It's a pleasure to be here and a privilege to contribute to your education. Remember, you're in healthcare now, too, and so you contribute to the health and well-being of patients, and so I consider it to be a really important duty to participate in your education and hope to be of help to you today and tomorrow. So let's talk about what are sometimes referred to as the solid organs of the GI tract, although these organs are actually both solid and hollow, depending on how you think about it, which is kind of a common theme in medicine. There's always sort of a but or a however to everything, and I'm going to try to clear some of that up as we go. So then when you look at the liver, the gallbladder, and the pancreas, some of it's easy to see in these pictures because it's pretty obvious with the liver, which is the largest solid organ in your body. The largest organ is your skin, technically, or depending on how you think about it, even your blood could be considered a liquid organ. But of the internal organs, the liver is the largest one. It's so large, in fact, that on the right side, which there's a right lobe of the liver and there's a left lobe of the liver. We'll talk about that in a minute. Your liver is so large that on the right side, your kidney's an inch or two below the left kidney to make room for that big right lobe of the liver. But the solid organs are the liver, the gallbladder, and the pancreas, and then you just heard about what's often referred to as the hollow organs, the esophagus, the stomach, the large and small intestine. The liver is a vital organ, and that's not a word to throw around. What do we mean by a vital organ? A vital organ is an organ that you cannot live without. It's necessary for life. If you didn't have your liver, if it shut down completely, you might live a day or so, and that would be about it. And if your liver is not working at all, you might need a liver transplant in order to survive. Contrast that with, say, the pancreas. And we'll talk a little about pancreatic function in a minute, but if you didn't have a pancreas, we could supplement you with the endocrine secretions of the pancreas, and we could supplement you with the digestive enzymes that the pancreas makes, and you could live without your pancreas. Might not be the most comfortable life. Might have a lot of issues, but you could actually live without it. So it's not a vital organ, at least in that technical sense. There's always a however, right? You might have really brittle diabetes without your pancreas. You might not have perfect digestion without a pancreas, but you could survive for a long time without it. So it's not technically a vital organ. But the liver is a vital organ. We cannot replace, at least yet, the function of your liver without giving you another one or a part of one in order to survive. When we say it's in the right upper abdomen, it actually spans the whole upper part of your belly, but the left side is smaller than the right side. In fact, the right lobe of the liver is probably about 60% to 70% of your liver, and the left side is about 30% to 35% of the size of your entire liver. So the two sides aren't sort of made equal, but you do have a left lobe and a right lobe to the liver in much the same way that you have a left lung and a right lung. You have a right kidney and a left kidney, a right arm, left arm, et cetera. So we have some redundancy in our bodies. And you don't have two livers, but you do have two lobes or two sides of your liver, but they're not the same size. Weighs three to four pounds, so that accounts for it being the largest internal organ in your body. And consider that it's full of blood all of the time, so it is a pretty heavy thing. We're going to talk about the blood supply, because the blood supply of the liver is very unique. It has only one output, one exhaust pipe, if you will, for blood, although there are kind of actually two pipes leading out of the liver if you consider the bile duct to be one. But it has two blood supplies, and those two blood supplies are very distinct, and we'll about their functions and what makes them different, hopefully in a way that's understandable. There's the hepatic artery, and there's the portal vein. Now you know that most veins carry blood away from the organ, but the portal vein actually carries blood into the liver, and you'll see why in a second. So we are full of plumbing. Kind of like your house, right? So there's sort of the equivalent of hot and cold water pipes. There's clean water, there's dirty water being carried out, and you have an HVAC system, which is your respiratory system. And a lot of the pipes are kind of bundled together and run side by side, kind of like they do in your house or in your car or what have you. Now you see in this picture that there are the hepatic veins here that are leading blood out of the liver. And we just got done saying that the portal vein, on the other hand, doesn't lead out of the liver. It leads into the liver. The hepatic artery, like any other artery, supplies oxygenated blood to the liver. Let's talk about how all these pipes work and work together. And then we'll talk about the bile duct, which is a separate set of pipes. Starting with the hepatic artery, because it's like pretty much any other artery, it receives oxygenated blood. So your heart receives deoxygenated blood, blood that's been used up by your body. That goes into the right side of the heart, and the right side of the heart pumps that deoxygenated blood into your lungs. And as you breathe, that oxygen in your lungs attaches to the deoxygenated red blood cells in the lung. And that reoxygenated blood is pumped back to the left side of your heart. And the left side of your heart then pumps that reoxygenated blood out to every cell in your body to supply it with oxygen again. And that blood goes through a great big artery out of the heart called the aorta, which is the size of a garden hose. And that aorta then ramifies into smaller and smaller arteries until it gets to the size of a capillary where it interacts with every cell in your body. And that's how the cells buried deep inside your body get oxygen, even though they're not on the surface where they can contact atmospheric air. So one of those ramifications is the hepatic artery, which is that red set of pipes that you see there. And that is there to carry blood that is oxygenated to every cell in your liver so that your liver cells can receive oxygen to survive. So then, why do you need a portal vein? Remember that, and we're going to talk about physiology in a second, but we need to touch on it to understand the anatomy here. One of the things that your liver does is it takes the nutrients that your intestine absorbs after digestion from the enzymes, like Dr. Carpenter just described to you. Those nutrients have to get to your liver. Your liver has to metabolize them and package them and then distribute that through your bloodstream to the rest of your body's cells. How do those nutrients that are digested in the lumen of your intestine and then get absorbed by your intestine get to the liver? Well, they get to the liver on a conveyor belt. And that conveyor belt, that portal, is called the portal vein. So that portal vein is a really special pipe. It's the pipe. It's a set of pipes that go from your small intestine to the liver to convey those nutrients up to the liver to be processed by the liver. Does that make sense? That's why it's called the portal vein. It's a portal. It's a conveyor belt. But that's not all it does. Because that blood that is going from the intestines up to your liver still has some oxygen in it. And so that oxygen is also available to the liver. So the liver is actually getting really richly oxygenated blood from the hepatic artery. But it's also getting some still oxygenated blood from the portal vein in addition to tons of nutrients that are floating up that portal vein to your liver. Nobody taught it to me that way. And it took me a little time to figure out that that's what's really going on. See, it's easier than they would have you believe. They just need to explain it that way. And that portal vein is huge. It actually supplies about at least two-thirds of the blood to your liver. So there's a lot more blood volume getting to your liver through the portal vein than through the hepatic artery. Does that make sense? Two inputs, two blood inputs to your liver, both distinct and very important. They both carry oxygen. But one of them is carrying tons of nutrients as well, and that's the portal vein. The blood output is singular, and that is the hepatic vein, which is going to then take that deoxygenated blood as well as metabolized nutrients and stuff out of your liver back to your heart to be run through your lungs for reoxygenation and then redistributed to your body. That's how that circuit works. Now I was alluding that there's a second exhaust pipe or outlet from your liver that's a pipe, but it doesn't carry blood. That's the bile duct. We'll talk about that more in a moment. So biliary refers to the bile duct system, and this is that other outlet from your liver that is carrying bile, which Dr. Carpenter alluded to. Bile is made by the liver cell, the hepatocyte, and it is secreted into bile canaliculi, which are the tiniest bile ducts that run between every couple of liver cells, if that makes sense. So the bile is made by the liver, and it is transported into tiny little ducts, and those creaks flow into rivers, and the river flows into yet a bigger river, and then ultimately into the left and right hepatic ducts, which you'll see the main left duct here and the main right duct there. And then they join at what's called the confluence or the bifurcation or the hilum. Many words for one thing. It's just an intersection. And then it flows down the common duct, which is the tree trunk part of the bile duct, and the root of that tree empties into the intestine through the ampulla. Now there is a gallbladder, which is a bile storage tank. That's basically what that is. It actually secretes some mucus and other things, but that's a detail that's not that important to you. It is mainly a tank to store bile, and you'll see why you store it in a second. Basically anywhere above where the cystic duct, which is the duct that joins the gallbladder, the bile duct, enters into the common duct up to the bifurcation is called the common hepatic duct. And the common duct or the tree trunk part of the bile duct that is below the cystic duct insertion is called the common bile duct. So common bile duct and common hepatic duct. Left and right hepatic ducts, and then the intra-hepatic ducts or intra-hepatic branches upstream all the way until you get to the tiny little canaliculi that are between the liver cells. Dr. Carpenter talked to you a bit about the ampulla. And the ampulla is that area where the lowest part of the bile duct is joined by the main pancreatic duct or the duct of weirsung, as it's called in anatomy class. That whole intersection in the second portion of the duodenum, pardon me, the second portion of the duodenum there, I don't think this pointer's working so I'm going to use this cursor here. This one? There we go. Thank you very much. This whole area is called the ampulla. Sometimes you'll hear people calling this little mound where the opening into the duodenum is, you'll hear them calling that the papilla, papilla, okay, the major papilla. In fact, there's a minor papilla, too, which I think is shown in the next slide. So ampulla is the region, and that little pouty structure where the opening is is the papilla. Is that clear so far? Okay. So the liver produces bile, and to simplify it a bit, bile's a detergent. It's other things, but its main digestive function is that it is a detergent. The food that you eat has fat and oils in it. Without some of those fats and oils, you actually couldn't survive. But your body's mostly a sack of water, and water and oil don't mix. So you need to throw some detergent in there to solubilize that fat and oil that's in the food that you eat, and bile is that detergent. The fat and oil in the food that you don't eat that's left on the dish, you got to throw a different kind of detergent on it, and that's, well, Dr. Carpenter said Dawn, so we'll call it Dawn. So it's that sort of thing, if that makes sense. That's what bile is, that green stuff. When you vomit, it tastes bitter. It tastes bitter because it's soap. We just said that the gallbladder is a storage tank for bile, and you'd have a hard time getting that tank to fill if there weren't a dam downstream to make the river back up. That dam is a little muscle right here, which is closed most of the time. It's called the sphincter of ody. And cholecystokinin, which is a hormone, when you eat a fatty meal, when that hormone is released into the blood, it stimulates the gallbladder to contract, but it also makes the ring-like sphincter muscle at the bottom of the bile duct there relax because you don't want to squeeze this against a closed door, right, or that doesn't work. So that hormone makes this muscle relax to make that outlet open at the same time that the gallbladder squeezes out the bile so that you have lots of bile available when you eat a fatty meal. Does that make sense? Okay. So we just said that, and we said that there are essential fats and oils, and that stuff's not going to mix with your body water without a detergent. So that is what the bile does. So the liver makes stuff. It synthesizes things, a lot of it's proteins, like clotting factors that help you clot your blood when you have an injury, say, so that you don't keep bleeding. Also it can make glucose, which is sugar that's necessary for all of your cells to function. That's called gluconeogenesis. And also makes all sorts of proteins, including albumin, that's a key protein in your blood, and can also make cholesterol, which isn't necessarily a bad thing. Cholesterol's an important building block in the membrane of every cell in your body. So the liver makes a lot of things. It stores a number of things. It takes single units of sugar, glucose, and stores them as a chain called glycogen, a polymer of glucose. So you can store up glycogen to break it down to glucose when you need it the most. It can store a number of vitamins and elements and minerals, things like iron and copper. It not only makes it, it can also break it. The liver can metabolize and break down a number of things, including medications, drugs, toxins, including alcohol, and other things. So it's a very powerful organ. It can synthesize things, it can store things, and it can break things down as well. The pancreas is another solid digestive organ, but as you can see what I was saying earlier is that the solid organs are also hollow because they secrete things. So they do actually have outlet pipes. The pancreas is kind of two organs in one. It's a digestive organ, so it makes digestive enzymes, which it secretes through the pancreatic duct. It also makes bicarbonate, which is a base that's secreted to neutralize the acid of the stomach, and it is also an endocrine organ. So living on the pancreas, mostly in the tail and part of the body, are various endocrine cells called islet cells, and endocrine cells secrete their products directly into the bloodstream. They are signaling proteins that tell other cells what to do and are secreted directly in the bloodstream. So the endocrine cells of the pancreas do not secrete their products into the pancreatic duct. They do not do that. Bicarbonate and digestive enzymes are secreted by the acinar cells, the digestive stuff-making cells of the pancreas into the duct, and they flow out of the same opening as the bile duct. But the endocrine cells of the pancreas secrete insulin, glucagon, and somatostatin directly into the bloodstream. I want to make that very clear. And those endocrine cells and what they do are frequently largely the work of an endocrinologist, not a gastroenterologist. So we don't tend to be the primary doctors taking care of diabetes, for example. That's an endocrinologist. But those insulin-producing cells, which are the beta islet cells, actually happen to live on the pancreas or in the pancreas. So the pancreas is kind of two different organs, a digestive organ and an endocrine organ. So the digestive enzymes break down fats. Those are lipases. They break down carbohydrates. And they break down proteins, lipases, amylases, proteases. They produce bicarbonate to neutralize stomach acid. So that's the exocrine or digestive part of the pancreas. And the endocrine part we just talked about. Endocrine is made by islet cells, beta islet cells. Glucagon is made by alpha islet cells and somatostatin by delta islet cells. And that ends this lecture. Thank you very much. Thank you.

GI tract

liver

gallbladder

pancreas

bile

digestion