The pancreas secretes pancreatic juice, an alkaline fluid rich in digestive enzymes and bicarbonate that is delivered to the duodenum to finish digestion.
What pancreatic juice is made of
Pancreatic juice is a watery solution that contains three main components:
- Digestive enzymes: proteases (trypsinogen, chymotrypsinogen), lipase, amylase, and nucleases are produced as inactive zymogens and become active in the small intestine.
- Bicarbonate ions: secreted by duct cells to raise the pH and neutralise the acidic chyme from the stomach.
- Water and electrolytes: provide the fluid medium for enzyme activity.
How the juice reaches the intestine
Acinar cells in the pancreas synthesize the enzymes and release them into tiny ducts. These ducts merge into the main pancreatic duct (Wirsung), which joins the common bile duct at the ampulla of Vater. When the sphincter of Oddi relaxes, the combined flow of bile and pancreatic juice empties into the duodenum.
When the pancreas releases juice
Secretion is tightly regulated. The sight, smell, or thought of food activates the vagus nerve (cephalic phase), prompting a modest release. The biggest surge occurs in the intestinal phase, when acidic chyme enters the duodenum.
Two hormones control the response:
- Secretin – released by duodenal S‑cells in response to low pH; it stimulates duct cells to pour out bicarbonate‑rich fluid.
- Cholecystokinin (CCK) – released by I‑cells when fats and proteins are present; it triggers acinar cells to discharge enzyme‑laden juice.
Functions of the enzymes
Once in the duodenum, the enzymes become active and perform specific tasks:
- Proteases break proteins into peptides and amino acids.
- Pancreatic lipase with bile salts splits triglycerides into free fatty acids and monoglycerides.
- Alpha‑amylase converts starches into maltose and dextrins.
- Nucleases degrade dietary DNA and RNA into nucleotides.
Clinical relevance
If pancreatic juice flow is blocked or its composition altered, digestion suffers. Conditions such as chronic pancreatitis, cystic fibrosis, or duct obstruction can reduce enzyme delivery, leading to malabsorption, fatty stools, and nutrient deficiencies. Enzyme replacement therapy mimics the natural juice to restore proper digestion.