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40 Cards in this Set
- Front
- Back
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differentiate intestinal crypt vs. villus cells
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crypt - secretory
villus - absorptive |
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differentiate the electrolyte content of normal gastric, duodenal, jejunal, ileal, and colonic (Na, Cl, K, HCO3)
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Gastric – Na(140), Cl(100), K(10), HCO3(0)
Duodenum – Na(140), Cl(100), K(5), HCO3(100) Jejunum – Na(140), Cl(100), K(6), HCO3(30) Ileum – Na(140), Cl(60), K(8), HCO3(70) Colon – Na(40), Cl(15), K(90), HCO3(30) |
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calculated stool osmolality
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2 x stool(Na+K)
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normal value for both osmotic and secretory diarrheas
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280-310 msomols
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which type of diarrhea will have an osmolar gap of > 100 mosmols
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osmotic diarrhea
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what can cause very low or very high stool osmolality
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very low - contamination with water
very high - contamination with urine |
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mechanism by which cholera toxin induces diarrhea
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1. binds crypt cells and increases cAMP to stimulate electrogenic anion secretion via CFTR channel
2. stimulates enteric nervous system to eventually release VIP which stimulates crypt cell anion secretion 3. increased cAMP in the villus cells and colonic lining cells decreases electroneutral NaCl absorption |
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what is still intact in cholera toxin-induced diarrhea
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electrogenic absorption (Na-glucose)
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mechanism of how VIP is stimulated in cholera toxin-induced diarrhea
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Cholera toxin also stimulates anion secretion by activating enteric nervous system. Increased cAMP production in enterochromaffin cells release serotonin and neurotensin. These stimulate nerves in the mysenteric plexus to release ACh and substance P which travel to the submucosal plexus and cause those nerves to release VIP. VIP then stimulates crypt cell anion secretion via cAMP mediated mechanism
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differentiate stool Na and K concentrations as well as acid-base state in secretory vs. osmotic diarrhea
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secretory - higher Na(>90) and K(>40), alkaline stool due to HCO3
osmotic - lower Na(<60) and K(<30), acidic stool due to lactic acid from bacteria metabolism |
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differentiate volume and Na state in patients with osmotic vs. secretory diarrhea
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osmotic - hypovolemic hypernatremia because loose more H20 than Na in stool
secretory - isotonic hypovolemia because fluid loss is isotonic |
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differentiate fluid replacement in osmotic vs. secretory diarrhea
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osmotic - hypotonic saline because patient has hypernatremic hypovolemia
secretory - isotonic saline |
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what will oral replacement therapy contain for person with cholera-induced secretory diarrhea
Why will this not work for EPEC |
oral rehydration solutions contain glucose and electrolytes so Na is absorbed via Na-glucose transport
EPEC has dysfunctional Na-glucose transport |
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causes for osmotic diarrhea
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celiac disease (sprue)
enzyme deficiencies cathartics |
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causes for secretory diarrhea
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stimulant laxative abuse
V. cholera ETEC VIP secreting tumor Gastrin secreting tumor Diseases of the Ileum |
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mechanism of secretory in Ileal disease
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decreased bile absorption leads to increased amounts of deconjugated bile acids by colonic bacteria. These are incorporated into the lipid matrix of surface membrane which end up activating anion secretion via cAMP-mediated mechanisms
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mechanism for diarrhea that develops in long-standing DM
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diabetic autonomic neuropathy leads to decreased peristalsis and bacterial overgrowth. the increased bacteria proliferate and deconjugate bile acids. These are incorporated into the membrane and cause secretory diarrhea.
Osmotic diarrhea is also seen due to bacteria proteases causing inactivation of brush border enzymes needed for carbohydrate absorption |
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invades the intestinal mucosa and decreases NaCl absorption by knocking our Na-H and Na-glucose transport processes
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EPEC
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mechanism of diarrhea that develops from viral gastroenteritis
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viral gastroenteritis destroys small intestinal villus cells as well as colonic lining cells. These cells are replaced by crypt cells resulting in crypt hyperplasia; crypt lack brush-border enzymes as result in osmotic diarrhea as well a secretory due to crypt hyperplasia
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differentiate small bowel and large bowel diarrhea
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small bowel - large volume stool with 3-4 movements a day
large bowel - small volumes of stool with 8-10 movements a day |
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what does the jejunal electroneutral Na absorption lack compared to ileal and colonic
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Cl-HCO3 exchanger
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what is the net effect of the dual electroneutral exchangers in the ileum and colon
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H and HCO3 secretion
Na and Cl absorption |
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how many Na is absorbed with every glucose molecule
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Two Na for every glucose
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what is electrogenic Na absorption in the colon stimulated by
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aldosterone
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how does aldosterone increase K secretion in the colon during kidney failure
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aldosterone-mediated electrogenic Na absorption stimulates paracellular K secretion due to luminal negativity as well as trancellular K secretion via crypt cells
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what second messenger stimulates Cl secretion via CFTR channel
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increased intracellular cAMP
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what are the predominant anions of the upper and lower GI tract
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upper - chloride
lower - bicarb |
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regardless of the type of meal, content of the GI tract are isotonic to plasma by the time they reach the proximal jejunum
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**
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why are bicarb concentrations lower in the jejunum and colon compared to the ileum
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jejunum - buffer stomach acid
colon - buffer bacterial organic acids |
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why could there be serum hypokalmia in person with cholera toxin diarrhea
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cholera toxin stimulates transcellular K secretion and HCO3 secretion in the colon
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diarrhea that is persistent with fasting and commonly has nocturnal diarrhea
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secretory
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diarrhea that is associated with non anion-gap metabolic acidosis
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secretory due to fecal HCO3 loss
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mechanism of secretory diarrhea in V. parahaemolyticus
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V. parahaemolytic activates Ca leading to Cl secretion via calcium-activated chloride channels
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cramp-like abbominal pain that is relieved with defecation
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IBS
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IBS with increased number of serotonin containing enterochromaffin cells
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diarrhea-predominant IBS
*relieved with 5-HT3 receptor antagonist |
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IBS with vagal hypofunction
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constipation-predominant IBS
*relieved with 5-HT4 receptor agonists |
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causes of intestinal enterocyte damage leading to diarrhea
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viral gastroenteritis
EPEC celiac disease inflammatory bowel disease |
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diarrhea in newborns associated with large amounts of Cl in the stool leading to metabolic alkalosis
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congenital chloridorrhea
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what is missing in congenital chloridorrhea
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Cl/HCO3 exchange in the ileum and colon
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diarrhea associated with metabolic alkalosis
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congenital chloridorrhea
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