This content is recorded exclusively for Dr. Young's anatomy class. It is not to be uploaded or distributed to any social media sites or streaming sites and not to be used without the permission of Dr. Young. Welcome to chapter 5, Integumentary System. Integumentary is just a fancy word for skin, so that's what we're looking at in this chapter. We're looking at the skin.
Here's a picture of our skin and it's broken down into our different sections. So if you look at the cutaneous membrane, you have the epidermis, the top layer, the dermis, that middle layer, and then they also have the hypodermis. But you'll see they have down here labeled that it's not part of the skin, but a lot of times this is thrown in with the epidermis and the hypodermis is the fatty layer that's right underneath.
actual skin. That fatty layer is where a lot of our blood vessels are actually going to run. A lot of accessory structures to the skin.
So we have hairs, sweat glands, oil glands, nails are going to be part of the accessory structures. We have all those sensory receptors that we're going to find within the skin. Erector Pili muscles are actually the little hair or the little muscles attached to hairs that'll give you goosebumps or goose pimples.
A lot of different accessory structures and we're going to look at some of those as we kind of go through here. A really important thing that's talked about on this slide is that the epidermis is avascular. The very top layer, that very top layer epidermis, doesn't have blood vessels running through it. That's why you can take your fingernail and scratch your skin and just not bleed all over the place. It actually relies on diffusion from the blood vessels coming up from the hypodermis going into the dermis.
And then it has to get all its nutrients and oxygen from that lower dermal layer. So that top layer is actually a lot of dead cells that we're always continuously sloughing off and replacing. And we're going to see especially... A lot of places in the body we even have a nice top keratin layer that kind of helps to make our skin waterproof. Here we're looking at the hypodermis a little bit closer.
That's that very bottom layer mainly made up of fat, but it does have some loose connective tissue in it. This is where those big blood vessels are gonna run. So if you do cut yourself deep enough and start bleeding a lot, you know you got down all the way to that hypodermis. So looking at some of the big functions of the skin here, protection is a huge one.
So it doesn't only protect us by keeping things out we want out and keeping things we want in, but we can also bump into things, we can touch things, and it doesn't damage us because we have all those layers stacked up on top of each other. It also does help with the immune system because white blood cells can actually live in that dermis, and if something does penetrate the skin, then those white blood cells can hopefully... kill it off before it gets any further.
A lot of different receptors in the skin for sensation. So touch receptors, we kind of looked at this in lab a little bit when we did the two-point discrimination with a little compass. So depending on how close those receptors are packed together is going to depend how sensitive the skin is. And then of course thermoreceptors, thermoregulation. We're going to have thermoreceptors also found in the skin, but sweat glands also help us to cool off.
So As we start to overheat, then a sweat glands can open up, release the sweat, and it evaporates on the skin and actually helps us to cool off. So we can thermoregulate with that skin as well. All right, looking at the epidermis closer. The epidermis is going to be composed of several different layers.
So we are going to have that stratified squamous epithelium in there. But we're also going to have a lot of keratinocytes that are responsible for making keratin. And that keratin is going to give us that nice waterproof membrane that sits on top of the skin.
The epidermis has several different layers to it. The very first layer, or the very bottom base layer, is the stratum basale. This is what it's most commonly called.
You will see a couple other names, and one is right here beside it. These are the germ cells. or the stem cells, but they're making up the very base.
So these are the cells that are actively going to divide, making more and more cells as our top cells kind of get sloughed off. And what we have going on is basically just a rotation of cells. So the top cells slough off and the bottom cells work their way up to the top.
That stratum basale is generally just one cell layer thick. It's just that very first layer of cells on the very base. The next layer up is going to be the stratum spinosum. This is going to be keratinocytes that have slightly started to dehydrate. It's called the stratum spinosum because when you look at it the cells actually look spiny because some of the cytoskeleton actually kind of starts to poke out of that plasma membrane as the cells slowly dehydrate.
The next layer up is the stratum granulosum. So the stratum granulosum is actively making keratin, but there at the same time those cells are getting closer to the top and still dehydrating more. This layer is usually darker.
It will stay in that darker purple color, and if you look at it closer underneath the microscope, if we could get blow it up big enough, then you would see little granules actually starting to form in there as well. Stratum lucidum. Don't worry about stratum lucidum. This is only found in really thick skin and it's literally a clear layer where some of those keratinocytes literally start to kind of separate from the epidermis a little bit. Don't worry about that one.
Stratum corneum is the very top layer of dead cells. These are dead keratinocytes. These are really what's providing that nice waterproof top.
Those get sloughed off and we're always continuously replacing them. So here's a good picture if we start from the bottom and kind of work our way up. Stratum basale, so you can see underneath we even have a small slice of the dermis. That's not part of the epidermis, but you can still see that irregular connective tissue.
The stratum basale will be the very first row of dark purple cells. Stratum spinosum is a really nice thick layer above that stratum basale. These are all pretty healthy active cells even though they're starting to dehydrate a little bit Really making the keratin any keratinocytes that are in.
Stratum granulosum is the darker purple layer kind of sandwiched It looks like right in the middle. So These still making keratin, but they're starting to dehydrate more. Look at them closer. They kind of look granular. And then the very top layer is going to be that stratum corneum.
So that's all those dead keratinocytes layering the very top. If it's thick skin, like on your palms or your soles, that's going to be a really large layer. If it's thin skin, like your back, you might just have one or two layers of that stratum corneum or those dead keratinocytes. We do find other cells in the epidermis other than just stratophytes, coimus epithelium, keratinocytes.
We do have dendritic cells. These are just macrophages. A macrophage is going to be an immune cell that eats anything that shouldn't be there. When they're found in the skin, we call them dendritic cells or Langerhans cells.
Langerhan was the person that discovered them. These are going to eat or phagocytose anything that shouldn't be there. Merkel cells.
These are light touch receptors. So really sensitive, fine, light touch Merkel cells. Sometimes these are just called touch receptors. And that's perfectly fine too.
Merkel there again was the person that discovered them. We also have quite a few melanocytes. So melanocytes are going to produce melanin.
that's going to be responsible for the color of the skin. Everyone has about the same number of melanocytes. It just depends how active they are.
If your melanocytes are really active, then you have a darker color skin. If your melanocytes aren't very active, then you have a lighter color skin. These are also what's responsible for causing a sun tan whenever you've been out in the sun for too long.
Those are making extra pigment. and that's what the melanin is, it's extra pigment that's going to help to protect us from the sun a little. So the more sun you get, the more active these are, the more pigment that they're going to make.
And or it can be completely genetic if you're just looking at skin color. If genetically, if they're made to produce more melanin, you end up with a darker color skin. Genetically, if they produce less melanin, you end up with lighter color skin.
Thick skin and shi- Versus thin skin, so we looked at this already. Like we said, it's all about that stratum corneum, that very top layer of dead keratin cells. If you have a lot, then you're going to be looking at areas like the palms, the soles of the feet that come in contact with a lot of surfaces. If it's thin skin, it's going to be places like the back, the forearms, areas where you don't constantly touch things all the time.
Whenever we do form a callus, this is just really, really, really thick skin with lots of layers of stratum corneum and a lot of dead keratinocytes on it. So if you do have an area that gets overused, hit the same place over and over and over again, that's where a callus comes from. It's literally just extra layers providing extra protection.
And here's picture difference between thick and thin skin. So here on the left you can see the thick skin, huge stratum corneum, a lot of layers, you can see the very top is sloughing off. Versus thin skin, you only have a few layers of stratum corneum or a few layers of dead keratinocytes up there. So it's literally we have all the others are same, stratum basale, stratum spinosum, stratum granulosum, but that stratum corneum is the one that makes it look quite a bit different. All right, looking at the dermis a little bit closer.
So when we look at the dermis, we said it's that irregular connective tissue. It's still going to have a blood supply running through it, and it has to supply everything the epidermis needs. We find all the sensory receptors, and this is also what is going to anchor the epidermis so it just doesn't fall off.
We have two big layers to this dermis. Papillary layer. This is going to be the thinner of the two layers.
This is more loose connective tissue rather than the irregular. So it's kind of that extra packing that's thrown in there. I don't necessarily care too much that you know the difference between the papillary layer and the reticular layer that we're going to look at. I would rather just be focused on what you find overall in this. The dermal papillae is found in that top papillary layer.
This is basically going to be tiny little projections that comes in contact with the epidermis. They kind of look like little hills that go up and down. This is what's going to actually connect the epidermis with the dermis.
This is the area that's going to have small capillaries that's responsible for getting that epidermis everything it needs. And this is also where we find Meissner's corpuscles or tactile corpuscles. These two are used for light touch, they're light touch receptors.
So we have a lot of these in the fingertips, a lot of times more sensitive your touch is, you find a lot of these tactile corpuscles. In the deeper reticular layer, this is that dense irregular connective tissue that we've seen and what we mainly talk about when we talk about this. It can move in all different directions and it really keeps that skin stable. In the reticular layer, Deeper down, we tend to find what's called laminated corpuscles or piscinian corpuscles.
Piscinian is just the person that discovered them. Of course, named them after himself. Laminated, if you laminate something, it's layer after layer after layer. A laminated corpuscle is the same thing. It's layer after layer after layer.
It actually kind of looks like a thumbprint. But the big way you can tell these versus your tactile corpuscles, the tactile corpuscles are... closer to the surface.
They're used for fine touch. These are deeper down in the dermis. These are going to be used for pressure whenever you press down on your skin and or vibrations.
Always look like a thumbprint, always deeper down in that dermis. And here's a good picture of the dermis. So you can see up here close to the surface on this left-hand side in the drawing you can really see that tactile corpuscle.
As you go deeper, you can see that lamellated corpuscle. So tactile, light touch, lamellated, has layer after layer after layer, kind of looks like a thumbprint. That's going to be for that pressure or vibration. Looking at some of our skin markings, so dermal ridges. Whenever we look at the dermal ridges, what we're really looking at are fingerprints.
So up in that papillary layer, where we have that connection between the epidermis and the dermis. This is where we have a dermal ridge. The epidermal ridge is going to grip really strong to that dermal layer underneath it, and when you see those waves in the tissue going up and down, you can see it on the stratum basale, and you can see it at the very top of that dermis. They literally interlock with each other, kind of like puzzle pieces, and every time that wave goes up, that's what's pushing that skin up and actually making a fingerprint. So when we look at it here, you can see that nice wave pattern.
So the epidermis is the darker purple and you can see that stratum basale going up and down. Those are making up the epidermal ridges and then the dermal ridges underneath, you can still see that connective tissue going all the way and pushing in up. into that epidermis. Every time it pushes up, that's what's causing those raised ridges that actually makes her fingerprints. So when you're looking at the fingerprints, you're literally looking at what makes up that connection between the epidermis connecting to the dermis, which is kind of cool because it's something we can actually see.
We also have natural lines of connection that run all the way through the skin called cleavage lines. If you're a plastic surgeon, you're really good at cutting with these cleavage lines. And everyone's skin or everyone's cleavage lines tend to run in the same general directions.
And we do kind of have maps, I'll show you on the next picture, of how these cleavage lines run. These cleavage lines, if you cut with them and sew them up, they don't leave very much of a scar or any scar at all. That's why this is how plastic surgeons make their money. I get rid of those scars.
General surgeon doesn't care about cleavage lines too much. You're just trying to save your life. So they may cut across them, sew them up, and you end up with a scar, but they saved your life. So when we look at these cleavage lines on our map, there tends to be a general direction that our skin is kind of organized in.
It's still irregular connective tissue, but it tends to run in one direction or another. So if you cut with the line... sew it up.
It heals a lot better. You're left with little to no scar. If you cut across those lines, You break those tension lines, those cleavage lines, and then you end up with a bigger scar. All right, looking at some of the accessory structures here. If we start out with the hairs.
So we have several hairs that are going to be running through the skin. Attached to these hairs are going to be little erector pili muscles. That's what's going to be causing our goosebumps whenever we look at them.
So when we look at the hair coming up, we have a dermal root that's located down in the dermis, and then we have the hair root that's actually going to come up and turn into the hair shaft and exit through that epidermis. A lot of the times we're also going to have sweat glands attached to these, especially oil glands. So oil glands can run right up with the hairs, and then where you have a hair coming out, it can also...
produce oil and that hair root and hair shaft can actually be the exit out for that oil as well. Nails! Nails are an accessory structure of the skin. I'm not going to go through all the different structures and makeup of our nails. They do provide a little extra hard protection right there on actually the dorsal side or posterior side of your hands.
That way when we have our fingers curled and if we run into something it doesn't really damage any of those layers of the skin at all. You can live without your nails though. You can take nails off and be perfectly fine. It's not fun but it can happen. Literally nails are made of hard keratin.
That's really all they are. Glands. We've been talking about glands this entire time. So sweat glands are really plentiful. You have sebaceous or oil glands.
Sebum is usually what we call our oil. You find these running all throughout the skin. Cancer of the skin is a big problem. Cancer of the skin is the most common disease in the world.
Mainly because your skin is highly mitotically active, which means it's always dividing. It gets damaged all the time. We damage it. We cut it, we run into things, and then just the radiation from the sun is going to damage it.
So cancer becomes a big problem. Luckily, most skin cancers are benign and we can catch them before they do spread. But melanoma is, of course, the one you hear about the most because that's the one that does metastasize or it grows fast and it can move and get into other parts of the body. So we have to be really careful. Here we're going to look at the most common cancers of the skin actually caused by UV radiation or caused by sun damage.
Basal cell carcinoma is the most common type of skin cancer and you see basal it comes from that stratum basale because that layer is the most active it's always dividing making new cells so it's the most common one if it gets damaged it breaks its checkpoints, and you start to get that uncontrolled cell cycle, that uncontrolled growth, because those checkpoints have been damaged by that UV radiation. The good thing about our basal cell carcinoma is that it doesn't usually metastasize. It generally stays just within the skin.
This always appears as a kind of red, irritated nodule with a little crater. the center. You can see in this picture it almost has a little dimple in the center. That's a telltale sign that it's a basal cell carcinoma. These can generally just be cut out, removed, and you're good to go because they don't spread.
Squamous cell carcinoma, so this is the second most common. So after you get past those stem cells, a lot of our skin is made up of stratified squamous epithelium. So This is what's making up the second most common skin cancer here.
The kind of big giveaway is that you have scaly plaques that bleed. So they ulcerate. They have little ulcers or sores in them that end up bleeding. And if you look at this one, it does look a lot more scaly. And then you're going to have that blood with it.
These are more likely to metastasize or move. These we want to get taken care of as soon as possible. possible.
Usually people come in with these a little bit more often. A lot of times people may not even know they have a basal cell carcinoma. Because it doesn't bleed, it usually doesn't cause them a ton of problems.
But when this thing starts bleeding, we want to hopefully get it taken care of before that. But then people usually start coming in. Melanoma.
So this is the one that you hear about a lot because it grows fast. So melanoma. the melanocyte. The melanocytes is where our melanoma comes from. So when those melanocytes get their cell cycle broke and they start dividing uncontrollably, that's our melanoma.
The reason why this spreads easier and faster than some of our other skin cancers is because those melanocytes have big long arms that stick out through the skin and they're always actively producing that melanin. So if one of these starts growing uncontrollably, those big long arms can actually start to extend down deeper, get into blood vessels, and then if that cell divides again, one of those cells can actually get into blood vessels, and then that can move all throughout the body. So we have to catch our melanomas as early as possible.
When you're trying to find a melanoma, or if you're not sure, is it a mold? Is it melanoma? What's going on with it? We have an ABCDE rule. A is for asymmetrical shape.
So the first thing you look at is a shape. Moles should have a nice symmetrical shape to them. They should look relatively round.
If you look at this picture, asymmetrical, it has no consistent border. They're just all weird funky shapes. They're not nice and round and uniform.
B is border irregularity. If you look at the border of this picture, some areas are dark, some areas are brown, some areas are red, and they get lighter, darker, it kind of looks fuzzy, there's no sharp border to it, that's also a bad sign. Along with that goes color. If you have multiple different colors within that, that's another bad sign.
Moles for the most part, sharp borders. Generally one solid color and then diameter. What size is it?
We usually say six millimeters It's about the size of a pencil eraser If it starts getting larger than that that's when we start to get concerned or if you have a mole and then all of a sudden it starts to get bigger or You have a small place that stayed the same size and all of a sudden it gets bigger and bigger from that that's a concern. And then along with growing, evolving. If it changes size, if it changes shape, if the border starts to look different, if anything starts to change with it, that's also when we start to get concerned. So we kind of follow these ABCDE rules to determine whether it's melanoma or not. If we even think that there's a possibility of it, or generally if any molar...
colored region does start to change in any way, we'll automatically biopsy it, remove it, just to make sure it's not melanoma. Because we don't want these things to spread because they can spread fast and they can be really deadly.