Pancreas (anatomy)

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Transcript
00:00One of the reasons I think I'm still in Swansea is because of those beautiful views and being
00:20by the sea. I think I'd miss living by the sea if I wasn't living by the sea anymore.
00:25Anyway, this week I'm going to talk about the pancreas. We've been doing various gastrointestinal
00:41tract stuff the last few weeks. There are a whole bunch of accessory organs or associated
00:47organs of the GI tract and the abdomen. Let's have a look at the pancreas. It's another
00:50one of those organs that's absolutely vital for life but you might not know where it is
00:55or exactly what it does. So, the pancreas. Let's have a look at its structure, its parts,
01:06where it is. We'll have a look in the abdomen and see what is around it so that if you're
01:10then looking maybe at transverse CT scan images or transverse MR images you can work out where
01:16the pancreas is because it's kind of just a squidgy bit of tissue, a squidgy bit of
01:19soft tissue, but you can work out where it is in relation to the other organs around
01:22it. We'll look at the blood supply. We'll look at where it is in relation to the GI
01:28tract. We'll talk about its exocrine function, its endocrine function. We'll have a little
01:31look at the histology, a little look at the cells and the ducting and stuff and we'll
01:36talk about what happens when it doesn't work quite how it should work. Shall we?
01:40So, let's have a look and see where it is first. You can see the lab's got a bit of
01:43a funky set up today. We're in the middle of a formative exam week for the first years
01:47so the room is set up for OSCEs. You know OSCEs? Like clinical skills exams? So you've
01:52got, you can be poking and prodding each other and actors and that. Anyway, it's tomorrow
01:58I think so I'd better tidy up after myself. Right, there's the liver. So we're taking
02:02the liver out. Remember the liver is wrapping around the inferior vena cava. So the inferior
02:07vena cava is going up there into the heart. Here's the stomach. Notice we've got the diaphragm
02:12here. So we've got a series of ribs here. Look, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. So
02:20there's the spleen around here, right? 9, 10, 11th ribs. So you see the level we're
02:27at? If we take away the stomach, now we see the pancreas. Here's the pancreas here. Right,
02:37so there's the large colon there. There's the greater omentum on that side. Here's
02:41the pancreas and here's the spleen here. The esophagus is just poking out there. This
02:49is kind of diaphragm curving around behind it. If I take off, so if I'm taking off the
02:59pancreas, here's the left kidney here, there's the left adrenal gland. So the pancreas is
03:05cutting across the upper half of the left kidney, isn't it? Right, and notice how here
03:16we've got the abdominal aorta and the inferior vena cava and these are the branches of, look,
03:22there's the celiac trunk, there's the superior mesenteric artery and there's the inferior
03:27mesenteric artery there. So the pancreas is overlying all of that stuff. And most of these
03:33things, so the stomach and the large intestine and the small intestine, of course, are within
03:37the peritoneal cavity or within the greater sac. Where's the pancreas in relation to the
03:42peritoneum then? Well, it's retroperitoneal. So the peritoneum is covering the pancreas
03:47and it's covering the kidneys. And the stomach is then attached to the spleen and the posterior
03:52abdominal wall by mesentery. So the stomach is within the peritoneal cavity but the pancreas
03:58is retroperitoneal. And we can see, here's the duodenum here and it's curling around
04:04and we can't see all of it because the large intestine's in the way, but the pancreas is
04:09nestled into the curve of the duodenum. So the duodenum is partly retroperitoneal and
04:15partly in the peritoneal cavity. We can see up here, there's the celiac trunk and it's
04:21giving off some blood vessels there. So if I take this model, which is some of that stuff
04:41taken out, right? You can see there's the pancreas here and there's the duodenum curling
04:45around it. And the duodenum is really important to the pancreas. The pancreas is really important
04:50to the duodenum. The pancreas itself has a head at this end and what we call an unsunit
04:56process which is difficult to see here, but there's a bit of pancreatic tissue hanging
05:01down here into the curve of the duodenum. So it's got the head and then the neck and
05:05then the tail of the pancreas extends out into the hilum of, this is the spleen here.
05:10And we can see the blood supply to the pancreas quite nicely. This is it here. Now, as I said,
05:17that's the celiac trunk, which is here coming out of the abdominal aorta. And the celiac
05:23trunk then is giving off a number of arteries, but one of its arteries is this one here.
05:26This is the splenic artery and clearly it's supplying blood to the spleen over here. But
05:31the splenic artery is running along the superior edge of the pancreas. And in fact, when we
05:37look at this in cadavers and in people, we see that it's kind of wiggly. It's kind of
05:41a wiggly artery and it's maybe a little bit embedded in the tissue around here. Just on
05:47the other side there, posteriorly, here's the splenic vein draining blood from the spleen
05:52back to the portal vein. In fact, the portal vein forms as the splenic vein joins with
05:56the inferior mesenteric vein here and there's the superior mesenteric vein joining with
06:01it.
06:06So the blood supply to the pancreas then is from the celiac trunk. We do have these pancreatic
06:14duodenal arteries here looping around. We've got superior and inferior. We've got anterior
06:21and posterior. They're largely supplying blood to the duodenum as much as anything else,
06:25but obviously they're probably going to be supplying blood to the head of the pancreas
06:28in the incident process as well. But it's this splenic artery that here that's sending
06:31off lots of little blood vessels into the pancreas and that's supplying blood to the
06:34pancreas. And then the splenic vein is draining blood from the pancreas. And that's really
06:38important because the pancreas, it chucks out a load of hormones, right? So it does
06:44stuff with the blood and does stuff with other bits of the body, which leads us into the
06:49functions of the pancreas. So if we look at the cells within the pancreas, we find two
06:56types of cells, two groups of cells. We find that most of the pancreas is made up of exocrine
07:03cells. So exocrine cells, exocrine means to be secreting through a duct onto an external
07:10surface. And in the case of the pancreas, it's these exocrine cells are producing a
07:15secretion that's secreted into the GI tracts. And the GI tract, the gastrointestinal tract
07:21is considered an external surface within us, right? An external internal surface, right?
07:25There's a tube running through us, open either end. See what I mean? Most of the cells of
07:32the pancreas are making pancreatic juice, this exocrine secretion that's secreted into
07:38the duodenum and that aids with digestion. And then within the pancreas, we see clusters
07:45of cells, little islands of cells, which get called islets or islets of Langerhans after
07:49the guy that first described them. And in those islets, we find endocrine cells and
07:57those endocrine cells are secreting hormones. So endocrine means to be putting something
08:02into the blood that affects other parts of the body. So the endocrine cells, we have
08:07alpha, well, we've got alpha cells, beta cells, and delta cells. They're the ones right to
08:11start with. Alpha cells produce glucagon, beta cells produce insulin, and delta cells
08:18produce somatostatin. So this leads us to probably the most famous function of the pancreas
08:24and that's regulating blood glucose. So glucagon is secreted when blood glucose levels are
08:33low and they encourage the release of stored glucose, as in glycogen, to be released from
08:40things like the liver, where glycogen is stored, into the blood. So the glucose levels come
08:46up again, right? Because you use glucose as an energy source for all your cells around
08:49the body. Insulin does the opposite. So you just had a big meal, all that's been digested,
08:55you got loads of glucose in your blood. Insulin goes into the blood and tells all the cells
08:59of the body, liver and other things as well, to take that sugar and store it away. Store
09:04that glucose as glycogen for a bit until we need it. So that then brings the blood sugar
09:08levels down. So glucagon and insulin work in opposition to manage blood glucose levels.
09:14Obviously there are other parts of the body involved in this. But it's in type 1 diabetes
09:19where beta cells of the pancreas are destroyed, it's usually an autoimmune thing, right? And
09:27someone then doesn't have enough beta cells, doesn't produce enough insulin. So then they
09:32have to do this manually. They have to manage what they eat and they have to inject insulin
09:37regularly to manage their blood glucose levels themselves, which is an arduous process. You
09:42have to measure your blood glucose and keep track of that and, you know, it's a bit of
09:47a pain. Type 2 diabetes is different. That's where the cells of the body start to become
09:53a bit indifferent to insulin and just say, we see sugar all the time, it's cool, don't
09:58worry about it. And you get a whole bunch of other problems. But type 1 diabetes is
10:02caused by a loss of beta cells in the islets in the pancreas, so you can't make enough
10:08insulin. Now there are also gamma and epsilon cells. Now somatostatin produced by the delta
10:15cells generally suppresses the production of all the gastrointestinal hormones. So we
10:23talk about the GI tract and the pancreas as well. They're innervated by sympathetic and
10:27parasympathetic nervous systems and we talk about the parasympathetic nervous system as
10:31being involved in rest and digest functions, right? So parasympathetic innervation stimulates
10:35the GI tract to digest stuff and absorb stuff, right? But in fact, a lot of these organs
10:43and a lot of these secretions and a lot of the control is actually endocrine. So there
10:48are hormones secreted and these balances of hormones, we've got the pituitary gland and
10:51other bits of the body, they all work together in concert to manage the activity of the GI
10:56tract. So somatostatin will slow down the activity of the stomach and hormones being
11:04produced by other parts of the GI tract and that sort of thing. And the somatostatin will
11:08also affect the production of glucagon and insulin, right? So we've got all these. Right,
11:12if I start talking about physiology, we will be here all day. The gamma cells make pancreatic
11:17polypeptide which also regulates activity of pancreatic endocrine cells and the epsilon
11:25cells make ghrelin. Ghrelin is most famous as being like the hunger hormone, regulates
11:31appetite, right? So if you've got lots of ghrelin, you feel full, you feel saturated,
11:37you feel, you know, something like that, anyway. So those are the endocrine cells of the pancreas
11:43within the islets of Langerhans. Now the exocrine cells, we've got these secretory cells kind
11:50of arranged in like around an acinus, right? It's kind of on a curve and they're secreting
11:56into a space and then that, what they secrete into, that space goes into a duct and that
12:01duct goes into other ducts and other ducts and other ducts and eventually you see this
12:05duct here. So this is the main pancreatic duct running the length of the pancreas. We've
12:11got this herringbone shape because we can see the other ducts ducting into it. The exocrine
12:15secretions of the pancreas are things like trypsin, chymotrypsin, amylase. And we've
12:21talked before about how, so trypsin and chymotrypsin are proteases, so they break down proteins.
12:30You're made of proteins, so proteases are quite dangerous to you, right? So we've got
12:34a tissue secreting dangerous things that could break the tissue down. So they're secreted
12:40by the cells and they're packaged up nice and tidily in an inactive form and then they
12:45pass along the main pancreatic duct and are secreted into the duodenum here and it's in
12:51the duodenum that they get activated. Again, more physiology. You want to know how? That's
12:56another day. So these enzymes, ideally, they get activated in the duodenum and then those
13:02proteases can break down the proteins. We've also got pancreatic lipase that's going to
13:06break down fats. We've got amylase that's going to break down starches into, what, maltose?
13:17We've got gelatinase, elastase, you've got deoxyribonuclease and that sort of thing.
13:25So there's a whole bunch of things being secreted by the pancreas that help with digestion in
13:28the duodenum. That's the important bit, right? So these exocrine secretions from the pancreas
13:32secrete into the duodenum. Now, can you see there's two ducts here? There's a main pancreatic
13:37duct which is actually the inferior one, the lower one here. Then there's an accessory
13:41pancreatic duct here which is a little ditty one. Now, this occurs because in the embryo
13:48there's a simple gut tube and it's held in place by, up at the level of the stomach,
13:54there's a posterior, like a dorsal mesentery, which we call the mesogastrium, gaster, because
13:59it's next to the stomach. And there's a ventral mesogastrium, because it's at the level of
14:03the stomach, between the future stomach tube and the anterior abdominal wall. And then
14:08we see a couple of buds growing from the early GI tract. And those buds go on and form
14:14various things. They form the liver and the gallbladder and they form two pancreases.
14:20So there's an anterior pancreatic bud and there's a posterior pancreatic bud, or dorsal
14:24and ventral if you like. And then the stomach, right? The stomach rotates around and pulls
14:30the duodenum with it and stuff like that. And when it does that, it brings these two
14:34pancreatic buds around and they meet together. So that's why, when we look at the adult pancreas,
14:42we see two ducts, because really the uncinate process down here, that's kind of the other
14:46bud, right? The little bud. And this is the big bud, the big pancreatic bud here. Those
14:51two pancreatic buds have been brought together and they have their own duct because that's
14:55how they formed. They ducted from the GI tract and then they formed. Basically, this is endoderm
15:02because this is the GI tract, so endoderm is forming the innermost layer. And then the
15:07cells of the pancreas are formed from endoderm. They follow different differentiation pathways,
15:10whether to become exocrine cells or endocrine cells, and then further differentiate it into
15:14becoming all those different cells we've been talking about. Anyway, so this main pancreatic
15:23duct in most people collects most of the exocrine secretions and ducts into the duodenum here.
15:35And the other thing is, right, you see the green tube here? Now, I said that the gallbladder and
15:40the liver also grow out in the same outpouching, right? So there's another tube connecting the
15:45gallbladder and the liver because bile comes from the liver, right? And then backs up and
15:50gets stored in the gallbladder. Anyway, this is the common bile duct. So the bile duct also loops
15:56around. The bile duct and the main pancreatic duct both duct into the duodenum at the same point
16:02through the same hole. Now, the common bile duct has its own sphincter of smooth muscle,
16:08which it can close off. And the main pancreatic duct has its own sphincter of smooth muscle,
16:13which it can also close off. But it's obscured by this blood vessel here. But just before
16:20those two ducts come together and duct into the duodenum at the same place, there's an ampulla.
16:25So an ampulla, ampule, right? You know, it's, you've got a tube and it kind of, you know,
16:33right, ampulla, kind of a little bit of a dilation of a tube. So there's a hepatopancreatic ampulla
16:41as those two tubes meet, which also, which used to get called the ampulla of Vata.
16:47And then they both, around the ampulla of Vata or the hepatopancreatic ampulla,
16:53there's another smooth muscle sphincter, which is the hepatopancreatic sphincter
16:58or the sphincter of Ody, which is a great name, but it is his old name.
17:04So all those sphincters then can control the flow of exocrine pancreatic juice into the duodenum
17:11and bile from the common bile duct into the duodenum. And that's what we see in about 90%
17:18of people, we see that organization. And this accessory pancreatic duct up here
17:22just drains his pancreatic juice into the main duct and it pops out there. But in about nine
17:27or 10% of people, you'll see a second opening up here in the duodenum. This is the descending or
17:33second part of the duodenum, by the way. And there will be the accessory pancreatic duct will open
17:40at an accessory papilla. So there's a little papilla, a little mound
17:46in here where the main pancreatic duct opens in some people. And in fact, on this model,
17:52there is a second opening there. So if you're doing an endoscopic process and you're looking
17:58down the duodenum and you find one opening and then you find a second opening, that's fine.
18:04It's not terribly unusual. So that's how the exocrine secretion of the pancreas gets into
18:09the duodenum. The endocrine secretion goes straight into the blood. All right, so that's
18:12some of the functioning of the pancreas. Now we were looking at structures nearby.
18:16There's another cool thing to notice. So you remember that the abdominal aorta is running
18:24just posterior to it and we can see the celiac trunk here. Now that we've talked about the
18:29duodenum curling around and the pancreas running across, can you see here? Look how the
18:36superior mesenteric artery and superior mesenteric vein appear from between the pancreas and the
18:46duodenum and then they run anteriorly. So that's another good landmark. That's how you find the
18:50superior mesenteric artery, right? Oh, also the epithelial cells of the pancreas make bicarbonate.
19:01Stomach makes acid, bicarbonate neutralizes the acids from the stomach, comes from the pancreas.
19:07So what could go wrong with the pancreas then? Well, we've already talked about diabetes
19:11and loss of the beta cells, loss of the ability to produce as much insulin as you need.
19:17Actually, from a tissue engineering standpoint, now that you know about the embryology,
19:25it would be possible, wouldn't it, to take embryonic stem cells and then differentiate
19:30them into endoderm and then into, you know, down a GI tract pathway and into pancreatic cells and
19:37you could, if you could work it out, you could cause these cells to differentiate into
19:42beta cells and you could take your population of beta cells and say inject them into the portal
19:48vein and they would seed the liver or something like that and then the patient would have
19:55beta cells and they could produce insulin. Would that be a cure for type 1 diabetes? Maybe.
19:59People have already tried that and it seems to be working. I think the latest idea is to
20:04package these cells in a different manner and put them under the skin and what have you, but
20:08cool, huh? Tissue engineering, got to understand the embryology and blah blah blah blah blah.
20:13So that's type 1 diabetes. Now, because the bile duct and the main pancreatic duct are ducked
20:21into the duodenum in the same place, you've heard of gallstones, right? So you can get stones in the
20:28biliary tree in the bile duct. You get them in different places and it's possible, of course,
20:32that the bile stone, if it's formed higher up, could move down the common bile duct. So it's
20:36possible that you could get a gallstone lodging in here, say in the hepatopancreatic ampulla,
20:43which would not only prevent bile from going into the duodenum, but it would also prevent
20:49exocrine pancreatic juice from passing from the pancreas into the duodenum.
20:53Now, what do you think that would lead to? Well, you'd get, you know, you wouldn't be able to get
21:00rid of all the bilirubin from the liver. So you start to get rising levels of bilirubin, so the
21:07colour of the skin would become yellow, would become jaundiced, right? So you'd see some liver
21:11dysfunction, but also you'd start to see signs of acute pancreatitis. You'd start to get inflammation
21:16of the pancreas and damage to the pancreas, which would be bad. You can get acute pancreatitis for
21:22other reasons as well. So, you know, I said that we've got these dangerous proteases, these enzymes
21:28which could digest tissues, proteins of the pancreas, and they're packaged up and then released
21:35safely into the duodenum. Well, if that process is broken down, if that packaging isn't made correctly,
21:41if those proteases, if those dangerous enzymes aren't safely packaged away, then they can
21:48damage the pancreas. And then you'll see inflammation of the pancreas. And again,
21:53acute pancreatitis, you kind of get this pain developing and this sort of thing. So acute
21:58pancreatitis is dangerous, and it has something like a 10% mortality rate, so it's very dangerous.
22:05And you usually get like an onset of mild pain, which gets worse and worse and worse.
22:10The pain gets worse with eating. Makes sense, because of course you've got all the triggers to
22:16make your pancreatic juice and secrete it and put it in the duodenum, but it can't get into the
22:19duodenum. Or it's damaging the pancreas, so pain increases. People tend to be very, very
22:24ill with acute pancreatitis. You have to go to hospital and often get a nice surgeon to help you
22:30out. So acute pancreatitis can be caused by a couple of things. Think gallstones here, and think
22:37poor packaging of those dangerous enzymes. So that might be a result of use of a certain drug,
22:41or alcohol, or you know, something like that. What else? Oh, pancreatic cancer. Pancreatic
22:50cancer is very, very dangerous. Acute pancreatitis can be difficult to diagnose,
22:57because there's a lot going on around here. Pancreatic cancer likewise can be very difficult
23:03to spot and to diagnose. If the cancer forms up here somewhere, then the pancreas is probably
23:08functioning just fine, and there are very few signs that there's a tumour forming in the pancreas.
23:13And the tumour can spread quite easily from the pancreas. Now, if the tumour forms in the head
23:17of the pancreas, that's better, because it's going to block the ducts down here and may lead to signs
23:26of acute pancreatitis and jaundice much earlier. So you get an early sign of a problem, and then
23:32you can hopefully diagnose pancreatic cancer and remove it early. But the reason pancreatic cancer
23:37is so dangerous is because it'll often form in the tail of the pancreas and give virtually no
23:44warning signs at all, and it'll get larger and spread. So it has a very high mortality rate. I
23:49think you get, does it get called the silent cancer or something like that? So pancreatic
23:54cancer, very, very dangerous. So how's that? We've looked to see where the pancreas is.
23:59So if you're looking at a transverse section of the abdomen on CT or MR, for example,
24:05then look for the pancreas posterior to the stomach. The stomach you might see as a dark
24:12space with air in it. Anterior to the aorta. You should be able to spot the aorta and the inferior
24:18vena cava. Anterior to the kidneys. Those are your landmarks, right? So anterior to the left kidney
24:24there. And if you've got the spleen in your section, you're probably too high. We've talked
24:29about the functions of the pancreas generally. There's a huge amount of physiology going on
24:34there, but that's somebody else's job. We've talked about what can go wrong with the pancreas.
24:37We've talked about the blood supply. I briefly talked about the innervation. So there's
24:42parasympathetic and sympathetic innervation to the pancreas, but most of the control of the
24:46pancreas is endocrine. It's under hormonal control. Parasympathetic innervation is through
24:52the vagus nerve, of course, everything through the vagus nerve down here. And there you go.
24:57So quick overview of quick. Yeah, when do I ever do anything quick? Look at the anatomy of the
25:04pancreas. Hopefully it'll serve you in good stead. Right, what's left in the abdomen to talk about
25:10next time.
25:40Bye.