What percentage of liquids does the colon absorb?
1.5 lt/ day
What is the maximum absorptive capacity of the intestine?
Small intestine: ~12 L/day
Colon: 4–6 L/day.
What two intestinal structures determine absorption vs secretion?
Villi → absorptive
Crypts → secretory.
Importance of short chain fatty acids
Mantains colonic epithilum function, modulates inflammatory and metabolic processes, and mantains microbiome (“feeds enterocytes”)
What objective criteria define diarrhea?
Passage of ≥3 unformed stools in 24 hours or stool weight >250 g/day, often with increased frequency, volume, urgency, and decreased stool consistency.
How is diarrhea classified by duration?
Acute: <14 days
Persistent: 14–30 days
Chronic: >30 days.
Frequent small-volume stools with urgency but normal stool mass suggests what condition?
Pseudodiarrhea.
What are the major pathophysiologic mechanisms of diarrhea?
Enhanced mucosal secretion
Impaired absorption/digestion
Increased epithelial permeability
Reduced absorptive surface area
Altered intestinal motility
Increased luminal osmolarity.
What is osmotic diarrhea?
Poorly absorbed solutes increase luminal osmolarity, drawing water into the intestine (e.g., laxatives, malabsorption).
Which mechanism causes diarrhea in cholera and enterotoxigenic E. coli?
Excessive intestinal secretion (secretory diarrhea).
Which infections reduce absorptive surface area leading to diarrhea?
Rotavirus, norovirus, and Giardia infections.
What clinical features suggest small intestinal diarrhea?
Large-volume stools
Minimal urgency
No tenesmus.
What features suggest colonic diarrhea (dysentery)?
Frequent small-volume stools
Blood/mucus
Tenesmus and urgency.
What defines dysentery?
Bloody diarrhea caused by inflammatory invasion of the colon.
What percentage of acute diarrhea is caused by infectious agents?
> 90%
What are common noninfectious causes of acute diarrhea?
Medications
Toxic ingestion
Ischemia
What medication class is the most common noninfectious cause of acute diarrhea?
Antibiotic
Which five populations are at high risk for infectious diarrhea?
Travelers
Consumers of contaminated foods
Immunocompromised patients
Daycare attendees
Institutionalized persons.
What is the most common cause of traveler’s diarrhea?
Enterotoxigenic Escherichia coli (ETEC).
Common cause of secretory diarrhea
Cholerae, VIP, Ach, serotonine, bile acids and inflammatory mediators.
What warning signs suggest severe diarrheal disease requiring evaluation?
High fever
Bloody stools
Severe abdominal pain
Dehydration
Symptoms >3–4 days.
What stool test detects inflammatory diarrhea?
Fecal leukocytes or fecal lactoferrin/calprotectin.
When should stool cultures be obtained in diarrhea?
Severe disease
Fever >38.9°C
Bloody stools
Immunocompromised host.
What pathogens are commonly detected on routine stool culture?
Salmonella, Shigella, and Campylobacter.
