Physiology of Stomach PDF

‫بسم هللا الرحمن الرحيم‬ NILE VALLEY UNIVERSITY FACULTY OF MEDICINE Physiology of Stomach Dr: Mohammed Nour Assistant professor of physiology  Structure of the stomach  Functions of stomach  Components of gastric secretion  Mechanism of HCl formation  Gastric digestive enzymes  Fact...

‫بسم هللا الرحمن الرحيم‬ NILE VALLEY UNIVERSITY FACULTY OF MEDICINE Physiology of Stomach Dr: Mohammed Nour Assistant professor of physiology  Structure of the stomach  Functions of stomach  Components of gastric secretion  Mechanism of HCl formation  Gastric digestive enzymes  Factors affecting gastric secretion.  Control of gastric secretion  Gastric motility and emptying.  Vomiting  Consequences of gastrectomy.  Stomach is a fibromuscular bag located between the esophagus and the doudenum.  Consists of: Cardia Fundus Body Pyloric antrum Pylorus  Storage of food up to 4 h  Protection by: HCl (Kills bacteria)  Endocrine function (Gastrin).  Facilitate absorption of iron and calcium.  Produce intrinsic factor (vit B12 absorption).  Regulate delivery of food in to duodenum.  Volume about 2-3 L/day  Main constituents are:  HCl  Digestive enzymes (Pepsinogen)  Mucus  Electrolytes  Intrinsic factor.  Sources of H+ Dissociation of H2O Oxidation of Glucose CO2 + H2O CA H2CO3 H+ + HCO3+  H+enter canaliculi by:- H+-K+ ATPase pump in Exchange to K+ Against concentration gradient  HCO3+enters the blood in exchange to Cl-Which enters the cell  Cl- enter the canaliculi.  In the canaliculi :- H+ + Cl- HCl  For each H+ ion secreted to the lumen , HCO3+ enters the blood.  If secretion of HCl is increased e.g following a meal (or repeated vomiting) , the pH of the blood becomes alkaline = Post prandial alkaline tide  Muscarinic receptors for acetylcholine G receptors for gastrin  H2 receptors for histamine  PG receptors for prostaglandins (inhibitory)  Killsingested bacteria  Activate pepsinogen to pepsin & allow its action.  Stimulate the secretion of pepsinogen  Facilitates iron and calcium absorption.  Somatostatin Released from D cells in the antrum & intestine when pH drops to 2.5 or less Inhibit G cells (Gastrin) Inhibit parietal cells  Prostaglandins Inhibits HCl Increases mucus and HCO3- secretion When decreased by aspirin, it causes peptic ulcer.  Occurs in 3 phases: Cephalic phase (20%). Gastric phase (70%). Intestinal phase (10%). Mainly inhibitory , secretin and CCK from small intestine inhibit gastric secretion.  It has two layers:  Outer layer: mucous.  Inner layer: HCO3.  Function :  It protects the gastric mucosa from action of gastric acid and pepsin.  Motor functions of the stomach:  Storage or receive food.  Mixing & delivering of food to the duodenum.  When food enters the stomach , the following types of movement occur :- Receptive relaxation Peristalsis Motor migrating complex (MMC)  Occurs in the upper part of the stomach (fundus + body).  Allow the stomach to accommodate large volume of food with minimal increase in intragastric pressure.  Control by vagovagal reflex through NO& VIP.  Occurs in the lower part (distal stomach)  Mixes food and allow it to pass through the pylorus to the duodenum.   Peristaltic waves occur in fasting state or between meals every 90 min.  Removes remnants of food and so prevent growth of bacteria.  Disappears on eating.  For optimal digestion and absorption the chyme must deliver at constant rate to the duodenum ,so gastric emptying must be regulated.  Volume of gastric content  Consistency of gastric content  Type of food  PH of gastric content  Osmolarity of gastric content  Neuralfactors(Enterogastric reflex).  Hormonal factors. THANKS