The pancreas is an elongated organ, light tan or pinkish in color, that lies in close proximity to the duodenum. It is covered with a very thin connective tissue capsule which extends inward as septa, partitioning the gland into lobules. The image to the right shows a portion of a canine pancreas nestled next to the duodenum.

The bulk of the pancreas is composed of pancreatic exocrine cells and their associated ducts. Embedded within this exocrine tissue are roughly one million small clusters of cells called the Islets of Langerhans, which are the endocrine cells of the pancreas and secrete insulin, glucagon and several other hormones.

In this histologic image of an equine pancreas, a single islet is seen in the middle as a large, pale-staining cluster of cells. All of the surrounding tissue is exocrine.

The lumen of an acinus communicates directly with intralobular ducts, which coalesce into interlobular ducts and then into the major pancreatic duct. Epithelial cells of the intralobular ducts actually project "back" into the lumen of the acinus, where they are called centroacinar cells. The anatomy of the main pancreatic duct varies among species. In some animals, two ducts enter the duodenum rather than a single duct. In some species, the main pancreatic duct fuses with the common bile duct just before its entry into the duodenum.

Next page > Gross and Microscopic Anatomy of the Pancreas > Exocrine Secretions of the Pancreas > Control of Pancreatic Exocrine Secretion