connective tissue. An essential but under-exposed tissue type. There are different types of connective tissue and the term connective tissue is confusing. So let me explain it briefly. Connective tissues are different types of tissues. Namely basic connective tissue. This is a term that no one uses, but for this presentation it is necessary to use it. Otherwise it will get super heated. This group also includes fat. Then you have cartilage, bone and blood. Here you have it again, but in a diagram. So all of these things are connective tissues. This consists of the group of elementary connective tissue. Which in turn consists of. And now it gets confusing, three variants of collagenous connective tissue. In short: connective tissue and fat. Then we have cartilage, bone and blood. Those are simple. I understand it's a bit dizzying, but you have to understand that when people use the word connective tissue in everyday use , they mean these three collagenous connective tissues. Yes, but if you look purely at the classification of tissues in general, so nerve tissue, muscle tissue, epithelium, then all these things belong to the group of connective tissues. Good? But why do these different tissues belong to the same group of connective tissues? Well, they have something in common. This is because they all have a limited amount of cells. Those are the blue dots. And they are located in a large amount of extracellular matrix. That 's the rest. Extracellular matrix is the material outside the cell that often gives the tissue its properties as a whole. Example: Cartilage cells make a matrix consisting of a type of proteoglycan and collagen. These molecules are strong yet flexible. And that is also the property of cartilage as a whole. Strong yet flexible. It is the matrix that usually determines the properties of the tissue. Okay, I'm going to go through those four groups now. We start with basic connective tissue. So that is the group that consists of three variants of collagenous connective tissue and fat. Starting with those collagenous connective tissue variants. So this is what we call connective tissue in everyday use. So when a pathologist says connective tissue, he means this type of tissue. It consists of fibroblasts with the occasional inflammatory cell such as a lymphocyte or a macrophage. macroage. If these are in the tissue itself , they are called zeiocytes. The connective tissue matrix is clearly visible in this elastin stain. This is an elastin dye. The extracellular matrix of connective tissue is collagen. So that's the pink that's in between here. And the black ones are the elastin fibers. And they provide the elasticity. I have it again in some sort of schedule. Here you see the elements again. Between all those fibers and cells there is also a kind of gelatinous material. And that's what you call the ground substance. These are proteins, glycosamines, glycans, proteoglyans and glycoproteins. And they provide for the diffusion of nutrients and also give some structure to the tissue. Well, that basic connective tissue comes in three varieties. Namely loose, irregular connective tissue. You often find this under epithelium, for example in the intestines. It provides some support and structure, but is not too stiff. Dense irregular connective tissue, which is somewhat stiffer, has more collagen bundles and is found, for example, in the dermis of the skin. Of course, it needs to be a bit sturdier . And then you have dense regular connective tissue. And you find this mainly in the tendons of the muscles. These must of course be very regular, because they are always loaded in the same way and must therefore also be strong in that direction. And that's why all those collagen fibers lie in the same direction. And then you have this odd one out that is basic connective tissue. And that's cool. Fat is everywhere. It insulates. It stores energy-rich lip and that gives some support. It is the only connective tissue without extracellular matrix. Because the lipid, the fat, is in the fat cell. So that is intracellularly here and here and here. In the H&E stain, lipids are washed away and it appears as if the cells are empty, but this is not the case, because they have simply been washed away. Okay, that was the basic connective tissue. Now for something easy. Cartilage. Cartilage comes in three varieties. Hyaline, elastic and fibrotic. I'll go over them quietly. Hyaline cartilage provides shape, is firm, but also smooth. You will find it in the ribs and nose where it is primarily shaping and provides strength, and in the joints where its smoothness ensures smooth movement. Then the rare elastic cartilage. Dat ook vorm , maar is wat flexibelmeer dan hy kraakbeen . You will also find this in the auricle and the epiglottus. That's the stutter valve. In no other places. Yes, a tiny bit around the duct of the ductus, but that's it. Finally, fibrotic cartilage. This provides strength, especially where there is a lot of axial pressure. So press from top to bottom. And it gives a bit of a dampening effect. You will also find it between the vertebrae in the intervertebral discs. They have to withstand a lot of active pressure when standing or sitting. And you find it in the minor scapulae or menisk, whatever the plural of meniskus may be. Whatever the knee fight needs a lot of cushioning especially when you are redet. Then there's a small problem that all the cartilage has. Cartilage has no Here you see the cartilage. Cartilage has no blood vessels in it. Those lie here and here. So they are outside. So when the cartilage breaks down it heals notoriously poorly. Then the bone. Of course, everyone knows bone inside and out , but bone is a very alive tissue type. It gives shape to the body. It provides strength and protection. And it's where blood is formed. The formation of blood is called hematopoiesis. Bones have an outer layer that is very thick. That's what you call the cortex. This gives strength and shape to the bone. Then you have those thin strips. Those are called the kicks. These form the interior of the bone. And that's what you call the weaving bone. Because that looks a bit like a sieve. And then you have the space in between. There lies the marrow. There are many blood cells in different stages of maturation and that is what we call the bone marrow. There are also some fat cells in between. The bone tissue itself is made up of those concentric rings. Yes, I think that's wonderful to see. And those rings are called osteons. Inside there is a small corridor. And those passages are called the Haverse kanaals. And that is where the blood vessels and sometimes a nerve are located. The cells within the bone matrix, that's all of these things. Here, here, here. That's what you call the osteon. And the matrix itself. So that pink material is calcium phosphate. Calcium and phosphate are very important elements for all kinds of processes in the body. Not just for the bones. A bone therefore functions as a kind of storage place for those elements. It is therefore constantly being built up and broken down, which means that calcium and phosphate levels in the blood can vary. Bone tissue is also maintained through this build-up and breakdown . The cells that do this are the so-called osteoblasts and osteosten. The blasts build it up and the clasts break it down. Here you see at the edge of the bone matrix those osteoblasts and clasts . Here you have them too and here. Uh, but you can't really tell them apart. So those are the osteoblasts and clasts mixed together. Okay, then the last one. Blood. Another well-known tissue type, but it is a very special one because it is fluid. Just as well. The blood ensures the transport of nutrients, and of course oxygen, and the removal of all kinds of metabolic waste products that the body produces. It is part of the immune system and it ensures the body's fluid balance. Blood consists of four parts. You have red blood cells, also known as erythrocytes, which transport oxygen and CO2. The platelets that ensure blood clotting. The white blood cells, also called leukocytes, are part of our immune system. And finally, the largest part of your blood, which is blood plasma. And that carries a catalog of things from glucose to hormones. Basically anything that is even slightly dissolved in moisture will transport it. Don't click away yet. We 're almost there. I've covered all the things , but there's one more diagram I have to show you and that's this one. Because when connective tissue degenerates into malignant disease and thus becomes cancerous, it is given the suffix sarcoma. A sarcoma is a malignant tumor of what we call the soft tissues. There are a few other things that go into it, but mostly it's connective tissue. Blood is of course an exception, because it has its own names, such as leukemias and lymphomas. But most connective tissues as they become lighter are sarcomas. Sarcomas are extremely rare. I mean, everyone knows someone with cancer or maybe even someone with lymphoma. But you rarely hear about sarcoma. And that's because most connective tissue cells almost never divide. So they also have a very small chance of becoming lighter. Okay, those were the connective tissues. Now we are really done.