The Anatomy of the Pancreas

The pancreas produces insulin and other enzymes essential to digestion

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Located in the upper abdomen between the spleen and the duodenum (the uppermost section of the small intestine just past the stomach) in, the pancreas is an important digestive and endocrine organ. Serving this dual function, it’s made up of two kinds of glands: exocrine and endocrine. The former of these produce enzymes for digestion, while the latter contribute hormones to the bloodstream. It has an elongated shape that tapers from widest to narrowest as it goes from right to left, resembling a single quotation mark that’s been rotated 90 degrees to the left.

Diseases or disorders of the pancreas can be dangerous, disruptive, and require serious medical attention. The most common of these are pancreatitis (an inflammation of this organ), pancreatic cancer, and perforation (in which digestive enzymes cause holes in the surface). Notably, pancreas function can become severely impacted by diabetes mellitus types I and II, which impact insulin production.      

Anatomy

Structure

The pancreas is an elongated organ that’s approximately 15 centimeters (cm) long and has a tapered shape. Anatomically speaking, it’s divided into four sections:

  • Head: The head of the pancreas is, as the name implies, the widest portion of the organ. It lies against the descending and horizontal portions of the duodenum, which has a C-shape. Projecting downward from the left, at lateral border is the uncinate process, a small portion of the organ that joins with the superior mesenteric vein. This section also has a bile duct, which plays a role in digestion.
  • Neck: Usually measuring only about 2 cm, the neck of the pancreas connects the head with the body.
  • Body: Widening after the neck, the body of the pancreas crosses the center of the body, with its front portion enclosed in the peritoneum (the dense layer of tissue that surrounds the abdomen), and its rear touching the aorta, the superior mesenteric artery, and left kidney, among other anatomical structures.
  • Tail: The narrowing end of the pancreas represents its tail, which lies just in front of the left kidney. It’s here that you find the primary pancreatic duct that secretes insulin and digestive enzymes.

Notably, the pancreas is composed of two different types of cells, and these determine a great deal about its function. Approximately 80% of the organ is composed of exocrine pancreatic tissue, which is made of specialized cells called “pancreatic acini.” These produce enzymes that combine with bile to serve in digestion. Most of the remaining cells are endocrine cells, and make up portions of the pancreas called “islets of Langerhans;” these are associated with hormone production that can access the bloodstream directly. 

It’s also important to understand the pancreas’s system of ducts as these are essential to its function. Along the length of the organ—from head to tail—is the main pancreatic duct (also known as the “Wirsung duct”), which connects with the bile duct in the head to form the ampulla of Vater, which opens into the duodenum. Movement of bile through this duct is regulated by a smooth muscle structure called the sphincter of Oddi, which prevents material from the intestines from accessing the pancreas. The other ducts also have sphincters that control the outflow of hormones and enzymes.

Location

The pancreas sits in the upper abdomen, at the level of the L1 and L2 vertebrae of the lower back, and it slants slightly as it moves across the posterior abdominal wall. To its right is the duodenum, which wraps around the head of the pancreas, and to its left is the spleen. It sits in front of the left kidney, the left suprarenal gland (which produces hormones such as adrenaline) and aorta, and just below and behind the stomach. The pancreas is what’s called a “retroperitoneal” organ, meaning the peritoneum—an abdominal membrane—is to its front.

Anatomical Variations

Most variations in the anatomy of the pancreas have to do with its system of ducts. It’s important to note that these cases are relatively rare, as approximately 95% of people do not display any variants. By far the most commonly observed of these is a condition called “pancreas divisum,” in which there is abnormal or absent fusion of pancreatic ducts, a case which is estimated to affect between 3% and 14% of the general population. Furthermore, in about 3% to 5% of cases, pancreatic tissue is erroneously found in the stomach or small intestine, though this rarely leads to health problems.    

In much rarer cases, doctors have observed a couple other kinds of variants. These include “ansa pancreatica,” in which the main pancreatic duct and the accessory pancreatic duct are erroneously connected, as well as annular pancreas, wherein the shape of the organ is different, and a ring of pancreatic tissue surrounds the duodenum. In addition, the pancreas can be subject to “duplication anomalies,” in which the main duct is duplicated, which can lead to health problems.

Function

What makes the pancreas unique is that it serves both exocrine and endocrine functions. The former of these means that this organ releases important digestive enzymes to other organs, and in that capacity, it synthesizes and delivers zymogen, an inactivated enzyme, to the duodenum of the small intestine. This substance is activated as it leaves the pancreas by proteolytic enzymes and is converted into several different active digestive substances, including active peptidases, amylases, lipases and nucleases, all of which help break down food coming from the stomach.  

The endocrine function of this organ involves secreting two hormones directly into the bloodstream from the islets of Langerhans. These are insulin and glucagon, which are primarily involved in regulating sugar (glucose) levels in the blood. Whenever the body has sufficient energy, insulin signals liver, muscle, and fat cells to start taking up this glucose in the blood, thereby regulating blood sugar. In contrast, glucagon prevents these levels from dropping to low, stimulating organs to produce and secrete glucose. Ensuring a proper balance here is essential for health.

Associated Conditions

The pancreas can play a role in or be affected by a number of health conditions and diseases. These include:

  • Perforation: Disorders in pancreatic structure can lead to holes in the organ, in which case digestive enzymes leak into the abdominal cavity. In turn, this can damage the pancreas, itself, as well as other organs in the area. Treatment often entails surgically removing the pancreas, which is effective but means the patient will have to take supplemental enzymes and blood glucose regulators for the rest of their life.  
  • Pancreatic cancer: This kind of cancer is particularly dangerous because it is usually only caught in a very late stage. Risk factors for this condition include smoking, obesity, diabetes, as well as the presence of colon cancer. As with other types of cancer, treatments can include surgery, radiotherapy, chemotherapy, immunotherapy, as well as targeted work. 
  • Type 1 diabetes: This is an autoimmune disorder in which the immune system attacks cells involved in the production of insulin. It is the most common type of childhood diabetes, with a peak of incidence around puberty, although it can arise in adults as well. It leads to dangerous blood-sugar levels. As such, those with it require insulin injections to survive.
  • Type 2 diabetes: The more common form of this disease, type 2 diabetes leads to excessively elevated blood sugar levels due to insulin resistance and an impaired ability of the pancreas to secrete this hormone. Treatment for this condition ranges from ensuring changes in diet and lifestyle to taking one of a class of drugs called biguanides.
  • Pancreatitis: This disease is characterized by the inflammation of the pancreas, as a result of its being damaged by digestive enzymes; it can be acute (more temporary) or chronic. It occurs due to recurrent gallstones (mineral deposits in the gallbladder), excessive alcohol use, measles, mumps, scorpion stings, as well as deficiencies in alpha-1 antitrypsin, an important protein. As a result, patients feel constant pain in the upper abdomen that radiates to other parts of the body. In about 15% of acute cases, this leads to low blood pressure, dehydration, as well as kidney or heart failure. While milder cases can resolve on their own, treatment involves everything from taking antibiotics to surgery.    
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