Explain the activation cascade of pancreatic zymogens leading to active proteases.

• A. Enterokinase activates trypsinogen to trypsin; trypsin activates other zymogens into active proteases
• B. Trypsin activates enterokinase; chymotrypsinogen to trypsin
• C. Secretin activates proteases directly
• D. Lipase activates amylase

Answer: (A)

Activation of pancreatic proteases starts in the small intestine and hinges on a proteolytic cascade. Enteropeptidase (enterokinase) on the duodenal brush border cleaves trypsinogen to active trypsin. Once trypsin is formed, it acts as a master activator, cleaving and converting other pancreatic zymogens into their active enzymes—for example, chymotrypsinogen becomes chymotrypsin and procarboxypeptidases become active carboxypeptidases, with further amplification as any additional precursor enzymes are activated. This arrangement keeps enzymes inactive until they reach the gut lumen, protecting the pancreas from autodigestion and ensuring coordinated digestion.

The other ideas don’t fit because secretin mainly stimulates bicarbonate secretion to neutralize acid, not proteolytic activation; lipase and amylase activation involve different mechanisms and are not initiated by lipase or similar triggers. Thus, the described activation sequence—enterokinase activating trypsinogen, followed by trypsin activating the other zymogens—best explains the process.