So this week we're going to be talking about the integumentary system and that system is going to include your skin and all of the accessory structures that go along with your skin such as your hair, your fingernails, and also your glands found in the skin like your sweat glands and sebaceous glands. So we're going to get into the parts of the skin today and then I'm going to get into the different layers of the skin. and more specifically get into the layers of the epidermis and what is happening in each one of those layers. So let's start with this top model here. This is a model of the skin obviously and so it has two layers to it.
Okay the skin is made of two layers. Those are the epidermis and the dermis. All right so you have the epidermis is this top layer here and if you look closely it's all of this colored in brown.
Okay that is all epidermal tissue. I'm kind of coloring in here. The dermis is colored in that pink color, okay, and it's the deeper layer of the skin. So all of this here is dermal tissue. Now the epidermis is made of stratified squamous epithelium, and we kind of got into that back in the tissues chapter.
Hopefully you remember that. The dermis, this deeper layer that's all colored in pink down here, is made of dense irregular connective tissue. Okay, so those are the two layers of the skin, the epidermis and the dermis.
The hypodermis sits underneath the dermis and it's mostly made of adipose tissue. Okay, it's used for cushioning and a little insulation to the skin, adds a little insulation to the skin. But the hypodermis is not technically a layer of the skin. So do not get that confused.
Okay, the epidermis and the dermis are the only two major layers of the skin. Now, let's look around within these layers. Okay, so you might notice hair follicles.
So if you look closely, you'll see some hairs kind of sprouting up out of the skin here. And down beneath the surface of the skin, you'll see that those hairs are growing from hair follicles. Okay.
Those hair follicles are made of both epidermal and dermal tissue and those cells are constantly going through mitosis to allow that hair to grow. Okay, but the hair follicle itself sits kind of deep down in the dermis here. So there's one hair follicle, here's another one over here.
Another thing you might notice is if you look closely there are no there's no blood supply. in the epidermis. So again, the epidermis is this kind of brownish layer. There is no blood supply there.
All of the blood supply for your skin is found down in the dermis of the skin, that deeper layer of the skin. So the epidermis actually has no direct blood supply. It has to get all of its oxygen and nutrients from those blood vessels down in the dermis.
Another thing I want to point out, are the glands found down in the dermis. Okay, so if you look closely, there's this little gland that kind of looks like a water hose or a snake that's kind of coiled up. And then you can see the little duct coming out to the surface of the skin there.
Those are eccrine sweat glands. Okay, there's sweat glands that produce normal sweat that you would normally think of that helps cool you down whenever you get hot. Okay.
Those are found pretty widespread throughout the skin, and they're a little bit different from an apocrine sweat gland. Now, apocrine sweat glands are only found in two areas. They're found in your armpits, and they're found in the genital region. And those glands actually don't become active until you reach puberty.
That's when they start producing their sweat, and their sweat's a little more of a milky substance. And when it gets broken down by bacteria on the skin, it causes a foul odor, which is your body odor. Now, Ekren sweat glands, again, they just produce your normal sweat that's made whenever you get too hot, and that sweat can pull up on the surface of your skin. It can be evaporated off of the skin, and when it evaporates off, it also pulls some heat with it, and so that helps cool you down.
So those are found deep down in the dermis as well. And then we also have sebaceous glands. So if you look by this hair follicle here, I'm going to circle some of these.
Here's some little sebaceous glands. These are also known as oil glands. These produce a secretion called sebum or oil.
And that sebum gets excreted directly into the hair follicle. will travel up with the hair as it grows. So it grows up and out with the hair.
And that oil is used to help keep your skin soft, keep it from getting too dry and brittle, you know, and helps kind of lubricate it a little bit, if you will. It also helps keep the hair nice and soft, keeps it from getting too dry and breaking. Okay.
All right. Another thing you might notice are these erector pili muscles, this little muscle right here. Now that muscle is a form of smooth muscle and you have an erector pili muscle attached to every one of your hair follicles down in the skin and when those muscles contract they pull on the hair follicle and it causes your hair to stand upright. Okay so that smooth muscle contracting also produces a little bit of heat which is why when you get cold you typically get chill bumps right or goosebumps because those muscles are contracting to try to produce a little extra heat for you and when they contract.
that hair stands on end okay all right so let's move down to the epidermis oh let me go one more thing so back down in the dermis all right let's look at the dermis one more time and i already went through all these structures of the dermis let me just clear all this off i want to point out one more thing and that is that the dermis has two layers to it okay So you have this upper papillary layer, more superficial layer of the dermis, and you have the deeper layer of the dermis called the reticular layer. Now the papillary layer, if you look closely, it has projections that dip up into the epidermis. Looks kind of like waves almost.
Those little waves are called dermal papillae. papillae. And when you have those dermal papillae in areas, especially in thick skin, okay, which we'll get into what thick skin is in just a second. When you have dermal papillae in areas of thick skin, it forms friction ridges, okay?
And those can be very prominent and easily seen on the palms of your hands, especially on the fingertips. They actually form your fingerprints, okay? So those dermal papillae of the papillary layer of the dermis help form your fingerprints.
So let's get down into this picture here. Now this picture is showing the layers of the epidermis. So it's basically this upper layer right here, this more superficial layer colored in brown. We took it, zoomed in a whole lot, and you're seeing the individual layers and structures of the epidermis. Keep in mind that there's no direct blood supply to the epidermis.
So all the blood supply is having to come from the dermis, which is underneath it. So if you look at this picture, all of this colored in this yellow color is epidermal tissue. This down here in pink is the dermis. So that's connective tissue.
So don't get those mixed up. So let's go ahead and define what thick skin and... thin skin are. Okay, let's do that right down here. So thick skin.
Thick skin is only found in two areas on your body, okay? And those are the palms of your hands and the soles of your feet, okay? So the bottom of your feet, basically.
Thin skin. is found everywhere else. So all the other skin on your body besides the palms of your hands and the soles of your feet is made of thick, thin skin.
Sorry, thin skin. Now what is the difference between thick skin and thin skin? Well, it's essentially just one layer, okay?
Thick skin contains five layers that make it up, whereas thin skin contains four layers. Now if you think about where thick skin is found, why do you think it has an extra layer there? Well, it's for protection, okay? If you think about it, you use the palms of your hands and the soles of your feet pretty much all day every day.
You're grabbing things, you're manipulating things, you're walking on the soles of your feet, right? So you're using them constantly and they're being exposed to friction and abrasion constantly. So those two areas need an extra layer of protection, okay?
Which is why they have or contain thick skin. rather than thin. Now this picture up here, this model This model is showing an image of thin skin, so it's only going to be showing four layers here, but I'll tell you where that fifth layer would be found if we were in thick skin.
Okay, so let's start at the deepest layer of the dermis. So this one's sitting right on top of the epidermis here. This layer is called the stratum basale, and the cells found in the stratum basale are going to be... constantly undergoing mitosis. They're constantly undergoing cell division and that is helped to help replace the cells that are being lost in the upper layers of the epidermis because you lose skin cells all day every day.
Okay so these cells divide and as they divide they push all of the cells above them up in cell layer and the cells just keep moving up and up and up all day right they keep getting replaced all day every day. You'll also notice that there are a couple of other cell types just besides the dividing cells. We have some melanocytes.
Those are colored in gray here. Now those are used to produce the pigment melanin, which gives your skin its color. Typically the darker your skin is, the more melanin that is produced by your melanocytes. Now interestingly enough, we all have the same number of melanocytes, roughly, but some are much better at producing melanin than others.
And that melanin, that pigment, is used to protect your underlying tissues from UV radiation or sunlight. This purple looking cell right here is called a Merkel cell. And those cells are used for sensory purposes, usually for sense of touch. This Langerhans cell, colored in blue, is a type of dendritic cell, which is a type of white blood cell.
Okay, part of your immune system. And it's used to help search for anything that should not be there within the skin, like bacterial cells or anything that might be foreign that might make its way down into the epidermal layers. So those longer hind cells are good at phagocytosis or ingesting material and digesting it, helping get rid of it. Okay, clean it out for us.
All right. Now up above the stratum basale, we have the stratum spinosum, and that's this whole layer here. Now if you look closely, you can see that the cells have what look kind of like little polka dots or little spines sticking off of them. And what those are is the cells are actually accumulating a protein called precarotin, right, precarotin, which will eventually kind of mature into keratin. Now, keratin is a protein that makes these cells very tough, and it also helps make them waterproof, all right?
So, we're not constantly losing water through the surface of our skin, or vice versa, we're constantly absorbing water, right? So, that keratin helps prevent us from losing too much water or absorbing too much water through the surface of our skin. Again, the keratin also helps make the cells tough because their major function and purpose is for protection of everything underneath the skin.
Okay, so that's what's happening in the stratum spinosum. Those cells are accumulating that precarotin. Now in this layer here, the stratum granulosum, those cells are starting to accumulate granules, okay, which is essentially a byproduct of the cell organelles kind of breaking apart.
or deteriorating and the overall the cell starting to get ready to die okay so these cells in this layer are getting ready to go through what we call apoptosis which is programmed cell death now why do you think these cells are starting to die as they're moving up in cell layer what are they moving away from they're moving away from their blood supply okay all the blood supply remember is down here in the dermis So as those cells move up in cell layer, they're getting further and further away from the oxygen and the nutrients that they need to survive, and they're going to start dying because of that. Okay, up above the stratum granulosum, we have the stratum corneum, which is the outermost layer of the epidermis, and this layer is entirely made up of dead flattened keratinocytes. So these are dead cells that have accumulated tons of keratin to help make them tough. and to help make them waterproof.
Okay now if we were in an area of thick skin, remember I told you guys we would have an extra layer if we were in thick skin, well that layer would be found in between the stratum granulosum and the stratum corneum, so right in here, and it is actually called the stratum lucidum. Now it's just kind of a thin colorless layer of cells. that is used just to add an extra layer of protection, okay, to that tissue. That's essentially its only purpose. All right, so you guys go through the skin, go through the parts of the skin, and these layers of the epidermis, and let me know if you have any