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47 Cards in this Set
- Front
- Back
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Controlled by.. |
Autonomic system - Parasympathetic (excitatory) - Sympathetic (inhibitory) - Enteric (excitatory and inhibitory) |
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What is the enteric nervous system? |
- Network that monitors and regulates digestive tract tone, mobility, secretion, and blood flow - Includes myenteric plexus and submucosal plexus |
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Gastric disorders |
Peptic ulcer disease Gastroesophageal reflux disease |
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Microscopic Stomach Anatomy |
- Mucous cells that secrete gastric mucous - Parietal cells that secrete HCl --> they contain canaliculi in apical surface to increase SA - Enterochromaffin-like cells (ECL) --> neuroendocrine cells --> in the gastric mucosa below epithelium, near parietal cells |
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Pharmacology of stomach acidity |
- Primary mechanism via H+/K+ ATPase in apical membrane of parietal cells - Paracrine release of histamine from ECL cells --> H2 histamine receptors --> Basal secretion levels
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Acid release is stimulated by? |
- Neurocrine release of ACh (parasympathetic, enteric nervous system) - Endocrine release of gastrin (enteric nervous system peptide) |
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What stimulates ECL cell-mediated acid release? |
- ACh and gastrin |
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Functions of hydrochloric acid |
- Activates pepsin and lingual lipase - Breaks up connective tissues and plant cell walls (helps liquefy food to form chyme) - Contributes to nonspecific disease resistance by destroying pathogens
- pH of gastric juice: 1.5-3.5 |
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Protection of the stomach |
- Mucus: resists acid and enzyme action on gastric mucosa - Both mucus and HCO3- secretion are stimulated by prostaglandins (PGE2) - Tight junctions -> epithelial cells - Continuous epithelial cell replacement |
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What are prostaglandins? |
- Locally acting drugs produced by almost all body tissues - Derived from membrane phospholipids
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What happens when PGE2/PGI2 bind to local receptors? |
1) Inhibit H+/K+ ATPase protein in parietal cells 2) Stimulate production/release of mucus and bicarbonate ions |
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What inhibits the action of prostaglandins? |
- NSAIDs |
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Homeostasis of the stomach |
- Continuous equilibrium between 1) Acidity level 2) Protective balances
- Regulated by enteric nervous system, prostaglandins, and presence of food in digestive tract |
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What is peptic ulcer disease? |
- Acid-induced gastritis leading to erosion of stomach lining - Pepsin and hydrochloric acid activity |
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What causes ulcer? |
- Over 90% of ulcers correlated with presence of Helicobacter pylori in the GI tract or NSAID-related inhibition of mucus secretion - H. pylori (80% of case) |
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Principles of treatment |
- Neutralize or reduce gastric levels of H+ - Strengthen/enhance protective forces --> Enhance natural mucus level |
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Antacids |
- Earliest form of treatment for GI distress - Hydroxide and/or carbonate salts - Neutralization of acid in stomach |
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Side effects of antacids |
- May affect drug solubility/absorption - Carbonate-based salts, belching - Al3+ salts produce constipation - Mg2+ salts produce diarrhea
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Solution for antacid side-effects |
- Give mixture --> Balance side effects --> Preserve bowel function |
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H2 Receptor Antagonists |
- Primary treatment until early to mid 1990's - They are competitive, selective blockers of histamine H2 receptors in parietal cells - No HCl release...
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Clinically approved OTC remedies |
- TIDINES - cimetidine |
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Side effects of H2 receptor antagonists |
- Low side effect profile - But could cross placenta and enter breast milk |
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Proton pump inhibitors |
- MOST effective suppressor of gastric acid release - "PRAZOLE" |
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Example of proton pump inhibitor |
Omeprazole |
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Characteristics of protein pump inhibitors |
- Short serum half-life (1-2 hours) - Ingested as prodrug - Irreversible inactivation of H+/K+ ATPase enzyme - Lengthly effect (2-3 days) - Require new synthesis and membrane insertion (18-24 hours) |
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Mucus/Buffer Stabilizing Agents |
- Misoprostol - Sucralfate |
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Misoprostol |
- Prostaglandin E analogue - DIRECT effect on parietal cells (inhibitory) --> reduce H+ release - Mucus cells (stimulatory) --> inc. mucus HCO3 secretion
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When would misoprostol be useful? |
- Useful in NSAID-induced ulcers |
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Sucralfate |
- Aluminate-sucrose bonds bind to charged groups --> cross-link and polymerize to form protective layer - Viscous, sticky protective gel --> prevents mucus degradation by pepsin |
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What is the major side effect of sucralfate? |
- Constipation |
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Current and combined therapies |
Prophylaxis vs. treatment - Histamine antagonists less useful - Proton pump inhibitors more useful --> Enhance suppression; all pathways blocked - Sucralfate => preventive measure |
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H. Pylori treatment |
- Reduce H+ is good, but there is a 80% chance of relapse without eradication of bacteria - Standard therapy: PPI, clarithromycin, and amoxicillin for 14 days aka. triple therapy |
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NSAID-related ulcers |
- Stop NSAID use - PPIs |
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GERD (Gastroesophageal reflex disease) |
- Stomach/duodenal reflux into esophagus - Mild cases: heart burn, & mild regurgitation |
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Treatment for GERD |
- Lifestyle changes (eating full meal) - Limit NSAID use - Neutralizing acid/esophageal contents (protective) - Stimulate gastric emptying (via. pyloric sphincter) - prokinetic agents |
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Prokinetic agents |
- Stimulates neurons of the enteric nervous system --> gastric emptying --> intestinal motility |
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Example of prokinetic agent |
Domperidone --> D2 (dopamine receptor) antagonist |
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Treatment of diarrhea, constipation... |
- Diet management - Tweaking current pharmacological regime --> Avoid side effects - Stimulate enteric nervous system to produce a bowel movement (laxatives) |
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Bulk laxatives |
- Altered dietary intake (dietary fiber) --> indigestible, water-absorbing molecules to the colon - Therapeutic mechanism: ability to absorb/retain water - Stimulate GI tract to induce bowel movement |
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Osmotic laxatives |
- Poorly absorbed salts, fatty acids, carbohydrates - Increased water retention, stimulating peristalsis - ie. saline purgatives (magnesium sulfate) - ie. lactulose, sorbitol, mannitol |
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Stimulant/contact laxatives |
- Senna preparation --> sennosides --> released anthracene compounds that stimulate myenteric plexus (smooth muscle activity)
ie. castor oil - avoid as long term therapy |
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Stool softeners |
- Docusate - Anionic surfactant, allows mixing of fatty/aqueous substances - Widespread use - Mineral oil |
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Prokinetic drugs |
- Domperidone, metoclopramide --> stimulates GI motility - Cisapride (serotonin antagonist) --> only GI stimulation |
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What is diarrhea? |
- Depends on:
1) Cause 2) Nutritional/health state of individual 3) Inconvenience to medical emergency |
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Treatment of diarrhea |
- Maintenance of fluid and electrolyte balance - Use of anti-infective agents - Non-antimicrobial antidiarrheal agents |
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Anti-motility agents |
Opiates - act on mu receptors in ENS ie. loperamide Anti-muscarinics? - Not effective |
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Adsorbants |
kaolin, pectin, chalk... - similar to bulk laxatives
- adsorb water - peptol-bismol |
