W11 Antacids, H2 Antagonists & Proton Pump Inhibitors, Promotility Agents, Laxatives, Emetics & Antiemetics Flashcards

Question

Prokinetics- Serotonergic Agonists (substituted benzamides)

Answer 1

Cisapride and Prucalopride * Cisapride activate serotonin receptors (5HT4 receptors) to release acetylcholine * Their actions are also blocked by atropine * Treat mild to moderate gastroesophageal reflux, gastroparesis * Minor side effects ------ serious cardiac risks Aim: ability to accelerate intestinal transit, reduce esophageal acid exposure, and promote gastric emptying ....Lots of drugs developed and withdrawn * Prucalopride a selective serotonin 5HT4-receptor agonist with prokinetic properties * Prucalopride is recommended as an option for the treatment of chronic * Tx constipation only in women for whom treatment with at least two laxatives from different classes, at the highest tolerated recommended doses for at least 6 months, has failed to provide adequate relief and invasive treatment for constipation is being considered.

Answer 2

Erythromycin (macrolide antibiotic) * Indicated for GI stasis - enhances peristalsis by acting on motilin receptors or by releasing motilin * Their actions appear to be mediated by acetylcholine since they are also blocked by atropine. * Motilin agonists may increase gastric tone or inhibit gastric accommodation and, potentially, worsen symptoms, even when gastric emptying improves

Answer 3

* By the time the digested food (chyme) reaches the large intestine, most of the nutrients have been absorbed * The primary role of the large intestine is to convert chyme into faeces for excretion * Lacks villi and has many crypts of Lieberkühn * The crypts consist of simple short glands lined by mucus-secreting goblet cells * The epithelial cells contain almost no digestive enzymes * The mucosa, like that of the small intestine, has a high capability for active absorption of sodium, Cl and water. * The outer longitudinal muscle layer is modified to form three longitudinal bands called tenia coli visible on the outer surface. * Since the muscle bands are shorter than the length of the colon, the colonic wall is sacculated and forms haustra.

Answer 4

* Mucus – neutralises any acid, protects against irritation, lubricates, and provides a binding medium for faeces. * Stimulation of the pelvic nerves (nerves of defecation reflex) cause: * Increaseinperistalticmotilityofthecolon * Marked increase in mucus secretion * Bacterial infection – mucosa secrete water and electrolytes & alkaline mucus to dilute irritating factors through rapid bowel movement (stimulant laxatives) Absorbs water, NaCl, K, vit K

Answer 5

Water * About 0.5- 1.5L/day is absorbed. Water * The net water loss is 100-200 ml/day Sodium * In the presence of Na+-K+ ATPase at the basolateral membrane, Na+ is actively absorbed and K+ is secreted into the lumen of colon Chloride * Cl- is absorbed in exchange for HCO3 - which is secreted Vitamins * Vitamins as vit. K, biotin, B5 , folic acid and some aa and short chain FA from bacterial fermentation of CHO are absorbed * It does not absorb vitamin B12! Misc * Certain drugs as steroids and aspirin may be absorbed * Reabsorption of organic wastes (urobilinogens & Stercobilinogen) and toxins * Reabsorption of bile salts

Answer 6

Haustrations - Mixing Movement * Themotoreventsinproximalcolon(cecum&ascendingcolon). * Ring-like contractions (2.5 cm) of circular muscles divide the colon into pockets (haustra). (The longitudinal muscle also contracts at the same time) * Uniform repetition of haustra occurs along the colon. * Net forward propulsion happens when sequential migration of haustra occurs along the length of bowel. Segmenting contractions throughout the day Mass propagated contractions 3 – 10 time as day Propulsive - Mass Movement * Themotoreventsindistalcolon(transverse&descending colon). * Startsinthemiddleoftransversecolon,15minsafter breakfast. * Constrictive ring occurs at a distended point, then 20 cm of the colon distal to constriction, contracts as a unit forcing the faecal mass down the colon. * Precededbyrelaxationofcircularmuscle&downstream disappearance of haustral contractions.

Answer 7

* Allow defecation reflex. * Stretch of rectal wall is sent to SC by pelvic nerve. * Efferent pelvic impulses cause reflex contraction of rectum & relaxation of internal anal sphincter. * Followed by reduction in tonic impulses to external anal sphincter, so it relaxes voluntary. * Faeces leave rectum assisted by voluntary straining & contraction of pelvic floor muscles.

Answer 8

* Inhibited defecation reflex from cerebral cortex * Maintain voluntary tonic contraction of external anal sphincter. * Override tonic contraction of internal anal sphincter * Urge passes * People who too often inhibit their natural reflexes are likely to become severely constipated.

Answer 9

* Decrease in stool passage frequency = small, hard stools faecal impaction * Difficulty initiating bowel movements (normal -3 x week on Western diet) Poor diet – lack of fibre (resists digestion – bulking agents) Decreased motility of GI tract – disorders: IBS, medications: opioids Blockage – colonic carcinoma, swollen diverticulum, anal fissures, Haemorrhoids (painful) Medications: 1. Bulk-forming agents 2. Stimulant laxatives 3. Osmotic laxatives 4. Stool softeners

Answer 10

e.g. Magnesium citrate and sodium phosphate can be used rectally to cleanse bowels prior to procedures * Magnesium containing laxatives should be avoided in children, renal impairment, cardiac conditions, pre-existing electrolyte imbalance * INCREASED risked of hypermagnesemia [heart block/ neuromuscular block/ CNS depression] * INCREASED risked of hyperphosphatemia [acute renal failure, metabolic acidosis, hypocalcemia/ death]

Answer 11

1. Inflammatory diarrhoea causes inflammation of the gastrointestinal epithelium and this usually happens with invasive pathogens or as a result of a chronic inflammatory bowel disease, and usually there are systemic symptoms like fever. 2. Non-inflammatory diarrhoea can be either secretory or osmotic * Secretory water and electrolyte secretion and decreased absorption * Osmotic ingested nutrients aren’t fully absorbed (e.g. lactose), and they remain in the intestinal lumen and pull in water through the process of osmosis

Answer 12

1. Bloody, mucus stools, severe pain and fever – Slamonella, Shigella, Yersinia, Campylobactor and Enteroinvasive E.coli 2. Non-inflammatory: stress, medication, toxins, pathogens (timing of onset gives clues to bacteria), and virus – assoc. vomiting

Answer 13

* Tx dehydration – oral rehydration solutions (isotonic to replace electrolytes) * Dietary adjustments – avoid dairy * Antibiotics * Antimotility drug loperamide * Codeine phosphate - μ and ƍ receptors

Answer 14

Geographic disparity in cause * West- inflammatory bowel disease OR malabsorption syndromes (e.g.lactose intolerance, celiac disease) * East–Infectious organisms *Persistence of acute diarrhoea despite Tx=immunocompromised Diagnosis * Inflammatorymarkers:ESR,C-reactiveprotein * Anaemia:bleeding * Malnutrition: protein, albumin * StoolculturesandAbtestingforHIV

Answer 15

CTZ- chemoreceptor trigger zone Signals Vomiting Center Or Motion/Morning sickness- vestibular and cerbellar nuclei- signal to vomiting centre= vomiting reflex look at diagram on slide

Answer 16

1. Pre-ejection phase − Prodromal nausea − Salivation − Retrograde intestinal contraction which forces intestinal contents into the stomach 2. Retching Phase − Deep inspiration and breath-holding to splint the chest − Epiglottic closure − Elevation of the soft palate (prevents nasal soiling) 3. Expulsive phase − Relaxation of oesophageal sphincters − Pyloric contraction − Violent contraction of the diaphragm and abdominal muscles

Answer 17

1. Histamine 1 Receptor antagonists (antihistamines) e.g. promethazine (used for motion/morning sickness) 2. 5-HT3 Receptor antagonists * ...setron drugs e.g. ondansetron * GI and CTZ (used for chemo/radiation/post-op sickness) 3. Dopamine 2 Receptor antagonists * antipsychotics (...azine) * Metaclopromide * Droperidol * Haloperidol (used for chemo/radiation/post-op sickness) 4. Muscarinic Receptor antagonists e.g. Ayucine (used in prophylaxis)

Answer 18

Drug selectively binds to its receptor Blocks signalling pathway Inhibits stimulation of GI tract, diaphragm and abdominal muscles (not given in 1st trimester usually)

W11 Antacids, H2 Antagonists & Proton Pump Inhibitors, Promotility Agents, Laxatives, Emetics & Antiemetics Flashcards

Lectures: Disorders of the GI System, Antacids, H2 Antagonists, PPI's, Promility agents, Constipation and the need for laxatives, Emetics, Genes and digestive, GI inflammatory diseases (44 cards)