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Stomach

Stomach. J-shaped organ lies below the diaphragm Sphincters at both ends Outer serosa covers smooth muscle layers Inner layer of glandular epithelium faces lumen. Capacity: 1-1.5 L FUNCTIONS: Acts as a Reservoir. Digestive /Secretory action.

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Stomach

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  1. Stomach • J-shaped organ lies below the diaphragm • Sphincters at both ends • Outer serosa covers smooth muscle layers • Inner layer of glandular epithelium faces lumen

  2. Capacity: 1-1.5 L FUNCTIONS: • Acts as a Reservoir. • Digestive /Secretory action. Gastric juice. • Mechanical function. Churning/grinding, Propulsive action • Protective function. Hcl

  3. Absorptive function. Alcohol and Water • Excretory function. Vomiting • Haemopoietic function. IF ,conversion of ferric to ferrous • Endocrine function. Gastrin

  4. GLANDS OF STOMACH • FUNDIC GLANDS • PYLORIC GLANDS • CARDIAC GLANDS

  5. Gastric glands. Three types. • Cardiac glands. • Oxyntic glands. Mucous cells Oxyntic /Parietal cells Chief /Peptic cell Endocrine cell • Pyloric glands.

  6. The cardiac glands: Present between the lower oesophageal sphincter. Contain mainly mucous secreting cells. Mucous and Bicarbonate.

  7. Oxyntic glands: Mucous cell Present in the neck region. Secretes Mucous and bicarbonate ions Oxyntic /Parietal cell: Present mainly in the neck region of the gland. Secretes Intrinsic factor and Hcl

  8. Chief cells /Peptic cells: Present toward the base of the gland. Secretes Pepsinogen. Endocrine cells / Enterochromaffin cells: • SecretesHistamine, Glucagon ,VIP Somatostatin, .

  9. Pyloric glands: Present in the Pyloric- Antral region. Mainly contain mucous cells and G-cells. Secretes Mucus and Gastrin

  10. MUCIN HCl , Intrinsic factor GASTRIN HISTAMINE PEPSINOGEN RENIN GELATINASE

  11. Composition of gastric juice • 1200 - 1500 ml /day • Water - 99.55% • Solids- 0.5% • pH: 1- 2 • Inorganic substances: Na+, K+, Mg+, H+, Hcl,Cl-, HCO3-

  12. Composition of gastric juice • Organic substances • PEPSONIGEN Pepsin 2. RENIN- present in infants and animals (curdles milk) 3. GASTRIC LIPASE 4. GASTRIC AMYLASE 4. UREASE – hydrolyses urea to ammonia 5. Mucous Hcl 6.Intrinsic factor 7. Gelatinase

  13. HCL Enzymes: • Pepsinogen Pepsin. Digestion of Protein

  14. 2. Rennin: in infants Curdles the milk 3. Gelatinase: Liquefies Gelatin 4. Gastric Lipase Weak fat splitting enzymes

  15. Lysosomes: Bacteriocidal enzymes. • Urease: Hydrolyse Urea to produce Ammonia. • Carbonic anhydrase.

  16. Functions of HCl • Activation of Pepsinogen to Pepsin • Provides acid medium for action of Pepsin • Bacteriolytic • HCl in duodenum increases & stimulate the secretion of bile from liver & pancreatic juice • Increase digestibility of Proteins • Conversion of ferrous to ferric.

  17. Secretion of Hcl consists of two components 1.Secretion of H+ ions into the lumen. 2. Secretion of Cl- ions into the lumen

  18. PARIETAL CELL LUMEN OF CANALICULUS BLOOD Co2+H20H2Co3 Carbonic anhydrase Hco3 Hco3 H+ H+ H+ K+ K+ HCl Cl- H+K+ATPase Cl- Cl- Na+ Na+ Na+ K+ K+ K+ H2O H2O H2O MECHANISM OF GASTRIC ACID SECRETION

  19. The Cl- ions come from the blood and are actively secreted into the lumen creating a negativity. • K+ ions enter the lumen due to an electric gradient • H+ ions are formed by dissociation of H2CO3 and are actively secreted into the lumen in exchange with one K+ ion (This is coupled by H+-K+ pump). • H2CO3 is formed in the parietal cell by hydration of CO2

  20. For each H+ ion secreted one Cl- is secreted and oneHCO3 ion is absorbed into the blood. As a result pH increases towards alkalinity. The kidney excretes these excess of HCO3 ion into the urine. This is called “ POST PRANDIAL ALKALINE TIDE” • Water moves into the lumen passively • H+ combines with Cl- and forms HCl

  21. PHASES OF GASTRIC SECRETION • Cephalic phase • Gastric phase • Intestinal phase • Interdigestive phase

  22. Food in the oral cavity Unconditioned Reflex Chief cell and Parietal cell NTS Direct effect G cells Sight ,Smell Thought of Food Cortex Hypothalamus Limbic system Conditioned Reflex HCl and Enzymes Gastrin NEURAL REGULATION DURING CEPHALIC PHASE

  23. Gastric phase • The food in the stomach causes the gastric juice secretion due to nervous and hormonal mechanism • This phase is account for 2/3rd of gastric secretion.

  24. GASTRIC PHASE 1.Local myentric reflex 2.Vagovagal reflex 3. Gastrin

  25. Food in the stomach Ach release Direct ACID AND ENZYME SECRETION G RP Gastrin Local and Neural Mechanism Histamine release Distension of Gastric mucosa ECL cells Direct GASTRIC PHASE

  26. Intestinal phase • Presence of food in the upper portion of small intestine (duodenum) also cause the release of gastric secretion. • Initial phase –gastric secretion is increased by gut gastrin • Late phase –gastric secretion is inhibited by intestinal factors by means of humoral & nervous mechanism.

  27. CHYME IN THE INTESTINE GASTRIN STOMACH Secretion Of Gastric juice INTESTINAL PHASE stimulation Secretin CCK-PZ Somatostatin GIP VIP Inhibition

  28. Enterogastric reflex: Food in the duodenum  stretch  sympathetic nerve stimulation  inhibition of gastric secretion and motility.

  29. Inter-digestive phase • In between meals; few ml of gastric secretion occur mainly non-oxyntic type (composed of mucus and very little pepsin and almost no acid). • This fluid is actually slightly alkaline contain moderate quantity of sodium bicarbonate. • However, strong emotional stimuli increases this phase secretion to 50ml or more gastric juice per hour of highly peptic and highly acidic,

  30. EXPERIMENTS TO SHOW THE REGULATION OF GASTRIC JUICE

  31. At different points along the dogs' digestive tracts, the Russian physiologist Ivan Petrovich Pavlov (1848-1936) surgically created pockets ("Pavlov pouches") , the aim being to study the physiology of secreation gasrtic juice at different phases and in 1904 (the 4th year it was awarded) he received the Nobel Prize for "his work on the physiology of digestion.

  32. Pavlov‘s pouch: vagus is secretomotor nerve, food in stomach causes gastric juicesecretion by the release of gastrin.

  33. Heidenhain pouch(denervatedantral pouch): It is a small pocket of the stomach that has been surgically separated from the body of the stomach.It is used to demonstate the role of sympathetic nerve and hormonal regulation of gasticsecreation after cutting vagus nerve and made to drain to the exterior. • Bickels pouch :Even sympathetic nerve fibers are cut by removing the blood vessels and is used to demonstrate the role of hormone in gastric secretion. • Farrel and Ivy pouch :It is used to study the role of hormone during gastric and intestinal phases of gastic secretion.

  34. SHAM FEEDING Oesophagus is cut and tied to skin is used to show cephalic phase

  35. Gastric Empting

  36. The rate at which substances leaves the stomach and enters the duodenum. Regulated by: • Stomach factors. • Duodenal factors. • Neural factors. • Hormonal factors

  37. Stomach factors: • Volume of gastric contents: Increase in gastric content facilitates gastric emptying. 2. Consistency of food: • Liquids-Semisolids-Solids • Chemical composition: • Carbohydrates-proteins-fats.

  38. 3. Acidity: Weak acids and neutral solutions -Strong acids. 4. Osmolar concentration : Higher the Osmolar concentration – slower emptying.

  39. Duodenal factors: • Distension of duodenum: Reflexly inhibit gastric emptying through sympathetic nerves. Prevent the overloading of the duodenum with partially digested food. 3.Acid in the duodenum: Reduces the gastric motility mediated through Enterogastrone , CCK-PZ , Secretin , VIP etc

  40. Neural: Parasympathetic : increase. Sympathetic : decrease. Hormonal: Gastrin –facilitates VIP , CCK-PZ, Secretin etc – decrease

  41. Vomiting / Emesis:

  42. Is a reflex act by which the upper GIT is relieved of its contents through the mouth. Initiated by stimulating vomiting centre.

  43. THREE PHASES: • Nausea • Retching • Gastric evacuation/vomiting

  44. Nausea: Conscious recognition of subconscious excitation in the area in the medulla closely associated with or a part of the vomiting centre. • Development of duodenal, jejanal contractions • Increase salivation, Yawning,Rapid deep irregular breathing.

  45. Retching: Intermittent forceful contractions of diaphragm and abdominal wall. • LES closes. • Pyloric part contact ,Stomach relaxes. • LES opens ,Oesophagus relaxes. • UES relaxes ,soft palate pushes upwards.

  46. Gastric evacuation/vomiting: • Deep breath. • Glottis closed • Oesophagus contracts. • Contents of the stomach is thrown out.

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