Stimulation of pancreatic juice is through both neural reflexes initiated inthe duodenum as well as the release of local duodenal hormones.

The hormones that are mainly responsible for the release of pancreatic juice are secretin and cholecystokinin (CCK).

Release of secretin occurs in response to a fall in the duodenal pH to around 4.5, follwing entry of chyme from the stomach.

Secretin stimulates the production of bicarbonate by the pancreas - acts as a negative feedback.

CCK is releases as a response to the presence of fat and protein in the chyme.

CCK stimulates the production of pancreatic enzymes.

As partly digested protein and fat are the most powerful stimulants for CCK release, a positive feedbak mechanism occurs untill all the chyme passes through the duodenum.