Expansion
Bicarbonate from duct cells under secretin, enzymes from acinar cells under cholecystokinin
Expansion
Duct cells produce an alkaline, watery secretion
- Stimulated by secretin, released when duodenal pH falls below about 4.5
- Rich in bicarbonate, up to 140 mmol/l, neutralising gastric acid so that pancreatic enzymes can work at their optimum pH of 7 to 8
- Volume about 1.5 litres a day
Acinar cells produce digestive enzymes
- Stimulated by cholecystokinin and by vagal input
- Proteases secreted as inactive zymogens: trypsinogen, chymotrypsinogen, procarboxypeptidase
- Amylase and lipase secreted in active form
Protection against autodigestion: zymogen packaging, the trypsin inhibitor SPINK1, and activation only in the duodenum where enterokinase converts trypsinogen to trypsin, which then activates the rest. Failure of these safeguards is central to acute pancreatitis.
Symptoms of insufficiency appear only when about 90 per cent of function is lost, giving steatorrhoea because lipase is lost first and has no alternative source.