we're going to talk about the epidermal layers so if you remember there are four major types of cells there's keratinous sites which make up the majority melanocytes which are going to produce melanin Merkel cells which help detect light touch and then Langerhans which are an immune cell now all of these cells are going to be found within the layers of the epidermis now that we have two types of epidermis we have thick skin and thin skin and this picture over here is representing thick skin now in thick skin we have five layers stratum basale stratum spinosum stratum granulosum stratum lucidum stratum corneum these five layers are going to be found in thick skin now in thin skin we are going to be missing stratum lucidum but how we're going to discuss this is we're going to go through all the layers and talk about their properties so the first layer is going to be stratum vesali the Solley sounds like basement so this is the bottom most layer of the epidermis the stratum basale layer is going to be connected to the basement membrane by he need asthma's ohms we're gonna find all four cell types in it as well as stem cells stem cells are the cells that are able to differentiate into other cells when needed and this is what makes the basalt layer very proliferating the basalt layer is only going to be one layer thick it's gonna be more cuboidal shaped cells and all the cells are going to be living we find the basalt layer in both thick and thin skin the next layer is the spinosum layer the spinosum layer is usually around eight to ten layers of living keratinocytes so this tells us the spinosum layer is living again mostly keratinocytes the cells in the spinosum layer are going to be connected to each other by mostly desmosomes but there will be some gap junctions in there to allow communication the Basava spinosum layer is found in both thick and thin skin the next layer is the stratum granulosum the stratum granulosum is usually around three to five layers thick it is gonna be made of keratinocytes but what's unique about this layer is I call it the party layer because everything's happening in this layer in the granulosa layer the cells go in living but by the time they exit the layer in this area right here the cells are going to die so we call this apoptosis the reason the cells are dying is because keratinization is occuring if you remember the keratin is actually become inactivated in this layer so those Tohno filaments are being converted they are being converted into keratin now the protein that helps this happen is going to be care to Highland so it's in the granule Olsson layer that keratinization is becoming prominent so keratins become an active and it's also in this layer that lipids are going to start surrounding the cells because the lamella granules are releasing the lipids so in Grady Wilson the cells move in while they're living so in this area they're gonna be living but as they continue to move up they're gonna go through apoptosis and died care the granulosa is found in both thick and thin skin and the cells going living but by the time they exit they are dead the next layer is lucidum it gets its name because it means clear so when this layer gets stained it stays pretty clear this is the lucidum layer right here so you can see that white are going across is right here also the lucidum layer is only found in thick skin so only in thick this is the layer that makes thick and thin different now the difference in lucidum though is that it's only going to be composed of keratinocytes and we have to remember what happened in granulosa the cells died so this means that the Hasidim layer is living our dead if you said dead you're correct so the lucidum is only thick skin and it's composed of dead keratinocytes this is the layer that makes thick infants in difference now the last layer is corneum corneum is going to differ in size depending on if we're in thicker thin skin so that just tells us that corneum is found in both thick and thin skin corneum is the most superior layer so it's the superficial layer that you actually touch it is in both the convinced skin and it's composed of dead keratinocytes it can be anywhere from 20 to 40 layers thick so a quick overview our most deep layer is the basalt layer then we have spinosum granulosa lucidum if it's thick skin and then corneum an easy way to remember this is to create a mnemonic device the magnum onic device i use goes from deepest to superficial and it's before sex get latex condoms so before is from tasali sex venosum get granule sim latex lucidum condoms corneum the goes from deepest the most superficial because that's the way the cells move up through the layers now I'm going to ask a few questions which layer is only found in thick skin so take a moment think about it lucidum is correct which layer does apoptosis occur in granule Wilson's correct which layer is connected to the basement membrane by he me desmosomes the Solly's correct which two layers are completely dead lucidum and corneum are correct so there's lots of different questions that can be asked so you just want to always kind of want to think about what makes a layer unique how are most of the cells connected to each other what type of Junction desmosomes is correct so this is just an overview of pretty much everything that we've gone over with the epidermis you can see we've labeled the layers Visalli layers venosum granule olson lucidum cornea it tells you the type of cells that are present so we have our dead keratinocytes we have our living keratinocytes we have your Langerhans you have your Merkel cells you have melanocytes and then it also gives you a nice pictorial vision so right here we have stem cells remember they are proliferative so they're easily able to divide rapidly and replace lost cells now the process of going from super from deep to superficial so new cells to dead cells that sloth off takes approximately one month so I want you to take a moment and pause your computer and try to go through and answer what each of these picture are each of these letters is depicting once you get done and you can just double check yourself by going back to this picture now a little clinical correlation is the disease epidermolysis bullosa okay this disease has different levels it can be treatable or it can be fatal it depends on how severe it is and basically what happens is the Junction's have faulty proteins and they aren't able to secure the epidermal cells together or the epidermis to the basement membrane so your skin is basically sloughing off and you're constantly gonna have sores blisters and besides that it's extremely painful your skin is always going to be infected so again there are different layer levels of this and this one in this picture it is a relatively severe one but the individual was able to live a a lengthier life than most so but you can see based on the appearance that it is a debilitating disease