Have you ever realized that at your deepest, most inner core you’re not really you. Well, think about it. The minute you eatsomething and swallow it and it passes in throughyour gastrointestinal tract, that’s the external environment. That food that you just took in was a part of the outside world, and the tract that it’sgoing to follow in through from your mouth till the point that you expel it in the bathroom is actually not you. That’s the external environment. How weird is that? So in this video, we’re going to do an overview of the gastrointestinal tract. I’ll talk about eachof the individual parts and what they’re main,overall functions are, and then in subsequentvideos I’ll go through each of these individual parts and give a more detailed explanation of how they do what they do. All right, so starting off, of course, the first place our foodis ever going to go to is our mouth, or the oral cavity. The main functions that wehave achieved in the mouth include chewing, the morcellation of food. Also very important is hydrolysis. As you might recall from biochemistry, hydrolysis is just the enzymatic digestion or the enzymatic breakdown. Where chewing is the physical breakdown, hydrolysis is the enzyme-assistedbreakdown of food. So as we break down food, the goal here is to make what’s called a bolus, just a sphere of digested food that can then be swallowed and passed on into our next structure. After we swallow the food, where do you think it goes? This guy right here, andthat’s the esophagus, the esophagus. This, I think, is oneof the more boring parts of the GI tract, because all we do here is just propel our bolus. We just pass it on down to the next guy. We don’t even really do anything to it. Kind of boring. But the next guy is alittle more exciting. Now we get to the stomach. A lot of action going on in the stomach, one of my favorite parts of the GI tract. The stomach is responsiblefor multiple things, including churning, whichis a lot like chewing, except that there aresort of more dimensions of contraction affecting the food and breaking it down. We also have hydrolysis going on here, the enzyme-assisted breakdown of food. In addition to that, you canstore food in your stomach if it’s not time to pass it on to the next component of your GI tract. The overall goal here is tomake what’s called chyme. So we take our bolus, and wesort of melt it down, per se, into this more fluid type of substance that we can pass on to our intestines. So we’re moving on now to our intestines.

Starting now from aboutthis point right here, we get our duodenum, and then this kind of circulates around here, and then we end up at this point. Everything in between,I’ll draw it way out here, I’m just going to grouptogether for right now as the small intestine. The small intestine. There are three parts to this, and we’ll talk about thatin a subsequent video, but the main functionsthat we achieve here are hydrolysis, and also theabsorption of nutrients. Notice this is kind of thefirst part of your GI tract that you’re finally takingin some of the break down food products, andusing them for nutrition to make other products in your body. Great. Now that we have gone through the small intestine, whatdo you think shows up next? Starting from after thesmall intestine ended, all the way through thislined structure right here, we are going to be passingthrough the large intestine. The large intestine. Do you guys remember the othername for the large intestine? It starts with a C. If you said “colon,” absolutely right. The colon is also one of the more boring parts of the GI tract, because really all we have going on here is absorption, but notof nutrients per se, more like things like water,or ions, or vitamin K, just things like that are absorbed in the large intestine, so not a very high yield place for acquiring nutrients. Then after that, we’regoing to pass food on to this structure here. This is called the rectum. The rectum. Kind of like the stomach of the GI tract, the rectum serves for storage, We hold on to our processed food, if we can call it thatanymore at this point, and it’s held there until we deem it an appropriate time to expel the food. So when it’s time to expel the food, it’ll come out through the anus, through expulsion, expulsion.

So those are all the key components of our gastrointestinal tract. There are some other accessory organs that are involved here in digestion, and I’ll have videos thattalk about them as well. Those include things like the liver, the gallbladder, the pancreas, and those will come upin subsequent videos.

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