As we talk about the stomach, we need to introduce sort of the major regions and structures of the stomach. In other words, we're now gonna go over the gross anatomy of the stomach. Alright. So here we have an image of the stomach. You can see the, esophagus entering in over there, and here you can see the duodenum or that first region of the small intestine that chyme will enter as it leaves the stomach. So let's just jump right in and start naming regions here. The first one we want to identify is called the cardia. So the cardia, we've highlighted here in green, and we're going to say that this is the upper portion near the junction with the esophagus. So remember, to leave the esophagus, the bolus is going to pass through the cardiac sphincter. So it passes through the cardiac sphincter into the cardia. And cardiac, remember, that refers to the heart. So these are sorta right up at the top of the stomach, right next to the heart. Alright. So we move from the cardia, and then the next region we want to talk about is this part where it sort of bulges upwards. The stomach actually sort of goes up a little bit from where it joins with the esophagus, and that part is called the fundus, and we've highlighted it in purple here on our image. So the fundus, I sort of think of as the roof of the stomach. It's that region where, again, it sort of bulges upwards a little bit even above where the esophagus joins. Well, our next one, this is really the majority of the stomach we're going to call the body. So here we can see the body, most of the stomach here. We're gonna say it's that main j shaped region. It has this sort of curve to it, kind of like a j. But you will notice there's another word you may need to know for this. Sometimes the body is called the corpus. If you do need to remember corpus, I still remember it as body, and I just remind myself that a dead body is a corpse. So that corpus or body, that's the main section of the stomach. Alright. As we come down, we have one more region that we need to talk about. This final region, we're actually gonna break up into some smaller regions, but let's look at the whole thing first. We call this the pyloric part. Now, that second word part, that's actually part of the name. It is called the pyloric part, and that name comes from well, pyloric comes from the Greek for gatekeeper. So this final region of the stomach is the gatekeeper. It decides what kind goes in gets to leave the stomach, go gets to go through that final sphincter and enter into the small intestine. But we can break this pyloric part up into 3 different sections. So let's look at them. The first one we are going to call the pyloric antrum. And you can see we've highlighted that here in pink. The antrum is just that first part connected to the body. And it's not what it means, but that word, antrum, reminds me of the word entry. So the pyloricantrum, I think of as the entry to the pyloric part. It's just the first part you come to. Alright. So from the pyloric antrum, then we have the pyloric canal. This is as this pyloric part gets narrower heading towards the small intestine, you reach the pyloric canal, and we're just going to say that this is the final section before the sphincter. Well, the sphincter, that's our last region of this pyloric part. The pyloric sphincter, this is the valve that separates the stomach from the duodenum. So there is a valve at the end. A sphincter, remember, a sphincter is just a muscle that squeezes down like this. So when it's squeezed down, chyme can't leave the stomach. When it loosens up a bit, that chyme can pass through that pyloric sphincter and enter into the first section of the small intestine, the duodenum. Alright. Now I realize remembering these can be a little difficult. It may just seem like a bunch of random words. The way I remember it I got a little memory tool for you here. I say, hey, my car is fun, but the body is a pile of junk. Alright. So my car, the cardia, is fun, the fundus, but the body, the body or corpus is a pile the pyloric part of junk. Alright. So those are the major regions of the stomach. There are a couple other things we need to note here. You'll note where we cut away the stomach to see the inside. When you see the inside of stomach, it has this really wrinkly appearance. And if you've ever eaten stomach, or tripe is what it's called, it's very noticeable. Well, the wrinkly appearance is because of the rugae, and the rugae are inner folds in an empty stomach. The stomach can expand a lot, and so when it's stretched out, you don't have these rugae. But when it's not stretched out, the stomach gets a lot smaller and that sort of extra tissue kind of folds up and makes all these wrinkles that are really noticeable in an empty stomach, again called the rugae. Alright. The last things we want to note here are the curvatures of the stomach. There's 2 curvatures we want to call out. The first is the lesser curvature. And so we can see here there's sort of this sort of sharper, smaller curve on the inside or upper part of the stomach there. We're going to call this the inside curve. And then we also have the greater curvature, and you can probably guess where that's gonna be. Well, on the outside of the stomach here, we have this big curve. That's the greater curvature, and all I'm gonna say here is that's the outer curve. Alright. So that is our gross anatomy. We're gonna dive in and look at this tissue and figure out what makes up the wall of the stomach next. It's gonna be fun. I'll see you there.
2
example
The Stomach Example 1
Video duration:
4m
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Video transcript
Alright. Our example here says that below is an image of a stomach in cross section taken from a cadaver. Now for each number, correctly label the region or structure by writing the corresponding letter from the list. So we see here, here is the stomach in cross section. We can see the esophagus is up at this end, so, the bolus would enter in this way, and then we have the duodenum or the small intestine down at this end, so the chyme would come out in this direction. We see these different numbers on here that we have to fill in. We see our list here. It looks like it's in alphabetical order from a through h. Alright. So as we go through this, first, I just wanna remember those major regions of the stomach. Let me see if I can pull those up off the top of my head. Remember, we had a memory tool for that. So do you remember those 4 major regions? Well, I said the car or my car, that's the cardia, is fun, that's the fundus, But the body the body is a pile, a pyloric part, of junk. Alright. So those are the 4 major regions, and we said that was basically in order. So knowing that, we should be able to put these on the lines in the right places. So where do you want to put the cardia? Cardia here is letter b. So I'm going to place that one first. Well, as you enter the stomach, you enter right here at number 5. So that's the cardia. Now what about the fundus? Fundus here is c. So where am I gonna put that? Remember, the fundus is that part that sort of sticks up a little bit next to the cardia, so c is gonna go on this line right now next to 6. Alright. Then what about the body? Well, body's letter a here. So which part is the body? Well, the body, that's the main part here that's gonna get the a right next to 7. And then pyloric part, remember we had different, parts, different regions of the pyloric part. We have three things that we're gonna label here. So that means that these three here are other regions the stomach. That's all gonna be part of the pyloric part. Alright. So let's label those. Well for me, the first and easiest one to do is actually the sphincter. So which number here do you think represents the pyloric sphincter? Pyloric sphincter, remember, that's the way out of the stomach. That's that valve that regulates what can leave the stomach. So I'm gonna put h on number 1. That's that sphincter there. And then we have the pyloric antrum and the pyloric canal. Now the way I remember these 2, remember I said that that word antrum kind of reminds me of the word entry. So it would be the entry into the pyloric part. So knowing that, which which letter would you put on each line? Well, I'm gonna say that well, the chyme is gonna sort of gonna enter the pyloric part in this direction. So the entry to the pyloric part, that antrum would be on, number 3 there. So that gets the f, and then it's gonna narrow down for the pyloric canal that gets the g. Now in real reality, these are probably labeled a little bit too far or over the antrum and the canal would really be a little bit closer to the pyloric sphincter, but we get the idea. Alright. Well, we got 2 more things to label here. We have the greater curvature and the lesser curvature, and lucky we, I got two arrows there that show curves, and one's bigger than the other. So which one do you think is the greater curvature? Well, I'm going to say that that is number 8 here. D because that's the outside curve, which is bigger. And then the lesser curvature would be number 4. I'm gonna put the e on that line because that inside curve is smaller. Alright. We got one more question here. What do we call the wrinkled structures visible on the inside of the stomach? So when we look at the stomach, we see these wrinkled structures here. We said that those are present when the stomach is empty and they kind of go away when it's filled. Do you remember what those are called? They were the rugae. Alright. And with that, we've labeled our stomach. We've answered our question. Example problems after this. Give them a try.
3
Problem
Problem
Food entering the stomach will first pass through the:
A
Fundus.
B
Body.
C
Pyloric antrum.
D
Cardia.
4
Problem
Problem
Which area/structure is NOT a component of the pyloric part of the stomach?
A
Pyloric fundus.
B
Pyloric antrum.
C
Pyloric sphincter.
D
Pyloric canal.
5
concept
Layers of the Stomach
Video duration:
6m
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Video transcript
Now that we've introduced the gross anatomy in the stomach and we've identified the major regions of the stomach, we wanna zoom in on the stomach wall and identify the layers of that stomach wall. So we're gonna just start by saying that the stomach wall contains the same four layers as the rest of the GI tract, but with certain modifications. So remember from your esophagus to your anus, the structure of that alimentary canal is basically the same, but there are some gonna be some unique things along the way, and here we wanna identify those unique things in the stomach. Now before we do, let's just orient ourselves to our image here. We have a cross section of that stomach wall. It's not exactly to scale, but it's drawn so that we can see the different layers clearly. Now in this drawing, the lumen would be sort of up here at the top, so that's sort of the inside of the stomach. You'd then go down through the wall 1, 2, 3, 4 layers there, each shown in a different color. And then the outside of the stomach, that would be down at the bottom. Alright. So the first layer we wanna talk about, the top of our drawing here, this is that innermost layer, the mucosa, and we'll just note the mucosa, that's the part that's closest to the lumen. So the stomach acid, the kind that's in the stomach, it's gonna be up against this mucosa. Alright. So the mucosa is gonna be made of mucus cells. That's gonna be that stomach epithelium, and it is going to be simple columnar cells. And now simple columnar cells, they make up that epithelium of the entire alimentary canal, and we can see those in our drawing here. That's these cells sort of lining the tops there in pink. But what makes it unique in the stomach is we're gonna have this mucosal barrier, this thick alkaline mucus that is there for protection. Alright. Alkaline, that means basic or a high pH, because remember, the stomach is filled with acid. This really corrosive low pH liquid. So the stomach lining has this thick mucus barrier that's alkaline to protect the cells underneath. You don't want that acid digesting or breaking down those cells underneath it. And if there's a break in that mucosal barrier, well, then you will have damage to the stomach lining, and that's what we call an ulcer. And you don't want that. Alright. Now we have that mucosal barrier, but also between all the cells, we're gonna have tight junctions. Those tight junctions are also gonna prevent that leakage of the gastric juice. Alright. Now it's not a smooth lining as you can see here. Well, remember, we have the rugae of the stomach, but here we're talking even at a smaller level. At an even smaller level, you can see all along here these sort of holes. And these holes, well, you can see they lead down to glands that are down here deeper in the mucosa. But right now we're just talking about sort of these holes and the starts of these sort of tunnels leading into the mucosa. Those are called the gastric pits. The gastric pits are these openings to the glands or the gastric glands. Now you can see these gastric glands here sort of deep in the mucosa there. We're not going to talk about them here because we're going to go into a lot more detail on those in a future video coming up. Alright. So that's the mucosa. As we move down from the mucosa, we reach the submucosa, and that's this layer here. And the submucosa is connective tissue with arteries, veins, and lymph vessels. That's basically what it is throughout the entire alimentary canal. There's nothing really unique that you need to know about for the submucosa in the stomach, so we're not going to spend much time on it. Alright. Moving down from there, we reach the muscularis externa, and that's this section here, that muscular wall of the stomach. Now the stomach is going to have 3 layers of muscle. Now if you know your alimentary canal and your muscularis externa, that may have sort of your ears may have heard something funny there because the rest of the alimentary canal has only 2 layers. So in the stomach, we have this oblique layer, and that's gonna be the innermost layer. So in our image here, it's this layer, this top layer here. You can see we sort of try to draw the, the the cells there sort cut at a bit of an angle. So oblique means at an angle. So it means if you think of the sort of length of the stomach, this layer is running sort of at an angle to that length. So it's the innermost layer, and we are gonna say here it is only in the stomach. This stomach has an extra layer of muscle, meaning it is an extra muscular portion of this alimentary canal. Alright. Now, outside of the oblique layer, we have the circular layer. That's that middle layer that you see here in this drawing. Here, we're sort of trying to show those cells cut in cross section there. That circular layer, like the rest of the alimentary canal, the cells are running sort of perpendicular to the length of the alimentary canal. So when they, squeeze in, they squeeze in in a skirt circular way. Then we have the longitudinal layer. That's this layer on the bottom. That's the outermost layer and the longitudinal layer. Those cells are running lengthwise sort of parallel to the length of the alimentary canal. So when they contract sort of the whole alimentary canal, the stomach would sort of almost shrink in length. Okay. So that's that muscularis externa. The important part, the the stomach has that extra oblique layer. Alright. Finally, we have the serosa, and here we see the serosa in green on the outside. And remember, in the serosa here, that's that peritoneum. And since it's attached to the stomach wall, it would be the visceral peritoneum. Now remember the peritoneum, it's covering really the majority of these digestive organs, so it's a really complex membrane. In this section on the stomach, we just want to note that it's going to be continuous with the momentum. So coming off, sort of, the lesser curve and the greater curve of the stomach is going to be this peritoneum, and it goes into these portions where the peritoneum doesn't directly attach to other organs and it makes sort of like a sheet. And those sheets are called the lesser and the greater omentums. Those are really, noticeable, especially if you do a dissection. So especially if you're doing a dissection class, there's a good chance you're going to have to identify those. Alright. So that's the stomach. We're gonna dive into those gastric glands and see what's being made there in a lot more detail coming up. But first, we have example and practice problems. You should give them a try.
6
example
The Stomach Example 2
Video duration:
1m
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Video transcript
Our question tells us that a peptic ulcer occurs when the lining of the stomach is breached and gastric juice digests the underlying tissues. Most peptic ulcers are caused by a bacterial infection caused by the bacterium h pylori. Alright. So our question then is a, which layer of the stomach would you expect to be most vulnerable to damage by ulcers? And it lists the mucosa, the submucosa, the muscularis, externa, and the serosa. So what do you think? Alright. Well, the innermost lining of the stomach, that is the mucosa. But in a peptic ulcer, it says that that innermost lining is breached and the underlying tissues are damaged. That would be the submucosa. Alright. So the submucosa and ulcer is actually defined by the mucosa being breached and the submucosa underneath it being damaged. Alright. Now what structure or features in the stomach prevent, prevent gastric juices from damaging that tissue? Well, remember we said we had a mucosal barrier, and that mucosal barrier, that was a thick alkaline mucus to protect those underlying tissues. Alright. With that, we know we don't want an ulcer. We got practice after this. Give it a try.
7
Problem
Problem
Which layer of the muscularis externa only exists in the stomach?
A
Oblique layer.
B
Circular layer.
C
Transverse layer.
D
Longitudinal layer.
8
Problem
Problem
Rugae are formed by the two inner most layer of the stomach adjacent to the lumen when the stomach is empty. Knowing this, which stomach layers form the rugae?
A
Muscularis externa & Mucosa.
B
Submucosa & Serosa.
C
Submucosa & Mucosa.
D
Serosa & Muscularis externa.
9
concept
Stomach Glands
Video duration:
7m
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Video transcript
Now I wanna zoom in on the stomach mucosa just a little bit more and talk about the stomach glands or what we're gonna call the gastric glands. And that's because these gastric glands are gonna produce the liquid that does the chemical digestion in the stomach. So we'll start off just by saying here that within the mucosae, there are specialized structures that secrete that liquid that we are gonna call gastric juice. And gastric juice is going to be this acidic, enzyme rich fluid. And so the acidity combined with those enzymes, that's what's gonna do that chemical digestion. Alright. As we look at the structure here, there's gonna be 2 major structures we want to identify. 1 we've looked at, briefly before and that's those gastric pits. These are the tunnel like structures connecting the gastric gland to the lumen, and as you travel down that gastric pit, travel down that tunnel, you will reach the gastric gland. So in our image here, you can see this would be the lumen or that inside of the stomach here, and we see some gastric pits, and then we see one in cross section, that tunnel like structure, and as you go down it, we reach the bottom half of this image, which is the gastric gland. We have all these cells that are color coded there that we're gonna talk about as we go. So we can label this the gastric pit is a sort of top half. Oh, I spelled that wrong. The gastric pit is this top half of this image here, and the gastric gland is the bottom half that we're gonna talk about. Alright. So gastric glands, let's identify these cells. First up, we have the mucus neck cells. So we can see here we have all these sort of purple cells near the top, and their name tells you most of what you need to know about it. They are mucus neck cells. They're in the neck, so the sort of top part of the gland. And what do they make? They make a mucus, and it's an acidic mucus. Now remember the lining of the stomach, we have all these mucus cells. They make an alkaline mucus, and that alkaline mucus protects the stomach from the acidic, gastric juice. The big difference here is as you get into this gland, well, these mucus neck cells now make an acidic mucus. Now just to be really clear, the acidic mucus, this is not what makes your gastric juice acidic. We're just talking that the mucus changes from alkaline to acidic as you enter the gland. Alright. What makes your gastric juice acidic then? Well, that's gonna be the parietal cells. The parietal cells, you can see here, sort of spread around in blue, and they have this kind of unique, like, forked structure to them that you can see there in the image just a little bit. So we said they make that gastric juice acidic by MACH ing hydrochloric acid or as I'll write here, HCl. So they make HCl and also importantly a protein called intrinsic factor. Intrinsic factor. Alright. Well, let's first talk about the hydrochloric acid. Hydrochloric acid is gonna participate in that chemical digestion, chiefly by denaturing proteins. Now remember proteins are three-dimensional structures made up of long chains of amino acids. So to denature them means to break up that three-dimensional structure, but not to actually break the bonds between the amino acids yet. That's gonna happen from enzymes later on. Now it's also going to kill bacteria. Right. You take a lot of bacteria in when you eat and you don't want that stuff, all of that stuff, colonizing your body. So one of the first lines of events is this hydrochloric acid. It's gonna do some other chemical digestion as well. For example, it helps to break down some cell walls so that enzymes can digest the insides of cells and plants and so on. But we want to focus in on those proteins and killing bacteria. Alright. We also have intrinsic factor. And intrinsic factor is this protein that's gonna be important for vitamin b 12 absorption. Now you don't actually absorb your vitamin b 12 until later on in the small intestine. But we need to call this out here because if you don't get the intrinsic factor, this protein in the stomach, you won't absorb that b 12 later on. Alright. Our next type of cells is going to be the chief cells. And, well, if the parietal cells made the hydrochloric acid that participated in chemical digestion, It's the chief cells that makes the enzymes. And so we see these sort of down near the bottom of these gastric glands and these orange cells there. And so we're gonna say here that these make these enzymes pepsinogen and lipase. Now technically, pepsinogen isn't an enzyme. It's an enzyme precursor. And under acidic conditions, like in the stomach, pepsinogen, this enzyme precursor, gets converted into the enzyme pepsin. Right. So we have 2 enzymes there that are now active, sort of, produced by these chief cells, pepsin and lipase. Pepsin is an, enzyme that digests proteins. So we had the HCL, the hydrochloric acid that denature the proteins. Now the pepsin can come in and actually break some of those bonds between the amino acids. Lipase. Lipase is gonna digest fats, and we can break down that word. Ace means it's an enzymes. What does it break down? It breaks down lipids. So lipids lipase digest fats or lipids. Now protein digestion and lipid digestion is going to continue with enzymes in the small intestine. In fact, most, lipid digestion happens in the small intestine, but these do get started here. Our final type of cell that we want to talk about is going to be enteroendocrine cells. And enteroendocrine cells, you can see in green here. Just a few of them compared to everything else, and we can break down this word. Entero means gut and endocrine, well, refers to endocrine function sending out hormones. So these cells release hormones and paracrine molecules. So hormones are chemical signals that travel in the blood. Paracrine molecules are chemical signal that signals cells nearby. So it's gonna release both of those, and, actually, some of the molecules, it just depends on what they attach to, whether they act as a hormone or a paragon molecule. So just some examples here are things like histamines, gastrin, serotonin, somatostatin. I just want to call out gastrin as one of those things that does both. Gastrin, if it, binds to one of these, parietal cells, is gonna instruct them to start making stomach acid. However, if it ends up in the blood, there's also gonna be target cells for that gastrin in, for example, the gallbladder and the pancreas, which is going to instruct them to get ready to, to release the fluids that they either store or produce. Alright. Now as I look at all of this, honestly, I can remember mucus neck cells and enteroendocrine cells pretty well, but I always get parietal cells and chief cells confused. So to keep this straight in my head, we have this little memory tool. We have parietal cells lower pH. Chief cells chop the proteins and also the lipids. Right? So the parietal cells, remember, they make that hydrochloric acid that affects pH. Chief cells, they make those enzymes, which cut cut things up like proteins and lipids. Alright. With that, we have examples and practice problems to follow. Give them a try.
10
example
The Stomach Example 3
Video duration:
2m
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Video transcript
Our example asks us to match the molecules below with the cell type that secretes it. And it says that certain cells may secrete more than one product and not all molecules may be used. So we have 4 cell types here. We have enteroendocrine cells, we have mucus nut cells, chief cells, and parietal cells. Alright. So we have our different molecules here. Let's go through them 1 by 1. What about HCl? What secretes that hydrochloric acid? Well, we said the p in parietal is for pH. So parietal cells release that HCl, so I'm going to put an a here. Alright. Then what about hormones? Well hormones are part of the endocrine system, so it's going to be those entero endocrine cells that release hormones. So I'm going to put a b there on line number 1. Alright. And then what about pepsin? Well, remember, the chief cells chop the proteins, we said, because they release those enzymes, which break up proteins and pepsin is that enzyme. But technically, chief cells, remember, release the precursor molecule pepsinogen, and pepsinogen gets converted into pepsin in the stomach. So if we're being real technical, pepsin doesn't get secreted. Pepsinogen gets secreted, and pepsinogen gets converted to pepsin. So I'm not gonna put a c anywhere here, but as I look down f, well, f is pepsinogen. So I'm gonna go ahead and put, pepsinogen on that line next to those chief cells because those chief cells chop the proteins. They make the pepsinogen, which gets converted to pepsin, which digest proteins. Alright. Well, that leaves us with 2 more acidic mucus. Alright. What releases an acidic mucus? Well, remember most of the stomach has that alkaline mucus, but as you enter into the gastric gland, those mucus next cells make an acidic mucus. So I'm gonna put d here next to the mucus next cells. Alright. And that leaves us with one more, paracrins. Alright. What releases paracrins or paracrine molecules? Remember, paracrins are very similar to hormones. They just don't travel through the blood. So the same cells are gonna, release them, those enteroendocrine cells. So I'm gonna put an e here on that first line next to b. And with that, well, we answer the question.
11
Problem
Problem
Within the gastric glands, which cells would you expect to find closest to the gastric pits?
A
Chief cells.
B
Enteroendocrine cells.
C
Parietal cells.
D
Mucous neck cells.
12
Problem
Problem
Proton Pump Inhibitors (or PPIs) are some of the widely used drugs in the world and are prescribed for chronic heartburn/acid reflux. They work by inhibiting the movement of H+ ions across the membrane into the gastric juice, thereby lowering the concentration of HCl. As described, which cell of the gastric glands would you expect PPIs to affect?
A
Chief cells.
B
Enteroendocrine cells.
C
Mucous neck cells.
D
Parietal cells.
13
concept
Digestion in the Stomach
Video duration:
4m
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Video transcript
We now want to spend some time talking about digestion in the stomach because for all the parts that we've talked about, what the job of the stomach really is is to start breaking down food so that we can eventually absorb those nutrients. So we're just gonna start by saying that both mechanical and chemical digestion occur in the stomach. And we're gonna talk about mechanical digestion first. Well, because it's a little simpler, but also you probably don't think of the stomach doing mechanical digestion as much as you do chemical digestion. Right? We're all aware of stomach acid, but actually physically breaking up the food is something that the stomach does as well. So mechanical digestion, we just wanna know that this is non specific to any macronutrient. Right? So anything thing that's in the stomach is gonna go through mechanical digestion, and it just works through well, remember, the stomach is this muscular bag. So waves of, muscular contraction we call peristalsis, and it's just gonna cause this mixing of the chyme and the gastric juices. Remember, the goal of mechanical digestion is to break up food and mix it in with the liquid so that there's a lot of surface area for those food molecules so that enzymes can access them. Well, in the stomach, as we said, it's happening through peristalsis. Peristalsis is this wave of muscle contraction, and we can see this in our image here. We see sort of 1, 2, 3. You see this ring of muscle contraction sort of going down the stomach, so it's squeezing in, and that wave sort of moves downwards. And as it does, it's just sloshing around the kind that's in there. It pushes down. Some of this kind actually is gonna go through the pyloric sphincter. Now if it doesn't go through the pyloric pyloric sphincter though, as this sort of wave of muscle contraction makes it all the way to the bottom here, well, then that chyme sort of squishes back in the other way. So what you can think of imagine if you had a piece of bread and you put it in a plastic bag, and you didn't add any acid or anything to it. You just added water. And now just squeeze down on this bag over and over again. You can imagine that pretty quickly that bread is just gonna break up and turn into mush. Instead of being a piece of bread, it's gonna be all these bread little particles with tons of surface area so chemicals can access them and start chemical digestion. So that's what we're doing now. Chemical digestion. Alright. So in the stomach, we're gonna have multiple chemicals that contribute to digestion of macromolecules. The first one is the one I'm sure you're aware of is hydrochloric acid, h c l, that stomach acid. Alright. So this hydrochloric acid causes a very low pH. We're talking about somewhere in the range of 1.5 to 3.5, very acidic, and that acidity is going to denature proteins. So remember, proteins are these chains of amino acids that are folded up in three-dimensional structures. So to denature them, we're breaking up that three-dimensional structure, but we're not actually breaking the bonds between the amino acids yet. Now the hydrochloric acid, this acidity is also gonna break down a lot of cell walls. This allows us to sort of access what's inside the cells and digest those molecules. And importantly, it's also going to kill a lot of stuff in your mouth, you don't want every bacteria going in colonizing your gut or making you sick. So the back the stomach acid kills a lot of that bacteria as sort of first line of defense. Alright. So that's the acid, but we also have some enzymes in there. The one that we really want to identify is pepsin, and pepsin is gonna be this enzyme that breaks proteins into amino acids. Right? So the hydrochloric acid denatures the proteins, the peptin, that's actually going to break those peptide bonds and break it into amino acids because that's what can get absorbed later on in the small intestine. Now pepsin is only going to be work. It's activated and it's only going to work in a low pH environment. The stomach. All right. Now we're also going to have some lipases in here. Lipases. Remember, these are enzymes that begin lipid digestion or what we can call lipolysis, breaking those lipids into fatty acids that can be absorbed. Alright. Now quickly, if you wanna remember your pepsin and your lipase, just simple alliteration. Pepsin is for protein. Lipase is for lipids. Alright. So that's how digestion works in the stomach. If we wanna break these things down anymore, we gotta move on to the small intestine. But before then, we got practice and examples. I'll see you there.
14
example
The Stomach Example 4
Video duration:
2m
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Video transcript
Our example tells us that digestion in the stomach is due to several individual factors. We want to match the factor on the left with its digestive function on the right and some factors may match with more than one function. Alright. So our factors here, we have mechanical digestion by peristalsis, hydrochloric acid, pepsin, and lipase. And we have different functions over here on the right. So let's go through them 1 by 1. Alright. Protein denaturation. Which one of these things denatures proteins? When we said protein denaturation, that was due to the hydrochloric acid. So I'm going to put an a on that line there. Alright. Next, we have protein hydrolysis. Alright. Protein hydrolysis, that's actually breaking the bonds in that amino acid chain, breaking those peptide bonds. That would be due to pepsin. So pepsin, that enzyme. I'm going to put a b on that line there. Next, we have mixing chyme and gastric juice. What would mix chyme and gastric juice? Well, mechanical digestion by peristalsis. That gets a c there. Remember, that's just those waves of muscle contraction that's just sloshing everything around. Alright. Next up, we have lipolysis. Well, lipolysis, the breaking down of lipids, that would happen by lipase, the enzyme that breaks down fats. So I'm gonna put a d on that line there. Alright. Our lines are full, but we got more to go. We have e, increasing surface area of food particles. What would do that? Well, increasing the surface area, that's just sort of physically breaking up the food. That would be through mechanical digestion by peristalsis. So this first line gets an e on it. And then finally, we have killing bacteria. All right. So which of these things is going to help kill the bacteria? On the stomach killing bacteria, that hydrochloric acid, HCL, that's gonna help kill bacteria and be one of those first lines of defense from fight to keep your body, from being overrun by bacterial infection. Alright. With that, we've matched all our functions to our factors. We did our job. Good work.
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Problem
Problem
Mixing of the chyme with gastric juice is achieved via:
A
Skeletal muscle contractions.
B
Rhythmic contractions of pacemaker cells.
C
Segmentation by contraction of non-adjacent muscles.
D
Peristaltic waves of smooth muscle contraction.
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Problem
Problem
Which of the following statements about chemical digestion in the stomach are correct:
I. Lipid digestion is begun by enzymes known as lipases.
II. HCl is breaks starches into component monosaccharides.
III. Proteins are denatured by the protein pepsin.