10.04 Stomach

In this lesson we're going to talk about the stomach.

The stomach is a j shaped organ, is located in the upper-left quadrant just below the diaphragm. It's broken up into several different divisions, with the cardiac sphincter being the most Superior or near the top. Then there's the fundus, which is along this top curvature. Then there's the Corpus which is the main body of the stomach. That flows into the antrum and then it leaves to the pylorus. There are two sphincters that we want to look at, which are the cardiac or the gastroesophageal sphincter, and the pyloric sphincter. The cardiac sphincter really isn't a sphincter but it's this layer of round muscle that keeps food from regurgitating back into the esophagus. Now the pyloric sphincter there is a ring of muscle and it's going to be at the end of the stomach and that keeps the contents better in the stomach to stay in the stomach and then as food exits the stomach and goes into the duodenum, that'll keep food from flowing backward. There are also two curvatures which we talked about and that is the Lesser curvature which is closer to the liver, and then the greater curvature which is closer to the spleen.

So besides the mouth and esophagus, the stomach is that next step along the pathway for food to get digested. There are two processes that are the main focus when it comes to digestion and that's chemical and physical digestion. In the stomach physical digestion happens and that's due to contractions that break down the food and mix the contents up. Then there's also chemical digestion which helped contribute to breaking down food. This is done with gastric juices, primarily hydrochloric acid and pepsin. The other thing that's important about the stomach is that it kind of sequester or isolate vitamin B12 and absorbs it here.

Just like the other layers of the GI tract there are four main layers. Just the Tunica serosa, the Tunica muscularis, the Tunica submucosa, and the Tunica mucosa. This is going from the outside in. With the stomach does level of the Tunica serosa is a serous membrane that helps to reduce friction. Now there are double layers at curvature and what the double layer means is that the omentum, or connective tissue in the stomach, it helps to align outside of that Tunica serosa and house to suspend it and it's right location. The Lesser omentum is going to keep it suspended near the liver, and the greater omentum helps to cover other organs for cushioning and protection.
The Tunica muscularis is that muscle layer, and in the stomach if there are three layers. There's an outer, middle, and inner. The outer layer is longitudinal, the middle is circular and the inner is oblique. And what that means is that the muscle layers are laid out in a certain formation. So the outer layer all the muscle is laid out long ways, in the middle layer there in a circular formation, and in the inner layer their kind of into this oblique or diagonal Direction.

With the Tunica submucosa its main purpose is to connect the Tunica muscularis and the Tunica mucosa so it wants to connect the inside layer of the stomach to the muscle layer of the stomach.

With the stomach the Tunica mucosa is really important. And the reason is because it has lots of cells that help to digest food. There are several cells that we look at when talking about the Tunica mucosa and they are parietal cells, Chief cells, and mucous neck cells. The parietal cells secrete hydrogen and chloride and also intrinsic factor.

The intrinsic factor is really important because it binds to B12 for transport and then it goes down into the ileum in the small intestine where it's absorbed. If there's somebody that doesn't have the intrinsic factor, that's going to lead to a vitamin B12 deficiency and something called pernicious anemia.

And the chief cells are really important because what they do is they making release pepsinogen. Pepsinogen is later converted to pepsin which is important for digestion. Mucous neck cells are also really important because they help to secrete mucus to coat that inner surface of the stomach so that the really acidic environment doesn't break down all the tissue.

Another really important feature in the stomach is something called rugae and what rugae is is that there are these folds. And the folds happened because the Tunica submucosa in the Tunica mucosa create folds when the stomach is empty and then we'll stretch out. And that helps to increase the surface area inside the stomach so that there's more absorption that can happen.



Okay so let's recap.

Just like with the other layers of the GI tract, we have four layers and they are the serosa, muscularis, submucosa and mucosa.

The stomach is really important because it does both physical and chemical digestion. The physical digestion is a result of that smooth muscle Contracting and mixing the food content, and the chemical digestion is do to hydrochloric acid and pepsin helping to break down food.

The Tunica mucosa is really important because it's got those gastric glands and they're going to secrete this different enzymes that help to break down food.

And lastly the rugae really important because they help to increase its surface area because of the Tunica mucosa and the tunic of submucosa helped to create those longitudinal Folds.

And that's it for our lesson on the stomach. Make sure you check out all resources attached to this lesson. Now, go out and be your best self today, and as always, happy nursing!