diarrhoea

Question 1

what is diarrhoea?

Answer 1

increase in faecal water content with accompanying increase in frequency, fluidity/ volume of faeces

Question 2

how does the majority of water reabsorption occur?

Answer 2

passive osmosis

also active Na and therefore water reabsorption

Question 3

where is most fluid reabsorbed

Answer 3

distal jejunum and ileum

Question 4

what are the 5 mechanisms of diarrhoea?

Answer 4

permeability, secretory, motility, osmotic and mixed

Question 5

describe permeability diarrhoea

Answer 5

infiltrative disease (inflammatory/ neoplastic) causes reduced SA of villi and increased leakiness (less absorbed and more lost)

Question 6

describe secretory diarrhoea

Answer 6

interference with cell physiology - failure of active Cl/ water uptake or increased activity of Na pumps so water follows passively into lumen

Question 7

describe motility diarrhoea

Answer 7

increased transit rate preventing absorption. could be sue to toxin/ secondary to distension of gut with fluid

Question 8

describe osmotic diarrhoea

Answer 8

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)

Question 9

describe mixed diarrhoea

Answer 9

a mixture of all = most common type

Question 10

what are the consequences of diarrhoea? and what do they lead to?

Answer 10

dehydration; water - haemoconcentration, sodium; hypovolaemic shock

potassium loss - hypo
bicarbonate loss - metabolic acidosis

Question 11

define malabsorption

Answer 11

= defective absorption of nutrient resulting from interference with the digestive and/ or absorptive phases in the processes of that molecule

Question 12

what are the 3 mechanisms of malabsorption?

Answer 12

luminal, mucosal, transport

Question 13

describe luminal malabsorption

Answer 13

lack of pancreatic enzymes (exocrine), impaired micelle formation (bile delivery, formation, loss), bacterial overgrowth.

Question 14

describe mucosal malabsorption

Answer 14

villus atrophy (SA), immature enterocytes have no brush border enzymes, inflammation, weight loss drugs, neoplasia

Question 15

describe transport malabsorption

Answer 15

impaired lymphatic flow/ abnormal motility

Question 16

list ways to treat diarrhoea

Answer 16

fluid therapy, specific and non-specific drugs

Question 17

describe methods of fluid therapy

Answer 17

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

Question 18

what specific drugs are used to treat diarrhoea

Answer 18

antibacterials/ parasites, diet change (allergy), anti-inflammatory/ immunosuppressive drugs e.g. sulfasalazine; pro-drug cleaved by colonic bacteria. treats colitis SE = dry eye

Question 19

what 3 non-specific drug types are used to treat D?

Answer 19

mucosal protectants and adsorbents, motility modifiers and prokinetics

Question 20

name a mucosal protectant and adsorbent and describe its properties

Answer 20

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)

Question 21

name 2 types of motility modifiers

Answer 21

opioids and antimuscarinic drugs

Question 22

how do opioids work?

Answer 22

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)

Question 23

how do anti-muscarinics work?

Answer 23

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)

Question 24

how do prokinetics work?

Answer 24

increase motility as ileus could be a cause/ consequence of diarrhoea

Question 25

name a prokinetic and describe its properties

Answer 25

metoclopramide = anti-emetic too. stimulates release of Ach. effective in stomach and prox. duodenum. increases tone of LES so prevents reflux.

Question 26

name another main prokinetic and describe its properties

Answer 26

cisapride. now withdrawn due to safety. increased LES tone, decreased pyloric. produces propulsive peristaltic waves through all of GI tract. indicated for reflux, ileus in rabbits and horses

Question 27

name and describe properties of a prokinetic antibiotic

Answer 27

erythromycin. used at lower than antimicrobial doses (V) stimulates more migrating motor complexes