Acute Pancreatitis II: Pathophysiology

Acute pancreatitis begins with injury to pancreatic acinar cells, typically caused by gallstones or alcohol. This injury triggers premature activation of trypsinogen to trypsin within the pancreas. Trypsin then activates other digestive enzymes like chymotrypsin and elastase, which break down pancreatic tissue and cause local inflammation, swelling, hemorrhage, and fat necrosis.

Injured acinar cells absorb excess calcium, leading to sustained intracellular calcium overload. This disrupts mitochondrial ATP production and stresses the endoplasmic reticulum, impairing protein folding and secretion. Additionally, dysfunctional autophagy allows digestive enzymes to accumulate, and cathepsin B leaks from lysosomes, further activating trypsinogen and worsening cellular damage.

Injured pancreatic cells release proinflammatory mediators including interleukin-1, interleukin-6, and tumor necrosis factor. These cytokines recruit neutrophils, increase vascular permeability, and amplify the local immune response. Neutrophils may also release extracellular traps that obstruct small ducts and perpetuate tissue injury, driving the inflammatory cascade.

Lipase-mediated fat breakdown in and around the pancreas releases free fatty acids. These fatty acids bind to calcium and form insoluble soaps in surrounding tissues through a process called fat saponification. This binding of calcium reduces circulating calcium levels, contributing to hypocalcemia, which may be clinically significant in acute pancreatitis patients.

If inflammation extends beyond the pancreas, circulating cytokines and pancreatic enzymes can damage distant organs. This systemic response may cause acute respiratory distress syndrome, kidney injury, or cardiovascular instability. Complications include pancreatic necrosis, pseudocysts, systemic inflammatory response syndrome, and shock, ranging from localized tissue damage to severe multi-organ dysfunction.

Premature trypsin activation initiates autodigestion, where activated digestive enzymes break down pancreatic tissue itself. This self-digestion causes local inflammation, tissue swelling, hemorrhage, and fat necrosis. The cascade of enzyme activation and tissue destruction creates a self-perpetuating cycle of cellular injury and inflammatory response within the pancreas.

Calcium overload stresses the endoplasmic reticulum, impairing its ability to fold and secrete proteins properly. This dysfunction, combined with impaired autophagy, causes digestive enzymes to accumulate within cells. The accumulation of misfolded proteins and retained enzymes amplifies intracellular damage and triggers further release of inflammatory signals that perpetuate the disease process.