1. Anatomy and Physiology 

The pancreas is an endocrine and exocrine organ located retroperitoneally in the upper abdomen overlying the spine. The head and uncinate process lie within the curve of the duodenum, while the body and tail extend to the gastric border of the spleen. The pancreas is supplied by the gastroduodenal arteries and by branches of the splenic artery. The splenic vein and artery run superiorly and posteriorly; the mesenteric vein lies in the angle between the head and body of the gland. At this point the superior mesenteric vein and splenic vein join to form the portal vein (Figure 1).

The islets of Langerhans, clumps of cells scattered throughout the gland, produce the endocrine secretion of the pancreas. Their hormones, secreted directly into capillaries, include insulin, which is produced by the beta cells, and glucagon, pancreatic peptide, somatostatin and other hormones secreted by nonbeta cells.

The exocrine portion of the pancreas accounts for about 80% of the total glandular volume. It consists of at least two functional units: acinar cells, which secrete primarily digestive enzymes; and centroacinar or ductal cells, which secrete fluids and electrolytes (Figure 2). Pancreatic secretion is regulated by several peptides that are released from the gastrointestinal tract. Some of these peptides, such as secretin and cholecystokinin (CCK), stimulate pancreatic secretions, whereas somatostatin and pancreatic polypeptide inhibit their release. The pancreas secretes about 20 digestive enzymes and cofactors. Some enzymes are activated in the duodenum by enterokinases and calcium (Figure 3). These enzymes account for most of the intraluminal digestion of dietary proteins, triglycerides and carbohydrates. They are also important in the cleavage of certain vitamins (such as A and B₁₂) from carrier molecules, thereby allowing them to be absorbed efficiently. Because pancreatic enzymes are secreted in great excess, maldigestion and serious nutritional deficiencies occur only when over 90% of the gland has been destroyed.