[box type=”download”] Principal constituents of the exocrine pancreatic juice Function and origin of CCK Function and origin of secretin [/box]
The exocrine pancreas secretes pancreatic juice into the duodenum via the pancreatic duct that opens into the gastrointestinal (GI) tract at the same site as the common bile duct.
When food is present in the duodenum, a small sphincter (sphincter of Oddi) relaxes, allowing both bile and pancreatic secretions to enter the tract.
Pancreatic juice is secreted by the acinar cells includes
–pancreatic amylase, which breaks down carbohydrates to monosaccharides;
–pancreatic lipase, which breaks down fats to glycerol and fatty acids;
–ribonuclease and deoxyribonuclease, which breakdown nucleic acids and free mononucleotides;
–and a variety of proteolytic enzymes (trypsin, chymotrypsin, elastase and carboxypeptidase), which break down proteins into small peptides and amino acids.
The hormone cholecystokinin (CCK), released into the bloodstream by the duodenal cells in response to the presence of amino acids and fatty acids in the chyme, is responsible for the secretion of the pancreatic enzymes.
The other major secretions, besides the enzymes, are water and bicarbonate ions.
The volume of pancreatic juice secreted precisely neutralizes the acid content of the chyme.
This is caused by the acid in the duodenum releasing secretin from its walls into the bloodstream.
Secretin stimulates the production of water and bicarbonate ions from the duct system.
Approximately 1 L of pancreatic juice is secreted per day from a normal individual.