The pancreas is really two glands that are intimately mixed together into one organ. The bulk of the pancreas is composed of “exocrine” cells that produce enzymes to help with the digestion of food. These exocrine cells release their enzymes into a series of progressively larger tubes (called ducts) that eventually join together to form the main pancreatic duct. The main pancreatic duct runs the length of the pancreas and drains the fluid produced by the exocrine cells into the duodenum, the first part of the small bowel.
The second functional component of the pancreas is the "endocrine" pancreas. The endocrine pancreas is composed of small islands of cells, called the islets of Langerhans. These endocrine cells don’t release their secretions into the pancreatic ducts, instead they release hormones, such as insulin and glucagon, into the blood stream, and these hormones in turn help control blood sugar (glucose) levels.
Acinar cells are the exocrine (exo=outward) cells of the pancreas that produce and transport enzymes that are passed into the duodenum where they assist in the digestion of food.
|Islets of Langerhans||The islets of Langerhans are the endocrine (endo= within) cells of the pancreas that produce and secrete hormones such as insulin and glucagon into the bloodstream. The pancreatic hormones, insulin and glucagon, work together to maintain the proper level of sugar (glucose) in the blood. Blood sugar is used by the body for energy.|
An understanding of the two functional components of the pancreas is important for two reasons.
First, as they grow large tumors of the pancreas will interfere with both of these important bodily functions. When tumors block the exocrine system, patients can develop pancreatitis and pain from the abnormal release of digestive enzymes into the substance of the pancreas instead of into the bowel, and they can develop digestive problems, such as diarrhea, from the incomplete digestion of food. When tumors destroy the endocrine function of the pancreas, patients can develop sugar diabetes (abnormally high blood sugar levels).
The second reason that the two functional components of the pancreas are important to understand is that tumors can arise in either component. The vast majority of tumors of the pancreas arise in the exocrine part and these cancers look like pancreatic ducts under the microscope. These tumors are therefore called "ductal adenocarcinomas," or simply "adenocarcinoma," or even more simply "pancreatic cancer." Less commonly, tumors arise from the endocrine component of the pancreas and these endocrine tumors are called "pancreatic neuroendocrine tumors," or "islet cell tumors" for short.
The pancreas is an integral part of the digestive system, and the flow of the digestive system is often altered during the surgical treatment of pancreatic cancer. Therefore it is helpful to review the normal flow of food and the flow of digestive enzymes of the pancreas before reading about surgical treatment.
Food is carried from the mouth to the stomach by the esophagus. The esophagus is a tube that descends from the mouth down into the abdomen. In the abdomen, the esophagus empties into the stomach where digestive acids made by the stomach break down the food. From the stomach, the partially digested food flows directly into the first part of the small intestine, called the duodenum. It is here in the duodenum that bile from the liver and digestive enzymes from the pancreas enter the digestive system.
The duodenum then leads to the other parts of the small bowel, the jejunum and ileum, where further digestion of food takes place. The ileum then empties into the large bowel (also known as the large intestine), and finally completely digestive material passes out of the body through the anus.
Bile is important to understand because the flow of bile is often blocked by pancreatic cancers, and because the flow of bile is altered during surgery for pancreatic cancer. Bile is a greenish-yellow fluid that aids in the digestion of fats in food. After being produced by cells in the liver, the bile travels down through the bile ducts which merge with the cystic duct from the gallbladder to form the common bile duct. The gallbladder stores extra bile until needed. The common bile duct then passes through the head of the pancreas and joins the pancreatic duct to form the ampulla of Vater which then empties into the duodenum. The flow of bile is indicated by the green arrows.
Understanding that the tube (duct) carrying bile from the liver passes through the pancreas on its way to the intestine, helps us understand why some people with pancreatic cancer develop jaundice (an abnormal yellowing of the skin and eyes). Pancreatic cancers in the head of the pancreas (the bile duct passes through the head of the pancreas) can block the bile duct and in so doing can block the flow of bile out of the liver. The bile backs up and causes jaundice.
Instead of carrying bile, the pancreatic duct carries the fluid containing the digestive enzymes produced by the acinar cells (exocrine cells) of the pancreas. The main pancreatic duct is normally only one-sixteenth of an inch in diameter and it has many small side branches. The main pancreatic duct merges with the bile duct in the head of the pancreas to form the ampulla of Vater (a widening of the duct just before it enters the duodenum). Just as was true for bile, the flow of pancreatic fluid is often blocked by tumors of the pancreas, and altered by pancreatic surgery. The flow of pancreatic fluid is indicated by the dark yellow arrow.