In this video, we're going to talk about key features of the 5th and final epidermal cell layer in our lesson, which is the stratum corneum. This layer is the most superficial epidermal cell layer and is immediately adjacent to the external environment. The stratum corneum consists of these dead keratinocyte cells that are fully packed with keratin and that have a H2O or a water-resistant glycolipid membrane. This allows 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 helps to prevent our body from losing too much water to the environment. Although these cells are dead, they are still tightly and firmly connected by tight junctions and desmosomes, allowing them to create an effective barrier to microbes and chemicals that may try to penetrate our skin. Also, the keratinocyte cells of the stratum corneum are regularly shed, cast off, or washed off of the surface of the epidermis.
Notice over here in this diagram, the most superficial layer that is in color is the stratum corneum. You can see these keratinocyte cells that are flaking off, or shedding, or casting off, and being washed, or rubbed off. This is a natural process that occurs over time, but also any kind of friction, anytime we touch something, cells can flake off of the epidermis, the superficial side of the epidermis from the stratum corneum. Because these cells are regularly shed off, they need to be replaced by cells that are deeper in the epidermis. 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.
Ultimately, those cells are going to be shed or cast off of the stratum corneum. Cells can remain in the stratum corneum for maybe about 2 weeks or so; it depends, and it can be different for different people. Eventually, those keratinocyte cells are going to be shed or cast off. In fact, in an average lifetime, a person could shed about 40 pounds worth of these epidermal skin flakes, which is quite a lot if you think about it. Again, those cells that are shed off ultimately need to be replaced by underlying cells.
This cycle brings us back to the original layer. Notice here we have an image of our analogy where Carry the Keratinocyte is a cloud top Casper that is casting off of the corneum. Hopefully, this can help you remember some of the features of the stratum corneum. This here 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.