The pancreas is a gland organ in both the digestive and endocrine systems of vertebrates. It is both an endocrine gland that produces several important hormones which play an important role in the breaking down of carbohydrates, as well as an exocrine gland, secreting digestive enzymes that pass into the small intestine. These enzymes help in the further breakdown of food for absortion of nutrients in the small intestine. According to its functions, the pancreas can be divided into two parts; the endocrine and the exocrine.
The part of the pancreas with endocrine function is made up of cell clusters called islets of Langerhans. There are four main cell types in the islets. Although they are difficult to distinguish using standard staining techniques, they can be classified by their secretion: α cells secrete glucagon, β cells secrete insulin, δ cells secrete somatostatin, and PP cells secrete pancreatic polypeptide. The islets are a compact collection of hundreds of thousands of endocrine cells arranged in clusters and cords which are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, by either cytoplasmic processes or by direct apposition.
The exocrine pancreas produces digestive enzymes and an alkaline fluid, and secretes them into the small intestine through a system of exocrine ducts in response to the small intestine hormones secretin and cholecystokinin. Digestive enzymes include trypsin, chymotrypsin, pancreatic lipase, and pancreatic amylase, and are produced and secreted by acinar cells of the exocrine pancreas. Specific cells that line the pancreatic ducts, called centroacinar cells, secrete a bicarbonate and salt-rich solution into the small intestine.
The pancreas receives regulatory innervation via hormones in the blood and through the autonomic nervous system. These two inputs regulate the secretory activity of the pancreas.