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:
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.
Pancreatic juice is a colorless liquid composed of water, salts, sodium bicarbonate, and enzymes secreted by the exocrine cells.
During digestion, chyme reaching the duodenum triggers secretin release, which stimulates the secretion and delivery of pancreatic juice into the small intestine.
Another duodenal hormone, cholecystokinin, released after a fatty meal also stimulates the release of pancreatic juice.
The epithelial lining of the ducts secretes the non-enzymatic components of pancreatic juice that make it alkaline.
This alkalinity buffers the acidity of chyme, providing an ideal pH for the action of digestive enzymes in the small intestine.
The acinar cells secrete the enzymes present in pancreatic juice, including amylases to digest starch, lipases to digest lipids, and nucleases that digest nucleic acids.
However, the majority of enzymes in pancreatic juice are protein-digesting proteases, produced in an inactive form.
Trypsin, secreted as trypsinogen, is activated in the duodenum by enterokinase.
Trypsin then activates other protease precursors, such as chymotrypsinogen, procarboxypeptidase, and proelastase.
繁體中文
