L14 1502 2024 Stomach GI FINAL PDF

1502 Stomach Fall 2024 Lecture 14 Tuesday Sept. 24: 10am Dr. Al-Nakkash [email protected] 1  Learning Objectives 1. Ide...

1502 Stomach Fall 2024 Lecture 14 Tuesday Sept. 24: 10am Dr. Al-Nakkash [email protected] 1  Learning Objectives 1. Identify basic stomach anatomy. 2. Explain the main functions of the stomach. 3. Describe gastric filling & receptive relaxation. 4. Describe factors that regulate gastric emptying: duodenal & stomach factors 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion and Pepsinogen 6. Describe the control of gastric secretion: Cephalic, gastric and intestinal phases 7. Identify the role of the gastric mucosal border, Pathophys: Peptic ulcers. © L. Al-Nakkash 2024 2  Stomach Fundus – above LES Otherwise called? LES Body - main part Does the thin amount of Antrum - lower part smooth muscle thick vary? YES Muscle thickness difference - – important for Gastric motility ↑SM →↑ strength of contraction Pyloric sphincter – – between stomach & duodenum © L. Al-Nakkash 2024 1. Identify basic stomach anatomy. 3  Stomach – 3 MAIN functions 1. Storage – Allows emptying into small intestine at a rate appropriate for optimal digestion & absorption. 2. Secretes HCl – Used to start protein digestion. 3. Mixing – Mixing movements pulverize food with gastric secretions. What do we call the end product in the stomach? chyme © L. Al-Nakkash 2024 4 2. Explain the main functions of the stomach.  Gastric Filling – Receptive Relaxation Empty - stomach volume ~ 50 ml Full - filled expansion ~ 1500 ml We can accommodate a large change in volume. what are the folds known as? rugae How can the stomach accommodate this big ↑volume? – The folds flatten with food intake & flatten out as stomach relaxes. – Reflex relaxation = receptive relaxation. – Allows the stomach to accommodate an ↑ volume. – Triggered by eating & mediated by the vagus nerve. © L. Al-Nakkash 2024 3. Describe gastric filling & receptive relaxation. 5  From, Sherwood retropulsion © L. Al-Nakkash 2024 3. Describe gastric filling & receptive relaxation. 6  Gastric Emptying STOMACH: factors that modify rate of gastric emptying. 1. Amount of chyme in stomach – Stomach empty rate = proportional to volume of chyme in it. 2. Stomach distension → ↑ gastric motility, via: – Directly stretching the smooth muscle. – Involvement of intrinsic plexuses & vagus nerve. – Gastrin release. 3. Chyme fluidity – direct effect on gastric emptying – ↑__________________________________________________ fluidity → faster emptying. ↓ fluidity → slower emptying. Emptying of gastric contents into duodenum may take several hours © L. Al-Nakkash 2024 4. Describe factors that regulate gastric emptying: duodenal & stomach factors 7  Gastric Emptying DUODENUM: factors that modify rate of gastric emptying. (in duodenum & jejunum mucosa) Fat in duodenum inhibits emptying of gastric contents. Mediated by CCK – secreted by I cells Would gastric emptying be slower after a fat-rich meal? Yes Acid in duodenum inhibits emptying of gastric contents. Mediated by reflexes in the enteric nervous system. Stomach secretes HCl → acidic chyme empties into duodenum → neutralized by NaHCO3 in duodenum. From where? pancreas Unneutralized H+ in duodenum → inhibits gastric emptying until complete neutralization occurs. – Unneutralized H+ in duodenum → effects pancreatic enzymes – how? Inactivates enzymes © L. Al-Nakkash 2024 4. Describe factors that regulate gastric emptying: duodenal & stomach factors 8  Duodenal factors that modify rate of gastric emptying Hypertonicity in duodenum If absorption rate of amino acids & glucose doesn’t keep up with rate of protein & carb. digestion – These stay in the chyme, – This will ↑ osmolarity of the duodenal contents, – Water will move towards them & enter duodenal lumen. To prevent this – gastric emptying is reflexly inhibited when there is an ↑ osmolarity of duodenal contents. Distension of duodenum chyme in duodenum → inhibit gastric emptying → allows duodenum time to catch up © L. Al-Nakkash 2024 4. Describe factors that regulate gastric emptying: duodenal & stomach factors 9  Gastric Digestive Juice Stomach secretes gastric juice Secretion is from cells in the gastric mucosa (2 areas): – Oxyntic mucosa and Pyloric gland area Mucosa Gastric pit Submucosa Oxyntic Gastric gland Pyloric gland mucosa area Found where? Stomach lumen – lined with gastric pits Found where? body & fundus antrum base of gastric pits = gastric glands. © L. Al-Nakkash 2024 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion, Pepsinogen 10  Gastric Secretory Cells Oxyntic Glands Lines body & fundus in BODY between gastric pits, Surface cover gastric mucosa epithelial cells Gastric pit Line gastric pits & entrance of glands Mucous What do they secrete? Thin watery mucus cells Gastric gland Line deeper parts of gastric glands Chief cells What do they secrete? pepsinogen Line deeper parts of gastric glands Parietal What do they secrete? HCl (oxyntic) cells Enterochomaffin- In gastric glands like (ECL) cells What do they secrete? histamine © L. Al-Nakkash 2024 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion, Pepsinogen 11  In pyloric gland area Gastrin Lines antrum Comes from: G cells When: in response to eating Actions of gastrin: Stimulates G cells H+ secretion Growth of gastric D cells from? mucosa parietal trophic somatostatin cells effect What does it inhibit? HCl secretion, gastrin release, histamine release © L. Al-Nakkash 2024 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion, Pepsinogen 12  HCl Secretion by Parietal Cells Omeprazole: proton pump inhibitor 3 5 4 2 4 + cAMP 1 Cl-follows H+ secretion Costanzo © L. Al-Nakkash 2024 13 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion, Pepsinogen  Regulation of H+ secretion by parietal cells Costanzo Agonists Antagonists Agonists can be potentiative- ACh & Gastrin also stimulate Prilosec histamine release from Inhibits H+/K+ATPase ECL cells. © L. Al-Nakkash 2024 14 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion, Pepsinogen  Functions of HCl Has several functions to assist with digestion: 1. Activates pepsinogen (enzyme precurser) to pepsin. 2. Aids in the breakdown of connective tissue & proteins – good for enzymatic attack - smaller food particles made. 3. Kills most microorganisms ingested with food © L. Al-Nakkash 2024 15 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion, Pepsinogen  Pepsinogen Pepsinogen secreted into gastric lumen inactive HCl cleaves it, converting it to pepsin active Pepsin acts on other pepsinogens to produce more pepsin An active enzyme activating other same enzyme molecules = an autocatalytic process Parietal cells Self activating Pepsin initiates protein digestion Chief cells → splits some AA linkages into peptides. Works best in HCl environment. © L. Al-Nakkash 2024 16 5. Identify the functions of the gastric secretory cells: Gastrin, HCl secretion, Pepsinogen Control of Gastric Secretion Costanzo Intestinal phase – secretions are slowed as chyme moves into the intestine © L. Al-Nakkash 2024 17 6. Describe the control of gastric secretion: Cephalic, gastric and intestinal phases  Gastric Secretion Decreases as Food Empties From Stomach into Intestine Factors that ↓ gastric secretion: Meal moves from stomach – duodenum. →remove major stimulus for gastric secretion, what is the original stimulus?presence of food in stomach Foods leave stomach – gastric juices accumulate. →↓gastric pH → ↑ somatostatin release From? D cells in antrum ↓ gastric secretion – Somatostatin is inhibitory → it will ___ Fat, acid, duodenal distension, all ↓ gastric secretion. © L. Al-Nakkash 2024 18 6. Describe the control of gastric secretion: Cephalic, gastric and intestinal phases  Mucus is Protective What does mucus do? 1. Protects against mechanical injury. Surface of gastric mucosa covered by mucus layer. 2. Protects stomach wall from self- Derived from surface epithelial digestion; inhibits pepsin. cells and mucus cells. 3. Protects against acid injury; neutralizes HCl near gastric lining Acidic, pH 2 Acidic, pH 7 Costanzo © L. Al-Nakkash 2024 7. Identify the role of the gastric mucosal border and Pathophys: Peptic ulcers. 19  Peptic Ulcers Broken gastric mucosal barrier. - due to reflux in the esophagus. - Due to dumping of excessive acidic gastric contents into the duodenum. Helicobacter pylori a bacterium - causes > 80% PU. Causes persistent inflammatory response. Other contributing factors for PU: Ethyl alcohol, NSAIDs, Stress, Smoking © L. Al-Nakkash 2024 7. Identify the role of the gastric mucosal border and Pathophys: Peptic ulcers. 20  The stomach can accommodate an ↑ volume True / False The presence of acid in the duodenum speeds up gastric emptying True/False Gastrin is the only agonist to stimulate parietal cell H+ secretion True/False Gastric contractions that propel chyme against a closed pyloric sphincter result in retropulsion. True/False Pepsinogen is in its inactive form when secreted, True / False Most gastric secretion occurs during the intestinal phase True/False PU can be caused by a broken GMB due to excessive NSAID use True/False © L. Al-Nakkash 2024 21  The stomach can accommodate an ↑ volume True / False Receptive relaxation = rugae flatten Allows ↑volume without change in pressure The presence of acid in the duodenum speeds up gastric emptying True/False Slows it: gives the duod time to catch up Gastrin is the only agonist to stimulate parietal cell H+ secretion True/False Histamine, Gastrin & Acetylcholine Gastric contractions that propel chyme against a closed pyloric sphincter result in retropulsion. True/False Retropulsion mixes it more in the stomach & breaks the food down into small particles. Pepsinogen is in its inactive form when secreted, True / False Pepsinogen is inactive. HCl converts pepsinogen → active pepsin Most gastric secretion occurs during the intestinal phase True/False No, MOST is in the gastric phase PU can be caused by a broken GMB due to excessive NSAID use True/False © L. Al-Nakkash 2024 22