Overview
Clinical Meaning
Acute pancreatitis begins with premature intracellular activation of trypsinogen to trypsin within pancreatic acinar cells, initiating an autodigestive cascade.
Acute pancreatitis begins with premature intracellular activation of trypsinogen to trypsin within pancreatic acinar cells, initiating an autodigestive cascade. Normally, protective mechanisms prevent this: trypsinogen is stored as an inactive zymogen in membrane-bound granules, pancreatic secretory trypsin inhibitor (SPINK1) neutralizes prematurely activated trypsin, and autolysis pathways degrade excess active enzymes. When these safeguards are overwhelmed — by gallstone impaction at the ampulla of Vater (causing ductal hypertension and reflux of bile into the pancreatic duct), alcohol toxicity (direct acinar cell injury plus oxidative stress from acetaldehyde metabolism), or hypertriglyceridemia (toxic free fatty acid accumulation) — active trypsin triggers a chain reaction activating elastase (which digests blood vessel walls causing hemorrhage), phospholipase A2 (which destroys cell membranes and generates toxic lysophosphatidylcholine), and lipase (which digests peripancreatic fat, releasing free fatty acids that bind calcium causing hypocalcemia through fat saponification). The local inflammatory response releases TNF-alpha, IL-1, and IL-6, which activate the systemic inflammatory response syndrome (SIRS). In severe cases, this progresses to necrotizing pancreatitis where >30% of the pancreatic parenchyma undergoes coagulative necrosis from ischemia caused by microvascular thrombosis and vasospasm....