27.30 : Pancreatic Juice and Secretion

Pancreatic juice is a clear fluid produced by the pancreas, containing water, salts, sodium bicarbonate, and enzymes vital for digestion in the small intestine. It helps break down large molecules, facilitating nutrient absorption.

When acidic chyme from the stomach enters the duodenum, it triggers the release of secretin, a hormone that prompts pancreatic juice secretion. After a fatty meal, cholecystokinin, another hormone, stimulates gallbladder contraction and enhances enzyme-rich pancreatic secretions, both critical for fat digestion. Together, these hormones ensure the timely delivery of pancreatic juice for efficient digestion.

The ducts' epithelial cells secrete bicarbonate, making pancreatic juice alkaline, which neutralizes stomach acid and creates a suitable pH for enzymes in the duodenum.

Acinar cells in the pancreas produce digestive enzymes, including:

1. Amylases for breaking down carbohydrates.
2. Lipases for fat digestion.
3. Nucleases for digesting nucleic acids.

The most abundant enzymes, however, are proteases produced as inactive precursors called zymogens to prevent them from digesting pancreatic tissue. For instance, trypsin is released as an inactive precursor called trypsinogen. Upon reaching the duodenum, trypsinogen encounters enterokinase, an enzyme in the intestinal lining that activates it into trypsin. Activated trypsin then triggers a cascade, activating other protease precursors, including chymotrypsinogen (which becomes chymotrypsin), procarboxypeptidase (which becomes carboxypeptidase), and proelastase (which becomes elastase). Together, these activated enzymes efficiently digest proteins into absorbable amino acids.

Overall, pancreatic juice is essential for nutrient breakdown and absorption, with its enzymes carefully regulated to support digestive health.