Pathophysiology of Diarrhea Flashcards
define diarrhea
-presence of excess water in feces due to excessive secretions and/or decreased absorption
-results in severe electrolyte depletion, acid-base imbalance, and dehydration
-history and physical exam are an important first step to classify!
describe the normal intestine
- fluid derived from ingesta and normal secretions
-secretions from stomach, intestine, pancreas, gallbladder - most fluid absorbed in the small intestine, finite capacity in the colon
-tight junctions permissive to small molecules and water in the small intestine
-in horses!! most water is absorbed in the cecum and colon - normally: absorption exceeds secretion
describe the secretory mechanism of diarrhea (3)
- increased secretion of chloride, sodium, and other electrolytes
- exudation of fluid secondary to inflammation can also contribute
-thanks to prostaglandins, cytokines - luminal contents can shift osmotic gradient, leading to a secondary secretory diarrhea
-osmotic diarrhea
describe increased secretion of chloride resulting in diarrhea
- mediation of cAMP results in:
-reduced passive transfer water absorption
-promotion of chloride secretion - infectious causes:
-E. coli, salmonella enterica - non-infectious causes:
-vasoactive intestinal polypeptides in pancreatic islet cell tumorw
-histamine from mast cell tumors
describe enterotoxigenic E. coli (ETEC)
- more common in calves, piglets, and lambs
- fimbriae adhere to microvilli
-fimbriae adhesions are age-dependent - enterotoxins bind to guanylate cyclase C receptor, Gsalpha protein
-heat stable toxin
-heat labile toxin - increased levels of cGMP, cAMP result in:
-secretion of chloride
-blocks sodium absorption - osmotic gradient results in secretory diarrhea
- intestines are dilated, edematous, and have congested blood vessels
describe the malabsorptive mechanism of diarrhea
- impaired ability to absorb nutrients due to villous damage/atrophy or maldigested digesta
- distinction into protein -losing and non-protein losing enteropathy based on clinicopathologic findings
-severe hypoproteinemia, hypoalbuminemia more severe in protein losing
what are the 4 major mechanisms of malabsorptive diarrhea?
- loss of protein through damaged mucosa:
-associated with ruptured lymphatic vessels - loss of surface area to absorb solutes
-loss of microvilli
-overall villous atrophy - increased thickness of the lamina propria: due to
-inflammatory cells
-fibrosis
-neoplasia cells - loss of digestive enzymes to break down food
-exocrine pancreatic insufficiency: maldigestion
-loss of villous enterocytes
describe protein losing enteropathies
- loss of protein, often associated with damage to lymphatic vessels
-results in severe hypoproteinemia/hypoalbuminemia - infectious causes:
-parasites (nematodes, strongyloides)
-Johne’s (causes lymphadenitis) - non-infectious:
-lymphangiectasia
-lymphoma
-IBD
describe non-protein losing enteropathies
- impaired absorption of electrolytes and nutrients
-can still have some hypoproteinemia - mucosa or digesta problem
-large, undigested solute lead to osmotic diarrhea - infectious causes:
-Johne’s
-rotavirus
-cryptosporidium
-coccidia - non-infectious:
-laxatives
-grain overload
-dietary-responsive
-antibiotic-responsive
describe lymphangiectasia
- dogs
- dilation, obstruction, and/or dysfunction of lymphatic vessels
- rupture of lymphatics:
-lymphatic fluid rich in protein leaks out - loss of lymphatic fluid into lumen leads to malabsorptive diarrhea (protein losing enteropathy)
describe rotavirus
- in rat pups, calves, foals, lambs, pigs, kits, puppies
- targets villous enterocytes, causing
-impaired absorption of small solutes
-impaired production of enzymes - villous atrophy leads to malabsorptive diarrhea (non protein losing enteropathy)
- secretory enterotoxin nonstructural protein also increases chloride secretion (secretory diarrhea too!)
describe the increased permeability mechanism of diarrhea
- inflammation or destruction of mucosal barrier and vasculature leads to
- leaky tight junctions which can permit macromolecules to leak out
-see protein losing enteropathy - junctional complexes are sensitive to starling forces
- infectious causes:
-C. perfringens
-E. coli
-Lawsonia intracellularis
-parvovirus
-parasites - noninfectious:
-amyloidosis
-lymphoma
-CHF
-portal hypertension
describe clostridium perfringens, type C
- in piglets, foals, lambs, kids, and calves
- alpha toxin (CPA) and beta toxin (CPB)
- bacterial overgrowth results in CPB production
-CPB is trypsin labile (trypsin will break it down, neonates are trypsin deficient)
-sweet potatoes are trypsin inhibitors, so high sweet potato diet can predispose an adult! - forms pores in endothelial cells, resulting in:
-influx of Ca, Na, and Cl
-cell swelling
-death - disruption of blood vessels causes increased permeability diarrhea
- ischemic necrosis of mucosa also contributes to increased permeability
- grossly, will see acute hemorrhagic enteritis (gas bubble formation), and subacute necrotizing enteritis
describe abnormal motility mechanism of diarrhea
- minor cause/contributor to diarrhea
- hypermotility can lead to less efficient absorption of water and nutrients
-primary disease not described in vet med - hypomotility promotes bacterial overgrowth
- infectious causes:
-parasites - non-infectious causes:
-peritonitis
-drugs
-dysautonomia
-behavioral: nervous/excitement
describe ceca number
dogs and horses only have 1
birds have paired
lots of species variation in shape and size!
describe what the cut surface of an intestine looks like indicates about the lesion
solid: tumor, granulation tissue
friable: necrosis from inflammation, tumor
hemorrhagic: hematoma, hemangiosarcoma
mucoid: necrosis, mucus-producing tumor
cystic: parasite, tumor
