 Hey everybody, Dr. O here. Welcome to the Integumentary System. So the Integumentary System is one of my favorites to talk about for several reasons. Number one, it's large, right? Your skin is about 16% of your body weight. It's usually one and a half to two square meters. It is technically the largest organ in your body. But it also does so much more than you'd imagine. Like you see skin here and we know some of the things that skin does, but it does so much more than the average person imagines. Like if I were to tell you that your skin is part of your immune system, maybe you'd understand that because it is a physical barrier. It keeps things like bacteria out. So it is part of your immune system in that way. But also there are immune cells in your skin, which we'll cover later. These dendritic cells. We'll cover that in a few videos. But it's also part of your endocrine system because we need skin and the cholesterol in our skin to produce vitamin D, which is not really a vitamin. It's a hormone. So it's part of your immune system and your endocrine system. It's also part of your nervous system because it's home to all of our sensory receptors that sense things like vibration, touch, pain, et cetera. It is part of our detoxification system because we excrete organic waste products with our sweat. So your liver and your kidneys play major roles in detoxification, but so does your skin. And it also is a major player in thermoregulation or maintaining a stable body temperature, whether it's hot or cold outside. And that's because your skin works with your blood like a radiator system. You can pull heat out of the body or force trap heat inside the body depending on what your skin and your blood is doing. So hopefully you understand now just a little bit of how important the integumentary system is. So what is the integumentary system? It's made up of two parts. We have the cutaneous membrane, which is your skin. So a membrane is always going to be an epithelial tissue with a connective tissue underneath it. So in this situation, the epithelial tissue is going to be the epidermis, which is the outer layer of the skin that we see that is avascular. So if you just scratch your skin and you don't get all the way through the epidermis, it won't bleed because the epidermis is avascular. Most parts of your body are going to be covered in thin skin, which has four strata or layers, but the palms of your hands and the soles of your feet are going to be covered by thick skin. They have an extra layer, but we'll cover that later. But just so you know, most skin is thin skin, except for the palms of the hands, soles of the feet are going to be thick skin because the epidermis is thicker there. Beneath the epidermis, we have the vascular dermis. So there is blood supply here. So if you cut yourself to the point where you bleed, you know you've gotten into the dermis there. So we have the epidermis with the underlying dermis. Those two things make up the cutaneous membrane or what we call our skin. Underneath that, we have what's called the hypodermis, which means below the dermis, or the subcutaneous layer, which means underneath the cutaneous membrane. So you've probably heard of the term hypodermis as far as hypodermic needles. This is where you give people injections because there's no vital organs there and you shouldn't hit anything vital when you give an injection there. So that's going to be the actual cutaneous membrane. Then all these accessory structures. So most of them, as you can see from this picture, they come from down in the dermis and they penetrate up through the epidermis, but the accessory structures we're going to cover are going to be hair and nails. I don't spend much time talking about those. But then we have the multicellular exocrine glands. So we'll look at primarily two types of sweat glands. We'll look at your sebaceous glands and we'll talk about a few of the other ones as well. So that is all the important stuff there to know. I think what else we talked about thin versus thick skin. I think that's a really good introduction. The only thing I didn't say was that the epidermis, the epithelial tissue that lines your skin, is stratified squamous epithelium, which means it's there for protection. But it's also a keratinized stratified squamous epithelium. The most abundant cell in the epidermis is something called a keratinocyte. So keratin is very important to your skin. It makes your skin tough, but it also makes it water resistant. That's what keeps the moisture in your body from being carried away. This is also why your skin doesn't have to constantly be bathed. Most of your epithelial tissues inside your body need to be covered in mucus to do their job. That's not the case with your skin because it's keratinized. So I think that's probably the last thing to say there. All right, that's an introduction to the Integra Mentory System. Follow me as we go through the whole system here. I hope this helps. Have a wonderful day. Be blessed.