The Epidermis: Cells - Video Tutorials & Practice Problems

Introduction to Cells of the Epidermis

In this video, we're going to focus on the epidermis, specifically the cells of the epidermis. Now, recall from our previous lesson videos that the epidermis is the outermost layer of the skin and is composed of stratified squamous epithelial tissue, or many layers of these flat or squished cells. Notice over here on the right we have a diagram of the integumentary system. And notice that the only layer that is colored is the epidermis, which you can see is the outermost layer of the skin. There are actually 4 main types of cells in the epidermis that we have numbered down below. They are keratinocytes, melanocytes, dendritic cells, and tactile epithelial cells. Moving forward in our course, we're going to talk more details about each of these four types of cells, starting with the keratinocytes in our next lesson video. So I'll see you all there.

Keratinocytes

In this video, we're going to talk about the 1st epidermal cell type in our lesson which are the keratinocytes. And so keratinocytes are actually the most abundant cell type in the epidermis by far. In fact, these keratinocytes can make up over 90% of the cells in the epidermis. And as their name implies, the keratinocytes are responsible for keratin production. Now these keratinocytes are actually specialized epithelial tissue cells. And because they are considered epithelial tissue, it's no surprise that they are going to be connected by tight junctions, which hold the keratinocytes really tightly together, creating a leak-proof barrier. And they're also held really firmly together by desmosomes, which allows for mechanical resilience. Now, the keratin that these keratinocytes produce are tough, fibrous, and water-resistant proteins that give the epidermis its protective properties. Providing both mechanical and tensile strength to the epidermis. Allowing the epidermis to resist forces in many different directions, while still remaining flexible at the same time. Now, it's also worthy of noting that keratin is also one of the main components of both hair and nails. And later in our course when we're talking about accessory structures of the integumentary system, we will talk more details about the structure and function of hair and nails. But for now, let's take a look at this image that we have down below.

And notice on the left-hand side we're showing you the diagram of the integumentary system. And notice that only the epidermis is being colored here in this image. Since that's what we're focusing on in this video. And notice that zooming into the epidermis here, we have these cells of the epidermis. And notice that the vast majority of the cells, again, over 90% of the cells in the epidermis are going to be these keratinocytes. And so, the keratinocytes are, of course, as their name implies, going to be producing the protein keratin. Which is being represented as this blue squiggly line that you see here. And the keratin is going to fill up the cytoplasm of these keratinocytes. And one thing that's important to note is that the superficial cells of the epidermis, or the cells of the epidermis that are closest to the surface, are actually going to be older cells than the cells that lie deeper in the epidermis. And so because that's the case, the cells that are more superficial and are older have had more time to produce more keratin. And so the superficial cells of the epidermis are going to have more keratin. And so that's one thing that you can notice here in this image. Notice that the cells that are more superficial, that are higher up here in our image, they are actually packed with a lot more keratin. Whereas the cells that are deeper and lie below, they actually are newer cells. And because they are newer, they have not quite had enough time to produce as much keratin. And so they have less keratin in them. However, as cells divide in the epidermis, these newer cells are pushed up into more superficial layers, and they have more time to produce more and more keratin. And so the cells become more and more keratinized, filled with keratin, as they move up into more superficial layers. And so, we'll get to talk more about this idea here later in our course as well, when we're talking about the layers of the epidermis. But for now, this here concludes our brief lesson on keratinocytes. And we'll be able to get some practice applying these concepts and learn about the other types of cells in the epidermis as we move forward in our course. So I'll see you all in our next video.

The Epidermis: Cells Example 1

So here we have an example problem that says, use the words in the word bank that you can see down below right here to fill in the blanks and complete the sentences that you can see down below here. And so notice that the words in the word bank are desmosomes, proteins, tight junctions, water, and barrier. And so, this first sentence says that keratin is one of the most abundant and important proteins in the human body. Now, this first blank here has to be filled with one of these words in the word bank. And so we know that keratin is not going to be a desmosome, nor is it a tight junction and of course, keratin is not water. And so, we're between proteins or barrier here for this first blank. Now, let's stick with proteins for now and we can always make a change later if we need to. So, it is the case that keratin is one of the most abundant and important proteins in the human body. And so, because we've used this word in the word bank we can go ahead and cross it off the list.

Now, the second sentence says that one of its primary roles is forming the skin barrier. Now, we know that one of its primary roles is not forming desmosomes nor is it forming tight junctions nor is it forming water. And so, we know that keratin's primary role is to form the skin barrier. And so that's going to be this next blank here. And we can cross it off our list.

The third sentence says, the tight junctions between keratinocytes and the epidermis protect the body from water loss, pathogens, and other harmful substances. Now, in terms of something this blank here, it's actually, going to be water loss. Since it doesn't make sense to have desmosome loss or tight junction loss but it is going to prevent water loss and so, water is going to be this this, 4th blank here. And so we can cross it off our list.

And so now that we know that this is going to prevent water loss, this blank right here must either be desmosomes or tight junctions. And of course, recall that tight junctions are going to hold the cells so tightly together that it creates a leak-proof barrier preventing water loss. So, the tight junctions are going to help, holding the keratinocytes very closely together in the epidermis and protect the body from water loss, pathogens, and other harmful substances. And so, of course, this means that the final blank here must be desmosomes. And so, desmosomes are also going to provide important connections. These desmosomes are going to connect keratinocytes very firmly together, and hold them to each other very firmly, providing mechanical strength to the skin.

This here concludes this example problem, and I'll see you all in our next video.

Would you expect to find more keratin in keratinocytes closer to the external surface of the skin (more superficial) or further from the external surface of the skin (deeper)?

• A. Deeper, because it's more important that the skin is water-resistant in deeper areas.
• B. More superficial because skin on the external surface needs to be tougher and more resistant.
• C. Neither, all keratinocytes have approximately the same amount of keratin.

Other Epidermal Cells

In this video, we're going to continue to talk about the cells of the epidermis. Notice in the top right we have the diagram of the integumentary system with only the epidermis, the outermost layer of the skin, colored since that's the main focus of this video. Recall from our previous lesson videos that we've already covered the most abundant cell type in the epidermis, which are the keratinocytes. In addition to those keratinocytes, there are also three other main types of cells found in the epidermis: melanocytes, dendritic cells, more specifically Langerhans cells, and tactile epithelial cells or Merkel cells. The melanocytes, as their name implies, are specialized epithelial tissue cells that produce melanin, a specialized pigment or molecular complex that interacts with light. The melanin pigment protects our skin from ultraviolet light from the sun, which can cause UV damage. These melanocytes are found in the deepest layer of the epidermis, called the stratum basale, which we'll discuss more later in our course when focusing on the layers of the epidermis. These melanocytes are essentially factories of melanin production and, as we'll learn later, the melanin plays a major role in skin pigmentation. The melanin produced by these melanocytes can also be transferred to neighboring keratinocytes so that they carry the melanin.

The next type of epidermal cells we cover are the dendritic cells, a type of immune cell. The dendritic cells specifically found in the epidermis are called Langerhans cells, named after a scientist. These dendritic or Langerhans cells are immune cells that help initiate immune responses. They scout the epidermis looking for signs of invasion or infection and, when such signs are found, can migrate out of the epidermis into the lymphatic system to travel to nearby lymph nodes where they activate other immune cells to help eliminate the invader or pathogen.

The last type of epidermal cell in this lesson are the tactile epithelial cells, also known as Merkel cells, named after a scientist. The term "tactile" is associated with the sense of touch, emphasizing that these cells work with nerves to detect touch and allow for sensations of touch. Like the melanocytes, Merkel cells are also found in the deepest layer of the epidermis. Later in our course, when focusing on the dermis, we will see there are also other structures involved with sensations of touch, in addition to Merkel cells.

If you look at our image below, you can see the middle part is just a zoom-in of the epidermis, highlighting the three main types of cells discussed. Notice that the vast majority of the cells outside these dotted circles are keratinocytes, which make up about 90% of the cells in the epidermis. The purple cell over here, zoomed in, is the melanocyte, which produces melanin. These dots throughout represent the melanin produced by the melanocytes, which plays a major role in skin pigmentation and also affects the color of our hair and eyes. The melanin can be transferred to neighboring keratinocytes. Above here in green, we have the dendritic cell, more specifically the Langerhans cell, which helps initiate immune responses. In the bottom right over here in blue is the tactile epithelial cell, also known as a Merkel cell, in close connection with the nervous tissue in yellow, which lies beneath and is closely associated with the Merkel cell, enabling sensations of touch.

This concludes our brief lesson on the other epidermal cells, and we'll be able to get some practice applying these concepts and learn more about the epidermis as we move forward in our course. I'll see you all in our next video.

The Epidermis: Cells Example 2

So, here we have an example problem that asks which cell types in the epidermis are responsible for preventing a pathogen from entering the body and causing infection? We've got these 4 potential answer options down below. And so recall from our previous lesson videos that there are 4 main types of cells found in the epidermis or the outermost layers of our skin. And those 4 main types of cells are keratinocytes, melanocytes, dendritic cells, specifically Langerhans cells, and tactile epithelial cells or Merkel cells.

And so, what you'll notice is that 3 of these options mention tactile epithelial cells. And recall that these tactile epithelial cells, their main function is to work with nerves to allow for touch sensations. And they're found toward the bottom of the epidermis in the deepest layer of the epidermis. And so these tactile epithelial cells, their main function is not to protect and prevent a pathogen from entering the body and causing infection. And so for that reason, we can actually eliminate options B, C, and D. And of course, this leaves us with answer option A. Which says keratinocytes and dendritic cells.

Now, recall that keratinocytes are going to make up about 90% of all of the epidermal cells. And so, they make up the vast majority of the epidermis. And these keratinocytes as their name implies, they create keratin which recall is a tough fibrous water resistant protein that gives the epidermis protective properties and allows it to serve as a very good barrier to things in the environment such as microbes for example. And recall that the dendritic cells, specifically Langerhans cells are immune cells that actually help to activate the immune system.

And so, together these keratinocytes and dendritic cells can help to prevent a pathogen from entering the body and causing infection. And so option A here is the correct answer to this example. That concludes this example and I'll see you all in our next video.

Which type of cells play the most important role in preventing skin cancer?

• A. Keratinocytes
• B. Melanocytes
• C. Dendritic cells
• D. Tactile epithelial cells

Which epidermal cell can roam in and out of the epidermis?

• A. Keratinocytes.
• B. Melanocytes.
• C. Dendritic cells.
• D. Tactile epithelial cells.

Imagine you're a doctor, and a patient comes to you with a rare medical condition. It seems that their epidermal cells are not producing keratin. Which of the following symptoms are they most likely to experience?

• A. They will have reduced sensitivity to touch.
• B. They're much more prone to sunburn.
• C. Their skin will tear easily upon exposure to mechanical stress.
• D. Their skin will harden significantly.