The exocrine pancreas is used to describe the role of the pancreas during digestion. The pancreas plays two roles within the bodies of vertebrates, that of an endocrine gland and that of an exocrine gland. As an endocrine gland, the pancreas secretes insulin, glucagon and somatostatin, which are all hormones. As an exocrine gland, it secretes pancreatic juice that contains digestive enzymes into the small intestine, which are proteins that aid in the digestion of food.
The pancreas is found below the stomach and beside the small intestine. It is not made up of two distinct parts, but instead the endocrine and exocrine pancreas are mixed together throughout the organ. Within the pancreas, clusters of ducts can be found, called acini. In response to stimulation by hormones secreted by the stomach in response to food entering the stomach, the pancreatic juices are released into the acini. From there, the juices drain into intralobular ducts and then the main pancreatic duct, which leads directly to the small intestine.
Pancreatic juice is released when food passes from the stomach into the small intestine. There are two different types of secretions that make up the pancreatic juice that is released by the exocrine pancreas. The three main types of enzymes found within the pancreatic juice are amylase, lipase and protease. Amylase is used to break starch down into smaller carbohydrates and sugar molecules. Lipase breaks down fats, while proteases digest proteins.
The majority of the digestion of protein within the body is due to the proteases found within the pancreatic juice. Several different proteases are secreted by the exocrine pancreas, but the major two are trypsin and chymotrypsin. The roles of both trypsin and chymotrypsin are to break down large protein molecules into smaller peptides. They do not break them down all the way into single amino acids though. The final step is carried out by other enzymes, peptidases, found within the small intestine.
The other type of secretion produced by the exocrine pancreas as part of the pancreatic juice is bicarbonate ions. The food that has been partially digested in the stomach, called chyme, is highly acidic due to the gastric found within the stomach. Bicarbonate ions are alkaline in nature so their role is to neutralize the partially digested food and liquid that passes into the small intestine and protect the intestinal cells from damage by the gastric acid. Bicarbonate ions are secreted from the cells lining the ducts of the exocrine pancreas.