Pancreatic Secretion PDF - Physiology

The learning Objectives Describe the exocrine pancreatic secretion. Explain the mechanism of exocrine pancreatic secretion. Pancreatic Exocrin...

The learning Objectives Describe the exocrine pancreatic secretion. Explain the mechanism of exocrine pancreatic secretion. Pancreatic Exocrine Secretion Discuss the control of exocrine pancreatic secretion. Discuss the definition and causes of exocrine pancreatic insufficiency (EPI)Exocrine pancreatic insufficiency (EPI) Dr. Sherin Magdi M.B.B.Ch , M.Sc , MD in Physiology Assistant professor 1 2 Physiology department-Medicine program Pancreatic secretion The Functional parts of pancreas The pancreas is a gland that contains 2 parts : 1-Endocrine part (islets of Langerhans): It secretes the hormones (insulin and glucagon). 2-Exocrine part: It consists of a compound acinar gland that secretes the pancreatic juice which is collected by a duct system drains into a main large duct which joins the common bile duct forming the ampulla of Vater which opens into the duodenum (its opening is controlled by the sphincter of Oddi.) 3 4  It is the most important digestive juice Its daily volume is about 1500 ml. Pancreatic bicarbonate secretion It is alkaline (pH about 8) because of its high HC03- content It is formed of 2 parts : When the pancreas is stimulated to secrete copious quantities I) A Watery part : of pancreatic juice, the bicarbonate ion concentration can It is a watery juice rich in HC03- that is secreted by the duct cells. rise to about 145 mEq/L , (about five times that of It is important as : bicarbonate ions in the plasma.) (a)It neutralizes the pH of the intestine to be suitable for the activity of the pancreatic and intestinal enzymes This can happen due to the ability of duct cells to secrete (b) It protects the duodenal mucosa from the harmful effects of HCI. sodium bicarbonate solution into the lumen of pancreatic ducts. 2) An enzymatic part : It is a viscid juice that is secreted by the pancreatic acini, and it is rich in digestive enzymes 5 6 1. Carbon dioxide diffuses to the interior of the cell from the 3. The overall movement of sodium and bicarbonate ions blood and, under the influence of carbonic anhydrase, combines from the blood into the duct lumen creates an osmotic with water to form carbonic acid (H2CO3). pressure gradient that drags water to the lumen of the pancreatic duct. 2.The carbonic acid in turn dissociates into bicarbonate ions and hydrogen ions (HCO3- and H+). The bicarbonate ions are actively secreted through the luminal border of the cell into the lumen of the duct. The hydrogen ions are exchanged for sodium ions through the blood border of the cell by a secondary active transport process. This supplies the sodium ions (Na+) that are transported through the luminal border into the pancreatic duct lumen to provide electrical neutrality for the secreted bicarbonate ions. 7 8  Pancreatic THE enzyme secretion PANCREATIC ENZYMES ( I ) Proteolytic (protein-splitting) enzymes These are normally secreted as inactive proenzymes and they become activated only in the small intestine. They include : (a)Trypsinogen : This is activated to trypsin in the small intestine by enzyme secreted by the duodenal mucosa called enterokinase (b) Chymotrypsinogens. (c) Procarboxypeptidases. (d) Proelastase. Secretion of Trypsin Inhibitor Prevents Digestion of the Pancreas. Fortunately, the same cells that secrete proteolytic enzymes into the acini of the pancreas simultaneously secrete another substance called trypsin inhibitor. This substance prevents activation of trypsin inside the secretory cells ,the acini and ducts of the pancreas. In addition, because it is trypsin that activates the other pancreatic proteolytic enzymes, trypsin inhibitor prevents activation of the other enzymes as well. 9 10 (2) Lipolytic ( lipid-splitting) enzymes Control of pancreatic secretion (a) Pancreatic lipase (b) Prophospholipase 1- Nervous control: (c) Cholesterolesterase Parasympathetic stimulation (vagal stimulation) can (3) Pancreatic amylase ( CHO-splitting) enzyme stimulate the acinar cells to produce the enzymatic part of the pancreatic juice All pancreatic proteolytic enzymes are secreted in an Sympathetic stimulation can decrease all the pancreatic inactive form to protect the pancreas against autodigestion, secretion. and they become activated only in the small intestine under 2-Hormonal control: the effect of trypsin. Secretin : It is secreted by the duodenal mucosa in response to the acid chyme delivered from the stomach. It stimulates secretion of watery part or the pancreatic juice 11 12  Phases of Pancreatic Secretion Cholecystokinin (CCK) : It is secreted by the duodenal mucosa in response to the Phase Stimulus Regulatory % of digestive products. pathway pancreatic It stimulates secretion of the enzymatic part of the pancreatic secretion juice Cephalic phase Vagal stimulation 20% smell,think or taste food. (Conditioned reflex) Presence of food in the mouth. (Unconditioned reflex). Gastric phase Presence of food in the Vagal stimulation 5-10% stomach Intestinal phase When the chyme Mainly Secretin 70% enters the small hormone intestine 13 14 Cystic fibrosis transmembrane conductance regulator (CFTR) Exocrine pancreatic insufficiency (EPI) It is a memberane protein anion channel that is encoded by the CFTR gene It is a condition in which the pancreas does not produce enough amount of the digestive The CFTR gene codes for ion channel protein that conducts chloride and bicarbonate ions enzymes needed to digest food. across epithelial cell membranes. So, an individual cannot absorb the necessary nutrients and vitamins. This leads to diarrhea, vitamin deficiency, and weight loss. Mutations of the CFTR gene affecting anion channel function lead to dysregulation of epithelial lining fluid (mucus) transport in the lung, pancreas and other organs, resulting Causes: in cystic fibrosis. Pancreatic cancer. Surgical removal of the pancreas. Complications include thickened mucus in the lungs with frequent respiratory infections, Obstructions of the pancreatic duct and pancreatic insufficiency Chronic Pancreatitis. Cystic fibrosis. Clinical features: Abdominal pain, gas and bloating. Fatty stool (pale, oily, foul-smelling stool that floats). Unexplained weight loss or failure to thrive in infants and children Treatment Pancreatic enzyme replacement therapy 15 16 Case scenario References A 30-year- woman comes to the physician because of recurrent abdominal cramps, bloating, and diarrhea for 4 Guyton and Hall Textbook of Medical Physiology 13th edition months. She describes her stools as greasy, foul-smelling, and Chapter 65. difficult to flush. During this time, she has had a 5-kg weight Ganong’s Review of Medical Physiology,23th Edition,section V loss. Her investigations shows low level of pancreatic , Chapter 26. enzymes. Which of the following hormones can help in treatment of this case? a) Secretin b) Gastrin c) Cholecystokinin. d) Somatostatin 17 18 Thank You 19