pancreatic juice
Summary
Pancreatic juice is the exocrine secretion of the pancreas, sent through the pancreatic duct into the duodenum. It contains bicarbonate, which neutralizes acidic chyme, and digestive enzymes (amylase, lipase, nucleases, proteases). Proteases are secreted as inactive zymogens, and enteropeptidase activates trypsinogen.
Detail
Meaning: Pancreatic juice is the exocrine secretion of the pancreas, carried by the pancreatic duct into the duodenum. Duct cells add bicarbonate, which neutralizes acidic chyme and sets a pH suited to the enzymes. Acinar cells add pancreatic amylase (starch), lipase (triglycerides), nucleases and proteases. The proteases are made as inactive zymogens (trypsinogen, chymotrypsinogen, procarboxypeptidase). Enteropeptidase on the duodenal brush border converts trypsinogen to trypsin, and trypsin then activates the other zymogens.
On the MCAT: Secretin, released by the duodenum in response to acid, stimulates bicarbonate secretion. Cholecystokinin (CCK), released in response to fats and amino acids, stimulates enzyme release. Questions ask which hormone does what, where a given macromolecule is digested, what happens if the duct is blocked, or why zymogens protect the pancreas from digesting itself.
Common confusion: Pancreatic juice is not bile. Bile is made by the liver, stored in the gallbladder, and emulsifies fat, but it contains no digestive enzymes. The fat-digesting enzyme is pancreatic lipase. Also keep the endocrine pancreas separate: insulin and glucagon enter the blood, not the duct.
Sources
- Campbell Biology
- Human Physiology: From Cells to Systems
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.