The pancreas is an elongated organ that lies behind and below the stomach. This mixed gland contains both exocrine and endocrine tissues. The predominant exocrine part consists of grape-like clusters of secretory cells that form sacs known as acini, which connect to ducts that eventually empty into the the first portion of the intestine called duodenum. The smaller part of the gland consists of isolated islands of endocrine tissue known as islets of Langerhans which are dispersed throughout the pancreas. The pancreas is largely responsible for maintaining blood glucose levels. The normal clinical range of blood glucose levels is 70 to 150 mg/dL (milligrams per deciliter). The pancreas can measure blood sugar and if it is high or low, the pancreas releases a hormone to correct the level. Blood glucose must be maintained at a certain level for cells to neither gain or lose water.
The most important hormones secreted by the pancreas are insulin and glucagon. Both play a role in proper metabolism of sugars and starches in the body. Insulin promotes the movement of glucose and other nutrients out of the blood and into cells. When blood glucose rises, insulin, released from the beta cells causes glucose to enter body cells to be used for energy. Also, it sometimes stimulates conversion of glucose to glycogen in the liver. Another pancreatic hormone, glucagon, promotes the movement of glucose into the blood when glucose levels are below normal. It causes the breakdown of stored liver glycogen to glucose, so that the sugar content of blood leaving the liver rises.
The exocrine pancreas secretes the pancreatic juice consisting of two components:
- Pancreatic enzymes actively secreted by the acinar cells that form the acini. These pancreactic enzymes are very important because they can almost completely digest food in the absence of all other digestive secretion.
- An aqueous alkaline solution rich in sodium bicarbonate (NaHCO3) actively secreted by the duct cells that line the pancreatic ducts. Sodium bicarbonate neutralizes the acidity of the chyme so that won't burn the intestines.
The acinar cells secrete three different types of enzymes:
- Proteolytic enzymes for protein digestion
- Pancreatic amylase for carbohydrate digestion
- Pancreatic lipase for fat digestion3
- Image credit: University of Colorado at Boulder
- The Language of Medicine. Davi-Ellen Chabner
- Human Physiology: From Cells to Systems. Lauralee Sherwood