diarrhoea Flashcards
what is diarrhoea?
increase in faecal water content with accompanying increase in frequency, fluidity/ volume of faeces
how does the majority of water reabsorption occur?
passive osmosis
also active Na and therefore water reabsorption
where is most fluid reabsorbed
distal jejunum and ileum
what are the 5 mechanisms of diarrhoea?
permeability, secretory, motility, osmotic and mixed
describe permeability diarrhoea
infiltrative disease (inflammatory/ neoplastic) causes reduced SA of villi and increased leakiness (less absorbed and more lost)
describe secretory diarrhoea
interference with cell physiology - failure of active Cl/ water uptake or increased activity of Na pumps so water follows passively into lumen
describe motility diarrhoea
increased transit rate preventing absorption. could be sue to toxin/ secondary to distension of gut with fluid
describe osmotic diarrhoea
net fluid movement into the gut lumen due to presence of osmotically active unabsorbed solute e.g. lactose. could be due to failure of digestion (enzyme deficiency), failure of absorption (villus atrophy/ enterocyte dysfunction)
describe mixed diarrhoea
a mixture of all = most common type
what are the consequences of diarrhoea? and what do they lead to?
dehydration; water - haemoconcentration, sodium; hypovolaemic shock
potassium loss - hypo
bicarbonate loss - metabolic acidosis
define malabsorption
= defective absorption of nutrient resulting from interference with the digestive and/ or absorptive phases in the processes of that molecule
what are the 3 mechanisms of malabsorption?
luminal, mucosal, transport
describe luminal malabsorption
lack of pancreatic enzymes (exocrine), impaired micelle formation (bile delivery, formation, loss), bacterial overgrowth.
describe mucosal malabsorption
villus atrophy (SA), immature enterocytes have no brush border enzymes, inflammation, weight loss drugs, neoplasia
describe transport malabsorption
impaired lymphatic flow/ abnormal motility
list ways to treat diarrhoea
fluid therapy, specific and non-specific drugs
describe methods of fluid therapy
can be given orally or IV. oral contains easily absorbed osmotically active nutrients that induce passive water reabsorption. will not work in secretory diarrhoea/ is V (may worsen initially)
IV - isotonic, Na containing so expands ECF, may contain K
what specific drugs are used to treat diarrhoea
antibacterials/ parasites, diet change (allergy), anti-inflammatory/ immunosuppressive drugs e.g. sulfasalazine; pro-drug cleaved by colonic bacteria. treats colitis SE = dry eye
what 3 non-specific drug types are used to treat D?
mucosal protectants and adsorbents, motility modifiers and prokinetics
name a mucosal protectant and adsorbent and describe its properties
kaolin (montmorillonite)/ pectin formulations - clay/ fruit sugar. bind water so alter stool consistency (aesthetic) and are cytoprotective. can combine products with kaolin e.g. bismuth (antibacterial properties)
name 2 types of motility modifiers
opioids and antimuscarinic drugs
how do opioids work?
most act on mu receptors, decrease propulsive peristalsis and increase segmentation so increase transit time. also anti-secretory and stimulate fluid absorption. side-effect = sedation and constipation.
2 synthetic opioids excluded from BBB - diphenoxylate (currently unavailable) and loperamide (causes sedation in dogs with MDR1 mutation as crosses BBB, immodium)
how do anti-muscarinics work?
antagonise M1 receptors so reduce parasymp activity (motility and secretions) limited efficacy and may paralyse gut. general use is for aesthetic reasons.
e.g. atropine, butylscopolamine (licensed)
how do prokinetics work?
increase motility as ileus could be a cause/ consequence of diarrhoea
