Pancreas
The pancreas is a soft oblong organ located in the upper central region of the abdominal cavity, just behind the lower surface of the stomach. It has three portions: an expanded medial portion called the head, a central portion called the body, and a tapering lateral portion called the tail. The head is partially encircled by the C-shaped duodenum, the first portion of the small intestine. The pancreas is both an exocrine gland and an en­docrine gland.
The exocrine portion of the pancreas consists of acinar cells (which ac­count for about 99 percent of all secretory cells in the pancreas) that are or­ganized into numerous small clusters called acini. The acinar cells secrete a clear fluid called pancreatic juice, which plays a critically important role in the digestion of food within the small intestine. The pancreatic juice is usu­ally delivered to the duodenum by way of two ducts, the main pancreatic duct and the accessory pancreatic duct. (In some people, the accessory duct disappears during development.) Pancreatic juice consists of water, elec­trolytes, sodium bicarbonate, and several digestive enzymes capable of di­gesting virtually all the nutrient molecules in food.
Among these enzymes are several protein-digesting enzymes (trypsin, chymotrypsin, carboxypeptidase, and elastase), a carbohydrate-digesting enzyme (pancreatic amylase), and a lipid-digesting enzyme (pancreatic li­pase). These enzymes do not digest the pancreas itself because they are not activated or provided with optimal ionic conditions until pancreatic juice enters the duodenum. The sodium bicarbonate establishes the opti­mal pH for the actions of pancreatic and intestinal enzymes within the small intestine.
The remaining 1 percent of the secretory cells form the endocrine por­tion of the pancreas. These cells are organized into clusters called pancre­atic islets (islets of Langerhans) that are scattered among the acini. These cells secrete several hormones, including glucagon (secreted by alpha cells) and insulin (secreted by beta cells), which play important roles in blood glu­cose regulation and carbohydrate metabolism. Diabetes mellitus is an en­docrine disorder that arises from hyposecretion of insulin or a decreased sensitivity of body cells to insulin.
References
Saladin, Kenneth S. Anatomy & Physiology: The Unity of Form and Function, 2nd ed. New York: McGraw-Hill, 2001.