 Thank you, guys. So today's topic is all of the histology that we will look at over the entire semester. And if that feels a little overwhelming to you, that probably means your brain is engaged and you're thinking about what we're about to do. All the histology that we're going to cover throughout the entire semester consists of 20 different types of tissue. So really, it's not as bad as it's going to seem. And all we're doing today is identifying the tissues by site. You should be able to look at a microscope slide and identify what kind of tissue is in there. And you don't have to know anything else except the tissue type. And I'm going to argue that by the end of this lecture, you will be ready to tackle that perhaps rather daunting task. So look at this. Where have we seen this before? Theme, why are we talking about theme number two from the last lecture? Well, my friend, Lise, let me tell you why we're doing this. I want to just review the hierarchy, the organization of living systems. I want to review it because I want you to constantly be thinking about where we are in the organization of the body systems or the human organism. So let's start by reminding ourselves that the organism is the biggest level of organization that we will be playing with in this class. And the human organism is made up of organ systems. And today, we are not looking at organ systems. In fact, we probably might not even mention them. Organ systems are made up of organs. And I'm going to tell you right now that we will look at organs today, but if you don't even think about it or... I'm certainly not going to test you on the organs that we're going to look at today because really all we care about are the tissues. And tissues are the groups of cells that work together for a common function and they make up the organs, that make up the organ systems, that make up the organism. Tissues are made of cells. And we know that the cells have within them or are made up of cellular organelles. So this is just review, right? You already know all this stuff. Like, dude, why are we doing this? Because histology... histology is the study of tissues. I wish I had better handwriting on this little tablet, but at least it's working today, which is a very happy thing, knock on wood. All right, so histo, we're focusing on tissue land. Now, there are obviously tissues are made up of cells, many different kinds of cells. In fact, I'm going to just throw this out there that, you know, in the human body, there are around 200 different kinds of cells. And if you take those guys and you combine them in different proportions and give them a job, you come up with your tissues. There are a couple cells that you're going to have to identify today, but not very many. There are a few organelles that we're going to know today. And the reason why we're going to know some organelles, like, think about this for a second. In fact, I think there's four. There's more than four organelles in your body. Let's do it like this. There's four that we're going to know today. And the reason why we're going to know these four is because we can actually see them. And identifying cells and cell parts that you can see helps you know what's a cell, what's something else, because probably at some point in lab, when you're looking at tissues, you're going to be like, dude, it looks like a flamingo vomited in this microscope and everything is pink. And sometimes it looks like that. And hopefully by the end of class, you'll be able to sort of decode the flamingo vomit. Identifying the cell membrane is something that will help you decode the vomit. Identifying the nucleus. If you can see the nucleus, you can be like, oh, that's a cell. Cool, I know that. Sometimes in the nucleus is a nucleolus. And the nucleolus is sometimes visible, sometimes not. If you're not careful, sometimes you think the nucleolus is the nucleus and the nucleus is the cell. So this is why sometimes we need to focus on these things. And then there's one more cellular organelle. Ah, the cytoplasm. The cytoplasm is just the fluid between the cell membrane and the nuclear membrane or the nucleus, the outline of the nucleus. And so anything, any space, you can't really see the cytoplasm, but you know that it's there or it was there in life. These four organelles, it's all you're going to need. That's going to help you identify the cells, which are going to help you identify the tissues and see what's going on. Now, what is a tissue? Let's do a definition, my friends. Shall we? Tissues are groups of cells, groups of different cells. Working together, don't mess with me. You don't mess with me. For a common function. If there's a group of cells and they're like working together, but they're not doing the same job, they're like working right next to each other, they probably are not part of the same tissue. They have to be working together for a common goal. So there are four tissue types, four big picture tissue types in the human body, and that's what we're going to talk about in today's lecture. The first tissue type is epithelial tissue. Yeah. Epithelial tissue. You know what? Most of the time, especially in anatomy, we do not allow abbreviations, for some reason we allow epithelial tissue to be abbreviated ET. Epithelial tissues, line spaces. And we have a couple, there's six different epithelial tissues that we're going to look at, there's actually more of them, and we'll talk about those next. In addition to epithelial tissues, which line spaces? There are connective tissues, or CT, another one you're allowed to actually, what's the word, abbreviate. I'm not even going to try to put a function or a definition for connective tissues, because basically they're crazy diverse, they're crazy diverse in structure and function, but there are 20 tissues that we're looking at today, 10 of them are connective tissues. So half the tissues we're looking at are connective tissues, and you really can't say all connective tissues have this function, you just can't. You can definitely say all epithelial tissues line spaces. Like that's something that, if you see a space, you know that there's going to be an epithelial layer right next to that space. So connective tissue, we're going to have to spend some time on it. The next tissue type, muscle tissue. That might be my favorite tissue, I mean I love them all, but muscles, muscle tissue is a contractile, and it's contractile because it actually has proteins that move, where they bind to something and then they move and that causes shortening of the tissue itself. Like muscle cells actually shorten, and when you stick one end of the cell on one thing and the other end on another thing, if you shorten it, you can actually move things. So muscle is a tissue for movement. And then our last tissue type is nervous tissue, don't worry, it doesn't stay nervous all the time. Sometimes it relaxes. Nervous tissue is responsible for coordinating communication. Let's just say communication. And it does this through electrical messages, which, oh my gosh, it's so freaking cool. And we're looking at one type of nervous tissue, we're looking at three types of muscle tissue. So muscle tissue and nervous tissue, really not a lot of stuff we're going to look at here. All right, so we're going to start out this survey looking at epithelial tissue, and let's start with kind of a broad overview of structure and function.