Pathophys of Diarrhea and Absorption Flashcards
3 ways to not absorb enough water in gut?
Impaired electrolyte absorption.
Excessive electrolyte secretion.
Osmotic retention of water intraluminally.
Are IBS and fecal incontinence diarrhea?
No.
What’s the arbitrary cutoff between acute and chronic diarrhea? Is there a physiological difference between the two?
4 weeks.
No, there’s no physiological difference.
(but acute tend to be more caused by infections, chronic by… other things)
What are 4 reasons that stuff could not be absorbed in the gut?
No breakdown.
Too fast of transit.
Too much input.
Cells can’t absorb.
2 reasons for too much excretion?
Leaky gut.
Uncontrolled cellular exchange (e.g. Cholera).
How does stool fluid osmolarity compare to that of the blood?
They’re equal. (Or rather, water will move to make them equal.)
What’s osmolarity of the blood, normally?
290 mOsm
How, mathematically, do you express the estimate of factors contributing to stool osmolarity?
290 mOsm = 2(Na + K) + (“other osmotically active stuff”)
What’s osmolar gap? The formula?
What does the osmolar gap represent?
Osm Gap = measured stool Osm - calculated stool Osm.
Osm Gap = measured Osm - 2(Na + K)
The osmolar gap represents “other solutes,” such as undigested carbs.
What is a normal Osm Gap value?
< 50 Osm.
What does measured stool Osm that’s really low (much less than 290 mOsm) suggest?
Some sort of dilution of the stool sample - urine, fistula, malingering, lab error, etc.
What do you conclude if the Osm gap is greater than 100 mOsm?
There’s some additional osmotically active stuff in the stool.
3 different things that if not broken down can be osmotically active and cause diarrhea?
What’s a common cause of stuff not being broken down?
Carbs, protein, fat.
Defective brush border enzymes is a common cause (not for fat, though!).
4 categories of things that can damage brush border of the small bowel?
Infections
Celiac
Loss of enzymes (eg. lactose intolerance)
Congenital (microvillous inclusion disease)
How can short gut syndrome cause diarrhea?
Electrolytes aren’t pumped in, and the colon can’t make up for it.
We’ll probably hear more about celiac… but what are some markers for it?
Villous atrophy
Crypt hyperplasia
Intraepithelial lymphocytosis
Anti-gliadin Abs
3 things that cause fat not to be broken down?
Pancreatic insufficiency (not enough lipase)
Molecules can’t be cleaved (Olestra…)
Not enough bile acid to form micelles
What do you call it when the colon has injured surface epithelium with lymphocytic infiltrate, but crypt cells look okay? What does this cause?
Lymphocytic colitis.
This results in net secretion of electrolytes -> watery diarrhea.
How can stimulant laxatives cause diarrhea? (how can the colon mucosal surface look grossly?)
Increased motility, and chronic use can damage surface epithelium.
(damage can appear as melanosis coli - brown colon mucosa)
2 organisms that cause unregulated ion secretion?
One non-infectious cause of unregulated ion secretion?
E. coli and V. cholera.
Non-infectious: Vasoactive hormones.
What does E. coli enterotoxin do?
Works through PKG, increases Cl- and bicarb secretion.
What does V. cholera enterotoxin do? (more specifics in the Infectious Diarrhea lecture)
Causes adenylate cyclase to be always active -> cAMP high all the time -> Cl- secreted nonstop -> watery diarrhea
What’s the etiology of vasoactive hormones that cause diarrhea?
Neuroendocrine tumors
Can the osmolality (…osmolarity too…?) of a stool sample change with time?
Yes. Bacteria can break down large molecules, disaccharides -> more small molecules, higher osmolarity.
