The pancreas is both an exocrine organ and an endocrine organ. This chapter is devoted to the exocrine pancreas. The exocrine pancreas is responsible for secretion of digestive enzymes, ions and water into the duodenum of the gastrointestinal tract. The digestive enzymes are essential for processing foodstuffs in meals to molecular constituents that can be absorbed across the gastrointestinal surface epithelium. Although enzymes from salivary glands, the stomach and the surface epithelium of the gastrointestinal tract also participate in the digestion of a meal, the exocrine pancreas plays a central and essential role in the digestive process. With loss of exocrine pancreatic function, absorption of nutrients in markedly compromised and malnutrition ensues.

The secretion of ions and water by the exocrine pancreas is also an essential function for the exocrine pancreas. The flow of ions and water is necessary to transport the digestive enzymes from their origin in the pancreatic acinar cells to the intestine. In addition, the pH of the pancreatic secretions is alkaline due to a very high concentration of NaHCO₃ (up to 140 mM). At least one major function of the NaHCO₃ is to neutralize the acidic pH of the gastric chyme delivered to the intestine from the stomach. A neutral pH in the intestinal lumen is necessary for optimal function of digestive enzymes as well as gastrointestinal surface epithelial function.

The exocrine pancreas has been of considerable interest to physiologists and other scientists for quite some time. In fact, the first demonstration of a hormone action was in the pancreas around the turn of the 20th century [1]. The pancreas has been the major organ used to demonstrate the mechanisms of synthesis and transport for exportable proteins [2] as well as the signaling pathways involved in regulated protein secretion [3]. Also, the mechanisms that underlie the ability of the exocrine pancreas to secrete very high concentrations of NaHCO₃ have been of great interest to physiologists and are still debated [4–6]. This chapter presents a concise description of the current understanding of exocrine pancreatic anatomy and function with consideration of how these are affected in disease states.