Video: Pancreatic duct system
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Today, we're in the middle of a mystery - a murder mystery. On August 22nd, 1643, Professor Johann Georg Wirsung was shot to death by a Belgian student named Jacques Cambier. Without any obvious mo... Read more
Today, we're in the middle of a mystery - a murder mystery. On August 22nd, 1643, Professor Johann Georg Wirsung was shot to death by a Belgian student named Jacques Cambier. Without any obvious motive for the murder, it was speculated in anatomical circles that Wirsung was murdered out of jealousy for his discovery. But what discovery might it have been?
Well, it happens that in the year before he was murdered, Professor Wirsung discovered a tube in the center of an organ, which was previously believed to only function as padding in the abdominal area. It was, of course, the pancreas. This allowed Professor Wirsung to deduce that the pancreas may have a more important previously unknown purpose. In celebration of his finding, this tube was named the duct of Wirsung. But did his discovery cost him his life? That's a mystery I can't solve, but I can help you with the enigma that is the pancreatic duct system.
You might be interested to know what exactly we'll cover in this tutorial, so let's have a quick overview. We'll start with a very quick review of the location and basic anatomy of the pancreas just to help you orientate yourself. Then we'll move on to the duct system, where we'll find two important ducts - the main pancreatic duct and the accessory pancreatic duct. With those in mind, we'll discuss the duct system and its components. Once we've covered all of that, we'll conclude as always with a clinical note.
So, what do you say? Are you ready to untangle the mystery of the pancreatic duct system? Then let's get started with the location and basic anatomy of the pancreas.
Okay, so what is the pancreas? Well, despite previous misconceptions, we now know that it's a really important organ of both the digestive and the endocrine systems, meaning it has a dual function. About eighty percent of its functional tissue is dedicated to producing enzymes essential for digestion, making the pancreas an exocrine organ. The rest of it is dedicated to producing hormones like glucagon and insulin, which also make it an endocrine gland. These hormones are essential in glucose metabolism which in simpler terms means they help to regulate blood sugar levels.
The pancreas is mostly contained in the upper left quadrant of the abdomen. Most of its parts lie posterior to the stomach, which has been removed in this image. In today's tutorial, we'll focus on the pancreas and the part of the small intestine related to it - the duodenum. If you would like to explore the anatomical relations of the pancreas in greater detail, be sure to check out our video on this topic.
Now moving on to the basic anatomy of the pancreas, we know that it has well-defined parts along its length. Beginning on the left-hand side, we have the tail, which is the tapered end of the organ located close to the spleen. Moving more medially, we find the body of the pancreas. You'll notice that it's wider than the tail and that it forms the largest part of the pancreas.
Next up we have the neck, which as you might have guessed, connects the body to the head of the pancreas. Finally, the inferior aspect of the head curves to the left to form the uncinate process. The name comes from the Latin word uncinatus, which means hooked and seems quite appropriate here.
If we take a closer look at the cellular makeup of the pancreas, we will see that it has two components - an endocrine component and an exocrine component. The endocrine component concerns this tissue here, which is known as a pancreatic islet of Langerhans, which produces hormones involved in glucose metabolism. These hormones are transported away from the pancreas via fenestrated capillaries within the islet. The exocrine component, on the other hand, concerns the tissues surrounding the pancreatic islets seen here. It is largely composed of acinar cells, which produce pancreatic juice containing a long list of enzymes used in digestion. This pancreatic juice is what's carried by the pancreatic duct system.
Alright, now that we have the whole backstory, let's move on now to the star of the show - the pancreatic duct system. Let's start with the smaller structure of the pancreatic ducts and take another look at these acinar cells which produce the pancreatic juice. These cells form little clusters, each of which is known as an acinus. The pancreatic juice is transported out of the acinus through short intercalated ducts which empty into intralobular ducts. Groups of these acini form lobules and the intralobular ducts from several lobules then join larger interlobular ducts or secondary ducts, which eventually empty into one large main pancreatic duct.
Let's talk about the main pancreatic duct or the duct of Wirsung in a little more detail. Yup, it's the same duct that we saw in our murder mystery that may have cost Professor Wirsung his life. The main pancreatic duct arises at the tail of the pancreas and this is where it's the narrowest, just around one millimeter in diameter. It runs along the length of the pancreas with interlobular ducts continuously joining at right angles, forming what is known as a herringbone pattern. As that happens, the main duct increases in caliber or diameter, and at the head of the pancreas, it's about three millimeters in diameter.
Also at the head of the pancreas, we have another duct which we need to mention. This duct is the bile duct, which is formed by the unification of the common hepatic duct and cystic duct which carry bile away from the liver and gallbladder, respectively. The reason we're mentioning the bile duct is due to the fact that it joins together with the main pancreatic duct to form a short channel known as the hepatopancreatic ampulla, which is also known as the ampulla of Vater or pancreaticobiliary junction. Just like our Dr. Wirsung, the ampulla of Vater is, of course, named after the first man to describe it - Abraham Vater. Fortunately, no one tried to take his life for his discovery. Another interesting fact about this duct is that it marks the transition between the foregut and the midgut.
The bile and digestive enzymes carried by the hepatopancreatic duct then enter the duodenum. Let's pause here for a minute for an overview of the different parts of the duodenum.
Related to the body of the pancreas, we have the first segment of the duodenum known as the pyloric canal, which is the transition between the stomach and the duodenum. At the end of the pyloric canal, we have the pyloric orifice, which is an opening into the superior duodenum. At the neck of the pancreas, you find the superior part of the duodenum. The C-shaped descending part of the duodenum houses the head of the pancreas. At its superior end, we have the superior duodenal flexure, and at its inferior end, we have a corresponding inferior flexure. At the inferior border of the uncinate process, we find the horizontal part of the duodenum. Moving laterally, it becomes the ascending part of the duodenum. And, lastly, in this image, we have the duodenojejunal flexure, which simply refers to the curved transition point between the duodenum and the jejunum.
Looking back to the hepatopancreatic duct, we can now see that it enters the descending part of the duodenum through the major duodenal papilla, which is an opening in the wall of the duodenum at around the L2 to L3 vertebral level. It pokes out between the circular folds which line all of the small intestine from a few centimeters below the pylorus, but are especially pronounced in the duodenal region.
Fun fact: In approximately twenty-five percent of people, the bile duct and the main pancreatic duct empty independently at the duodenal papilla.
Okay, let's take a moment now to think about how the pancreatic duct system works in the human body. The alimentary tract - or the organ through which food and liquid are passed as they make their way through the digestive system - is essentially a long tube that begins at the mouth and ends at the anus. If it were a simple network of tubes, there would be a constant outflow of fluid even when we are not digesting food. But the body is a beautifully tuned clever machine and has, of course, come up with the solution. At each of the ducts, we have a valve-like structure called the sphincter. When this band contracts, the outflow from the duct is reduced. When it relaxes, such as after we have ingested food, the flow is recovered.
In our pancreatic duct system, we have three sphincters. There is one controlling the flow of bile from the bile duct and another surrounding the pancreatic duct controlling the flow of pancreatic enzymes. The last sphincter is called the hepatopancreatic sphincter or the sphincter of Oddi, which surrounds the hepatopancreatic duct.
You might have already noticed that the main pancreatic duct is not the only duct in the pancreas. This little guy that you can see highlighted now is called the accessory pancreatic duct or the duct of Santorini and it drains the upper part of the head of the pancreas. Just like the main pancreatic duct, it empties into the descending part of the duodenum. However, it's connected to the duodenum through a different opening. This structure here is called the minor duodenal papilla. It's slightly smaller than the major duodenal papilla and sits a little bit superior to it.
Okay, now it's time to get clinical.
Today, we're talking about a condition with a bit of a strange name, which, to some of you might be more of a mystery than ProfessorWirsung's untimely death. The condition in question is pancreatolithiasis. This simply refers to the formation of stones or calculi in the pancreas. Formation of calculi is caused by chronic pancreatitis which is inflammation of the pancreas. This inflammation in itself has a varied etiology ranging from alcohol abuse to malfunctions of the parathyroid gland. However, this does not necessarily influence the formation of stones.
Calculi are associated with about fifty percent of cases of pancreatitis. Calculi may form in the parenchyma of the pancreas, but they are most common in the duct system - either in the main duct or one of the smaller branches. Calculi are deposits of calcium carbonate surrounding a central nidus, which refers to the center of the stone, which can contain materials like nickel, iron, and chromium.
The main symptom of these stones is pancreatic pain, which can seriously affect the patient's quality of life. The pain is a result of hypertension, which refers to the buildup of pressure in the blocked ducts. The treatment may be the most interesting part of pancreatic calculi. The stones may be located using endoscopic retrograde cholangiopancreatography, which is a procedure of lowering a tube into the duodenum through the mouth and injecting dye, which flows in the opposite direction to bile to localize the stones.
Smaller stones can then be extracted by making a small incision in the sphincter, while the larger stones need to be broken down using extracorporeal shock wave lithotripsy. This technique literally means breaking up the stones using ultrasound.
Okay, guys. That's everything we wanted to teach you today. Let's recap what we learned.
We started by briefly looking at the location of the pancreas in the body and its functions as an endocrine and exocrine gland. We also looked at the anatomical divisions of the pancreas, most of them related to a different part of the duodenum. We saw the tail first and then the body, which was released to the pyloric canal. We also saw the pyloric orifice constricted by the pyloric sphincter.
The neck was right next to the superior part of the duodenum; the head snugly fit into the C-shaped descending part of the duodenum with its superior and inferior duodenal flexures; and finally, the uncinate process was closely related to the horizontal part of the duodenum and also the ascending part of the duodenum. The duodenum ended with the duodenojejunal flexure - the transition point into the jejunum.
We then moved on to look at the internal structure of the pancreas to understand the complexity of the pancreatic duct system. We saw that the pancreatic enzymes are produced in acini, which empty into small intralobular ducts which then form larger interlobular ducts. These finally join the main pancreatic duct.
In the majority of people, the main pancreatic duct joins the bile duct to form the short hepatopancreatic ampulla in the head of the pancreas, which empties into the duodenum through the major duodenal papilla. We encountered a series of sphincters which control the outflow from the ducts. We saw the sphincter of the bile duct, the sphincter of the pancreatic duct, and the hepatopancreatic sphincter, also known as the sphincter of Oddi. We also identified the accessory pancreatic duct which, when present, drains the superior part of the head at the pancreas through the minor duodenal papilla into the descending part of the duodenum.
In our clinical notes, we looked at a painful condition known as pancreatolithiasis in which pancreatic calculi or stones form and block the pancreatic duct system.
And that concludes today's tutorial. We hope you enjoyed it and happy studying!