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Pancreatic ductal cells express receptors for a battery of hormones and neurotransmitters. Fluid and HCO 3 - secretion by duct cells are regulated by cAMP signals (74, 86) that synergizes with Ca 2+ to generate the physiological response(105).

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Fluid and enzyme secretion by acinar cells are controlled predominantly by an increase in cytoplasmic free Ca 2+ concentration ( i) (88, 106, 107). Pancreatic HCO 3 - secretion increases in response to ingestion of a meal, and is regulated by multiple neurohumoral inputs. Current understanding of the molecular mechanism of pancreatic HCO 3 - secretion was improved by the recent identification of ion transporters and channels, including the cystic fibrosis transmembrane conductance regulator (CFTR) (61), the electrogenic Na +-HCO 3 - co-transporter NBCe1-B (also known an pNBC1) (1), and the solute-linked carrier 26 (SLC26) transporters (25, 100), together with regulatory proteins, such as with-no-lysine kinase 1 (WNK1) (102), SPAK (30)and the inositol-1,4,5-triphosphate (IP 3) receptor binding protein released with IP 3 (IRBIT) (140).Дў. This remarkable transport performance has attracted much attention from pancreatologists and physiologists. In humans, dogs, cats, and guinea pigs, HCO 3 - concentration in postprandial pancreatic juice is higher than 140 mM (23, 74). According to the Henderson-Hasselbalch equation, at pH 7.4 and 5% CO 2, the HCO 3 - equilibrium concentration in plasma is approximately 25 mM. Duct cells modify the ionic composition of the fluid and secrete the bulk of the fluid and HCO 3 в€’of the pancreatic juice. Acinar cells secrete a small volume of isotonic, plasma-like, NaCl-rich fluid and digestive enzymes. The exocrine pancreas is composed of two major cell types, acinar and duct cells. The importance of HCO 3 - is highlighted in the abnormal HCO 3 - secretion in cystic fibrosis (CF), which causes poor mucin hydration and solubilization leading to obstruction of ductal structures of the pancreas, intestine, vas deferens and the lung (112, 113). In addition, HCO 3 в€’ acts as a moderate chaotropic ion that facilitates the solubilization of macromolecules, such as digestive enzymes and mucins (42). HCO 3 в€’ in pancreatic juice neutralizes gastric acid, and provides an optimal pH environment for digestive enzymes to function in the duodenum (74). HCO 3 - determines the pH of bodily fluids as a major buffer system that guards against toxic pH fluctuations (116). HCO 3 - plays essential roles in the digestive system. When stimulated, the pancreas secretes alkaline pancreatic juice containing copious amounts of bicarbonate (HCO 3 -) (23, 74). Bacteria in the small intestine produce some of the enzymes needed to digest carbohydrates.The human exocrine pancreas secretes 1-2 liters of pancreatic juice per day. The body completes the breakdown of proteins, and the final breakdown of starches produces glucose molecules that absorb into the blood. SMALL INTESTINEДigestive juice produced by the small intestine combines with pancreatic juice and bile to complete digestion. The bile acids dissolve fat into the watery contents of the intestine, much like how detergents dissolve grease from a frying pan, so the intestinal and pancreatic enzymes can digest the fat molecules. When a person eats, the gallbladder squeezes bile through the bile ducts, which connect the gallbladder and liver to the small intestine. The gallbladder stores bile between meals. The liver produces a digestive juice called bile. The pancreas delivers digestive juice to the small intestine through small tubes called ducts. The pancreas produces a juice containing several enzymes that break down carbohydrates, fats, and proteins in food. The glands in the stomach lining produce stomach acid and an enzyme that digests protein. Saliva also contains an enzyme that begins to break down the starches from food. Saliva produced by the salivary glands moistens food so it moves more easily through the esophagus into the stomach. How do digestive juices in each organ of the GI tract break down food?Дigestive juices contain enzymes-substances that speed up chemical reactions in the body-that break food down into different nutrients.

Pancreatic juices