CorpusHuman Anatomy
DigestiveFluid

Pancreatic juice

Succus pancreaticus

Pancreatic juice is the alkaline exocrine secretion of the pancreas, about 1–1.5 L a day at pH ≈8. It contains the enzymes that digest all major nutrients and enough bicarbonate to neutralise gastric acid.

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Overview

Volume≈1–1.5 L/day
pH≈8.0–8.3
[HCO₃⁻] at high flow≈120–140 mmol/L

Pancreatic juice is isotonic. As flow rises, HCO₃⁻ rises to about 120–140 mmol/L and Cl⁻ falls reciprocally. This neutralises acid chyme and raises duodenal pH to about 6–7. That protects the mucosa, lets pancreatic enzymes work at their optimum, and keeps bile salts soluble.

Activation of the proteases is a cascade. Enteropeptidase (enterokinase) on the duodenal brush border converts trypsinogen to trypsin. Trypsin then activates more trypsinogen and all the other zymogens: chymotrypsinogen, proelastase, procarboxypeptidases, procolipase and prophospholipase A2.

Secretion runs in three phases: cephalic (about 20%), gastric (about 5–10%) and intestinal (about 70%). Secretin, released from S cells when duodenal pH falls below about 4.5, produces a watery, bicarbonate-rich flow from the ducts. CCK, released from I cells by fatty acids and amino acids, produces an enzyme-rich flow from the acini. Each potentiates the other.

Parts & subdivisions

  1. Proteases (endopeptidases)
    Trypsin (cleaves after Arg and Lys), chymotrypsin (after aromatic residues), elastase (small neutral residues).
  2. Proteases (exopeptidases)
    Carboxypeptidase A (neutral and aromatic C-terminal residues) and B (basic C-terminal residues).
  3. Pancreatic α-amylase
    Hydrolyses α-1,4 bonds of starch to maltose, maltotriose and α-limit dextrins.
  4. Lipases
    Pancreatic lipase with colipase (positions 1 and 3 of triglyceride → 2-monoacylglycerol + 2 fatty acids); phospholipase A2; carboxyl ester lipase (cholesterol esters).
  5. Nucleases
    Ribonuclease and deoxyribonuclease.
  6. Bicarbonate
    Up to about 140 mmol/L. Neutralises gastric acid.

Function

  • Digests proteins, carbohydrates, lipids and nucleic acids.
  • Neutralises gastric acid in the duodenum.
Secretions

About 1–1.5 L/day, pH about 8.0–8.3, isotonic.

Regulation

Secretin (HCO₃⁻ and water); CCK and ACh (enzymes); potentiation between them. Inhibited by somatostatin, PYY and pancreatic polypeptide.

Clinical significance

Exocrine pancreatic insufficiency

Caused by chronic pancreatitis, cystic fibrosis, pancreatic cancer or pancreatectomy. Steatorrhoea appears only when lipase output falls below about 10% of normal. There is fat-soluble vitamin deficiency and weight loss, and faecal elastase is low. Treatment is pancreatic enzyme replacement with meals.

Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.