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1 Lec.7 24 April 2017 dr. baybeen Alselevany Pancreas Objectives 1. Physiological anatomy of pancreas &functions 2. Exocrine Function of pancreatic Functional Anatomy Composition. Regulation. Phases of pancreatic juice. Physiological anatomy of pancreas and functions The pancreas is a large compound gland, which lies parallel to and beneath the stomach. The pancreas consists of a head located within the curvature of the duodenum, and a body and tail which extends to the spleen .It has both endocrine and exocrine functions.a.Exocrine portion which secretes pancreatic juices. endocrine portion that secrete insulin and glucagon which are not secreted by the same pancreatic tissue that secretes intestinal pancreatic juice .Instead, insulin is secreted directly into the blood by islets of Langerhans that occur in islet patches throughout the pancreas. Exocrine function of pancreas Functional Anatomy The structure of the exocrine pancreas resembles a cluster of grapes with most of its internal structure similar to that of the salivary . glands .Digestive enzymes are secreted by the pancreatic acinar cells and bicarbonate by duct cells. The pancreatic juice flows into long pancreatic duct that joins the common bile duct immediately before it empties into the duodenum through the papilla of vater surrounded by the sphincter of Oddi . The pancreatic duct usually connects with bile duct from liver and gallbladder 1 2 Composition of pancreatic juice About 1500ml of pancreatic juice is secreted per day. 1. the two important components of pancreatic juice, are bicarbonate ions and water. 2. Pancreatic digestive enzyme. 3.ions such as Na+, K+ , Ca+ , Mg++ , HCO3- , Cl - , SO4 2 - , HPO4 2 –. A. Bicarbonate Ions (HCO3-): bicarbonate is secreted by duct cells. The two important components of pancreatic juice, are bicarbonate ions and water. Pancreatic juice is alkaline due to the presence of high concentration of bicarbonate (HCO3 - ) approximately 113meq/L.. Its pH 8 a. which provides a favorable condition for the action of digestive enzymes and helps to neutralize the acidic chyme as it arrives from the stomach. b.at the same time , the alkaline condition in the small intestine blocks the action of pepsin which might damage the duodenal wall. B. Pancreatic digestive Enzymes .The pancreas supplies the principal enzymes for the digestion of all major foodstuffs, proteins ,carbohydrates and fats. All pancreatic enzymes are synthesized and secreted by the acinar cells.a. digestive enzymes for carbohydrates are pancreatic amylase which hydrolyze carbohydrates such as starches, glycogen, and most other carbohydrates (except cellulose ) to form mostly disaccharides and a few disaccharides. b. The main enzymes for fat digestion are (1) pancreatic lipase, which is capable of hydrolyzing neutral fat into fatty acids and monoglycerides; (2) cholesterol esterase, which causes hydrolysis of cholesterol esters; and (3) phospholipase, which splits fatty acids from phospholipids. Pancreatic lipase and amylase are secreted as active enzymes. c. the protein splitting ( proteolytic ) enzymes are : trypsin , chymotrypsin , carboxypolypeptidase . When first synthesized in the pancreatic cells, the proteolytic digestive enzymes are in the inactive forms trypsinogen, chymotrypsinogen, and procarboxypolypeptidase, which are all inactive enzymatically. They become activated only after they are secreted into the intestinal tract. Trypsinogen is activated by an enzyme called enterorkinase which is secreted by the intestinal mucosa into the trypsin when chyme comes in contact with the mucosa. Also, trypsinogen can be autocatalytically activated by trypsin that has already been formed from previously secreted trypsinogen. Chymotrypsinogen is activated by trypsin to form chymotrypsin, and procarboxypolypeptidase is activated by trypsin into d carboxypolypeptide . 2 3 Trypsin Inhibitor It is important that proteolytic enzymes of the pancreatic juice not become activated after they have been secreted into the intestine because the trypsin and other enzymes would digest the pancreas itself. Fortunately, the same cells that secrete proteolytic enzymes secrete another enzyme called trypsin inhibitor which prevents activation of trypsin and prevents digestion of the pancreas itself. And because it is trypsin that activates other pancreatic proteolytic enzymes, trypsin inhibitor prevents activation of the others as well. C..ions such as cations Na+, K+ , Ca+ , Mg++ , and anions such as HCO3, Cl - , SO4 2 - , HPO4 2 –. Regulation of Pancreatic Secretion 1. Hormonal control 2.Neura control Hormonal control: Pancreatic secretion is mainly under hormonal control. a. CCK which is released from I – cells in the duodenum and jejunum. It's secreted in response to fat and protein products that enter the duodenum from stomach. CCK, passes by way of the blood and stimulate the acinar cells of pancreas causing production of large quantities of pancreatic digestive enzymes accounting for 70-80% and but relatively small quantities of water and bicarbonate to go with the enzymes. b. Secretin: is secreted from S-cell in the duodenum and jejunum in an inactive form pro-secretin. Secretin is secreted when highly acid food enters the small intestine. Its absorbed into the blood and stimulates secretion of large quantities of pancreatic juice rich in bicarbonate HCO3 and water but little amount of pancreatic enzyme,. Neutralization of acid chyme that enters into the duodenum by HCO3 - . This is a protective mechanism against the development of duodenal ulcers.. When acid chyme with pH less than 4.5 to 5.0 (about 3) enters the duodenum from the stomach, it causes duodenal mucosal release and activation of secretin, which is then absorbed into the blood. The one truly potent constituent of chyme that causes this secretin release is the hydrochloric acid from the stomach. 2. Neural control Acetylcholine, which is released from the parasympathetic vagus nerve endings and from other cholinergic nerves in the enteric nervous system.ACH stimulates secretion of large quantities of pancreatic digestive enzymes and small amounts water and HCO3. 3 4 Phases of Pancreatic Secretion 1. Cephalic phase 2. Gastric phase 3. Intestinal phase 1.Cephalic phase : During the cephalic phase of pancreatic secretion, the same nervous signals from the brain that cause secretion in the stomach also cause acetylcholine release by the vagal nerve endings in the pancreas. . This causes secretion moderate amounts of pancreatic enzymes after a meal, and also small amounts of HCO3 – and water are secreted. 2. Gastric phase: Distension of either the proximal or distal regions of the stomach stimulates pancreatic secretion by initiating vagovagal reflexes. Because these are mediated by acetylcholine, secretion is primarily release of small amounts of pancreatic enzymes after meal.. No role of gastrin on pancreatic secretion. 3. Intestinal phase: After the chyme leaves the stomach and enters the small intestine, a large amount of pancreatic secretion rich in bicarbonate is secreted, mainly in response to the hormone secretin. . 4