in this video, we're going to begin our lesson on the skin, which serves as a physical barrier in the first line defense of innate immunity. And so really there are two primary types of physical barriers of the first line defense and innate immunity. The first is going to be our skin and the second is going to be our mucous membranes. Now first we're going to talk more about the skin as a physical barrier and then later we'll talk more about mucous membranes as a physical barrier. Now, epithelial cells are important here because these are tightly packed skin cells that line the surfaces or the perimeter of the body. And so if we take a look at our map down below over here, notice that the first line defenses, specifically the physical barriers are being colored and highlighted here, and this includes our skin as well as our mucous membrane. And so moving forward, we'll first talk about the skin and then we'll talk about the mucus membranes later. And so notice everything else here is all great out because we're going to be talking about them and separate videos later down the line. But for now we're talking about the first line defenses, primarily the physical barriers including the skin and mucous membranes. And so I'll see you all in our next video to talk more about them

in this video, we're going to talk some more details about our skin and so recall that our skin serves as a physical barrier, that's part of the first line of defense of innate immunity and our skin is composed of two primary layers that we're going to talk about. The first layer is going to be the epidermis and the second layer is going to be the dermis. Now the epidermis is the outer surface layer and this outer surface layer is composed of many layers of epithelial cells. Now the outermost layer of the epidermis is composed of dead skin cells. And these dead skin cells are going to contain a water repelling protein called keratin. And so keratin. This water repelling protein that's found in hair and nails is going to help create a dry environment on our skin. And this dry environment on the skin can help prevent some microbial growth. And so some microbes are capable of tolerating dry environments. And so those will be able to grow in our skin. But other microbes cannot tolerate dry environments. And so that will prevent the growth of those microbes on our skin. Now in addition to this uh keratin that's going to help protect us from uh some microbial growth. Um Our skin will also shed the outer most layers of our skin will shed. And so the shedding of the outermost layer of the epidermis can help remove microbes on the skin by taking those microbes along with the shedding skin. And so those are protective features to help protect us from microbes. Now the second um layer of the skin is going to be the dermis and the dermis is going to be the inner layer of the skin that is actually going to be much thicker than the epidermis. And the dermis is composed of connective tissue. And this connective tissue makes the dermis extremely durable and very very tough to break, which is also going to contribute to prevent microbes from penetrating through our skin. And so if we take a look at our image down below, uh notice we're focusing in on the first line defense, specifically the skin as a physical barrier. And so notice here, we're showing you a little diagram of our skin. The outermost layer here is going to be the epidermis. Uh And so you can see here is another image of the epidermis here and um what you'll notice is that microbes are capable of growing on our skin. However, the keratin that's found in the outermost layer of the epidermis can help create a dry environment to limit the growth of microbes. Some microbes and also the outermost layer of our skin will shed. And that will also remove microbes along with it. Now beneath the epidermis. Here in this layer, what we have is the dermis and the dermis again consists of connective tissue, making it extremely durable and tough to break again, preventing these microbes from penetrating into our tissues. Uh And then of course underneath of the uh dermis layer is a layer of fat tissue called the subcutaneous layer that contains blood vessels, and so you can see the connective tissue and fat down below underneath of that. But ultimately, the main point of this video is to show that the skin serves as a physical barrier that's part of the first line of defense of innate immunity, and it can prevent microbes from penetrating into our body. And so this here concludes our brief lesson on the skin, and uh we'll be able to learn more and apply these concepts as we move forward. So I'll see you all in our next video.