[Music] hey there folks welcome back so in this chapter we're going to discuss the different types of tissues found in the human body the study of tissues in the human body well this is known as hystology and so hystology you're studying normal structures of tissues and tissues what this is is it's a group of structurally and functionally related cells and the external environment that holds those cells together and they all perform one common function so tissues share two basic components there's a discrete population of cells so each tissue type has a discrete type of cell they also have a surrounding extracellular Matrix often referred to as the ECM extra cellular matrix this is everything outside and surrounding those cells so the extracellular Matrix let's start with that that's composed of substances that can be in a liquid or a thick gel or even a solid and as I said this is what's surrounding the cells of the tissue the ECM performs a variety of functions and those functions include at the cellular level they direct the cells to their proper position within the tissue and then they hold the cells in place this allows for proper communication between the cells and it supports and protects the plasma membrane of the cells the ECM also Reg regulates the development the mitotic activity which is the cell division and the survival of the cells in the tissue now that's all at the cellular level at the tissue level what the extracellular Matrix does is it holds the tissues together it provides that tissue with strength and it can resist tensile or stretching and compressing forces so there are two main components of the extracellular Matrix there's the ground substance and there's the protein fibers so this ground substance this makes up most of the extracellular Matrix and it consists of what's known as interstital or extracellular fluid often called ECF the components of this fluid include things like water as well as nutrients and ions that have dissolved in the fluid there's also three families of macromolecules that are found in the ground substance one of these macromolecules is known as glycosaminoglycans or simply abbreviated as gags these glycosaminoglycans what they are is they conin these negatively charged sugars so glyco the first part of glycosaminoglycan glyco is referring to a sugar the sugar is negatively charged and a negative charge attracts any positively charged ions that are found in the extracellular fluid so these ions they're creating what's known as a concentration gradient a concentration gradient is necessary in order to create an important environment for things like diffusion and osmosis to occur now in order to help you remember what glycosaminoglycans do think G for glycos aminoglycan and G for gradient they are important for establishing gradients another macromolecule is the proteoglycans proteoglycans are proteins and this protein core of it helps to make the extracellular Matrix firmer and resistant to compression it also forms barriers to diffusion so in some cases we want diffusion to occur for substances to move from the cell into the extracellular fluid or vice versa from the extracellular fluid into the cell that is the job of creating those gradients from the glycosaminoglycans however in some instances within the body we don't want that diffusion to occur in that case you'll see many of these proteoglycans that are going to form a barrier to that diffusion so that things like invading microbes can't cross or even things that we don't want to go from one type of tissue into the fluids a third type of our ground substance macromolecule is the cell adhesion molecules these are also known simply as cans these adhere to the cells and they hold the cells together and they also hold them in place so they help to maintain normal tissue architecture now in addition to our ground substances the extra cellular matrix also contains protein fibers and there are three main protein fibers that will be found embedded within the ground substance these fibers are long molecules they're composed of multiple fibrous subunits they're kind of like this ropeik structure and they provide enormous tensile or stretching strength so as I had mentioned there are three different types of these protein fibers that are found in the extracellular Matrix the first type is the collagen fibers now these collagen fibers they are composed of multiple repeating subunits and they form this white fibrous protein the these proteins are resistant to tension they're resistant to the pooling and the stretching forces as well as pressures that are applied to the tisses there's also what are known as elastic fibers and these elastic fibers are mostly composed of the protein known as elastin so as the name implies they have this property of extensibility what extensibility is is the ability that allows the fiber to stretch up to one and a half times its normal resting length and this without breaking the fiber so extensibility is the ability to stretch there's also the property of elasticity what elasticity is is once that fiber is stretched out to that one and a half times its normal length it has the ability to go back to its normal resting length so extensibility is the ability to stretch where elasticity is the ability to return to its normal resting length we also have the third type of protein fiber that is the reticular fibers reticular fibers are thin short collagen fibers and they form a mesh work or a scaping so the collagen fibers alone they're thicker as compared to the reticular fibers which are much thinner and shorter the job of these reticular fibers is they support the cells and ground substance of many of the tissues and they mostly form this web like structure within the organs some of these organs such as the spleen or the lymph nodes this webik structure it's helping to trap any foreign cells cells like bacteria or cancerous cells so reticular fibers they form this kind of a mesh netting to help capture other foreign cells now that was the ground substance that's found in our tissues but remember the tissues they also composed of different cells so when it comes to looking at the interactions of the cells of our tissues first of all neighboring cells interact with each other there are cell Junctions that are found between neighboring cells and this is between the plasma membranes and they're linked by integral proteins so there are three major types of these cell Junctions first of all there is a tight Junction this is also known as an uding Junction these tight junctions they hold cells closely together they basically Stitch the neighboring cells together and this is so that the space between those cells is pretty much impermeable to movement of macromolecules trying to go down between these cells so these tight junctions they're forming a Tight Seal or a barrier creating an impenetrable sheet of cells in some tissues however these seals may not be complete so that can allow for some leakage to occur so where there's not a complete seal some molecules or substances will be able to travel down between the cells themselves so an example of this leaky cell is that cells of blood vessel walls they're sealed together with these tight junctions that's to prevent the loss of any of the blood cells that are traveling through that Hollow inner area of the blood vessel that Hollow area is known as Al Lumen so the blood cells travel through that inner Hollow Lumin you don't want them to exit the blood vessels but those blood vessels can become leaky because around sites of infection you do want some blood cells to exit the white blood cells because the white blood cells will travel to a site of infection along the blood vessels but once it gets to the site of infection it has to be able to leave the blood vessel and enter into the area of infection so we say that the blood vessels become leaky what that is is those tight junctions they're releasing their Tight Seal between the cells and if that Tight Seal lessens then a white blood cell can exit between the cells that make up the walls of the blood vessel and go out to that site of infection now another type of cell Junction is known as a desmosome desmosomes these are strong intercellular adhesive Junctions and they're found at basolateral membranes of things like epithelial cells and other types of tissues now we'll start to talk about the specific different types of tissues like epithelial tissue but these tesones the basolateral lateral here for this cell is between the neighboring cells it's along these sides and what these strong intercellular adhesive Junctions do is they mediate direct cell cell contact this also provides an Anchorage or an attachment site for these intermediate filaments the cytoskeleton found within the cell so it's an intercellular adhesive Junction inter means between these are Junctions between two neighboring cells but it also provides a support or an Anchorage point for intracellular structures such as the cytoskeleton so intra means within the cell the last type of cell Junction we're going to look at is the gap Junction now these Gap Junctions are basically small pores they're formed by these protein channels and they occur between the adjacent cells so here you can see Gap Junctions basically it's creating a tunnel connecting to neighboring cells these tunnels allow for small materials to flow freely between each of the cells cytoplasm so for example ions in this middle cell those ions can flow through the cytoplasm through this Gap Junction and into the cytoplasm of the neighboring cell these type of Junctions they're found between cells that communicate with electrical signals so for example cardiac muscle cells contain a lot of Gap Junctions so that all those cells can contract together in a synchronous beat now something I want to point out we just discussed the components of the extracellular Matrix and different types of cell Junctions but these amounts of these components they differ between the different types of tissues found in the body so not all of the tissue types have the same amount of the extracellular components they have differing amounts and they have different types of cell Junctions depending on the functioning of those different types of tissues all right so that's going to wrap it up for this video and I'll catch you next time when we start talking about the different types of specific tissues bye [Music]