Most of the pancreas is made up of exocrine tissue, which is arranged in small saclike structures called acini. The cells of these acini release secretions into tiny ducts that eventually unite with the pancreatic duct, which extends from the tail to the head of the pancreas. The pancreatic duct gets larger as it passes through the pancreas. This duct joins the common bile duct and then empties into the duodenum at the ampulla of Vater. The accessory pancreatic duct, also known as the duct of Santorini, extends from the head of the pancreas into the duodenum.When food enters the stomach, the intestinal mucosa releases the hormone secretin into the bloodstream. Secretin in turn stimulates the acinar cells and ducts to secrete pancreatic juice. An alkaline solution, the pancreatic juice consists of water, bicarbonate, electrolytes, and enzymes for food digestion. These pancreatic enzymes fall into three categories- proteolytic enzymes (trypsin and chymotrypsin), which break down proteins, pancreatic lipase, which helps digest fat and pancreatic amylase, which helps digest carbohydrates. The digestive enzymes and the other components of the pancreatic juice pass from the microscopic ducts into the pancreatic duct and then enter the duodenum. In the duodenum, the pancreatic juice neutralizes the acidic chyme from the stomach.

The pancreas protects itself from these digestive enzymes by secreting them in inactive forms. They don’t become active until they reach the digestive tract, where activating enzymes convert them. For example, trypsin is released from the pancreas as the zymogen trypsinogen, which is then converted to active trypsin by enterokinase in the intestine.