Diarrhea and Constipation

Question 1

What is the clinical definition of diarrhea?

Answer 1

3+ BMs/day OR stool wt > 200 g/day

Question 2

4 Major Categories of Diarrhea

Answer 2

• 1- Osmotic Diarrhea
  
  • Ingestion of poorly absorbed sugars, alcohols (mannitol, sorbitol) or ions (Mg, sulfate, phos)–> retention of water in lumen to maintain osmolality
  • Stool osmolal gap > 100 mOsm/kg
  • Subsides once stop eating offending agent
• 2- Secretory Diarrhea
  
  • Net secretion of Cl- or bicarb or inhibition of net Na absorption
  • Stool osmolal gap < 50 mOsm/kg
• 3- Abnormal Intestinal Motility
  
  • Neurohormonal (faster transit so less time for absorption)
  • OR slow transit –> bacteria overgrowth in SI –> disrupts digestion and electrolyte transport
• 4- Exudation from Inflammation (aka inflammatory diarrhea)
  
  • If inflammation or ulceration of mucosa then discharge mucus, proteins and blood into lumen which impairs water and electrolyte absorption

Question 3

Bile Salt Diarrhea

Answer 3

• Bile salts normally reabsorbed and recycled in terminal ileum SO if ileum resected then high amounts of bile salts in colon –> stimulate water secretion and inc motility in colon
• Tx - bile salt binders (cholestyramine)

Question 4

3 Causes of Secretory Diarrhea

Answer 4

• Most common cause = infection (enterotoxins inc secretion or block Na-H exchange)
• Endocrine tumors (secrete VIP or calcitonin which stimulate secretory cells)
• Lose SA for absorption as in resection or IBD

Question 5

Causes of Abnormal Intestinal Motility (both inc and dec)

Answer 5

Inc Motility

• DM, postprandial diarrhea, postvagotomy diarrhea, IBS
• Anxiety/stress –> corticotrophin releasing factor (receptors in brain and gut)
• Peptide-secreting tumors or hyperthryoidism
• Caffeine and theophylline/aminophylline can change motility via CNS stimulation

Dec Motility

-DM, scleroderma, systemic sclerosis

Question 6

Clinical Definition of Constipation + Accompanying Symptoms

Answer 6

• BM < 3x/wk
• Accompanied by… straining, bloating, ab pain, incomplete evacuation, hard/small stools, positional or digital manipulation

Question 7

2 General Categories of Constipation Causes

Answer 7

Luminal obstruction OR dec colonic propulsion

Question 8

13 Types of Meds That Cause Constipation

Answer 8

Antacids, anticholinergics, antidepressants, Ca channel blockers, cholestyramine, clonidine, diuretics, levodopa, narcotics, NSAIDs, psychotropics, anti-convulsants, sympathomimetics

Question 9

Colonic Transit Studies

Answer 9

Swallow radiopaque capsule then take mult images; should pass w/in 5 days

• If colon problem then see markers throughout colon at 5 days
• If outlet problem then see >20% of marker in rectum

Question 10

7 Classes of Laxatives

Answer 10

1- Bulk-Forming or Fiber Lax

    - Absorb water in intestine to make stool softer
    - Metamucil, Fiberall, etc

2- Stimulants

    - Cause rhythmic intestinal contractions
    - Dulcolax

3- Osmotic Agents

    - Cause water to flow into lumen
    - Miralax

4- Stool Softeners

    - Moisten stool and prevent dehydration
    - Used after preg or surgery
    - Electrolyte imbalances if extended use

5- Lubricants

    - Grease stool to inc movement
    - Mineral oil

6 - Saline Laxatives

    - Draw water into colon
    - Milk of Magnesia

7- Cl Channel Activators

    - Work in apical membrane; inc secretion and motility
    - Lubiprostone (Amitiza) safe for long-term use