'll try to set up a demonstration slide for that. The second type of loose connected tissue that we're going to have you learn about would be the adipose tissue or fat tissue. This slide here is going to look more familiar in a later lab, but this is the skin. From here to the surface, this is going to be the epidermis. You probably could tell me right now the type of ET, but if not, just realize that there are a lot of cell layers here. If we could look closely, these would be very thin cells at the surface, and so we would call this stratified squamous ET. This down below is also part of our skin, and this is a layer called the dermis that we're going to be learning a lot more about later. Even below that, you'll notice that there is then a transition into a type of tissue that has a lot of loose almost empty filled vacuoles. This is often referred to as our hypodermis or this can be the subcutaneous fat layer. If we look closely at this, we're going to start to see a lot of cells that have a very unique feature. The cell, for the most part, is filled with these empty vacuoles. The truth is they're not empty, and in the cell in an unprepared situation, they would be filled with lipids or fat. These are called adipocytes or fat cells. Fat cells are really unique because of these big cells. They have a nucleus. They have cytoplasm, but the nucleus and the cytoplasm tends to be pushed to the very edge. Most of this cell is then going to contain this fat-filled vacuole. Here we have a lot of adipocytes, these very loose large fat-filled cells. In addition to the adipocytes, you will also find at times, fibroblasts as before. You'll find the fibers. This stuff in here. These wavy kind of purple bands ... this is a lot of collagen. Collagen is still going to be present. This is connective tissue ... it's going to have an extracellular matrix. There's often elastic tissue and reticular fibers. These fibers are all present. It's just really what becomes so obvious and hopefully easy for you to distinguish would be these large adipocytes. Here's another slide of adipose tissue. Really, really, really large fat cells or adipocytes with large vacuoles filled with fat or lipids. Just not a lot of extracellular matrix but where it does exist, you're going to find collagen and elastic tissue and reticular fibers and such. The third type of connective tissue here is going to be referred to as reticular connective tissue. The thing that is defining this type of tissue is the prominent fiber ... the reticular fiber. This is the one that I mentioned was we were unable to see because of a special stain needed. In this case, we're giving you slides that have used this special stain. A couple places where you find reticular fibers and reticular tissue, in general, is in the spleen or the bone marrow or in this case the lymph nodes. All of these represent kind of these soft organs. Reticular fibers all of these dark stained fibers that you can see in this field of view, you can imagine creates this soft skeleton. This nice supportive structure which then can hold all the other cells in their place. This slide is from a lymph node, and lymph nodes as we'll learn later, are going to have a lot of lymphocytes ... a lot of white blood cells kind of held together in this nice fibrous network. It's the fibers ... the reticular fibers that you see all throughout that really define this tissue type. There's another slide. The same tissue types probably also a lymph node. We can see just really, really prominent darkly stained fibers. These are the reticular fibers that make up this kind of soft skeleton that supports some of these soft organs like lymph nodes and the spleen. It's in here that you should be able to recognize reticular fibers. That's about it from the slide. The next three tissue types are all going to be referred to as "dense" connective tissue, and that it really means that the fibers themselves are going to be more densely packed than we've been seeing. This next one, this could be from a ligament or a tendon, and this represents the dense regular connective tissue. By dense, we're referring to how densely packed the fibers are. The regular aspect of that name just tells us how regularly arranged the fibers are. Here we see a lot of really, really, really nice pink fibers that all seem to be parallel ... they're all running, in this case, left to right of our screen. Those are all collagen fibers. A lot of densely packed, regularly arranged collagen fibers with then very prominent nuclei that represent the fibroblasts. This dense regular connective tissue is the type of connective tissue that we see in tendons and ligaments and other places in the body, that we'll learn about, including the cornea of the eye. The fact that this is a regularly arranged collagen gives this a really strong feature. You can think about tendons and ligaments ... how strong and how hard it is actually to tear them. These are still flexible. You can bend them kind of up and down, but you're not going to pull them apart very well because of the collagen fibers. The next type of tissue is going to be dense irregular connective tissue. Really the only difference between dense regular, which we just saw, and dense irregular is how regularly shaped or arranged those collagen fibers are. This we saw earlier ... this is the skin. This time what I want to point out here is this area referred to as the dermis. We're actually going to look at a close-up view of this area. Before we were looking at it for the adipose tissue down below, but now you'll notice there's a lot of pink tissue that extends a lot of it directly below the epidermis but then also continues down. That pink tissue, when we look closely, is primarily this dense irregular CT. You'll notice there are fibroblasts or those are the cells that are prominently found throughout connective tissue. Unlike the loose areolar, we see a lot of the pink wavy bands ... this is the collagen. Unlike the site we just saw where we had nice parallel running collagen fibers, these are pretty irregular. Some of them are running up and down, some of them left and right. There doesn't seem to be any sort of direction to the angle or flow of these fibers. What that means is this tissue is going to provide a lot of support in all different ways. It can be pulling up and down left and right at an angle, and all of that is going to have collagen fibers that can support it. Which you can think of is probably pretty important for the support of our skin. This dense irregular connective tissue is going to be defined by the presence of collagen fibers, but are arranged in a more irregular pattern. You should still see the fibroblasts and particularly other cell types given where we are. The very last slide we have here. This is our final connective tissue that we're going to be learning today. This is elastic connective tissue. Really elastic connective tissue is defined by the prominent presence of elastic fibers. Elastic fibers, in this case, have been stained and these are these wavy black lines that you see throughout this tissue. This is actually the wall of the aorta. The wall of a really, really, large artery in our body. If you think about the aorta, it's constantly under high pressure when the heart pumps then lower pressure when the heart relaxes. That ability to stretch and accommodate high pressure, but then recoil to accommodate the low pressure is important for cardiovascular health. It's because this is a very close-up view of the wall of the aorta. It's because of these very regular arranged elastic bundles. These bundles of elastic tissue that are existing within the wall of this aorta help the aorta stretch their elastic and then also recoil. This is the only slide that we're going to ask you to be able to identify elastic tissue, and it's really these very clear black squiggly lines that are the elastic fibers that really define this feature. It's hard to see some of the other things here because of the stain. There's going to be a lot of muscle, in this case, smooth muscle between these. That's simply because of the overall structure of arteries is primarily smooth muscle and elastic tissue as we're going to learn later. For us today, for connective tissue proper this is going to represent our elastic connective tissue and the aorta is the one place we see it. As before, use this kind of preparing for lab, but in no way this should substitute for the time in lab.