 Hello, everybody. Today we're going to talk about the digestive system, and we're going to start out with our study of the gross anatomy of the digestive system by looking at some of the functions of the digestive system. So let's get started making a list of functions. I have six primary functions, and I'm actually, I can't help it. I have to draw you, even though I've got this lovely picture right here, I could use this picture. But you know what? We're going to get into the anatomy of all these parts and who these people are and what part is what in way more detail than we've got going on here. But I can't help it. I have to draw you a picture of your own digestive tube. Does this look familiar? You know it does. We did this, we drew this body when we were talking about epithelial tissue. Do you remember that? And remember how I had, oh, what is this? A smiling happy mouth. And what is this? I'm going to make it look like a sphincter. Dude, I'm not even going to comment on that. That's your anus. This is your digestive tube. We're going to name all the parts in this lecture, but I'm going to draw you a picture of all the functions of the digestive system. And we're going to start with the first one, which is basically ingestion of food particles into the mouth. One of the jobs of the digestive system is to ingest food. That makes sense, doesn't it? Imagine that. And look, I even drew it for you. Guess what? Another function. You have to draw you a piece of food that came in. Another function of the digestive system is to digest the food. Really? True story. What is digestion? Well, basically, when you digest something, you break it down into littler parts. How great is this? Look, I'm even going to label these. Digestion, this was number one. Digestion, this was number two. I broke it down into pieces. In our digestive system, there are two ways that we break things down. We can break things down chemically, or we can break them down mechanically. That says mechanically. Of course it does. When you break something down chemically, you actually add a chemical to it, and the chemical breaks the chemical bonds in the original substance, creating smaller particles. That's what digestion is. When you break something down mechanically, you actually apply a force to break the particles apart. The end result is exactly the same. You end up, you start out with a big particle, you end up with lots of little particles, which again is the definition of digestion. The third thing that happens in the digestive system, I'm going to draw it in a different color. The digestive system, the whole system moves substances through it. So it's called motility, but basically you're moving the particles through the GI tract. So look, I'm going to draw it like this. This is number three. These particles move, and I'm going to try and make my little purple particles. They just move through the digestive tract. As we examine our entire system, we're going to see different parts of the tube, and we're going to name all those different parts of the tube. And we'll notice that different parts of the tube have different functions, like different things are happening in each of the parts, but we have to move the food through the tube in order to get from the start to the finish, which makes complete sense. Of course it does. We also have, I love this one. Another function is secretion, and it's probably a good idea. We're going to see secretion in lots of different scenarios. Secretion is when, like, body cells, this is familiar to you, I know, that the epithelial cells lining the lumen of my digestive tube actually are producing substances, digestive chemicals, mucus, other enzymes. Even sometimes some waste products are actually secreted into the digestive tubing. But when a substance is moved from the inside of the body into the outside, into the tube, the process is secretion. Are some of these familiar? They're totally functions about the epithelial tissue, which is what the tubing is lined with. All right, number five. Why are we doing all, why? Digestive system, why? Because you're hungry. Your cute little cells are starving. And so another function of the digestive system is absorption. Again, hopefully familiar because this is actually a function of the epithelial tissues themselves. So once you break down your chemicals, your food, it gets digested into smaller pieces, what is the point of breaking it into smaller pieces in the first place? Well, your cells actually cannot use the hamburger directly. Your cells have to use the molecules in the hamburger. They can't make energy that you can use in an entire hamburger. So break it down. Don't leave it in the tube because guess where the tube is going? Yeah, that direction. Anything you leave in there is going to end up in your toilet. Hopefully it's your toilet. I don't really want to think about that too much. But anything that we want, we better get it out of there through the process of absorption. That's handy. And then anything that's left over, yes, the things that are left over. So we're going to take the little purple squares and anything that's left, we're going to eliminate elimination. Interestingly, the way we eliminate stuff in the digestive system is by going poo poo through the anus. So literally diarrhea. Diarrhea is awful because it's a huge issue if you have diarrhea and you can't get it under control because you actually are going to poop out all your nutrients. You're going to eliminate all of that stuff before you can absorb the good stuff. You can't absorb the water back in. You can't absorb the nutrients back in because you are pooping it out so fast that it is gone before you can absorb it. Those are all... That's a big picture overview of our functions of the digestive system. And now we're going to break down each individual part of our tube and talk about the unique features found in that part of the tube and some of the anatomical features and then some of the functions in each part.