 Hey everybody, Dr. Rowe. In this important video, we're going to do an overview of all of the organs of your digestive system. So obviously we're going to mine deeper of each of these structures is going to have its own video. But I want you to have one place where you can get a really big picture look at what each of them are doing. So here you see the gastrointestinal tract. So we'll start there with the GI tract from the mouth of the anus. And as we're going, we'll also talk about what are called the accessory organs or accessory structures of digestion. And that's going to be your salivary glands, your liver, your pancreas and your gallbladder. The accessory is probably not a great word. They're extremely vital. What that means though is they're just not part of the GI tract. Let's go ahead and dive in. As we're going through here, I'll also talk about the names that we've, the different names we use for food as we travel through the GI tract as well. So you see here the oral cavity, you have the mouth, the tongue and the salivary glands. Their job is going to be to start to mechanically break down your food by chewing it and mashing it and lubricating it with saliva. And also, you know, your tongue is going to be moving it around your teeth and mashing it up against your hard palate, et cetera. But while this mashing and physical breakdown is occurring, it's also being mixed with saliva, which saliva is primarily water, but there's immune components there. There are digestive enzymes there as well. So digestion does begin in the mouth too. We have salivary amylase, which can help break down carbohydrates. And then the salivary lipase, which can help break down fat. So protein digestion doesn't begin in the mouth, but a small amount of carb and fat digestion does occur. And the oral cavity, then we're going to, then as we swallow food, food, which is now going to be called a bolus. So once you've chewed it up into this mashed up lubricated oval or whatever, it's now going to be called a bolus. So this bolus of food is going to be swallowed from your oral cavity to your pharynx through your esophagus into your stomach. So the stomach is basically going to be a chamber full of acid with a really low pH. There's also going to be digestive enzymes. The primary function of the stomach is to churn and mix food together. Mix it with this acid and then the digestive enzymes to continue the digestive process. When I think of the stomach, think of protein for sure, because the stomach acid, the hydrochloric acid in your stomach is going to denature the proteins that you ate. And then also the peps and the main digestive enzyme in your stomach is going to break down proteins too. So the more protein there's in a meal, generally the longer the food will sit in your stomach. So the stomach is designed to help you break down the protein in your meals primarily, but it'll break everything down. Let's see, one interesting thing about the stomach, we'll cover this more later. Your stomach can't actually tolerate stomach contents. There's a thick layer of mucus that's on the surface of the stomach. So your stomach juice, these digestive enzymes, these acids should never actually touch the stomach. There should be a nice thick layer of mucus there protecting the stomach itself. All right, once the stomach is done and it's turned your food into this syrup, which is called chyme. So you see on the screen there how to spell it. So it was food when you put in your mouth, it was a bolus when you swallowed it. So it's called chyme. Now this syrup is going to be squirted into your small intestines, maybe a teaspoon at a time. And now we're into the small intestine, which 80 to 90% of digestion absorption takes place in the small intestine. This is the most important structure we have. Like other animals, that isn't true. If you look at like gorillas, their hindgut fermenters, their large intestines is way more important than their small intestine, but we're the opposite. Which means we're probably designed to eat food that's been cooked and or easier to digest types of food. We don't spend, what is it, I think they spend about 14 hours a day, something like that. They spend over half their day eating, you know, vegetation and breaking it down in this huge, large intestine, but we don't, of course. So we have our small intestine, three parts of the small intestine. You have the duodenum, which I call the mixing bowl. The jejunum, which this is really where most digestion absorption takes place. Then we have the ilium, the last part of the small intestine. It's famous for being the longest portion. It's also where like some of your bile and some of your vitamins might be absorbed there. That's the small intestine. So as food travels through, or it's now called chym, as chym travels through the small intestine, it's going to be chemically digested and broken down. What we can absorb is going to be absorbed, and what can't absorb is going to pass through the small intestine, and now we're in the large intestine, which begins with a structure called the cecum, this pouch that receives whatever's coming from the small intestine. Then we travel up the ascending colon, transverse colon, the descending colon, the sigmoid colon, which is known for its S-shaped kind of curve there, down into the rectum and anus. So in the large intestine, the key functions are the reabsorption of water. Like you've spewed liters of fluid into your GI tract every day to properly digest and move and absorb food. You want to reabsorb most of that, or else you would always have diarrhea, and that would be life-threatening. So one of the primary functions of the large intestine, the colon, is to reabsorb water, and in the rectum and anus, their job is the temporary storage of feces. Then you defecate to get rid of that. So I won't go into it here, but again, another very important thing happening in your large intestine is this huge relationship we have with our microbiome. You have about as many microbial cells, bacterial cells as you do human cells, and they do perform thousands of metabolic functions for you. They help train your immune system. They can alter behavior, et cetera, et cetera. Not beyond the scope of our class, but still just so fascinating, I can't help but bring it up a little bit. So that is a quick overview of all of the anatomy of the gastrointestinal tract. Now we're going to go back and look there at the accessory organs, and we have the liver. So the liver is wildly important. The liver does hundreds of different functions. We couldn't list them all here. But its primary role with the GI tract is going to be the production of bile, because the bile that's produced will then be stored and concentrated in the gall bladder, and that bile is going to be used to emulsify fat. So we'll cover all that later. So fat is much, much, much more digestible and absorbable if you have bile. So liver makes bile. The liver also receives almost everything. Almost all of what's absorbed in your GI tract goes straight to the liver. So the liver determines, should I store this? Should I detoxify this? Should I transport this, et cetera? So the liver is very, very important at receiving. It gets the first look at almost everything that comes in from your GI tract. How does it make the liver important? We already mentioned the gall bladder. It doesn't make anything. It stores and concentrates bile, so you can survive without a gall bladder, because your liver would still make the bile. And then the pancreas. Obviously, you know the pancreas from earlier chapters. It's endocrine rolls producing insulin, to lower blood sugar after meals, and glucagon to raise blood sugar between meals. But now we're talking about the exocrine pancreas, the digestive portion of the pancreas. Its job is going to be to make bicarbonate, which is a buffer that neutralizes the acid coming from the stomach. And then digestive enzymes. So most of the critically important digestive enzymes that break down your food are gonna come from the pancreas. All right, so that is the gastrointestinal tract and the accessory organs we covered so live already. Okay, I hope this helps. Have a wonderful day. Be blessed.