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Stomach

Stomach. Prof. K. Sivapalan. Stomach. Functions of the Stomach. Storage- receptive dilatation. Mixing- longitudinal, circular and oblique musculature. Slow release of Chyme- pylorus and sphincter Digestion- enzymes and acid. Eliminating noxious agents- acid. Absorption (facilitation)

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Stomach

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  1. Stomach Prof. K. Sivapalan.

  2. Stomach. Stomach

  3. Functions of the Stomach • Storage- receptive dilatation. • Mixing- longitudinal, circular and oblique musculature. • Slow release of Chyme- pylorus and sphincter • Digestion- enzymes and acid. • Eliminating noxious agents- acid. • Absorption (facilitation) • B12- intrinsic factor. • Iron and calcium- acid. Stomach

  4. Storage Function • Plasticity- distention causes dilation without increase of pressure. • It is promoted by vagal reflex during meal. Stomach

  5. Gastric Motility • Longitudinal and circular muscles- • incomplete peristalsis for milking the body of the stomach to leave solids and propel liquidized chyme into pylorus • complete peristalsis in the pylorus for emptying [pyloric pump]. • Oblique muscles- churning movements for mixing and grinding. Stomach

  6. Gastric Secretion • 2.5-3.0 liters per day. • Enzymes- pepsinogen and gastric lipase. [Chief cells] • Acid and intrinsic factor- [parietal or oxyntic cells] • Mucus by surface and neck cells in the fundus and the body, pylorus and cardia of the stomach. • It forms 2-3 mm thick cover over the epithelium. Stomach

  7. Acid Secretion • Canaliculi in cells with microvilli. • When activated, microvili develop and contain H+- K+ ATP ase. • H+ in the cell is exhanged to K+ in lumen [energy] • CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3– [Carbonic unhydrase] • HCO3– diffuses into ECF and blood [post prandial alkaline tide]. • pH in cell is 7.2, in the lumen- 0.8 Stomach

  8. Gastrin • Secreted by G cells in pylorus [andrum] • pH above 3 in andrum stimulate secretion and below 3 inhibit. • Vagal efferent stimulate secretion. • Actions: • ↑ gastric motility, ↑ acid and pepsinogen secretion, ↑ tone of lower esophageal [cardiac] sphincter, trophic action on mucosa of GIT. Stomach

  9. Cephalic phase:[↑] Sight, smell, thought of food Emotional states- anger, hostility ↑. Fear, depression ↓. Presence of food in the mouth Hypoglycemia Gastric phase:[↑] Stretch, chemicals – local reflex. Gastrin Vagal reflex Caffaine, nicotine Intestinal phase:[↓] Entero-gastric reflex (distention, acid, irritation to mucosa, digested food products) Secretin, cholecystokinin, Gastric inhibitory peptide. Control of Acid Secretion. Stomach

  10. Protection of Gastric Mucosa. • Mucus. • Turnover of surface cells. • Tight junctions in cells. • Control of acid secretion. • Alcohol, aspirin, acid in empty stomach, increased secretion of acid- weaken the above. ? Helicobacter Pylori in Under mucus layer • When protection fails, Peptic Ulcer. Stomach

  11. All factors that stimulate pyloric pump relax the pyloric sphincter. Type of food- carbohydrate fastest, protein next and fat slowest. Gastric factors:[↑] Degree of distention. Gastrin Intestinal factors:[↓] entero-gastric reflex Acid [pH- 3.5-4.0]and protein products. Distention of duodenum. Irritation to duodenal mucosa. High Osmolality hormonal Fatty food (CCK, GIP) Control of Gastric Motility and Emptying Stomach

  12. Lower Esophageal Sphincter • Internal- circular muscles. • External- part of diaphragm. • Sling fibers of the oblique muscles form a flap valve. • Acalasia: • Increased tone, incomplete relaxation due to failure of myenteric plexus development. Stomach

  13. Stimulus: Stomach- salt water, warm water, toxic substances. Abdominal viscera. Irritation to throat. Higher centre: ↑ intracranial pressure Bad sight, smell Feeling disgust, pain Labyrinthine stimulus. Emetic drugs Vomiting centre Situated in medulla. Effects: Nausea and excessive salivation. Glottis and nasopharynx closed. Lower esophageal sphincter relax ? reverse peristalsis from duodenum Pyloric sphincter closed Raised intra abdominal pressure- diaphragm and abdominal muscles. Forced expiration to empty esophagus. Vomiting Stomach

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