Dr Pradeep Kumar, Professor department of physiology, KGMU, Lucknow

Gastrointestinal functions Secretions from stomach and its regulation

To understand the physiology of Stomach and Gastric Juice secretions Functions of gastric juice Mechanism of HCl secretion Regulation of HCl secretion Peptic ulcer disease

 Food is stored in the stomach  Mixed with acid mucus and pepsin  Stomach also add significant amount of digestive juices to meal  As cephalic phase of gastric secretion start earlier  This food is released in steady in to the duodenum

It is a colorless, watery, acidic, digestive fluid produced in the stomach  Pale yellow in colour, pH is 1-3,  Per day secretion is 2-3 L.  Chemical composition;  it contains inorganic salts,and organic components that include,mucin, digestive enzymes, hormones, intrinsic factors

They secret HCl into the stomach ◦ This acid is important for activation of pepsinogen, inactivation of microorganisms, It also secrets the intrinsic factor, necessary for intestinal absorption of vitamin B12.

◦ It secrets pepsinogen(zymogen). Once secreted, pepsinogen is activated by stomach acid into the active protease pepsin, ◦ Gastric Lipase is also secreted by chief cells, responsible for the initiation of fat digestion

 G cells secretes gastrin hormone which in turn stimulate chief, parital and ECL cells  G cells are activated by GRP and inhibited by somatstatin

 ECL cells secretes Histamin  ses HCl sec.  D cells secretes somatostatin by the influence of HCl  Somatostatin inhibit G cell

Gastric acid sec. can be divided into three phases:  Cephalic phase mediated by the CNS and  triggered by smelling, chewing or even the thought of food. Mediated by the vagus and acounts for % of the acid secreted).  Gastric phase triggered by the presence of food in the stomach Accounts for 70-90% of the acid secretion  Intestinal phase. Presence of chyme, most  probably amino acids, in the intestine triggers  approximately 5% of the gastric acid secretion.

Stimulation of acid secretion – cephalic phase  blocked by vagotomy  sham feeding  hypoglycemia  role of GRP (bombesin)

Gastric phase  70% of acid response  distension  peptides

 Presence of chyme, most  probably amino acids, in the intestine triggers  approximately 5% of the gastric acid secretion.

HCl converts pepsinogen to pepsin for chemical digestion  provides optimal pH environment for pepsin  destroys some bacteria  stimulates the small intestinal mucosa to release Secretin and CCK  promotes the absorption of Ca 2+ and Fe 2+ in small intestine

2. Pepsinogen (precursor of pepsin)  digestion of proteins 3. Mucus  forms a protective barrier: Mucus-bicarbonate barrier 4. Intrinsic factor  combines with vitamin B 12 to make it absorbable

 Neurocrine (denoting an endocrine influence on or by the nerves).  Endocrine (gastrin)  Paracrine (histamine) in contrast to true endocrines these hormones are not released into the bloodstream but into the surrounding tissues and act in the immediate vicinity, e.g. intestinal mucosal hormones.

 Peptic ulcers: ◦ Erosions of the mucous membranes of the stomach or duodenum produced by action of HCl. Disruption of mucus barrier  Zollinger-Ellison syndrome: ◦ Ulcers of the duodenum are produced by excessive gastric acid secretions. Due to gastrinomas  Helicobacter pylori: ◦ Bacterium that resides in GI tract that may produce ulcers.  Acute gastritis: ◦ Histamine released by tissue damage and inflammation stimulate further acid secretion.

 Proton pump inhibitors (omeprazole),  Antibiotics assist in eradicating H. pylori bacteria.  Histamine 2 (H2) receptor antagonists (Ranitidine)  Local antacids  Life Style Changes

 Lippincott’s Illustrated Reviews: Physiology (2013)  Medical Physiology, UPDATED SECOND EDITION (Walter F. Boron, MD, PhD)  BERNE & LEVY, PHYSIOLOGY, SIXTH EDITION, UPDATED EDITION  Ganong’s Review of Medical Physiology, T W E N T Y -F O U R T H E D I T I O N

( A)When the stomach is distended by meal. (B) )When the PH of the gastric content is Decreased below 2. (C)If the fundic mucosa is anaesthesized. (D) If the vagi are Stimulate.

( A)It is Secreted at the pyloric antrum and reaches the fundus tohrough the gastric lumen. (B) It Promotes the secretion of pepsin, but not HCL. (C)Its Secretion Stimulated by secretin and GIP. (D) It is structurally similar to CCK. (E)It has +ve feedback relation with gastric acidity.

(A)Is a function of peptic cells. (B)Require no energy. (C)Occurs by passive diffusion of both H+and CL- in the gastric human. (D) Require presence of carbonic anhydrase enzyme.

a.HCL. b.Trypsin. c.Zymogen granules. d.Pepsinogen.

a.Microcytic anemia. b.Hyperchlorohydria. c.Steatorrhea. d.pernicious anemia.

a. Depends on presence of intrinsic factor. b. D epends on passive diffusion. c. Occurs in the jujenum. d. Occurs in the stomach.

a. Parietal cells of the stomach. b. Chief cells of the stomach. c. Upper duodenum. d. Beta cells of pancreas.

a. Occurs secondary to active transport of H ⁺ by the parietal cells into the lumen of the stomach b. Requires the presence of the carbonic anhydrase enzyme. c. Is increased by administration of histamine. d. All of the above.

a. Occurs when food reach the stomch. b. Isnot accompanied by release of GRP. c. Is controlled by the vagi nerves. d. Isnot blocked by injection of atropine.

A 45 years old man is found to have a condition in which the parietal cells of his stomach have been destroyed by an autoimmune mechanism. This condition is often associated with which of the following?: a.Prenicious anaemia. b.Gastric ulcerarion c.Steatorrhea. d.Protein deficiency.

Which of the following statements is correct?: a. The gastric juice contains pepsins, lipase and α-amylase enzymes. b. The only essential constituent of the gastric juice is the intrinsic factor. c. The hunger contractions disappear after bilateral vagotomy d. HCL is essential for both carbohydrate and fat digestion.

A 42years old salesman presents with the chief complaint of intermittent midepigastric pain that is relieved by antacids or eating. Gatric analysis reveals that basal and maximal acid output exceed normal values. The gastric hypersecretion can be explained by an increase in the plasma concentration of which of the following?: a.Somatostatin b.Histamine c.Gastrin d.Secretin e.Enterogastrone

About the cephalic phase of gastric secretion, all the following are true except: a.It occurs before food enters the stomach b.It’s inhibited by bilateral vagotomy c.It involves some release of gastrin d.It begins only when food is tasted and accounts for most of the gastric secretion

The gastric mucosal barrier is maintained by all the following except: a.The nature of the surface membrane of the gastric mucosal cells and the tight junctions between these cells. b.Certain prostaglandins and the alkaline mucous secretion of the stomach c.The mucus gel-like membrane that coats the gastric mucous membrane d.Administration of H ₂ receptor blocking drugs (e.g. cimetidine) e.Excessive amounts of bile salts,asprin or ethanol

Physiology day 2015

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