hi and welcome to this lecture on the integrer system in this lecture I am going to focus on the parts of the integrer system and more specifically the epidermis I will save the dermis and the hypodermis for other lectures well let's get started with the first one the integumentary system it consists of the skin and its derivatives some of its derivatives include the nails hair sweat glands and the sebaceous glands otherwise called the oil glands now the ingent is the skin covering the body we also call it the cutaneous membrane it is a barrier to the outside world it is that which separates the external from the internal environment we often use it as a visual indicator of our physiology and health and if you've ever heard of Dermatology it is the scientific study and treatment of the integumentary system it accounts for approximately 50% of All healthc Care here is a figure showing the skin and you can see that there is a lot to know about the skin let's just take a look at some of these here we have the general term the integrant which consists of the epidermis and the dermis notice that it does not include does not include the subcutaneous layer that is separate from the ingent now we are going to focus on the epidermis in this lecture and then later focus on the dermis in others the dermis is made up of the papillary layer which is the top layer and the reticular layer which is the bottom layer now in these layers we can see a lot of structures we can see those things such as a hair follicle that is the tube that houses the hair the hair itself we see sensory receptors here those are things that allow us to have touch we see them here and here as well there are many different cons within the skin we can see the epidermal Ridge which is here also called the dermal pill that you see here the dermal Pilla is the papillary layer and the epidermal Ridge is the stratum basali structure associated with the hair we can find the erector pilli muscle which is a muscle that serves no real function in humans we see the oil gland that is associated with the hair we can also see a sweat gland and the duct that leads to the surface of the skin we can also see the arteries and veins that is laying within the hypodermis and then coming towards the dermis and the epidermis but please notice that there is no artery or vein within the epidermis itself the epidermis is a vascular okay so let's move on to the next slide and learn about some of the parts now with the ingent or the skin we have the epidermis that is the top layer as you seen in the slide before you have five layers within the epidermis the stratum basali spinosum granulosum lucidum and corium here's a term that I have m my students learn or an acronym rather or saying it is big stinky gorillas like corn that's a nice easy little saying so that you can learn it from Deep to superficial now the first three layers are with living cartinos sites that's from here to there those are living and the last two are with dead cortinis sight and we're going to learn what katus sites are here in just a minute here's a picture showing the different layers and you can see that here is our dermis and then starts the epidermis with the basali the spinosum granulosum lucidum and corneum this is an artist representation and this is an actual picture of of skin now within that you can see some other things as well that I have not mentioned such as the cortinos sites the melanocytes dendritic cells and tactile cells and we will get into what each of those do here in just a little bit the first layer is the stratum basali it is the deepest epidermal layer it can also be called the stratum germinativum you may see that in in some books as well it is a single layer of cuboidal to low columnar cells it is attached to the basement membrane that is the membrane that connects the epidermis with the dermis and it is occupied by three main cell types you have the catinos sites lytes and tactile cells looking at the cortinos sites they are by far the most abundant cells in the epidermis that it is found in all layers and in this basale you see a lot of stem cells these stem cells are able to divide and then regenerate into new cells so as you lose cells at the surface of the skin you can replace those cells with new ones at the stratum basale and then they will work their way towards the stratum corium their name comes from the synthesis of a protein called keratin and this protein strengthens the epidermis it is a tough protein it is a little bit elastic second cell that I want to look at is the melanocytes the melanocytes are scattered among the cortinos sites though they are not nearly as many they produce and store the pigment melanin and this is the pigment that gives skin color or helps to give your skin color there are other pigments as well they are going to make these granules called m mosomes and then they transfer those into cortinos sites and these melanosomes will then accumulate in the ctin oyes and then it Shields the ctin oyes DNA from ultraviolet radiation such as from the skin and that is what gives us things such as Sun Tans Third Kind is the tactile cells these are also called Merkel cells they are relatively few in number but they give us a sensitivity to touch so when they are compressed if something is pushing against your skin they will release chemicals that stimulate sensory nerve endings and these sensory nerve endings then transmit that impulse to the brain so that your brain knows that you were touched in that spot second layer is the stratum spinosum now it is several layers thick whereas the Straton basali is mainly just one layer sometimes two it is also known as the spiny layer because of the way it appears in the microscope the cells that were made in the stratum basale are being pushed into this layer and as they are being pushed into this layer they begin to develop into specialized non dividing cortinos sites and these cartinos sites are going to start making a lot of keratin now these cros sites are attached by structures called intercellular Junctions specifically desmosomes which is a kind of intercellular Junction and these desmosomes they will literally attach one cell to the next now in the espinos you have the dendritic cells also called langeron cells and they are immune cells that will help initiate the immune response so if there is a pathogen within the epidermis these cells are the cells that will detect that pathogen and then tell the immune system that they need to get rid of it keep in mind also that they will respond to epidermal cancer cells in the stratum granulosum you have three to five layers of cortinos sites it is also called the granular layer it is above the stratum spinosum it is superficial to it and it is the first layer of catinis and that is where the cartinos sites are going to fill themselves with keratin and as they do the problem is that the Keratin causes the nucleus and organel to disintegrate and the fully kenized cell is dead but still structurally sound so it doesn't break apart however the process is not complete until you get in the layers above it the lucidum and corium now the stratum lucidum is two to three layers of cortinos sites it is translucent also known as the clear layer it is above or superficial to the stratum granulosum and it is found only on the thick skin which is the palms of the hands and soles of the feet it is also filled with that translucent protein aladan elidan is a intermediate in the Keratin maturation finally we have the stratum corium notice how many cell layers thick it is it is 20 to 30 layers of dead interlocking Cortino cells remember those desmosomes that I mentioned before that is what's locking them together they are a nucleate and and very tightly packed the plasma membrane is still there but it's enclosing all the Keratin that was added in the layers before it you may also see it called the hornik layer it is the most superficial layer of the epidermis it is that which you see on people and the surface is very unsuitable for the growth of many microorganisms and that's because of the exor glands such as these sweat glands it'll create something called the acid mantle as you look at the stratum corium there is a migration of cartinos sites through it it originates from the stem cells in the stratum basali and each of those new cortinos sites will migro through each layer to the stratum Corney over the period of approximately 2 weeks and as they migrate to this top they are undergoing those structural changes where they add the Keratin and the nucleus and organel die then they will remain in the stratum corium for another two weeks for a total of four weeks before they are Shed from the body here is the picture showing those layers keep in mind that the stratum basali is where you have the stem cells and these are the cells that are going to divide into the catinos sites and the ctin aites are going to move this direction up through the various layers until you get to the top and as it moves up they are going to become keratinized and lose their nucleus and organ gals so that at this spot you have keratinized stratified squa cells that are completely dead they are interlocking and they help create that barrier that is your skin now in the other figure we can see the dendritic cell which is the example of the white blood cell for the immune system the melanocytes these are the cells that will produce melanin and put those melanosomes into the cartinos sites around them so that they can have the melanin protection as well and then we have the tactile cell which is that cell that releases the chemical to the sensory nerve ending telling it that something had touched the skin in that spot now there is some variation within the epidermis people don't often realize that the epidermis is not uniform it changes from spot the spot within the body and that goes for the skin as well there is two different kinds we have the thick skin versus the thin skin now the thick skin as it sounds has all five layers of the epidermal strata we find it on the palms of the hands and soles of the feet as well as the surfaces of the fingers and toes it does contain sweat glands as I'm sure you can relate to if you are nervous in your hand sweat however it has no hair follicles or sebaceous glands often ranges from 0.4 to 0.6 mm thick contrast that with a thin skin where it is covering most of the body however it lacks the stratum lucidum so it doesn't contain all the layers and it has all three sweat glands hair follicles and the SE aous glands and it is generally from 0.075 to 0.15 mm thick which is very very thin here is two pictures of thick versus thin skin these are actual pictures of the skin themselves taken with a microscope we can see in the thick skin here is this stratum lucidum however you don't see that within the thin we go from the spinosum to the granulosum and there's no lucidum in between all right thanks for watching if this video has helped you please like And subscribe to my channel