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Raja Narayan 创建




did you know that the human stomach can store up to four liters of food at any time that's about as much as two coke bottles insane so in this video we're going to see how our stomach helps us process food it just received from the oral cavity and the esophagus so why don't we take a look just at the stomach here and I'll zoom in on it so that we can talk exclusively about what this guy is up to the stomach is primarily responsible for three steps first of all it's going to receive a bolus of food from the esophagus above this bolus is just food that's been turned into a sphere that can now be processed then the stomach can do two things here to help process the food even more the first thing the stomach does is that it churns this bolus or it churns the food the muscular walls of the stomach here allow it to compress down and break up this food even more in addition there's also a certain degree of hydrolysis hydrolysis or enzyme assisted degradation or breakdown of this bolus and we'll talk about the enzyme that's responsible for this process in a moment and that finally after we do all these things we receive a product that's called chyme chyme is just a mixture of whatever the bolus has been broken up to including the gastric enzymes and juices that we've used and then the food is going to actually just stay here for a little bit because the stomach also stores food it'll store the food until it's an appropriate time for the chyme to be squirted into the duodenum or the first part of the small intestine to be processed and that's why we can store up to two to four litres of food at any given time now what about the anatomy of the stomach here how do we release these enzymes and break down this bolus let's take a look at a little bit of gastric anatomy right about there and see how it's responsible for the breakdown of food here we can imagine that the stomach is lined with all these in foldings these in foldings of the gastric wall that helped to increase the surface area and in doing so there's actually a layer of cells that sit around here this layer of cells actually secretes a lot of the components of the gastric juice we're going to see and it's nicely ripe with a ton of important components and the main thing to remember in the stomach is that there are three types of cells that are involved here the first type I'm gonna talk about are called parietal cells parietal cells and the main thing that's released from parietal cells is hydro chloric acid hydrochloric acid it's a very acidic or a very corrosive acid that's actually more acidic than battery acid in addition to parietal cells we also have chief cells chief cells these guys secrete an enzyme called pepsin again pep Sinnoh gin and this is the inactive form of the enzyme pepsinogen is not active in fact in order for hydrolysis to occur we need an enzyme that's called pepsin how is pepsin made well we're gonna need pepsinogen to make it but the pepsinogen and whenever you see Jin GE n at the end of the name that means that it's almost there it's just needs to be processed in order to turn pepsinogen into pepsin we need hydrochloric acid which will break down this protein to turn it into this active form that can then be used for hydrolysis now what would happen if we just had a bunch of pepsin or a bunch of hydrochloric acid present in the stomach all the time what do you think would happen to the stomach they would probably eat itself alive isn't that right I mean you've got your cell membrane that definitely has a considerable amount of protein that should be present there and in addition you've got this really corrosive acidic substance that can eat through your stomach and that's actually how you have gastric ulcers but not all of us have gastric ulcers we also have in our gastric pits right here that help us prevent gastric ulcers from occurring in the first place well the third type of cell that we have sitting in here are actually called mucous cells mucus cells and just like the name suggests mucus cells release what's called mucin and this is a coating that will sit around the stomach to make sure that things like pepsin or hydrochloric acid don't degrade the stomach without mucus cells we would eat ourselves alive so as a review the three things the stomach will do for us is that it'll churn with it's very muscular walls to help break down the bolus in a very physical activity also there's an enzymatic or a chemical process that occurs here where we use pepsin to degrade food now pepsin itself only degrades one type of nutrient and that's protein this will break peptide bonds or the bond that connects amino acids to one another to degrade your protein macromolecules so that's the only type of nutrient that's broken down in your stomach once we hydrolyze a significant amount of the protein we're going to produce chyme that is stored in the stomach until it's the right time for it to be released into the next part of your GI tract called the duodenum the first part of the small intestine and that's how your stomach works