Enzyme Types and Their Targets
Pancreatic enzymes catalyze digestion in the small intestine. Pancreatic lipase hydrolyzes triglycerides to fatty acids and monoglycerides; pancreatic amylase continues carbohydrate breakdown started by salivary amylase. Proteases (trypsin, chymotrypsin, carboxypeptidases) break peptide bonds, producing amino acids and dipeptides. Pancreatic elastase and collagenase digest specific structural proteins. Ribonuclease and deoxyribonuclease process nucleic acids. Each enzyme requires optimal pH and cofactors.
Zymogen Activation Cascade
Pancreatic proteases are secreted as inactive zymogens to prevent pancreatic self-digestion. Trypsinogen enters the duodenum and is activated by enterokinase (an intestinal brush-border enzyme) to trypsin. Trypsin then activates other zymogens (chymotrypsinogen → chymotrypsin, proelastase → elastase) in a cascade. This elegant system prevents premature activation. Disorders affecting enterokinase (rare) or chronic pancreatic inflammation can impair this cascade, reducing protease activity despite adequate pancreatic function.
Bicarbonate Secretion
The pancreatic ducts secrete bicarbonate (HCO3-) to neutralize gastric acid entering the duodenum. pH rises from 2 to ~6-7 in the small intestine, optimal for pancreatic enzyme activity. Bicarbonate also prevents acid damage to intestinal epithelium. Cystic fibrosis (CF), with defective CFTR chloride channels, produces thick, alkaline-poor pancreatic secretions, causing enzyme obstruction and EPI (exocrine pancreatic insufficiency).
Exocrine Pancreatic Insufficiency (EPI)
EPI results from insufficient enzyme secretion (<10% of normal output), causing steatorrhea (fatty stools), fat-soluble vitamin malabsorption (A, D, E, K), and protein malnutrition. Causes: chronic pancreatitis (alcohol, autoimmune), cystic fibrosis, pancreatic cancer, post-pancreatectomy. Diagnosis via 72-hour fecal fat test (>7 g/day suggests EPI) or fecal pancreatic elastase-1 (<200 μg/g indicates EPI). Treatment: pancreatic enzyme replacement therapy (PERT) with lipase, amylase, protease tablets taken with meals.
Microbiota Consequences
EPI reduces substrate availability for fermentation; dysbiosis often follows. Undigested fat and protein reach the colon, altering bacterial communities (blooms of proteolytic bacteria, reduced SCFA producers). Paradoxically, EPI-associated dysbiosis may worsen malabsorption, creating a vicious cycle. PERT restoration can partially reverse dysbiotic changes if compliance is maintained.