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.