== Pancreas ==

The pancreas is both an exocrine and an endocrine gland. The exocrine pancreas is a compound tubuloacinar gland consisting of serous secretory cells arranged in acini. As a gland of external secretion, the serozymogenic products of the acini are conveyed to the lumen of the duodenum by means of a main excretory duct, the main pancreatic duct, and by an accessory pancreatic duct which in some individuals opens into the main duct before reaching the duodenum. The main duct extends the entire length of the gland receiving branches, interlobular ducts, from the individual lobules. Striated ducts are lacking in the pancreas. The only intralobular ducts are long narrow intercalated ducts with a low simple cuboidal epithelium, which open directly into interlobular ducts .

The endocrine pancreas secretes insulin and glucagon directly into the blood stream (capillaries) from irregularly dispersed aggregates of cells forming the pancreatic islets (of Langerhans). The islets are composed of anastomosing cords of cells, numerous capillaries and a fine framework of reticular fibers. They are usually directly surrounded by pancreatic acini, but islets can occur in the interlobular connective tissue. The islets range in size from only a few cells to islets containing thousands of cells. In the latter instance they are large enough to see with the unaided eye. The islets are more numerous in the tail than in any other portion of the pancreas.