I’m a week into my surgery placement, and so far it’s been absolutely nothing like an episode of Grey’s Anatomy. There’ve been no brawls in the operating theatre and no raging arguments over surgical management of patients. And there hasn’t been even a whiff of a romantic “will they/won’t they” storyline between doctors on the ward. I’m starting to think that Grey’s Anatomy just isn’t all that true to life. Plus, they’re still putting CT films up on light boxes at Seattle Grace Hospital. I think maybe they need to update their IT. It’s really much more convenient on a computer screen.
All that aside, I’ve learnt a boatload this week. My knowledge of anatomy is pretty good, even under pressure. Borders of the inguinal canal? Check. Layers of the abdominal wall? You got it! I’ve only made an idiot of myself once (that I’m aware of), and I spent yesterday afternoon examining hernias and then watching them get repaired in theatre. The day starts early, and Friday’s ward round definitely wins the prize for the shortest I’ve ever been on- from start to finish in just 17 minutes. And because of all this, there’s a lot of free time for independent study. And for drinking coffee, of course. One thing that did come up this week was pancreatitis, and as I didn’t know anything about it I thought it best to look it up before Monday morning rolls around. This is the first of 2 posts on this topic, and will cover the function and anatomy of the pancreas. Part 2 will be all about acute pancreatitis (which I’ve now posted, and you can find here! It includes a totally hilarious educational video made by and starring myself, so check it out).
It’s probably a good idea to remind ourselves of what the pancreas does, and do a bit of an anatomy refresher too.
The pancreas has both endocrine and exocrine functions.
The Endocrine Pancreas
is made up of Islets of Langerhans. The islets of Langerhans are made up of 4 different types of cells, which secrete substances into the blood:
Alpha cells– glucagon secreting
Beta cells– insulin secreting
Delta cells– somatostatin secreting (to regulate alpha and beta cell function)
PP cells– secrete pancreatic polypeptide, which regulates pancreatic and gastrointestinal secretions.
The Exocrine Pancreas
is involved in digestion, and to this end the pancreas secretes enzymes to assist digestion into the duodenum via the pancreatic ducts. Control of the exocrine function of the pancreas is by secretin, gastrin and cholecystokinin, which are secreted by cells in the stomach and duodenum. Two different cell types in the pancreas are responsible for its endocrine function:
Centroacinar cells– secrete bicarbonate ions to neutralize acidic chyme expelled from the stomach
Basophilic cells– secrete digestive enzymes, including proteases (trypsinogen, chymotrypsinogen), pancreatic lipase and amylase.
Anatomy of the Pancreas
The pancreas is a retroperitoneal organ, posterior to the stomach and between the duodenum on the right and the spleen on the left. The pancreas is divided into 4 parts- head, neck, body and tail.
The head of the pancreas is the part of the gland that the duodenum wraps around (to the right of the superior mesenteric vessels, ie, artery and vein). It attaches to the medial aspect of the descending and horizontal parts of the duodenum. The uncinate process (from the Latin “uncus” for hook) is a projection from the inferior part of the pancreatic head and extends medially to the left, posterior to the superior mesenteric artery. The head of the pancreas lies on top of the inferior vena cava, right renal artery and vein and the left renal vein. The bile duct lies in a groove on the posterosuperior surface of the head, or is embedded in its substance and opens in the descending part of the duodenum.
The neck of the pancreas overlies the superior mesenteric vessels. The anterior surface of the neck is covered by peritoneum and is adjacent to the pylorus of the stomach. The superior mesenteric vein joins the splenic vein posterior to the neck to form the portal vein.
The body of the pancreas continues from the neck and lies to the left of the superior mesenteric vessels, passing over the aorta and L2 vertebra. The anterior surface of the body of the pancreas is covered with peritoneum and forms part of the stomach bed. The posterior surface has no peritoneal covering and is in contact with the aorta, superior mesenteric artery, left suprarenal gland and left kidney and renal vessels.
The tail of the pancreas lies anteriorly to the left kidney, where it is closely related to the splenic hilum and the left colic flexure. The tail is relatively mobile and passes between the layers of the splenorenal ligament with the splenic vessels. The tip of the tail is usually blunted and turned superiorly.
The main pancreatic duct begins in the tail of the pancreas and runs through the parenchyma of the gland to the pancreatic head: here it turns inferiorly and is closely related to the bile duct. Usually, the main pancreatic duct and bile duct unite to form the short, dilated hepatopancreatic ampulla (of Vater), which opens into the descending part of the duodenum at the summit of the major duodenal papilla. At least 25% of the time, the ducts open into the duodenum separately. The sphincter of the bile duct (around the termination of the bile duct), and the hepatopncreatic sphincter (of Oddi)- around the hepatopancreatic ampulla- are smooth muscle sphincters that control the flow of bile and pancreatic juice into the duodenum. An accessory pancreatic duct opens into the duodenum at the minor duodenal papilla. Usually (60%), the accessory duct communicates with the main pancreatic duct. IN some cases, the main pancreatic duct is smaller than the accessory pancreatic duct and the two are not connected.
The pancreatic arteries derive mainly from the splenic artery, which forms several arcades with pancreatic branches of the gastroduodenal and superior mesenteric arteries. Supply of the pancreatic head is by the anterior and posterior superior pancreaticoduodenal arteries, branches of the gastroduodenal artery, and the anterior and posterior inferior pancreaticoduodenal arteries, branches of the SMA.