2013Stomach3 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.
2013Stomach4 Storage Function Plasticity- distention causes dilation without increase of pressure. It is promoted by vagal reflex during meal.
2013Stomach5 Gastric Motility Pacemaker at the proximal end of the greater curvature initiates motility. At rest- basal electrical rhythm- 3 per minute resulting in week contractions. Hunger contractions are strong contractions that are felt as hunger when stomach is empty. Motility is increased by parasympathetic stimulation, gastrin and local reflexes mediated by acetylcholine. It is decreased by sympathetic stimulation and vagotomy.
2013Stomach6 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.
2013Stomach7 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. Histamin
2013Stomach9 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] CO 2 + H 2 O ↔ H 2 CO 3 ↔ H + + HCO 3 – [Carbonic unhydrase] HCO 3 – diffuses into ECF and blood [post prandial alkaline tide]. pH in cell is 7.2, in the lumen- 0.8
2013Stomach10 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.
2013Stomach11 Control of Acid Secretion. 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.
2013Stomach13 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.
2013Stomach14 Control of Gastric Motility and Emptying 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)
2013Stomach15 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.
2013Stomach16 Vomiting 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.