 Hey everybody, Dr. O. So these are going to be all the tissue types or epithelial tissue types that we're going to talk about, but I didn't want to make one really long video so I'm going to break it down into four shorter ones. Let's go ahead and take a look in this video at the simple and stratified squamous epithelium. Remember squamous cells are going to be flattened, kind of look like fried eggs, circular cells. So simple squamous epithelium is going to be a single layer of these thin cells. This is the thinnest, most delicate tissue type in the body. Remember what I taught you in the last video? No means absorption and secretion. So there's not going to be any protection here, but it's designed to move material very quickly because it's only that one layer thick, which means that diffusion will occur very easily. Let's look at where you would find these. These are going to have to be in smooth protected areas because there's no protected nature here at all. But where do we move a lot of material? Where do we need a lot of diffusion? So the key examples here, the two I think of are the alveoli or the gas exchange surface of the lungs is going to be a key example. The second key one I think of is the endothelium that lines your heart and your blood vessels. The reason that term is important is because the actual cause of hardening of the arteries, heart disease, plaque forming in your arteries is endothelial dysfunction. Now what triggers that depends on the person, smoking, stress, whatever. But this endothelium is this fragile epithelial layer inside your blood vessels and when that gets damaged, that leads to a response that leads to plaque formation and hardening of your arteries. So the alveoli of the lungs and the endothelium lining your blood vessels are the two examples I want you to remember. But there is like the mesothelium, so the lining of your ventral body cavities, the pericardial cavity where the heart is, peritoneal cavity in your abdominal pelvic organs, etc. That's another good example. But just think real thin and delicate. So no protection but you see a ton of diffusion, a ton of movement here. That is simple squamous epithelium. Stratified squamous epithelium is going to be multiple layers of these thin flat cells. So anywhere there's going to be, you need a lot of protection from either chemical or physical attacks. You're going to see stratified squamous epithelium. We do have to further break this down into two categories though. We have keratinized stratified squamous epithelium. These cells are going to be packed with this water resistant protein called keratin. This is going to be your skin is a keratinized stratified squamous epithelium and the roof of your mouth has some as well. The benefit of keratinized stratified squamous epithelium is these areas don't need to be constantly lubricated because the other type, this regular stratified squamous epithelium or non-keratinized stratified squamous epithelium, say that three times fast, very tough, resists abrasion but it needs to be constantly lubricated. So think about the beginning and end of your GI tract to be the key examples there. The mouth and the throat and then the other end you have like the anus and you'll see the vagina is also going to be stratified squamous epithelium. So those are the key examples, remember the key function here is going to be protection from chemical or physical attack and that stratified and simple squamous epithelium. I hope this helps. Have a wonderful day. Be blessed.