Gastrointestinal Physiology

Gastrointestinal Physiology Secretory Functions of the Alimentary Tract PANCREATIC SECRETION • • The pancreatic digestive enzymes are secreted by pancreatic acini, and large volumes of sodium bicarbonate solution are secreted by the small ductules and larger ducts leading from the acini. The combined product of enzymes and sodium bicarbonate then flows through a long pancreatic duct that normally joins the hepatic duct immediately before it empties into the duodenum through the papilla of Vater, surrounded by the sphincter of Oddi. 1 Secretory Functions of the Alimentary Tract PANCREATIC SECRETION 2 Secretory Functions of the Alimentary Tract PANCREATIC SECRETION 3 Secretory Functions of the Alimentary Tract PANCREATIC SECRETION enterokinase trypsinogen trypsin Activates other protelolytic enzymes • Secretion of Trypsin Inhibitor Prevents Digestion of the Pancreas  • Acute pancreatitis When the pancreas becomes severely damaged or when a duct becomes blocked. Pancreatic secretions rapidly become activated and can literally digest the entire pancreas within a few hours. • 4 Secretory Functions of the Alimentary Tract Secretion of Bicarbonate Ions • Provides a large quantity of alkali in the pancreatic juice that serves to neutralize the HCl emptied into the duodenum from the stomach. Blood Na+ Lumen 5 Secretory Functions of the Alimentary Tract Regulation of Pancreatic Secretion Basic Stimuli That Cause Pancreatic Secretion 1. Acetylcholine 2. Cholecystokinin 3. Secretin  Acetylcholine and CCK, stimulate the acinar cells of the pancreas, causing production of large quantities of pancreatic digestive enzymes but relatively small quantities of water and electrolytes.  Secretin, stimulates secretion of large quantities of water solution of sodium bicarbonate by the pancreatic ductal epithelium. 6 Secretory Functions of the Alimentary Tract PANCREATIC SECRETION 7 Secretory Functions of the Alimentary Tract Phases of Pancreatic Secretion Cephalic Phases • • • 8 Acetylcholine release by the vagal nerve endings in the pancreas. Moderate amounts of enzymes to be secreted into the pancreatic acini, accounting for about 20 percent of the total secretion of pancreatic enzymes. Small amounts of water and electrolytes are secreted. Secretory Functions of the Alimentary Tract PANCREATIC SECRETION Gastric Phases • • 5 to 10 percent of pancreatic enzymes secreted after a meal. Small amounts of water and electrolytes are secreted along with the enzymes. 9 Secretory Functions of the Alimentary Tract PANCREATIC SECRETION Intestinal Phase • • 10 Secretin Stimulates Copious Secretion of Bicarbonate Ions Acid chyme with a pH less than 4.5 to 5.0 causes release and activation of secretin.