Approach to Diarrhea Flashcards
What is the normal stool pattern in the US? What is the main composition of stool?
3 BM/day to 3 BM/week is normal
Mostly made of water
What is the definition of diarrhea?
Increase in stool weight greater than 200 gms/24 hrs
What is the main purpose of the small intestine? What cells are specially designed for these tasks?
Villus cells: Specialized for absorption
Crypt cells: Sepcialized for secretion
What is the main purpose of the large intestine?
Mostly absorption of fluid and electrolytes
–No villous architecture
How much water is absorbed where in the bowels?
9L of fluid enters the bowel
- ->90% is absorbed in the small intestine
- ->90% of the remaining water is absorbed by the colon
Through what pathway is most of the water resorbed?
Paracellularly
What are the two key carriers and pumps in the GI tract?
SGLT1
Na/K ATPase
What is the purpose of the Na/K ATPase?
The Na/K ATPase is the key driver for absorption! Found on the basolateral membrane, it
Creates the gradient necessary for fueling a lot of the transmembrane carrier proteins (like SGLT1)
What drug is the Na/K ATPase sensitive to?
Digitalis
What is the role of the SGLT-1 carrier protein?
On the apical surface. It uses the gradient created and moves sodium and glucose together through the lumen and into the cell.
Mostly found in the villous areas
What are the predominant transport proteins in the crypts??
Na/K-2CL transporter on the basolateral membrane moves those ions INTO the cell.
- Cl channel allows chloride to enter the lumen
- Na+ follows the balance the negative charge
- This keeps the stool moist
What happens in CFTR mutation?
The chloride channel in the apical channel is mutated, preventing movement of Cl- and thus Na+
–>constipation
What is the main intracellular signaling molecule regulating all of this?
cyclic AMP
- ->Increase
- ->more secretion
- ->decreased absorption
What factors can activate cAMP formation intracellularly?
NE Somatostain VIP Prostaglandins Also, bacterial toxins
What are the four broad mechanisms of diarrhea?
- Osmotic
- Secretory
- Inflammatory
- Dysmotility
What are some key clinical hallmarks that would make you think of osmotic diarrhea?
- Ceases with fasting
- Increase in stool osmotic gap (>100)
- -(290-2*(Na+K))
What could cause osmotic diarrhea?
Sorbitol/lactulose
Milk of magnesia
Lactose intolerant people
Malabsorption of fat (steatorrhea)
What is the pathophysiology behind secretory diarrhea?
Hormone or toxin commandeers the normal mechanism of secretion by increasing intracellular cAMP
Ex: Vibrio cholera, gastrinomas, VIpomas, some laxatives
How do you treat cholera? Why?
Gatorade ORT (glucose + salt + water) -->Because the Na/Glucose cotransporter (SGLT1) is NOT controlled by cAMP!
What are the clinical hallmarks of secretory diarrhea?
- Fasting has no effect
2. No change in stool osmotic gap
What is lubiprostone?
A drug that activates chloride channels on the apical membrane, good for chronic constipation
What is the mechanism behind inflammatory diarrhea?
Mucosal ulceration and inflammation–>exudation of blood, lymph, mucus into the bowel lumen
–Epithelial cells destroyed
What is an example of noninfectious inflammatory diarrhea?
Crohn’s disease
What are the clniical hallmarks of inflammatory diarrhea?
- Bloody, mucoid stool
- Fever
- fecal leukocytes
What can infectious agents can cause inflammatory diarrhea?
EHEC (O157:H7)
C Difficile
Shigella, Campylobacter, salmonella, yersenia
What is the mechanism behind dysmotility type diarrhea?
Abnormal intestinal transit time=diarrhea
What is the archetypal scenario with dysmotility diarrhea?
Post surgical
- -Pyloroplasty, causing dumping syndrome
- -Vagotomy
What is dumping syndrome?
Large volumes of fluid and nutrients rapidly enter the duodenum
- -fluid shifts, stim of intestinal motility and decreased transit time
- -hypertonic chyme=osmotic diarrhea
- -Rapid bowel distention=secretory diarrhea
Which chronic disease are associated with dysmotility diarrhea?
scleroderma and diabetes
At what point do you differentiate between chronic versus acute diarrhea?
over and under 3 weeks
What is the most common cause of acute diarrhea?
INFECTIOUS!! Mostly norovirus
What would make you think acute diarrhea was something BESIDES norovirus?
The fact that they came to the doctor!
- Travel history/camping (ETEC, salmonella, shigella, giardia)
- Recent hospitalization (C Diff)
- Immunodeficiency (cryptosporidium)
IS norovirus an inflammatory or noninflammatory diarrhea?
NONinflammatory
What is the difference between inflammatory and noninflammatory diarrhea in terms of clinical presentation?
- -Inflammatory is bloody, mucoid, and small volume. pt is toxic and febrile
- -Noninflammatory diarrhea is mostly water, large volume
Examples of common causes of inflammatory diarrhea?
Shigella, Salmonella, Campylobacter, All EColi except ETEC
Examples of common causes of noninflammatory diarrhea?
Norovirus Cholera Giardia EteC Staph
How do you evaluate acute diarrhea?
Mostly by checking hydration status. and severe abdominal pain (think toxic megacolon 2ndary to infection)
What are some diagnostic tests to consider in acute diarrhea?
- Fecal leukocytes+culture: If positive, bacteria or IBD. If negative, think viral
- Toxin or antigen detection
- KBD for toxic megacolon
- Endoscopy for pseudomembranes
What should you eat if you have diarrhea?
Increase intake of salt, potassium, and carbs
Don’t eat milk products or things that increase intestinal motility
When should you not give antidiarrheal agents?
If inflammatory diarrhea, will worsen situation!
What are causes of chronic diarrhea?
- IBS
- Medications (digoxin, magnesium antacids, sweeteners like sorbitol or fructose)
- Too much caffeine! Fiber?
What is the single most valuable test in the case of chronic diarrhea?
48 hr stool collection
If low volume, IBS
r/o laxatives
Calculate osmotic gap
What do you want to make sure you do in a physical exam on someone with chronic diarrhea?
- Weigh the pt
- Skin exam
- Anorectal exam
What other diseases do you want to consider in chronic diarrhea? How do you diagnose them?
- Celiac’s disease (serum tissue transglutaminase and biopsy)
- Microscopic colitis (colon biopsy, shows up in middle aged peeps)
