 Hey everybody, Dr. O here, and this video we're going to talk about the stomach. So we'll cover the basic anatomy of the stomach, we'll talk about why it has a kind of special structure and we'll talk about some of its key functions. It's a real big picture. When you think of the stomach, you probably think of it as basically a bag full of acid. Now there's a lot of other digestive enzymes, there's a lot of other things going on, but that is one of its primary jobs is to be this bag full of acid and to have a low pH. Basic function of that low pH, not only does it kill a lot of bacteria that enter through your gastrointestinal tract, but also it helps to break down your food, especially it helps to denature protein, so to unwind protein so they can be properly digested. So the four parts of the stomach you see here, we have the cardia, the fundus, the body and the pylorus. So I'll just go in order here. The cardia is the portion of the stomach that's attached to the esophagus. So obviously when you think about the stomach and the esophagus, maybe you think of the gastroesophageal sphincter or the lower esophageal sphincter, that's what separates the two. If that sphincter's not working properly, people can develop reflux disease or heartburn or if it's chronic and persistent, it can be good. This gastroesophageal reflux disease. So that's the cardia. It doesn't have too many digestive functions, mainly it's just post-becovered mucus. The fundus is the portion of the stomach that's above the cardia there on the side. The fundus can actually hold food for a little bit, so some of the digestive enzymes from your mouth can still be active in your stomach for a little while while the food is sitting in the stomach before it plops down into the body where all the acid would be. It also captures gases, so as you're digesting your food or microbes are metabolizing your food, gases can be produced. This can be an issue, especially if you have low stomach acid. Your food can almost start to putrify inside your gut. Now this gas that can be captured can also cause issues with that gastroesophageal sphincter, can cause it to pop open, but that's kind of a more clinical issue. So cardia, just remember the part of the stomach that attaches to the esophagus. The fundus is that upper portion. The body is the largest portion of the stomach where most the activity is. And then the pylorus is going to be the part that connects the stomach to the small intestine, more specifically the duodenum of your small intestine. Other key features here looking at this image, you see what are called the rugae. So when the stomach, the stomach can obviously expand when you feel it full of food. When it's empty, it will fold down on itself and create these little folds called rugae. The other important thing you'll notice here, most hollow organs in your body have two layers of smooth muscle, longitudinal and circular layer usually. The stomach has a third, so it has an oblique layer. This is what allows the stomach to really compress and squeeze and churn and mix your food as it becomes kind in your stomach. So the third layer of smooth muscle is a very important anatomical feature when you're looking at the stomach. It's kind of interesting when I think of the stomach, the organ that's the most similar to it is actually your bladder. It has three layers of smooth muscle. It does have those folds called rugae in them as well. So those are the basic parts of the stomach. I think the next most important thing to note, I mentioned the stomach is a bag full of acid and enzymes, digestive enzymes. So how does the stomach not get digested? Well the key protective mechanism here is kind of two. Number one, the entire stomach should be lined with mucus, a mucus barrier that actually keeps stomach acid, stomach contents from coming into contact with the stomach. And that mucus barrier should be full of bicarbonate, which is a buffer to neutralize acids. So the pH of the actual lining of the stomach will be a lot higher than the lumen, where all the gastric juice is. The other key thing is because there is some wear and tear here between digestion and enzymes and acid, stem cells in the stomach are constantly replacing new cells. So your stomach is replaced every three to six days probably. All right, excuse me. I mentioned how there are some digestive enzymes here in the stomach, let's go ahead and talk about them. So just to quickly review, your mouth has salivary amylase, which obviously as you swallow would be active, but only until the pH in the stomach drops to destroy it. Your mouth also has lingual lipase, which helps break down fats. That's going to be active longer in the stomach because it can handle a lower pH, but the stomach itself will release the most important one is pepsin. It's actually released as an enzyme called pepsinogen and then the acidity of the stomach turns it into pepsin. So pepsin is the key enzyme in your stomach and it breaks down peptides, it breaks down proteins. But there's also an enzyme called gastric lipase, which will help break down lipids in the stomach. And then in children, there's an enzyme called renin, which actually renins the enzyme you use to curdle milk. So it helps with the digestion of milk protein. If you had a pukey child like I did when Oliver was young, we always called him a feta factory. He would drink milk, but if he threw up, it'd be cheese, right? And part of that is that curdling process caused by that renin. So those are some of the enzymes. We'll cover chemical digestion later. OK, one last thing, all those things are very important, but if you have to remove someone's stomach, there are ways to use digestive enzymes and other treatments for someone to survive without a stomach. But there is one function that you must account for if you remove someone's stomach or if someone has a severely damaged stomach. So one we haven't talked about yet. One of the key functions of the stomach is to produce intrinsic factor. So intrinsic factor is a chemical that's needed for the proper digestion absorption of B12. If you don't have intrinsic factor, you cannot absorb B12. So if someone would have to have their stomach removed, they would need a B12 injection. So that's something we cover more in nutrition, but still very interesting. All right, as far as how long food sits in the stomach, it's generally considered two to four hours based on what's in the meal. If it's just full of carbohydrates, it'll run right through you basically. Lipids and proteins have a higher satiety value because they keep food sitting in your stomach longer. So here we see the actual histology here, the lining, there's a lot of things going on here, but I'll just let you know the key things here. So hopefully you'll notice there, those gastric pits inside those gastric pits are gonna be where the key cells are that make the gastric juice that we need. And you can see them there on the right-hand side, the parietal cell and the chief cells of the two key ones. Parietal cells, their job is to make hydrochloric acid. So they're the ones that actually cause the acidic environment in the stomach. They also make intrinsic factor, what I just said that is needed for absorption of B12. Your chief cells, they're the ones that are gonna produce that pepsinogen. And remember, pepsinogen is one step away from being the enzyme pepsin. The reason these cells don't just produce pepsin is pepsin digest proteins. Your cells have made a protein, pepsin would just destroy your stomach. So it needs to be activated once it's secreted and out into the lumen of the stomach. All right, that's plenty to start with as far as the stomach goes. As you can see, it's a very, very important organ. I hope this helps. Have a wonderful day. Be blessed.