The Epidermis: Layers - Video Tutorials & Practice Problems
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1
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Introduction to Layers of the Epidermis
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In this video, we're going to continue to talk about the epidermis as we focus in on the layers of the epidermis. And so the epidermis or the outermost portion of our skin is actually composed of several distinct layers of cells. And so notice that down below, on the left hand side, we're showing you the diagram of the integumentary system. And once again, we're only coloring the epidermis or the outermost portion of our skin. And notice that zooming into the epidermis, we can clearly see that there are several distinct layers of cells. And so it's important to note that the term stratum is a term that means layer in Latin. And the plural form of this word is actually strad up, which means layers. Now notice that down below, we have listed and numbered the layers of the epidermis. And notice that the numbering is actually in order from the deepest layer of the epidermis, which is furthest away from the external environment to the most superficial layer of the epidermis, which is immediately adjacent to the external environment. And so the reason that we have these layers numbered in this particular order from deepest to most superficial is because that is the order that we are going to be covering these layers moving forward in our lesson and also numbering the layers in this particular order from deepest to most superficial is going to help us better understand the development of the cells in these layers over time. Now, the layers of the epidermis, in order from deepest to most superficial are the stratum bali, the stratum spinosa, the stratum granulosa, the stratum lucidum and the stratum corneum. Now, it's important to note that the number of layers of the epidermis can actually vary depending on the type of skin. And so there is what is known as thin skin and there's also what's known as thick skin. And in our next lesson video, we're going to distinguish further between thin skin and thick skin. But what's really important to note here in this video is that the stratum lucidum has an asterisk next to it. And this is because the stratum lucidum is a layer of the epidermis that is only found in thick skin and it is not found in thin skin. And so that's something that's very important to note. Now, we do have a memory tool to help you remember the layers of the epidermis in order from the deepest layer of the epidermis to the most superficial layer of the epidermis. And that memory tool is beautiful skin glow like crystals where the first letter of each of these words is a symbol to represent the first letter of each of the layers of the epidermis in order from the deepest layer to the most superficial layer. And so moving forward in our course, we're going to talk more details about each of these layers of the epidermis. And we'll also get to distinguish between thin skin and thick skin. So I'll see you all in our next video.
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concept
Thin vs. Thick Skin
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In this video, we're going to briefly distinguish between thin skin and thick skin. And so, although skin all over the external body is very similar in structure, there are some local variations that led to these two majorly recognized skin types. The first being thin skin and the second being thick skin. And so notice down below, we have a table comparing some of the major features of thin skin and thick skin. And so notice the left hand side has features of thin skin, whereas the right hand side has features of thick skin and so uh thin skin as its name implies is going to be thinner than thick skin. Because as we briefly mentioned in our last lesson video, thin skin has all of the layers of the epidermis except for the stratum lucidum, which is the second most superficial layer and so thin skin does not contain the stratum lucidum in its epidermis. Whereas thick skin is going to be thicker because it contains all of the layers of the epidermis, including the stratum lucidum. Now, thin skin actually makes up most of the skin on our body. Whereas thick skin is really only located in specific regions such as the palms of our hands, for example, and the soles of our feet. And so if you had to take a guess at what type of skin it is, you might as well go with thin skin because again, it makes up most of the skin on our body except for the skin in these particular regions. Now, thin skin actually contains hair follicles and oil glands as well. Whereas thick skin such as the palms of our hands and the soles of our feet do not contain any hair follicles or oil glands. Now, thin skin in general is going to have fewer sweat glands, whereas thick skin tends to have more sweat glands than thin skin. And so there are some other differences between thin skin and thick skin. But these are some of the major differences that we think you should be aware of for your exams. And so moving forward in our course, we'll be able to apply some of these concepts and learn more about the layers of the epidermis. So I'll see you all in our next video.
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example
The Epidermis: Layers Example 1
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So here we have an example problem that says, imagine you're a pathogen trying to enter a human body via the skin on a person's soul of the feet. Which layers of the epidermis do you have to get through? And in what order? And so to solve this problem, we need to recall the memory tool for remembering the layers of the epidermis in order from deep to superficial and recall that memory tool is beautiful skin glows like crystals. And so notice here, I've drawn a sketch of the memory tool, beautiful skin glows like crystals which again organizes these layers from deep to superficial and notice that the first letter of each of these words is going to represent the layers of the epidermis. And so you can see the layers are stratum bali stratum spinosa strata, granulosa, stratum lucidum and stratum corneum. Now, what we also need to realize is that the stratum lucidum is only going to be present in thick skin and it's absent in thin skin. And so we need to realize that we're entering the skin on a person's soul of the feet. And recall from our last lesson video that the sole of the feet is going to have thick skin. And so that means that the stratum lucidum is going to be present in this journey that the pathogen is taking. And so let's imagine again that we are this pathogen and let's represent the pathogen as this red dot We know that we're going to start outside of the body. And uh that means that we're going to start on the superficial side and we want to enter into the body, which means that we're going to need to cross through all of these layers to get deeper and deeper into the body. And so that means that in terms of the layers of the epidermis that we have to get through and the order that we need to go through them, uh it's going to be all five of the layers in this particular order from superficial to deep, starting with the stratum corneum, then the stratum lucidum, then the stratum granulosa, then the stratum spinosa and then finally entering through the stratum basal. And that is what's going to allow us to penetrate through the epidermis into deeper layers of the skin. And so uh this here concludes this example problem. Hopefully, you can see the value in this memory tool, beautiful skin glows like crystals and hopefully that can help you solve some of the problems. So I'll see you all in our next video
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concept
Keratinocyte Development in Epidermal Layers
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In this video, we're going to talk about Carnoy development over time in the epidermal layers while also introducing some really interesting analogies and some excellent memory tools that you can only find here on Pearson plus channels. And so notice in the top right, we have a diagram showing you the integumentary system. And once again, we're only coloring the epidermis or the outermost portion of the skin since that's the main focus of this video. And so notice that the image down below on the left hand side is really just a zoom in to the epidermis where you can see the layers of cells in the epidermis. And so the Carroo sites in the layers of the epidermis are actually in various stages of development. And so what's really important for you to know is that the Carnoy cells originate in the stratum bali, which recall is the deepest layer of the epidermis and is usually shown at the bottom of the diagrams of the epidermis. And over time as cells divide, these Carnoy cells are pushed upwards or pushed up into more superficial layers. And so what this means is that the cells that are deeper in the Strat and bali are going to be newer cells since this is where they originate. Whereas the cells that are more superficial are going to be older cells. And so if we take a look at the image down below, on the left hand side, again, this is just a zoom in to the epidermis. And so notice that the light pink that you see down below highlighted here represents the dermis that lies underneath of the epidermis. And so the first epidermal layer or the deepest epidermal layer is shown highlighted right here. And this is the strad and Vialli. The next layer of the epidermis is this larger layer that you can see right here that actually consists of multiple layers of cells as you can see. And this is the stratum spinosa. The next layer of the epidermis is highlighted here and that is the stratum granulosa. The next layer is highlighted here that is the stratum lucidum only found in thick skin. And then at the very top, what we have is the final most superficial layer of the epidermis in the stratum corneum. And so, uh again, the cells that are deeper in the stratum bali, uh they are originating in the stratum basal. And so the deeper cells are going to be newer cells as indicated here in our image. And then as the cells divide the Carroo sites are pushed upwards into more and more superficial layers. And so the superficial cells are going to be older cells. Now recall that carotenoids produced the protein Carotin. And so when they first originate in the strad and basal, they have not yet had enough time to produce a lot of Carotin. But as the cells are pushed up over time into more superficial layers, they've had more and more time to produce more and more Carotin. And so the cells that are more superficial are going to have more carrot than the cells that are deeper. Now, what you'll notice is that we have this really interesting analogy over here on the right, to help you remember the layers of the epidermis. And so this analogy entails a character called carry the Carroo site. And so notice that carry the Carroo site here is just a little baby and so carry the Caratti site is actually born in the stratum basal. And so you can think the be in stratum basal is for the bee and being born reminding you that the Carroo sites originate in this bottom uh layer. Now again, as the cells divide, they move up into more and more superficial layers. And so the next layer here is the stratum spinosa. And so notice that carry is sprouting in the stratum spinosa. And so Carrie is now an adult. Now again, the cells are going to continuously age and get pushed up over time into more superficial layers. And so notice that carry the Carroo site is now a granny in the granulosa. And so again, uh that is a helpful memory tool that can help you remember the layers in order of development. Now, in the stratum lucidum, uh what you'll notice is that unfortunately, carry is now lifeless. And so, in fact, the carat sites are actually dead in this layer of the stratum lucidum. And so notice that we're showing you a coffin here and you can see some images of carry the Carroo site and other more deep layers and so lifeless carry is actually locked in a thick coffin. And that thick coffin reminds you that this layer, the strain lucidum is only found in thick skin. And so ca lifeless carry is locked in a thick coffin in the stratum lucidum. And then finally, what we have at the top is the stratum corneum. And notice that carry the Carroo site is a cloud top Casper casting off of the corneum. And in fact, in this layer, the stratum corneum, the Carroo sites can actually cast off of the surface and actually be rubbed off. And so what that means is that the stratum Corum is constantly shedding cells. And so the cells in the stratum corneum need to be replaced by deeper cells. And so again, when the cells originate in the stratum basal, they will get pushed up into more and more superficial layers until ultimately they are shed off. And then again, they need to be replaced by cells that are dividing in the stratum basal. And recall from our previous lesson videos that the cells that are deepest in the epidermis are closest to the underlying vascular tissue. And so the dermis is going to be vascular and supply nutrients through the blood. And so the cells in the stratum bali have more access to more treats. And so they have more tendency to divide and as the cells get further and further away from the underlying connective tissue in the dermis, they have less and less access to the nutrients from the blood. And so they lose their capacity to divide as they move up into more superficial layers. And this is something, this is an idea that we'll get to talk more about as we move forward in our course and talk more details about the features of each of these layers of the epidermis. But for now, hopefully, this memory tool and this analogy can be helpful to you to remember Carnoy development in epidermal layers. And we'll be able to get some practice applying these concepts and learn more as we move forward. So I'll see you all in our next video.
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example
The Epidermis: Layers Example 2
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So here we have an example problem that says to label the epidermal strata or the epidermal layers in the image below. And so notice in the top right, we have the same diagram from our previous lesson videos where only the epidermis is colored. And so the epidermis is this outermost layer of the skin. And the epidermis itself is actually made of several layers of cells. And that's really what this larger image is all about. And so we do have multiple memory tools for helping you remember the layers of the epidermis. And so the first memory tool that we have is beautiful skin glows like crystals. And so notice that we've got that memory tool right here for you. And uh the first letter of each of these words represents one of the epidermal layers and they are organized from deep to superficial. And so if we use this memory tool, we can figure out the first word for each of these layers. And so of course, uh we can say that beautiful skin glows like crystals. And so that allows us to fill in this uh these blanks. Now, we also have other memory tools that we talked about in our previous lesson videos uh that include carry the Carnoy. And so uh notice in this diagram down below in light pink, this represents the underlying connective tissue that's part of the dermis of the skin. And the epidermis begins right here at this next layer. And so this is going to represent the stratum bali where carry the Carroo site is born and the Stratham basal is usually shown as the bottommost layer of the epidermis. And so uh you can think that the B and stratum basal is for the B and the Carroo site being born and also the B and bottom, since it's the bottommost layer, usually now uh in the next layer here, carry the Carnoy is sprouting in the stratum spinosa. And so the stratum spinosa is going to be this next layer here of uh cells where you can see it's quite a large layer, has many, many layers of cells and that is the stratum spinosa. Now, the next layer here, what you can see is that carry the Carroo site is aging into a granny in the stratum granulosa. And so notice that carry the carat tenno site is aging as it goes into more and more superficial layers. And so the stratum granulosa is represented as this layer that you can see highlighted here. Now, next, what we have is the stratum lucidum. And so in the stratum lucidum, it's only going to be found in thick skin. And so uh what you'll notice is that we have a coffin here because uh carry the Carroo site is lifeless in this layer. And so it's actually a layer of dead cells. And what you'll also notice is that carry the carat Tenno site is lifeless and locked inside of this thick coffin. Reminding us that the stratum lucidum is only found in thick skin and it's absent and thin skin. Then in the final layer, what we have is carry the Carnoy is a cloud top Casper casting off of this quorum, the stratum corneum. And so uh you can see here that in this layer, these cells can actually flake off into the environment and they need to be replaced by cells that are dividing in the deeper layers. And so as cells divide those cell, uh cells are going to continuously get pushed up into more superficial layers. So these cells toward the top are going to be older cells. And as you go down, the cells are going to be newer cells and younger cells. And so now that we've filled in and labeled all of the epidermal shred up, we've completed this example. So I'll see you all in our next video.
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Problem
Problem
Which of the epidermal layers is likely to have the greatest regenerative capacity (ability to divide)?
A
Stratum basale.
B
Stratum spinosum.
C
Stratum granulosum.
D
Stratum lucidum.
E
Stratum corneum.
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concept
Epidermal Layers: Stratum Basale (Basal Layer)
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In this video, we're going to begin talking about key features of each of the epidermal layers starting with the deepest epidermal layer of the stratum, the sally, which is also sometimes referred to as the basal layer since it's found on the basal surface of the tissue. Now, the strata bali or the basal layer is usually shown as the bottom layer in diagrams of the epidermis. And so you can think that the B and basal or the B and basal layer is for the B in the bottom layer. Now, the Strat basi or basal layer is actually made up of just one single row of cells, which is a unique feature of the stratum basal that does not apply to any of the other layers of the epidermis. And so notice over here on the right, we're showing you a diagram of all of the layers of the epidermis and notice that they're, they are all grayed out except for the stratum bali or the basal layer, which you can see is highlighted right here. And indeed, the stratum basal is just one single row of cells and in the stratum basal are what are known as stem cells. And these stem cells have the ability to proliferate or divide to create more stem cells. And they also have the ability to differentiate or change into other types of cells such as Caro sites, melanocytes or tactile epithelial cells, for example. And so they are able to do this and maintain the epidermis. And so, recall from our last lesson video that the cells on the superficial side of the epidermis actually cast off. And so they can be rubbed off. And these cells that are rubbed off of the epidermis or flake off of the epidermis need to be replaced by deeper cells. And so the stem cells help to maintain the epidermis. Now in the strata bali or basal layer, of course, it's going to contain carotenoids, which recall are the most abundant cell type in the epidermis and make up about 90% of all of the epidermal cells and the Carroo sites are shown highlighted here, but the strad and bali is also going to contain melanocytes, which recall from our previous lesson videos are shown as these purple cells and they produce the pigment melanin which protects our skin from UV light or ultraviolet light from the sun, which can cause damage. And so the melanocytes protect from UV damage by producing melanin. And again, that melanin can be transferred to Carroo sites that are neighboring the melanocyte. And so those Carroo sites can carry melanin that was originally produced by the melanocytes and then the shad and bali will also contain tactile epithelial cells or Merkel cells, which recall from our previous lesson videos, the term tactile is a term that means touch. And so these tactile epithelial cells work really really closely with nervous tissue as you can see here in yellow in order to allow for sensations of touch. And so, uh again over here in this diagram on the right, you can see the melanocytes and the tactile epithelial cells along with these Carroo sites as well. Now here what we have is an image from the analogy that we talked about in our previous lesson video. So this is carry the Carroo site as a baby and notice that carry the Carroo site, this baby is born in the stratum basal. And so this can remind you that the Carroo sites originate in the strata basal. And so these cells are going to be relatively new in the strata basal. And over time as cells divide the Carroo sites are going to get pushed up into more superficial layers. And as they get pushed up over time, they have more and more time to produce more and more Carotin. So the cells that are in more and more superficial layers will have more and more Carotin. And one thing to note is that the melanocytes and the tactile epithelial cells have functions that allow them to essentially remain localized in the uh Strat and basal. So the melanocytes and tactile epithelial cells are not going to get pushed up into more superficial layers. It's really just the carno sites that are pushed up into more superficial layers. And so this here concludes our lesson on the key features of the stratum bali the deepest layer of the epidermis. And so I'll see you all in our next video where we'll get to talk about the next superficial layer, which is the stratum spinosa.
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concept
Epidermal Layers: Stratum Spinosum (Spiny Layer)
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In this video, we're going to talk about key features of the second epidermal layer in our lesson, which is the stratum spinosa. And so the term spinosa actually means spiky or spiny, which is why this layer is also called the spiny layer. Now it gets its name from the spiky or spiny artifacts that appear during preparation of cells on this layer for microscopy. But those spiky or spiny artifacts do not exist in the actual living tissue. Now, the stratum spinosa or the spiny layer is the second deepest layer of the epidermis right behind the stratum bali. And so you can think that the S and spinosa or the S and spiny layer is for the S and the word second to remind you of the second deepest layer. Now, as you can see over here in this diagram where the stratum spinosa is colored like this. Most of the stratum spinosa consists of many rows of these dividing Carroo sites. Now, it is worthy of noting that the Carroo sites that are deeper in the stratum spinosa are actually closer to the underlying vascular connective tissue. And so they have more direct nutrients or more direct access to nutrients from those blood vessels. Whereas the cells that are more superficial in the stratum spinosa are further away from the underlying connective tissue. And so they have less access to nutrients from those vascular tissues. And because that's the case, the cells that are closer to the underlying tissue have more direct access and therefore have more capacity to divide. Whereas the cells that are further away are going to have less access to nutrients and therefore less capacity to divide. And so, in fact, as the cells divide and get pushed up into more and more superficial layers, what we'll notice is that the next layer, the cells have lost their capacity to divide entirely because they are so far away and have very, very limited access to any nutrients from underlying connective tissues. Now, it is worthy of noting that the stratum spinosa or the spiny layer is usually the thickest epidermal layer, especially in thin skin, but in thick skin, usually the stratum corneum is the thickest layer and the stratum corneum is the most superficial layer of the epidermis. Now, Carroo sites in the stratum spinosa or spiny layer will actually begin to flatten at the top of this layer. And so what you'll notice is that here in this diagram, the carno sites in the stratum spinosa are flattening toward the top of the layer or the more superficial side of the layer. And the reason that they flatten is because of their Carotin production. So recall that the deeper cells are newer cells since they originate in the Strat and Bali. But the more superficial cells are older cells. And so they've had more time to produce more carrot. And so that's why they start to flatten is due to that carrot production. Now, it's also worthy of noting that in the stratum spinosa is where we can find dendritic cells, specifically the lahan cells And recall that these dendritic cells or longer hound cells are immune cells that help to provide immunity by activating the immune system. And so later in our course, we'll get to talk more details about the exact functions of dendritic cells when we're focusing on the immune system. But really, these dendritic cells are just scavenging through the stratum spinosa of the epidemic, looking for signs of infection or invasion. And if they detect a sign of infection or invasion, they can actually migrate out of the epidermis into the lymphatic system, travel to a nearby lymph node to help activate other immune cells in that lymph node. And those other immune cells can generate a significant immune response to help prevent the infection. And so what you'll notice here is that we've got this image of our analogy. And so notice that carry the Carroo site in the stratum spinosa is starting to sprout and so now carry the Carroo site is this young adult. And so again, as cells divide, they will get pushed up into more superficial layers. And so the next superficial layer here is the stratum granulosa. And so we'll talk more about those key features in our next video. So I'll see you all there.
In this video, we're going to talk about key features of the third epidermal cell layer in our lesson, which is the stratum granulosa, also known as the granular layer. And so Carroo sites in this layer actually stop dividing. And so notice looking at this diagram on the right, the stratum granulosa or the granular layer is colored. And what you'll notice is that the cells in this layer are quite far from the underlying vascular connective tissue of the dermis, meaning that they have very limited access to nutrients from those blood vessels. And ultimately, this is the reason for why the cells in this layer stop dividing. Now, the Carroo sites in this layer are also going to begin to harden and begin to die. Now, the reason that the Carroo sites begin to harden is because of the process of carin, which as its name implies is the process where Caro sites fill up with lots and lots of carrot and ultimately, that helps to allow those carat sites to harden. Now recall from our previous lesson videos that Carotin is a very tough fibrous and water resistant protein produced by Carroo sites and it helps to give the epidermis its protective properties and helps to allow the epidermis to serve as an effective barrier. Now, as its name implies, the stratum granulosa or the granular layer is going to have Carroo sites that are filled with Granules. And so these Granules or containers within cells are going to help promote the hardening of the Carroo sites and the waterproofing of the stratum granulosa. And so under the microscope, the cells in the stratum granulosa do take on a noticeably different appearance with these Granules. And so notice that the Granules are all of these little dots packed within these Carroo sites and they can be visualized especially with the proper staining techniques. Now, the in terms of the types of Granules really, there are two main types of Granules used in uh the granulosa, the stratum granulosa and those two main types of Granules are Corado highland Granules which help with the aggregation of Carotin and ultimately help with the hardening of the Carroo sites. And then there are also Lamela Granules which are packed with a water resistant glycolipid. And ultimately, that glycolipid can be secreted into the environment, which helps to create a very waterproof layer in the stratum granulosa. Now, in the stratum granulosa or the granular layer, the Carroo sites. Uh what you'll notice is that the nuclei in the organelles within those Carroo sites are going to start to disintegrate in this layer. And ultimately, this is what causes these cells to die. And again, this is because they have limited access to nutrients and things of that nature. Now notice here that what we have is a an image of the analogy from our previous lesson videos. And so notice here we can we have carry the Carroo site is a granny in the granulosa. And so hopefully, that's a helpful memory tool to remind you that the stratum granulosa or the granular layer is going to have older cells that are still alive. But their nuclei and organelles are starting to disintegrate and wear down. And also they're packed with lots and lots of Granules. And so this here concludes our brief lesson on the stratum granulosa. And again, as the cells continuously divide, they'll get pushed up into more and more superficial layers. And the next superficial layer in the epidermis is the stratum lucidum, which is only found in thick skin. And so we'll talk about key features of that layer in our next video. So I'll see you all there.
10
concept
Epidermal Layers: Stratum Lucidum (Clear Layer)
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In this video, we're going to talk about the key features of the fourth epidermal cell layer in our lesson, which is the stratum lucidum, also known as the clear layer. And so this is a protective epidermal layer that is only present in thick skin such as the skin on the palms of our hands and the skin on the soles of our feet, which have to encounter a lot of friction since we're constantly grabbing things and our feet are constantly walking on the floors. And so evolutionarily, the thick skin has evolved to have this extra layer, this stratum lucidum. But again, the stratum lucidum or the clear layer is not present in thin skin, which makes up most of the skin on our body. And so most of the skin on our body does not have the stratum lucidum. And so the stratum lucidum or the clear layer of thick skin consists of these flattened, dead, densely packed and transparent Carnoy cells that actually lack organelles. And recall from our previous lesson video that the organelles are degraded in the previous epidermal cell layer of the stratum granulosa. And so notice over here in this diagram you can see the stratum lucidum or the clear layer as this relatively small layer of cells uh that are transparent and the lack of organelles in the cells of this layer contributes to its transparency. And this is why it's also known as the clear layer. Now notice here we have an image from the analogy from our previous lesson videos. And so we know that carry the carno site unfortunately, is going to be dead here and lifeless carry is locked in this thick coffin that you can see here. And uh that is going to remind us of the stratum lucidum. Now, you can see that there are these photographs of the previous epidermal cell layers, including the stratum granulosa, stratum spinosa and the stratum basal. And so this year concludes our brief lesson on the stratum lucidum or the clear layer. And again, as cells divide, these cells are going to continuously get pushed up into more superficial layers. And so the final superficial layer is the stratum corneum and we'll talk about that layer in our next video. So I'll see you all there.
11
concept
Epidermal Layers: Stratum Corneum
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In this video, we're going to talk about key features of the fifth and final epidermal cell layer in our lesson, which is the stratum corneum, which is actually the most superficial epidermal cell layer. And so it is immediately adjacent to the external environment. And so the stratum corneum consists of these dead Carnoy cells that are fully packed with Carotin and that have a H2O or a water resistant glycolipid membrane allowing them to create a waterproof barrier that prevents water from penetrating deeper into our body when we're taking a bath, for example, or swimming in a pool. But also that helps to prevent our body from losing too much water to the environment. Now, although these cells are dead, the cells still are tightly and firmly connected by tight junctions and desmosome allowing them to create an effective barrier to microbes and chemicals that may try to penetrate into our skin. Also, the Carnoy cells of the stratum corneum are regularly shed or cast or washed off of the surface of the epidermis. And so notice over here in this diagram, the most superficial layer that is in color is the stratum corneum. And notice that you can see these uh Carnoy cells that are flaking off or shedding or casting off and being washed or rubbed off. And so this is a natural process that occurs over time, but also any kind of friction. Any time we touch something, cells can flake off of the epidermis, the superficial side of the epidermis from the stratum corneum. And so, because these cells are regularly shed off, they actually need to be replaced by cells that are deeper in the epidermis. And so recall that the cells that are deepest in the epidermis are actively dividing. And as they divide, they push older cells into more superficial layers. And ultimately, those cells are going to be shed or cast off of the stratum corneum. And so cells can remain in the stratum corneum for maybe about two weeks or so, it depends uh and it can be different from for different people. But ultimately, eventually those Carnoy cells are going to be shed or cast off. In fact, in an average lifetime, a person could shed about £40 worth of these epidermal skin flicks, which is quite a lot if you think about it. And so again, those cells that are shed off, ultimately need to be replaced by underlying cells. And so really that is a cycle that brings us back to the original layer. And so notice here, we have an image of our analogy where carry the car tenno site is a cloud top Casper that is casting off of the corneum. And so hopefully, that can help you remember some of the features of the stratum corneum. And so this year concludes this lesson and I'll see you all in our next videos where we'll be able to apply these concepts and practice problems.
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example
The Epidermis: Layers Example 3
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So here we have an example problem that says, imagine you're a pathogen trying to enter a human body via the skin on a person's arm. Now, if you look at the skin on your arm, you'll notice that it has some hairs on it and that's an indication that this is going to be thin skin. And so we can go ahead and label the skin on a person's arm here as thin skin. Now, the problem here asks which layers of the epidermis do you have to get through? And in what order and what might be some challenges you encounter along the way and it ends with asking how would this journey differ if you were entering via the palm of their hand? Now, if you look at the skin on the palm of your hand, you'll notice that it does not have any hairs on it and that's an indication that it is thick skin. And so recall that the skin on the palm of your hand and the skin on the soles of your feet is going to have thick skin. Now, we're going to approach this problem by breaking it up into two parts the first part will focus on the epidermal layers. And the second part will focus on the challenges that the pathogen can encounter. And so of course, we know that the epidermal layers in thin skin are going to be different than the epidermal layers and thick skin. And of course, because thick skin is thicker, we know it's going to have more epidermal layers than thin skin. And so recall the memory tool that helps us remember the epidermal layers in order from the deepest layer to the most superficial layer is beautiful skin glows like crystals. And so that reminds us that it is the strad and basal, the stratum spinosa, the stratum granulosa, the stratum lucidum and the stratum corneum. And of course, thick skin is going to have all of these layers and recall that the stratum lucidum is unique to thick skin. It is only found in thick skin. And so in terms of the layers in thin skin, really, it's going to have the exact same layers. Uh The only difference is that once again, it's not going to have the stratum lucidum. So we can cross that one off. And so in terms of the pathogen, of course, the pathogen is going to start on the outside of the body. And that means it's going to start on the most superficial side of the epidermis. And so that means that the pathogen is going to start at the top and make its way down. And so in thin skin, such as the skin on a person's arm, the pathogen will need to go from uh starting from the stratum corneum to the stratum granulosa, then the stratum spinosa and ending with the stratum bali and then in thick skin, it'll make the same journey except again, it has to go through the stratum lucidum as well. And so really, that's the biggest difference between the journey the pathogen would need to take in thin skin versus thick skin. Now, in terms of some challenges that the pathogen will encounter along the way. Of course, it's going to encounter these really tightly and firmly connected Carotin filled Carroo sites which recall make up the vast majority of the epidermis. Something like 90% of the epidermal cells are Carroo sites and those really, really tightly packed Carroo sites are going to create a very difficult barrier uh or create a barrier that is very difficult for the pathogen to penetrate, penetrate through. And so the Carroo sites are found in all of these layers. And so uh that will create a challenge for the pathogen throughout its entire journey. Now, another challenge that the pathogen is going to encounter along the way are dendritic cells which were called dendritic cells are cells that basically scout the epidermis for signs of pathogens. And then they can actually leave the epidermis and alert the immune system and activate components of the immune system. And so, uh a pathogen would need to be able to evade these dendritic cells in order to uh be successful at invading the body. Now recall that these dendritic cells are predominantly found in the stratum spinosa layer. And so, um that is a challenge that the pathogen would encounter mainly when it gets to the stratum spinosa. And so this year concludes this example problem and I'll see you all in our next video.
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Problem
Problem
Which of the following layers of the epidermis is responsible for generating new epidermal cells?
A
Stratum basale.
B
Stratum spinosum.
C
Stratum granulosum.
D
Stratum corneum.
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Problem
Problem
Which of the following is true about thick skin?
A
Hair grows on thick skin.
B
There is no stratum corneum in thick skin.
C
Stratum lucidum is only found in thick skin.
D
Thick skin is only composed of stratum lucidum.
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Problem
Problem
Which epidermal layers contain dead, flattened keratinocytes?
A
Stratum basale and stratum corneum.
B
Stratum lucidum and stratum corneum.
C
Stratum granulosum and stratum spinosum.
D
Stratum granulosum and stratum lucidum.
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Problem
Problem
Why do the cells in the more superficial layers of the epidermis die?
A
They experience a great deal of mechanical stress.
B
They're exposed to oxygen in the air, causing them to age faster.
C
They're exposed to harsh chemicals contained in soaps, lotions, and other products.
D
They are far away from any blood supply, causing a lack of nutrients.
Do you want more practice?
We have more practice problems on The Epidermis: Layers