BIO 201 Dr. Kerry Henrickson 6.4 Integumentary Part Two >> All right. We're continuing on with part 2 of our introduction to the epidermis and the dermis. Okay I'm gonna talk very briefly about the types of cells we find there and let's start with the epidermis. And remember again I told you the epidermis is made up of stratified squamous epithelial cells that are highly keratinicized [assumed spelling] which means that they have lots of keratin which is that protein I talked about that is very tough and structurally very strong and also water resistant to prevent water loss from the body. We can call those simple stratified squamous epithelial cells that make up the epidermis; we can call them keratinocytes [assumed spelling] which literally means cells with keratin. These cytes are highly hydrophobic; they don't like water, in other words they repel water and again that has to do with the keratin being relatively water resistant. What holds keratins together is a special type of bond or a special type of junction I guess between cells called desmosomes. And if I were to draw to keratinocytes side by side like this the desmosomes would look like little spot weldings between the two cells. This allows the cells to stretch in relationship to each other without tearing apart from one another. If I instead have two cells and I literally superglued them together, which would be called a tight junction between them, anytime you stretched or pulled on them they'd just tear apart. Desmosomes by contrast allow for some give and stretch to the cells so that the skin can be pulled without tearing. Now remember that always immediately underneath epithelial tissue is a layer called the basement membrane. The basement membrane is not a cellular layer remember, but merely a layer of molecules, you can kind of think of it like a glue that attaches or glues the epithelial tissue to the underlying connective tissue. Let's take a look in this middle picture here this is a picture of stratified epithelial tissue, some of your skin, here is the lumen out here or the opening to the outside of your body, and here is where the basement membrane would be located, and immediately below it down here where I'm putting the X is where the underlying connective tissue is. Where I drew that black line is where the basement membrane is that glues the epidermis or the epithelial tissue to the underlying connective tissue. Now what happens if something goes wrong and the basement membrane molecules are not being manufactured properly by the body, well then I lose my ability to glue the epidermis to the underlying dermis and I get something that looks like this. In this individual the squamous cells, the stratified squamous epithelial, have separated from the underlying connective tissue here and we have a fluid filled pocket in between which we know of as blister. This is as condition that can happen just from regular friction, but if a person is genetically incapable of manufacturing one or more of the basement membrane molecules, then it's a genetic problem if it happens throughout their body. It's very difficult for their skin to remain attached to the underlying connective tissue and this can lead to a condition called [inaudible] and depending on, here's an example of what it looks like on the outside of the body. People that literally have blisters forming all the time, anytime they bump their skin on anything it separates from the underlying connective tissue filled with fluid and a blister is formed. It's a very painful condition, it also happens to be depending on how bad a version of it you have, it's a very lethal condition. Individuals can die from it. Okay. Now the epidermis is not only made up of all these keratinocytes with all the keratin in them there is a much less common type of cell called the melanocyte but it is a very important cell. Melanocytes manufacture that pigment I was talking about called melanin; and these melanocytes manufacture melanin and then they export it outside the cells and surrounding keratinocytes then endocytose [assumed spelling] take in or pull in that melanin and then they, as I said before, will arrange it so that the melanin is sitting over top of the nucleus so it protects from ultraviolet radiation from the sun. These melanocytes have a very spider like appearance to them. You can see in this picture down here some really nice example of some melanocytes. They obviously have a brownish color to them because they're making lots of melanin; and you can see that melanin is being exported and then taken in by cells up here to produce a darker skin tone. Many people think that individuals with darker color skin have more melanocytes; in actuality they don't have any more melanocytes than a light colored person it's just that they're melanocytes make more melanin than a light colored person's melanocytes do. Remember again that melanin; the whole purpose of it is to absorb ultraviolet radiation and protect the nucleus of the cell from DNA damage and also to protect against folic acid destruction. Now if a melanocyte becomes cancerous and this can happen, you have what's called a malignant melanoma. Malignant melanomas are the most dangerous kind of skin cancer; they're the ones that are most likely to metastasize to other parts of the body. This is an example of an individual that has a fairly severe malignant melanoma in the toe. All right. That's our brief introduction of the epidermis. In further lectures next week we'll go into more detail about all the different levels of the epidermis, et cetera but for now I'm going to move on to the dermis and remind you again about some of its general properties and what its function is for the body. The dermis is made up of lots of connective tissues so it's very strong. It lends support but remember because it's made up of dense irregular connective tissue, it has all those collagen fibers running in lots of different directions to it allows for a lot of flexibility, stretching and movement without tearing. The dermis consists of many fibroblasts remember which have the ability, those are the cells that make up the connective tissue proper and have the ability to give rights to new connective tissue; there are also a lot of the white blood cells that wander through the dermal layer looking for bacteria that have entered into the area that shouldn't be there or getting rid of them. Again the dermis has lots and lots of blood vessels in it which is really important not only for supplying the epidermis immediately above with nutrients and oxygen, but also helps to do things like manifest the heat of the body either by releasing heat to the environment or by retaining heat in the blood. And it also has a lot of different sensory receptor cells that are sensitive to things like pudge [assumed spelling] and pressure and heat and pain, and we will learn more about those near the end of the semester when we begin studying the nervous system. Now let me just talk very briefly about some skin related conditions and issues. If you see an individual get a reddish hue to their skin like when they exercise for a period of time the body tries to dissipate the heat by letting blood near the surface of the skin, that condition is called erythema which merely means redness. An erythrocyte is a red blood cell so eryth means red--erythema just means a reddish appearance to the skin. Jaundice is a yellowish appearance to the skin and it's normally an indicator that the liver is not functioning properly or that some other condition is overwhelming the liver. One thing is similar to having a tan, but the underlying cause of it is normally a condition called Addison's disease which is a hormonal disease that we will talk about next semester. Paler is having a very pale appearance to the skin and it's normally an indication that blood flow has been reduced to the area. Albinism is an inability to make melanin; genetically not capable of manufacturing melanin and I gave you an example here. Here is a picture of two brothers; one brother the one on the right over here has normal pigmentation but his brother on the left here is an albino--he does not have the ability to manufacture melanin so his skin tone is extremely light, his hair has no color to it, et cetera. A hematoma is literally just a bruise, okay? Where the hemangioma is something if you had them you've had them all your life because that is a birth mark. Okay. The next thing we're gonna talk about very briefly is how the skin goes about repairing itself because your skin is in contact with the external environment all of the time, it's having to be dealing with lots of damage to it on a constant basis. There are two different processes by which the skin can repair itself and what determines which of these two processes are used is just how extensive the damage is. In cases where it's a very slight damage, say you get a paper cut on your finger, that's a very thin cut, it's very small, in those cases we can simply have a process called regeneration, replace the damaged dermis and epidermis and no spar results and within a couple of days you're healed up. If the damage is more extensive, let's say you fall off your bike while you're riding your bike and you get a bunch of gravel damage to your knees, the gravel sort of tears up the skin on your knees; that would be a much larger area of damage and in those cases the process by which we repair is primarily fibrosis which usually leaves the formation of scar tissue. The reason is if you have a pretty large tear or cut in the skin, even with regeneration the epidermal cells on either side of the damage are not going to be eventually grown back into contact with each other and cover over the underlying connective tissue. So what ends up happening is the underlying connective tissue, the body is not able to repair the distance from here to here with epithelial tissue. Remember epithelial tissue has no blood vessels so its ability to repair itself is limited because it can't get enough nutrients and oxygen and the support to do massive amounts of mitosis. It can do limited amounts of mitosis so it can repair small damage, but larger damage it won't be able to replace and what will happen is the underlying dermis or connective tissue will grow up into that area and replace what had once been epidermis with dermis or connective tissue; and that's what causes the appearance of a scar. Remember it's the fibroblasts that are working to repair areas that the epidermis does not repair for itself. Now sometimes people experience severe burns that damage large quantities of skin, and in this case this is another example. This patient for example this is a huge area that was affected by burns. There's no way that the epidermal cells are going to be able to grow inward and meet to cover over all the skin that was lost. So what happens is if you were to leave this by itself, the only way this body could repair itself would be to replace the damaged epidermis with connective tissue or scar tissue and it would have a very, well it would look like a very large unattractive scar. One way that you can prevent that is to graft skin into the area; and they can do that quite effectively these days by harvesting skin from a place on the patient's body where their healthy skin is available and they literally shave it off with something that looks a little like a cheese grater in my opinion. Once they shave that skin off they run it through what looks like a pasta machine; I know this sounds like a cooking lesson but it's really not. That pasta machine looking thing punches a bunch of holes into this patch of skin and by punching all those holes that allows us to stretch the skin over a much larger area. So we can stretch that skin over the burned area which may be much larger than the size of the original piece of skin we extracted from a patient; and here you can see an individual whose had that very thing done and his skin has repaired itself and healed over and it's a much better result that having a large swatch of scar tissue in the area. All right the last thing I want to talk about very briefly are the different types of skin cancers. Carcinomas remember are any time I have cancer of the epithelial tissue. There are two main types of skin cancers, actually three main types, sorry. Basal cell carcinoma, squamous cell carcinomas and malignant melanomas. I've already told you about malignant melanomas. Basal cell carcinomas are cancers of the bottom layer of cells, the layer of cells closest to the basement membrane. Squamous cell carcinomas involve cells immediately above that, and when we start talking about the five distinct layers of the skin in a lecture next week, I will revisit this and review for you again the difference between basal and squamous cell carcinoma and I promise it will make more sense after we go through the different layers of skin than it does now. This individual here is somebody who had a very extensive skin cancer on the head, its grown into quite a tumor, and it reminds me to remind you that skins cells are common especially when you live in parts of the United States like Arizona where ultraviolet radiation levels are relatively high because we have a lot of sun over 300 days a year of sunshine. So it's worthwhile to remember some of the warning signs of skin cancer--anything that has any kind of thing that appears on the surface of the skin with an asymmetric shape to it rather than being a nice round mold for example if it has an irregular shape. If it's hard to tell where the border of that mold, for example, ends and regular tissue begins if it's a regular or diffuse border that could be another sign. If it has a multi-colored appearance to it or an iridescent or pearl-like sheen to it that could be an indication that it's something that you need to get checked out; and if it gets larger than 5 millimeters in diameter you should have it checked. So these are things to keep in mind. The earlier you can be checked for any cancer, the more likely you are to recover from it and survive; so if you see any of these signs you should always immediately get into your doctor just to be absolutely certain it isn't anything to worry about. At the end of this lecture next week we will go into more detail about the epidermis, about the dermis and about the epidermal derivative black nails and hair.
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