skin and skin is a very nice place to start because it has a lot of the essential building blocks of tissues as well and in this case we're going to take thin skin rather than thick skin in thin skin this stratum corium here which is keratinized or cornified material is thinner than the rest of the full thickness of the epidermis and that's why it's called thin skin generally thin uh skin is as thick or as thin as it has to be so in areas where you need more protection like your soles and Palms it's thicker skin and therefore the stratum corium is thicker than the rest of the epidermis uh let's go through the different layers of the epidermis which is the epithelial portion the dermis which is chiefly this connective tissue portion and what they call the hypodermis or subcut which is largely largely a fat perhaps loose connective tissue if you will uh even though we're going to go from top to bottom classically when you look at the epidermis itself as the first third of the project usually start from the base and go towards the top and uh in the skin the uh epithelium is keratinized and it's stratified the reason why it's Strat ified is because you need multiple protective layers and the general principle is towards the base of the epidermis where you see this vague thing called the basement membrane delineating the epidermis from the connective tissue of the dermis the cells are basically aligned in a uh cuboidal fashion towards the middle of the layering they are generally about as wide as they are long or there for they are cuboidal and certainly at the top they are very very flat or squamous and multi-layered or um uh stratified epithelium is always called by the uppermost layer so this is stratified squamous even though the more basil cells or the deeper cells are not technically squamous uh and of course lastly there's a layer in which you have a keratinized material but there is no no uh uh nucleus in it whatsoever that's a stratum corium so once again thin skin stratum corium is generally no thicker than the rest of the epidermis the columnar cells oriented at the base are what we call Basil cells in some of the books they call these the strum germinativum or perhaps the um uh there's another name for it which kind of escapes my mind so I'm not going to mention it most of the cells above the basil layer are cuboidal and they have little spaces between them and in these spaces if you were to put this on high power you would see tiny little step ladders in these spaces like they are prickly that's why this is often called the prickle cell layer or prickle cells but for the most part it's called the stratum spongiosum because they're also spongy uh towards the top uh you can get uh cells often and sometimes in some areas more than others in which you could see granules of kerat hyolin so that's called the stratum granulosum and in addition in some areas of the body but not this one there will be a very clear Zone approximately like this called the stratum lucidum because it's very clear before you get into the stratum corium so here's a stratum corium this might be a good case for stratum lucidum which is very thin and Lucid or clear looking here is the stratum spinosum and if I said spongiosum before that's just my Alzheimer's kicking in and here we have at the base the cells oriented in a columnar fashion the basil cells or stratum germinativum and often interspersed uh in the basil layer but also sometimes a little bit higher will be cells which you could have these very very fine little granules in them and these are melanocytes and technically they are not exactly derived from the same area that the rest of these squa cells or epidermal cells are right underneath that you have looser connective tissue which interweaves with the sinusoidal fashion of the lower uh epidermis this is called the uh um papillary dermis because it has a papillary or our finger like configuration denser connective tissue connective tissue below that which is very rich in elastic uh fibers is the reticular dermis in the reticular dermis and in the papillary dermis you may see skin appendages which is defined as hair follicles or sweat glands which we'll see later and then last but not least let's go down a little bit through this real much considerably thicker uh reticular dermis to get into an area that's very loose connective tissue and chiefly in fat and this is technically the hypodermis or subcutaneous fat or some people call it the subus so going backwards we have the hypodermis loose fatty connective tissue the reticular dermis which is the denser more uh thicker collagen bundles arranged every which way because the skin is subject to force forces in every direction then we have uh between the r pegs or the projections of the epidermis the papillary dermis because they look like papillary projections then we have the various layers of the epidermis and then because the stratum corium is thinner generally than the rest of the epidermis this is called thin skin here is a blood vessel probably an arterial here is a little nerve and here is a duct from a skin appendage most certainly a sweat gland because I don't really see any hair follicles in here at all so that is a duct of a sweat gland here's a blood vessel here's a blood vessel here's a thicker blood vessel probably an artery here's just fat there's a small blood vessel uh there's a [Music] nerve and you could probably recognize it better now blood V uh nerve blood vessel nerve uh dense collagen bundles of the reticular dermis and let's see if we could find some more uh skin appendages here uh perhaps if we look here we could see small asiner or tubular structures which have a very small loom in and you can see above them are these little docks leading up uh ultimately towards the epidermis to result in what we call pores these are the uh erine sweat glands ECC r i n they arrange in these little clusters they're very characteristic look like this they're different from the larger wider spaces we'll see in the apocrine sweat glands and the characteristic feature about them is they have a relatively clear cytoplasm the ducts which lead into these are a little bit darker and they are a double layer of uh cuboidal epithelium and we could see some Asin here we could see a duct here a duct here a duct here probably here and the rest of these are Asin and last but not least in the uh ocine I'm sorry the echine S sweat glands which we're dealing with now there are these little spindly cells towards the periphery and sometimes if you cut the gland tangentially like we have here you can see little cytoplasmic processes extend from them these are myoepithelial cells these are the contractile cells which assist in the expression of sweat uh from the ekine sweat gland uh is there anything else we want to talk about in this I'm sure from my first slide I went way over my three minute promise uh you could tell this is a large blood vessel a large artery you could tell the rest of this fat here's a little bit of loose connective tissue as part of that fat so if you would like to call the sub cutus or hypodermis uh perhaps loose connective tissue rather than fat you know be my guest here is a nerve here is a nerve here is a nerve and there's a large artery let's verify that yes this is all looks classically like nerve chiefly axon surrounded by uh Schwan cells some more over here uh here is a large artery probably seven or eight layers of smooth muscle there's your internal elastic lamina uh there's probably a small artery that's probably either an arterial or a vein it's hard to say that's a small blood vessel uh here's a vein I'm sorry here's a vein here's an artery and here's a nerve and you know what I don't really think I want to say anything more but I want to tell you we're going to have a lot of fun uh in the series of shotgun hystology thank you very much