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.
