Chapter 4: Physiology of Pancreas PDF

Chapter 4: Physiology of Pancreas Asst. Prof. Prom Vireak, MD Deputy Dean for Clinical Affairs, Faculty of Medicine  Objectives Understand the production of pancreatic enzymes Understand the roles of each of the main pancreatic enzymes...

Chapter 4: Physiology of Pancreas Asst. Prof. Prom Vireak, MD Deputy Dean for Clinical Affairs, Faculty of Medicine  Objectives Understand the production of pancreatic enzymes Understand the roles of each of the main pancreatic enzymes in the digestion of carbohydrates, proteins and fats Understand the mechanism of the regulation of pancreatic juice production and secretion Understand the role of bicarbonates in the pancreatic juice  Anatomy of Pancreas Pancreas is the mixed glands. Pancreas is divided in a head, neck, body and tail. There are two ducts of pancreas: Main pancreatic ducts (Wirsung) which joins with common bile duct to form an ampulla of Vater surrouding by the sphincter of Oddi (it opens into the descending part of the duodenum) Accesory pancreatic duct Secretion of digestive juice Exocrine function = pancreatic juice Pancreas Dual functions Endocrine function Production of hormones The fuctional unit of exocrine of pancreas is the acini and the ducts.  Digestive enzyme Wirsung Duct Ampulla of Vater Duodenum Volume: 1,5L/day Bicarbonate content is very high in pancreatic juice ( 110-150mEq/L) Making pancreatic juice highly alkaline, neutralizing the acid chyme to protect the intestinal mucosa Bicarbonate ions provide the required pH 7-9 for activiating the pancreatic enzymes  Function of Pancreatic Juice Pancreatic Juice’s functions: Digestive functions for protein and lipid, with minor role in carbohydrate digestion Neutralizing action (highly alkalin) https://www.youtube.com/watch?v=bqpHnOcWvdM  Digestion of Proteins The most important proteolytic enzymes: - Trypsin - Chymotrypsin - Carboxypeptidase Trypsin and chymotrypsin split the proteins to peptides but not individual amino acid. Carboxypetidase splits some peptides into amino acid  Trypsin Pancreatic Exocrine (pancreatic acini) Trypsinogene Autocatalytic action Enterokinase Brush-bordered cells of (enteropetidase) Duodenal mucus membrane Trypsin Trypsinogen is activated only when it reaches small intestine. Its activation to trypsin in pancreas is inhibited by trypsin inhbitor, deficiency of it à pancreas damage  Actions of Trypsin: Digestion of protein: Trypsin Protein Proteoses and peptides Powerful proteolytic Activating other enzymes of pancreatic juice: Chymotrypsin, carboxypetidases, elastase, lipase. Autocatalytic action Chymotrypsin Actions of chymotrypsin: Converting proteins to petides e.g. Digestion of milk protein Carboxypeptidase It is exopetidase breaking peptides to amino acids Digestion of Lipids The main enzymes for the digestion of Lipids = Lipolytic Enzymes Pancreatic lipase Hydrolyzing neutral fat into fatty acids and monoglycerides It is powerful lipolytic enzyme, 80% of fats are digested. Cholestrol esterhydrolase Hydrolyzing the cholesterol esters Phosopholipase A and B Split phospholipids to fatty acids  Digestion of Carbohydrates Pancreatic amylase = Amylolytic enzyme = hydrolyzes starches, glycogen and most of other carbohydrates (except cellulose) to disaccharides. Neutralizing Action of Pancreatic Juice When acid chyme enters the intestine from stomach, pancreatic juice with large quantity of bicabonate is released into intestine, making the pancreatic juice alkaline. It neuralizse the acidity of chyme in intestine so that it can be protected from destructive action of acid in chyme.  Regulation of Pancreatic Secretion The secretion of pancreatic juice is regulated by: Nervous factor: parasympathetic vagus nerve ending: acetylcholin Hormonal factors: cholecystokinin and secretin from mucosa of duodenum and jenjum There are 3 phases of pancreatic secretion Cephalic phase Gastric phase Intestinal phase These phases correspond with the three phase of gastric secretion Cephalic Phase Similar to gastric secretion, cephalic phase is regulated by the neurvous mechanism through reflex action. Two types of reflexes: Unconditioned reflex Inborn Simultaneously with cephalic phase of gastric secretion Presenting food in the mouth through vagal nerve à secreting acetylcholine pancreatic acini à stimulating pancreatic secretion Conditioned reflex Acquired by previous experience Simulus such as eye, ear, nose, thought à through vagal nerveà releasing acetylcholin à pancreatic acinià pancreatic secretion. Gastric Phase When food enters the stomach, gastrin is secreted from stomach. It is then transport to pancreas via blood, stimulating pancreatic secretion. The pancreatic juice secreted during this phase is rich in enzymes but less in water  Intestinal Phase Intestinal phase = when chyme enters the intestine Controlled by the hormones: Secretin Produced by S cells of mucous membrane in duodenum and jejunum It is secreted inactive as prosecretin and activated by acid chyme to secretin Action: Stimulating the ductal cells to produce high volume of bicarbonate ion. Cholecystokinin (CCK) Secreted by I cells in duodenal and jejunal mucosa Action: stimulating the acinar cell the seceretion of pancreatic juice rich in digestive enzyme.  Applied Physiology Pancreatitis: inflammation of pancreatic acini. Acute pancreatitis (more severe) Chronic pancreatitis (repeated acute inflammatory) Steatorrhea: Formatoin of bulky, foul smelly and frothy and clay-colored stools with large quantity of undigested fat. One of the case is lack of pancreatic lipase  Questions for study 1. What is pancreas? 2. Which pancreatic gland that secretes digestive enzymes? 3. What make pancreatic juice high alkalin? 4. What are the main functions of pancreatic juice? 5. What are the major proteolytic enzymes in pancreatic juice? Explain their actions. 6. What are the lipolytic enzymes? Which one is the most powerful lipolytic? Explain it action. 7. Which pancreatic enzyme that digests cabohydrate? What is its action? 8. Why pancreatic juice has to neutralize the acid chyme? 9. Explain briefly about the 3 phases of the regulation of pancreatic secretions.