Exocrine pancreas

Voiceover: So, the next organ we're going to talk about in our tour to abdomen is the pancreas. And I've drawn the pancreas right here. Let me just write that out. This is our pancreas, which I believe you may have heard about before. The pancreas sits below and behind the stomach, and it kind of hugs the first part of our small intestine here, which I think you may now recognize as called the duodenum. In fact, it wraps around a little more than what I've drawn right here. But just know that it sits back, way back over here. In fact, some say that the pancreas sits in a completely separate compartment from our stomach, our small intestine, our large intestine, even our liver. It sits not in the peritoneum. The peritoneum is where the rest of our gut sit. The peritoneum is just a fancy word for the abdomen. So, our stomach sits in our peritoneum, our liver sits in our peritoneum, the small intestine, the large intestine, all these guys sit in our peritoneum. But our pancreas is different because it sits in the retroperitoneum. And when we say retroperitoneum, that means it sits in the back of the abdomen. Now, it's not they're alone. A lot of our big vessels that run through the abdomen are also there. The abdominal aorta, the inferior vena cava, these things you may have heard of elsewhere. But it sits in this very different compartment. And in fact, medical professionals, the pancreas is actually a force to be reckoned with, for a couple of reasons. First of all, it releases a bunch of powerful enzymes. Powerful enzymes that we're going to talk about in a minute. And these powerful enzymes can digest a whole bunch of our macromolecules. Things that we eat, but also the things that line our cell membranes or make up other parts of our body. Not just in the retroperitoneum but in the peritoneum, the thorax, everywhere else in our body. So, it releases powerful enzymes. And two, the pancreas is little strange in that it's unencapsulated, unencapsulated, which is different from other organs like the liver. The liver has got the liver capsule. The kidney is covered by its own capsule, but the pancreas is essentially just a slurry of cells that's hanging somehow in the retroperitoneum. And that makes it a little difficult, especially for surgeons that have to operate nearby. You don't want to mess with the pancreas because it's got all these powerful enzymes that could cause a lot of damage around it if they were released. No wonder then, the pancreas has sort of earned itself a special nick name. Many physicians consider the pancreas to be the lion of the abdomen because of how important it is, and additionally, how powerful the enzymes are that come from it. So just like the lion in the jungle, you don't want to mess with the pancreas. So let's take a few minutes then and talk about what makes the pancreas so special. Physiologically, the pancreas releases two types of things or has two main components to it. One, there is the exocrine pancreas. And the idea behind the exocrine pancreas is that it takes salts, and I'll write it down here, enzymes. So, these powerful enzymes I talked about earlier. It takes these salts and enzymes and releases them in the duodenum or the duo-denum. And I think you remember where that is. That's the first part of the small intestine right after the stomach. And so our exocrine pancreas has four main roles that it accomplishes. So, firstly as you may recall. Because the pancreas releases its contents into the duodenum, think about what the duodenum is receiving right beforehand. As we talked about in the video on the stomach, we're getting a whole bunch of chyme that's been digested by gastric acid or hydrochloric acid. And so we'll need something to neutralize all that acid. And so the exocrine pancreas release bicarbonate. The bicarbonate here will serve to neutralize our gastric acid. So, we will neutralize the pH or the very low pH that we're receiving from the stomach in the form of gastric acid. And remember again, the gastric acid is hydrochloric acid. Next, as we move on, we will talk about some of those powerful enzymes that we discussed earlier. One of them that we briefly mentioned when we were talking about the mouth, is amylase. And if you recall, amylase is responsible for the breakdown of the starch. And if you remember, starch is just a whole bunch of carbohydrates stacked upon one another. And we break down starch into our smaller carbohydrates. So, I'll just write smaller carbs for right now. And so that will include things like those glucose monomers or even disaccharides. And then another enzyme that we also release from the exocrine pancreas into the duodenum is something called lipase. And lipase should be another throwback to the mouth because its name suggest that it breaks down lipids. So, specifically it will take triglycerides, which I can draw here. So, here is a triglyceride, right there. And you've got these fatty acid chains that are coming off the glycerol head. It will take triglycerides and it will break them down into free fatty acids. And so those will look like this. So that's the acid part and here's the fatty acid part, as well as things like monoglycerides. And monoglycerides look like this. And we're calling them mono because they've only got one fatty acid chain on them. We could also have diglycerides, which I think you might be able to guess what these guys look like. If I draw them out like here. Diglycerides are going to have two fatty acid chains on them. There you go. And then it also will release glycerol, glycerol. And glycerol is what happens when you get rid of all your fatty acid chains. And so you'll have some of these guys and they're all ... OH is right here. So that's what your lipase will do, and it's similar to the lingual lipase that you had in your mouth. But in the mouth, it was mainly for taste when you digested your triglyceride. In the duodenum, this enzyme works to break down triglycerides in a greater manner. And then finally, the last function of the exocrine pancreas involves its proteolytic enzymes. I'll just write proteolytic right here. And I'll expand. There are two types of proteolytic enzymes. There is trypsinogen that it releases, trypsinogen. There is trypsinogen and there is also chymo. This is a longer word, chymotrypsinogen. Trypsinogen. And I think there is a couple of light bulbs that should be coming on right now because whenever you see the suffix "ogen" as we see down here. That refers to something that's called a zymogen. A zymogen, which means an enzyme that is inactive right now because it has an extra bond. Usually, a peptide bond that needs to be broken in order for it to start doing its thing. So, trypsinogen is the inactive form of trypsin. Just like how chymotrypsinogen is the inactive form of chymotrypsin. And these guys need to be activated. And the way that's done is in the duodenum. There is an enzyme that sits there called enteropeptidase. There is a whole bunch of enteropeptidases that line the duodenum. Your enteropeptidase will break down trypsinogen to form trypsin. Trypsin is the active form that's then going to be able to break down proteins. And what we're doing here is actually causing a chain reaction. Because once trypsin is formed, the next step in activating chymotrypsinogen is accomplished by trypsin. Trypsin will cleave your chymotrypsinogen to form, and this is a very long word, chymotrypsin, chymotrypsin. And these guys will go wreak havoc and break down proteins in the duodenum. Now, my question to you is these are enzymes and they're inactive because of usually a single bond. But what happens when that bond that makes them inactive breaks? Say, if you're in a car accident and you get hit in the stomach and there was enough force there that can provide activation energy to break a bond and turn trypsinogen into trypsin. What would happen? Well, as we mentioned earlier, because the pancreas is unencapsulated, activated trypsin will go on to activate chymotrypsinogen into the chymotrypsin and then will break down proteins wherever they see them. And that can be membrane proteins. They could be proteins that are in the surface of the duodenum. They could be proteins that we digested in our food or they could be proteins that are present in the pancreas. So you can see why the pancreas is so feared. And that's why the pancreas is something you don't want to have damaged. Because we can activate these deadly enzymes that should be working in the duodenum.