Pancreatic Juice and Chyme Interaction in the Duodenum

Pancreatic secretions (1.5–3 L/day) enter the duodenum via major/minor papillae, mixing with acidic chyme from stomach.

Key Processes

1. Neutralization: Bicarbonate (HCO₃⁻, 80–140 mEq/L) raises pH from ~2 to 6–7 → optimal for pancreatic enzymes, protects mucosa.
2. Carbohydrate digestion: Pancreatic amylase → maltose, maltotriose, α-limit dextrins → brush border disaccharidases → monosaccharides.
3. Protein digestion: Trypsinogen → trypsin (enteropeptidase) → activates chymotrypsinogen, procarboxypeptidases, proelastase → peptides/amino acids.
4. Lipid digestion: Lipase + colipase + bile salts → 2-monoacylglycerol + fatty acids → mixed micelles → absorption.
5. Nucleic acid digestion: Ribonuclease, deoxyribonuclease → nucleotides → nucleosides → bases.

Regulation

• Secretin: S cells (duodenum) → low pH → ↑ bicarbonate secretion.
• CCK: I cells → fats/amino acids → ↑ enzyme secretion, gallbladder contraction.
• Vagal: Cephalic phase.

Clinical

Pancreatic insufficiency (chronic pancreatitis, CF, post-surgical) → maldigestion → steatorrhea, weight loss, deficiencies → pancreatic enzyme replacement therapy (PERT).