The Stomach - Online Tutor, Practice Problems & Exam Prep

The stomach plays a crucial role in digestion through mechanical and chemical processes. It consists of four main regions: the cardia, fundus, body (or corpus), and pyloric part, which includes the pyloric antrum, canal, and sphincter. The stomach wall has four layers: mucosa, submucosa, muscularis externa (with an additional oblique layer), and serosa. Gastric glands within the mucosa secrete gastric juice, containing hydrochloric acid (HCl) for protein denaturation and enzymes like pepsin for protein digestion, while lipase begins lipid digestion. Rugae allow for expansion, enhancing digestion efficiency.

Gross Anatomy of the Stomach

As we talk about the stomach, we need to introduce the major regions and structures of the stomach. In other words, we're now going to go over the gross anatomy of the stomach. Alright. So here we have an image of the stomach. You can see the esophagus entering 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. We've highlighted the cardia here in green, and we're going to say that this is the upper portion near the junction with the esophagus. 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. These are 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 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 think of as the roof of the stomach. It's that region where it 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. Here we can see the body, most of the stomach here. We're going to say it's that main J-shaped region. It has this sort of curve to it, kind of like a J. Sometimes the body is called the corpus. If you need to remember corpus, remind yourself 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 going to 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. 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. 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 although it's not what it means, that word, antrum, reminds me of the word entry. So the pyloric antrum, I think of as the entry to the pyloric part. It's just the first part you come to. From the pyloric antrum, then we have the pyloric canal. 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. There is a valve at the end. 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. 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. 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 a

Food entering the stomach will first pass through the:

• A. Fundus.
• B. Body.
• C. Pyloric antrum.
• D. Cardia.

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.

Layers of the Stomach

Now that we've introduced the gross anatomy of the stomach and we've identified the major regions of the stomach, we want to zoom in on the stomach wall and identify the layers of that stomach wall. So we're going to 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 unique things along the way, and here we want to 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.

The first layer we want to talk about, at the top of our drawing here, 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, is going to be up against this mucosa. Alright. So the mucosa is going to be made of mucus cells. That's going to be that stomach epithelium, and it is composed of simple columnar cells. And simple columnar cells make up that epithelium of the entire alimentary canal, and we can see those in our drawing here. Those are these cells sort of lining the tops there in pink. But what makes it unique in the stomach is we're going to have this mucosal barrier, this thick alkaline mucus that is there for protection. Alright. Alkaline, that means basic or 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.

Now we have that mucosal barrier, but also between all the cells, we're going to have tight junctions. Those tight junctions are also going to prevent the 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 sorts 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 these holes and the starts of these 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 about those in a future video coming up.

As we move down from the mucosa, we reach the submucosa, and that's this layer here. 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 the submucosa in the stomach, so we're not going to spend much time on it. Moving down from there, we reach the muscularis externa, and that's this section here, the 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 going to 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 cells there 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. It's the innermost layer, and we are going to 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. 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 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.

Finally, we have the serosa, and here we see the serosa in green on the outside. And remember, in the serosa here, that's the 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 omentum. 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're doing 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 going to 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.

The Stomach Example 2

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, 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 an ulcer are actually defined by the mucosa being breached and the submucosa underneath it being damaged. Alright. Now, what structure or features in the stomach prevent gastric juices from damaging that tissue? Well, remember we said we had a mucosal barrier, and that mucosal barrier 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.

Which layer of the muscularis externa only exists in the stomach?

• A. Oblique layer.
• B. Circular layer.
• C. Transverse layer.
• D. Longitudinal layer.

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.

Stomach Glands

Now I want to zoom in on the stomach mucosa just a little bit more and talk about the stomach glands, or what we're going to call the gastric glands. That's because these gastric glands are going to 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 going to call gastric juice. Gastric juice is going to be this acidic, enzyme-rich fluid. The acidity combined with those enzymes is what's going to do the chemical digestion.

As we look at the structure here, there are two major structures we want to identify: one 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. 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 going to talk about as we go. The gastric pit is the top half of this image here, and the gastric gland is the bottom half that we're going to talk about.

Gastric glands, let's identify these cells. First up, we have the mucus neck cells. 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 them. They are in the neck, so the top part of the gland, and what do they make? They make mucus, and it's an acidic mucus. Now remember, the lining of the stomach has all these mucus cells that make an alkaline mucus, which 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. This acidic mucus, just to be clear, is not what makes your gastric juice acidic.

What makes your gastric juice acidic then? Well, that's going to be the parietal cells. The parietal cells, you can see here, 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 they make the gastric juice acidic by producing hydrochloric acid, or HCl, and also importantly a protein called intrinsic factor. First, let's talk about the hydrochloric acid. Hydrochloric acid is going to participate in chemical digestion, chiefly by denaturing proteins. Now remember, proteins are three-dimensional structures made up of long chains of amino acids. 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 going to happen from enzymes later on. It's also going to kill bacteria. You take a lot of bacteria in when you eat, and you don't want all of that stuff colonizing your body. So one of the first lines of defense is this hydrochloric acid. It's going to 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 in plants and so on. But we want to focus in on those proteins and killing bacteria.

We also have intrinsic factor. Intrinsic factor is this protein that's going to be important for vitamin B12 absorption. Now you don't actually absorb your vitamin B12 until later on in the small intestine. But we need to call this out here because if you don't get the intrinsic factor in the stomach, you won't absorb that B12 later on.

Our next type of cells is going to be the chief cells. If the parietal cells made the hydrochloric acid that participated in chemical digestion, it's the chief cells that make the enzymes. We see these down near the bottom of these gastric glands, these orange cells there. They make enzymes pepsinogen and lipase. Technically, pepsinogen isn't an enzyme; it's an enzyme precursor. Under acidic conditions, like in the stomach, pepsinogen, this enzyme precursor, is converted into the enzyme pepsin. So we have two enzymes there that are now active, produced by these chief cells: pepsin, which digests proteins, and lipase, which digests fats. Lipase breaks down lipids. Protein digestion and lipid digestion are going to continue with enzymes in the small intestine. In fact, most lipid digestion happens in the small intestine, but it does 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. Entero means gut and endocrine refers to endocrine function, sending out hormones. So these cells release hormones and paracrine molecules. Hormones are chemical signals that travel in the blood. Paracrine molecules are chemical signals that signal cells nearby. They 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 paracrine molecule. 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 going to instruct them to start making stomach acid. However, if it ends up in the blood, there are also going to be target cells for that gastrin in, for example, the gallbladder and the pancreas, which is going to instruct them to get ready to release the fluids that they either store or produce.

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. Parietal cells lower pH. Chief cells chop the proteins and also the lipids. So the parietal cells, remember, they make the hydrochloric acid that affects pH. Chief cells, they make those enzymes, which cut things up like proteins and lipids.

With that, we have examples and practice problems to follow. Give them a try.

The Stomach Example 3

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 neck cells, chief cells, and parietal cells. Alright. So we have our different molecules here. Let's go through them one by one. 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 enteroendocrine 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 release the precursor molecule pepsinogen, and pepsinogen gets converted into pepsin in the stomach. 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 digests 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 neck cells make an acidic mucus. So I'm gonna put 'd' here next to the mucus neck cells. Alright. And that leaves us with one more, paracrines. Alright. What releases paracrines or paracrine molecules? Remember, paracrins are very similar to hormones. They just don't travel through the blood. So, the same cells are going to 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.

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.

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.

Digestion in the Stomach

We now want to spend some time talking about digestion in the stomach because, for all the parts that we've talked about, the job of the stomach really is to start breaking down food so that we can eventually absorb those nutrients. So we're just going to start by saying that both mechanical and chemical digestion occur in the stomach. And we're going to 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 want to know that this is non-specific to any macronutrient. Right? So anything that's in the stomach is going to 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 going to 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. Peristalis 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 chyme that's in there. It pushes down. Some of this chyme actually is going to go through the pyloric sphincter. Now, if it doesn't go through the 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 going to break up and turn into mush. Instead of being a piece of bread, it's going to 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 going to 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, HCl, 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. 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 going to 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 bacterium going in colonizing your gut or making you sick. So the stomach acid kills a lot of that bacteria as a 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 going to be this enzyme that breaks proteins into amino acids. Right? So the hydrochloric acid denatures the proteins, the pepsin, 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 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 want to remember your pepsin and your lipase, just simple alliteration. Pepsin is for protein. Lipase is for lipids. All right. So that's how digestion works in the stomach. If we want to 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.

The Stomach Example 4

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 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 one by one.

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.

Next, we have protein hydrolysis. Alright. Protein hydrolysis, that's actually breaking the bonds in the 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.

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.

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 finally, we have killing bacteria. Alright. So which of these things is going to help kill the bacteria? In the stomach, killing bacteria, that hydrochloric acid, HCl, that's gonna help kill bacteria and be one of those first lines of defense to keep your body from being overrun by bacterial infection.

With that, we've matched all our functions to our factors. We did our job. Good work.

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.

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.

• A. I only.
• B. I & II.
• C. II, & III.
• D. I, II, & III.

Here’s what students ask on this topic:

What are the major regions of the stomach and their functions?

The stomach has four main regions: the cardia, fundus, body (or corpus), and pyloric part. The cardia is the upper portion near the esophagus junction, allowing food entry through the cardiac sphincter. The fundus is the upper bulging part, acting as a storage area. The body, or corpus, is the main J-shaped region where most digestion occurs. The pyloric part, divided into the pyloric antrum, canal, and sphincter, regulates the passage of chyme into the small intestine. Each region plays a specific role in the mechanical and chemical digestion of food.

What are the layers of the stomach wall and their unique features?

The stomach wall consists of four layers: mucosa, submucosa, muscularis externa, and serosa. The mucosa, the innermost layer, contains mucus cells and a thick alkaline mucus barrier for protection against stomach acid. The submucosa is connective tissue with blood vessels and lymphatics. The muscularis externa has three muscle layers: oblique (unique to the stomach), circular, and longitudinal, aiding in mechanical digestion. The serosa, the outermost layer, is the visceral peritoneum, continuous with the omentum. These layers work together to facilitate digestion and protect the stomach.

How does mechanical digestion occur in the stomach?

Mechanical digestion in the stomach involves the physical breakdown of food through muscular contractions called peristalsis. The stomach's muscular wall, with its three layers (oblique, circular, and longitudinal), creates waves of contraction that mix the food with gastric juices, forming chyme. This process increases the surface area of the food, making it easier for enzymes to access and chemically digest the nutrients. Mechanical digestion is non-specific and affects all macronutrients present in the stomach.

What role does hydrochloric acid play in stomach digestion?

Hydrochloric acid (HCl) in the stomach creates a highly acidic environment with a pH of 1.5 to 3.5. This acidity denatures proteins, breaking their three-dimensional structure, and helps break down cell walls, making nutrients more accessible. HCl also activates the enzyme pepsin, which further digests proteins into amino acids. Additionally, the acidic environment kills harmful bacteria and pathogens ingested with food, providing a protective function.

What are gastric pits and their function in the stomach?

Gastric pits are small openings in the stomach's mucosa layer that lead to gastric glands. These pits are crucial for secreting gastric juice, which contains hydrochloric acid (HCl) and digestive enzymes like pepsin. The gastric glands located deeper in the mucosa produce these secretions, which then travel through the gastric pits to the stomach lumen. This process aids in the chemical digestion of food, breaking down proteins and lipids for nutrient absorption.