Pathophys of diarrhea: Marino Flashcards
Definition of diarrhea.
> 3 BM/day or >200g stool/day
regardless of consistency
What is the basis of normal fluid uptake by the intestines?
Give it to me in terms of channels/transporters.
Na+ uptake.
Small intestinal villi- Na+/Glu cotransporter and Na+/H+ exchanger
Large intestinal crypts- ENaC
Describe the pathophysiology of diarrhea.
1) incr. intralumenal fluid due to decr. absorption, incr. secretion or both*
-osmotic effect, secretory effect, or inflammation
Secretory most severe, can cause dehydration—> death
2) More rapid transit through GI tract (Taco Bell)
* probably also caused by Taco Bell
Describe causes of osmotic diarrhea by non-absorbable carbohydrates and electrolytes.
Non-absorbable carbs:
lactose (in lactose intolerance)
sorbitol, mannitol
lactulose (Rx for hepatic encephalopathy)
Non-absorbable electrolytes:
Mg2+ compounds (MOM, Maalox, Epsom salts)
Colonoscopy Golytely (PEG) prep
What is the key to all secretory diarrhea?
Too much Cl- secretion into the gut!
Give two examples in each of the following categories that lead to secretory diarrhea: Bacterial toxins (name species) Laxatives Medications Chemical irritants Neuroendocrine tumors
Bacteria- Y. pestis, V. cholerae, Heat stable E. coli
Lax- ExLax, DulcoLax, castor oil
Meds- Cholinergics, prostaglandins
Chemicals- bile, arsenic, caffeine, EtOH
Neuroendo tumors- VIPoma, carcinoid, med. carcinoma of thyroid
Describe the clinical features that help distinguish secretory from osmotic diarrhea.
OSMOTIC Moderate volume Resolves with fasting Much flatulence Stool pH 125
SECRETORY Voluminous, watery Persists during fasting No flatulence Stool pH 6-7 Osmolar gap
Describe the pathophys of inflammatory diarrhea.
Causative agent—> inflammatory cells—> flam. mediators—> Intestinal secretion
Causative agent—> inflammatory cells—> proteases, free radicals, complement, cytotoxic T cells —> enterocyte cell death —> villous atrophy, malabsorption
How do you identify Giardia, Entameba, and Cryptosporidium on histo from a biopsy?
Giardia- find the protazoa extracellularly in lumen
Entameba- flask-shaped ulcer invading mucosa–>submucosa
Crypto- round cells inside apex of enterocytes. (doesn’t look like they are actually inside)
MCC of traveler’s diarrhea:
EHEC
Clostridium difficile colitis (diarrhea): Risk factors Cause Dx Tx
RF: extremes of age, hospitilization, abx
Cause: Cytotoxins A and B
Dx- pseudomembranous colitis on endo. Stool assay for toxin A +/- B
Tx- stop offending abx. Metronidazole or vanc PO. Cholestyramine to bind toxins
What does pseudomembranous colitis look like on histo?
exploding volcano!
Describe duration, etiology, pathophys, prognosis, and management of chronic diarrhea.
duration- >3 wks
etiology- infectious, immune mediated, malabsorption
pathophys- osmotic, secretory (no mucosal injury), inflammatory (mucosal injury)
prognosis- variable
management- specific interventions req’d
Describe the clinical presentation of lactose intolerance and the reasoning.
Lactase insufficiency presents w/:
Flatulence (Hydrogen gas produced by bact. that are digesting the lactose instead of you)
Osmotic diarrhea (excess solute pulls water into lumen)
Acidic stool pH- byproduct of bacterial lactose breakdown
Talk about how bacterial overgrowth in small bowel is a problem and explain physiologically why and how this presents.
Not supposed to be bact. in small bowel to begin with.
Bact. unconjugate bile acids —> secretory diarrhea
Convert carbs and ketones —> short chain fatty acids –> osmotic diarrhea
