 In this video, I will describe the mechanisms regulating the secretion of pancreatic juice. The pancreas is an unusual organ in that it is both an endocrine gland as well as an exocrine gland. The endocrine functions of the pancreas result from pancreatic islets that contain alpha cells that secrete the hormone glucagon and beta cells that secrete the hormone insulin, and these hormones are major regulators of blood glucose concentration. The majority of the cells of the pancreas are exocrine cells known as the acener cells, and acener cells secrete pancreatic juice into the pancreatic ducts. Then pancreatic juice drains through the pancreatic ducts into the duodenum, where pancreatic juice mixes with acidic chyme from the stomach that enters into the small intestine first entering into the duodenum, the most proximal region of the small intestine. Pancreatic juice contains bicarbonate and digestive enzymes. The bicarbonate is a base that can react with the low pH acidic chyme in order to help neutralize the pH of chyme. So bicarbonate will raise the pH of the contents of the duodenum, neutralizing the acid that's coming from the stomach. But pancreatic juice also contains digestive enzymes. There are enzymes that are specific for the digestion of carbohydrates known as pancreatic amylase. There's also enzymes that are specific for the digestion of triglycerides, which are known as pancreatic lipase. And there's a variety of pancreatic proteases, enzymes that are important for digesting proteins. These pancreatic proteases are secreted as inactive precursors that then become activated in the duodenum. This is important because a protease could digest the proteins that are structural and functional proteins important for the acener cells. If the proteases became activated and started breaking down proteins inside of the acener cells, essentially the pancreas would be digesting itself. To prevent this, pancreatic proteases are secreted as inactive precursors. For example, there's an enzyme called trypsin, which is secreted as a precursor known as trypsinogen. Another enzyme, another protease known as chymotrypsin, is secreted as a precursor known as chymotrypsinogen. These enzymes will then become activated within the duodenum, where they can then participate in hydrolysis of the peptide bonds between amino acids within polypeptides. The secretion of pancreatic juice is under both neural as well as endocrine control. The parasympathetic division of the autonomic nervous system stimulates the secretion of pancreatic juice. Parasympathetic efferent fibers travel through cranial nerve number 10, the vagal nerve, to reach the pancreas and release the neurotransmitter acetylcholine to stimulate the secretion of pancreatic juice. When chemoreceptors in the small intestine detect a decrease in the pH of the contents of the duodenum, they stimulate the S cells in the small intestine to secrete the hormone secretion. Then, secretion will stimulate the acener cells in the pancreas to secrete bicarbonate. This functions as a negative feedback mechanism because bicarbonate will then have the action of increasing the pH of the contents of the duodenum. Similarly, the presence of fat in the duodenum is detected by chemoreceptors that stimulate the I cells of the small intestine to secrete CCK, colocystokinin. The intestinal hormone CCK then will stimulate acener cells of the pancreas to secrete digestive enzymes.