The pancreas is an accessory organ and exocrine gland of the digestive system, as well as a hormone producing endocrine gland. It is a retroperitoneal organ consisting of five parts and an internal system of ducts. The pancreas is supplied by pancreatic arteries stemming from surrounding vessels and is innervated by the vagus nerve (CN X), celiac plexus, and superior mesenteric plexus.
This organ is incredibly potent; unregulated, excessive functioning can result in autodigestion, while insufficiency can lead to coma. Spotting the latter situation typically involves an unconscious (diabetic) person who may have fruity breath.
External: head, uncinate process, neck, body, tail
Internal: main pancreatic duct (of Wirsung), accessory pancreatic duct
|Function||Digestion by releasing peptidases, lipases, nucleases, amylases
Hormonal regulation by releasing insulin (beta cells), glucagon (alpha cells), and somatostatin (delta cells)
|Blood vessels||Pancreaticoduodenal, splenic, gastroduodenal, and superior mesenteric arteries|
Parasympathetic: vagus nerve (CN X)
Sympathetic: greater and lesser splanchnic nerves
|Lymphatics||Pancreaticosplenic and pyloric lymph nodes|
In this article, we’ll explore the anatomy of the pancreas, including its location, blood supply, innervation, lymphatics, function, and some relevant clinical aspects.
The pancreas is an elongated organ (approximately 15 cm) which lies obliquely across the posterior abdominal wall, at the level of the L1 and L2 vertebral bodies. To put it in a clinical context, its oblique position makes it impossible to see the entire pancreas in a single transverse section. The pancreas comes in contact with several neighboring structures as it traverses the epigastric, left hypochondriac, and a small portion of the umbilical regions of the abdomen.
|Anterior||Stomach, lesser sac (omental bursa), transverse mesocolon, superior mesenteric artery|
|Posterior||Aorta, inferior vena cava, right renal artery, right and left renal veins, superior mesenteric vessels, splenic vein, hepatic portal vein, left kidney, left suprarenal gland|
|Medial||Duodenum (descending and horizontal parts)|
With the exception of the tail, the pancreas is situated in the retroperitoneal space of the abdominal cavity, in other words, behind the peritoneum.
Since you now have a clear understanding about the location of the pancreas, it is time to explore its anatomy. This parenchymatous organ is divided into five anatomical parts; the head, uncinate process, neck, body and tail.
The head is the expanded medial part of the pancreas. It lies directly against the descending and horizontal parts of the C-shaped duodenum which wraps around the pancreatic head. Projecting inferiorly from the head is the uncinate process, which extends posteriorly towards the superior mesenteric artery. Continuing laterally from the head is the neck, a short structure of approximately 2 cm that connects the head with the body. Posterior to the neck are the superior mesenteric artery and vein and the origin of the hepatic portal vein – formed by the union of the superior mesenteric and splenic veins.
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After the neck, the pancreas continues with the body, which consists of two surfaces (anterior and posterior) and two borders (superior and inferior). It is located anterior to the L2 vertebra, and also forms the floor of the omental bursa (lesser sac). The aorta, superior mesenteric artery, left renal vessels, left kidney, and left suprarenal gland are situated posterior to the pancreatic body. Finally, the intraperitoneal tail is the last part of the pancreas. It is closely related to the hilum of the spleen and runs with the splenic vessels in the splenorenal ligament.
Traveling within the entire pancreatic parenchyma from the tail to the head is the main pancreatic (Wirsung) duct. It connects with the bile duct in the head of the pancreas to form the hepatopancreatic duct, otherwise called the ampulla of Vater. This opens into the descending part of the duodenum at the major duodenal papilla. Flow through the ampulla of Vater is controlled by a smooth muscle sphincter called the (hepatopancreatic) sphincter of Oddi. It also prevents reflux of duodenal contents into the hepatopancreatic duct. The terminal parts of the main pancreatic and bile ducts also have sphincters, which play an important role in controlling the flow of pancreatic and bile fluids.
In addition to the main duct, the pancreas also contains an accessory duct. It communicates with the main pancreatic duct at the level of the pancreatic neck and opens into the descending part of the duodenum at the minor duodenal papilla.
The pancreas is a unique organ because it fulfills both exocrine and endocrine roles. Its exocrine function includes the synthesis and release of digestive enzymes into the duodenum of the small intestine. Its endocrine function involves the release of insulin and glucagon into the bloodstream, two important hormones responsible for regulating glucose, lipid, and protein metabolism.
The main players responsible for pancreatic function are endocrine and exocrine glands. The latter synthesize inactive pancreatic digestive enzymes (zymogens), which are released into the glandular and pancreatic ductal systems. Upon reaching the duodenum, the zymogens are activated by proteolytic enzymes, becoming active peptidases, amylases, lipases and nucleases which act to further digest food entering the small intestine from the stomach.
The endocrine function of the pancreas is carried out by the pancreatic islets of Langerhans. These endocrine glands secrete hormones directly into the bloodstream and consist of three main cell types (alpha, beta, and delta) which. Don’t worry, you don’t need to know the entire Greek alphabet to understand the functions of the pancreas! In a nutshell, beta cells secrete insulin, alpha cells release glucagon, and delta cells produce somatostatin. These hormones are crucial in regulating glucose metabolism and gastrointestinal functions.
The pancreas receives its blood supply from several sources. The uncinate process and head are supplied by the superior and inferior pancreaticoduodenal arteries, which are branches of the gastroduodenal and superior mesenteric arteries respectively. Each pancreaticoduodenal artery has anterior and posterior branches that project along the respective faces of the pancreatic neck where they form pancreaticoduodenal arcades and supply them with arterial blood.
In turn, the body and tail of the pancreas are supplied by pancreatic arteries that stem from the splenic, gastroduodenal, and superior mesenteric arteries. The major contributor is the splenic artery.
Pancreatic veins are responsible for draining deoxygenated blood from the pancreas. The anterior superior pancreaticoduodenal vein empties into the superior mesenteric vein, while the posterior variant empties into the hepatic portal vein. Both the anterior and posterior inferior pancreaticoduodenal veins drain into the superior mesenteric vein, while the pancreatic veins draining venous blood from the body and tail empty into the splenic vein.
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The pancreas receives involuntary innervation via the autonomic nervous system (ANS). Its parasympathetic innervation originates from the vagus nerve (CN X) and its sympathetic innervation from the greater and lesser splanchnic nerves (T5-T12). Both types of autonomic fibers travel until the celiac ganglion and superior mesenteric plexus, ultimately projecting onto the pancreas.
Inside the organ, they carry nerve impulses to the acinar cells and the pancreatic islets. Parasympathetic fibers induce secretion from acinar cells, ultimately resulting in the release of pancreatic juice, insulin and glucagon. In contrast, sympathetic fibers cause vasoconstriction and inhibition of exocrine secretion, in other words, inhibition of pancreatic juice. In relation to hormonal release, sympathetic innervation stimulates the release of glucagon but inhibits that of insulin.
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Lymph is drained from the body and tail of the pancreas via lymphatic vessels that empty into the pancreaticosplenic lymph nodes located along the splenic artery. The vessels draining the head empty into pyloric lymph nodes. Subsequently, lymph is transported to the superior mesenteric or celiac lymph nodes.
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Pancreatitis is an inflammatory process of the pancreas that can be acute or chronic. The most common causes of acute pancreatitis include gallstones (obstruction of pancreatic flow), and alcohol (increase in pancreatic enzyme synthesis). Acute pancreatitis manifests by severe epigastric pain, nausea, and vomiting. Physical examination reveals epigastric tenderness, hypoactive bowel sounds, fever, tachypnea, periumbilical and flank ecchymoses, and possibly jaundice if the cause is a gallstone. Laboratory investigations evidentiate elevated serum amylase and lipase levels. Management of acute pancreatitis involves fluid therapy, pain control, and close monitoring, and treatment of the underlying cause.
On the other hand, chronic pancreatitis involves a progressive inflammation over a long period of time that causes permanent structural damage. Chronic pancreatitis manifests quite nonspecifically or even asymptomatically until the appearance of pancreatic insufficiency. At that point, the patient starts to experience pale, clay-colored stools (steatorrhea) from fat malabsorption and diabetes. Management of chronic pancreatitis generally involves pain control, pancreatic enzyme supplements, as well as vitamin and lipase replacements.