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 basale, which is also sometimes referred to as the basal layer since it's found on the basal surface of the tissue. Now the Stratum basale or the basal layer is usually shown as the bottom layer in diagrams of the epidermis. And so you can think that the b in basale or the b in basal layer is for the b in the bottom layer. Now, the Stratum basale or Basal Layer is actually made up of just one single row of cells, which is a unique feature of the Stratum basale 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 all grayed out except for the stratum basale, or the basal layer, which you can see is highlighted right here. And indeed, the stratum basale is just one single row of cells. And in the stratum basale 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 keratinocytes, 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 Stratum basal or basal layer, of course, it's going to contain keratinocytes, which recall are the most abundant cell type in the epidermis and make up about 90% of all of the epidermal cells. And the keratinocytes are shown highlighted here. But the stratum basal 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 keratinocytes that are neighboring the melanocyte. And so those keratinocytes can carry melanin that was originally produced by the melanocytes. And then the Stratum basale 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 closely with nervous tissue, as you can see here in yellow, in order to allow for sensations of touch.

And so, again over here in this diagram on the right, you can see the melanocytes and the tactile epithelial cells along with these keratinocytes 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 Kary the keratinocyte as a baby. And notice that Kary the keratinocyte, this baby, is born in the stratum basale. And so this can remind you that the keratinocytes originate in the stratum basale.

And so these cells are going to be relatively new in the stratum basale. And over time, as cells divide, the keratinocytes 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 keratin. So, the cells that are in more and more superficial layers will have more and more keratin. 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 stratum basale.

So the melanocytes and tactile epithelial cells are not going to get pushed up into more superficial layers, It's really just the keratinocytes that are pushed up into more superficial layers. And so this here concludes our lesson on the key features of the stratum basale, 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 spinosum.