Diarrhea Flashcards
What should I know about colonic fluid balance?
The colonic absorptive capacity greatly exceeds daily absorption- you can hand an extra 3-4 L/day. But, loose stool occurs when daily fecal H2O output increases by only 50-60 mL: this represents a decrease in overall intestinal water absorption of only 1-2%
Describe the GI epithelial cell
Na/K ATPase on the basolateral side pumps out 3 Na and pumps in 2 K to establish a negative intracellular voltage and low intracellular Na conc. This provdes the basci mechanisms of ion, nutrient, and water transport: passive absorption of sodium into cell, active secretion of chloride, osmotic gradient to drive passive water absorption both paracellularly and through the cells.
Describe water absorption and secretion from duodenum to distal colon
all segements can absorb and secrete water. balance dependes on the presence of transporters/channels and the permeability of tissues/tight junctions (less perpeability as you move toward caudal end). Most Na absorption in the small intestine via Na channels, Na-H exchanges, nutrient coupled Na transport, and Aldo sensitive Na channel (in distal colon only).
What about horizontal differences in secretion and absorption?
crypts: secrete more than they absorp
enterocytes: absorb more than they secrete
discuss intestinal secretion
driven mostly by chloride secretion via apical CFTR channels (cAMP driven). Basolateral Na-K-Cl keeps everything electroneutral. Na follows Cl out (electrochemical gradient), and H2O follows.
How is secretion/absorption of water in the intestines regulated
cAMP, cGMP, Ca2+. incr. in any of these = incr. secretion and decr. absorption. Diarrhea happens when there is a decrease in absorption (usually) or an increase in secretion.
Diarrhea: definitions; chronic vs. acute
definition: increased liquidity and increased freq.
acute: less than 4 wks
chronic: 4 or more wks
mechanisms of diarrhea
osmotic, secretory, altered motility, exudative/inflammatory, fat malabsorption/maldigestion, mixed
Lactose intolerance: types, diarrhea class, pathyophysiology
may be congenital (rare) or acquired (very common). This is an osmotic diarrhea: lactose stays in the colon and pulls in water. Also, there is bacterial fermentation of the lactose: gas/bloating.
Examples of osmotic diarrhea
ingestion of poorly absorbable solutes: laculose, PEG, magnesium
ingestion of normally absorbable substances in person with a defect: celiac’s disease, lactose intolerance, fructose intolerance.
osmotic diarrhea dx and clinical features
unmeasured osmoles = large osmolar gap
stool osmotic gap: 290- (2(Na+K)). over 50 = osmotic diarrhea.
diarrhea occurs after ingestion of the agent; no nocturnal symptoms; sx improve with fasting
Cholera: diarrhea class and pathophysiology
enterotoxin-induced secretory diarrhea
cholera toxin induces cAMP production. cAMP stimulates CFTR channel and inhibits Na/H exchange: incr. Cl secretion and decr. Na and Cl absorption.
examples of secretory diarrhea
exogenous secretogogues, like cholera
endogenous secretogogues, like neuroendocrine tumors.
absence of normal Cl/HCO3 transporter: chongenital chloridorrhea, loss of infestinal surface, decreased blood flow.
secretory diarrhea dx
electrolyte conc. close to plasma conc (but normal stool should have low Na and high K). Osmotic gap under 50.
hyperthyroidism
rapid intestinal transit, even if the pt doesn’t have diarrhea symptoms. accelerated small intestine and whole gut transit. often accompanied by anxiety, palpitations, incr. sweating, feeling hot.
altered motility diarrhea: type examples, pathophysiology
combined secretory and osmotic mechanism
incr. gut motility –> decr. absorptive capacity (secretory) AND malabsorption of nutrients (osmotic).
seen in opiate withdrawal, hyperthyroid, post-vagotomy, IBS
Decr. gut motility can also give diarrhea d/t intestinal bacterial overgrowth (scleroderma/diabetes)
Ulcerative colitis: definition
inflammation and cellular desctuction –> breakdown of the epithelium
leakage of WBC and RBC into the lumen. May compromise the barrier function of the epithelium (tight junction loss, epithelial cell loss), leakage into colon d/t hydrostatic pressure.
multifactorial diarrhea )incr. prostaglandins are also pro-secretory agents).
other examples: shigellosis (no toxin), intestinal lymphangectasia
Fat malabsorption/maldigestion: pathophysiologies
disruption in fat solubilization (no bile: primary biliary cirrhosis), fat digestion (pancreatic exocrine insufficiency in chronic pancreatitis), or fat absorption (celiac’s). Undigested fat is lost in stool. Water also pulled in d/t osmotic gradient
Celiac’s disease diarrhea
osmotic force of unabsorbed gluten, villous atrophy and crypt hypertrophy –> incr. secretion/decr. absorption, unabsorbed bile acids/fatty acids, incr. prosecretory cytokines from inflammation
Clinical pearls: diarrhea
think about metformin causing diarrhea.
IBS definition
- abdominal pain associated with defecation (improves: part of criteria)
- variable stool consistency (part of criteria)
- periods of constipation
- long hx, often begining in adolescence
- passage of mucus
- exacerbated by stress
- Onse associated with a change in the freq of stool (part of criteria)
At least 3 days in last 3 months. must meet 2/3 defined criteria. If you suspect IBS, rule out celiacs and lactose intolerance with serology.
Diarrhea red flags
recent onset, old age, nocturnal diarrhea, weight loss, blood in stool, abdnomal labs showing anemia, elevated CRP, hypoalbuminemia
what does low fecal pH suggest? fecal WBC/lactoferrin? fecal occult blood?
carb malabsorption: low pH
WBC/lactoferrin/occult blood: inflammatory
diagnosis: osmotic diarrhea
food diary, lactose/sucrose breath testing, laxative screen
fecal fat conc.
above 9.5 strongly suggests pancreatic/biliary steatorrhea
above 7 g/100 g stool = abnormal
diarrhea drugs
opioid receptor agonists (incl. loperamide), alpha 2 adrenergic agonists, somatostatin analog, bile acid binding resin, fiber supplement.
