Pathophysiology of Small Intestine

Question 1

Mechanism/cause of diarrhea (general)

Answer 1

• occurs when colonic water load exceeds absorptive capacity
• A) small intestinal output substatantially increases
• B) colonic absorptive ability decreases/overwhelmed

Question 2

Major types of diarrhea

Answer 2

• watery stool
  
  • osmotic
  • secretory
• steatorrhea (fecal fat +)
  
  • malabsorption
  • maldigestion
• inflammatory/exudative (often bloody)
  
  • crohn’s
  • ischemia
  • invasive infection
• function (Irritable Bowel Syndrome)

Question 3

Definition/type of watery stool

Answer 3

• Watery = Stool osm gap= 290- 2(stool Na + stool K
• Osmotic (gap >50mOsm due to unmeasured Osm)
• Secretory (gap<50mOsm)

Question 4

Major causes of steatorrhea

Answer 4

• Malabsorption
  
  • i.Celiac
  • ii.Whipple’s disease
  • iii.Small bowel bacterial overgrowth
  • iv.Short gut (small bowel) from surgery
• Maldigestion
  
  • i.Pancreatic insufficiency
  • ii.Biliary obstruction

Question 5

Major causes of inflammatory/exudative diarrhea

Answer 5

• Crohn’s disease
• Ischemia
• Invasive infections (colon)
  
  • i.C. difficile
  • ii.EHEC
  • iii.Amebiasis
  • iv.Shigella

Question 6

Characteristics of Functional Diarrhea

Answer 6

• Functional = Irritable Bowel Syndrome
• Usually watery diarrhea
• Diagnosis of exclusion

Question 7

Major causes of fat malabsorption

Answer 7

• pancreatic insufficiency ==> impaired lipolysis
  
  • chronic pancreatitis <==alcoholism
• liver disease ==> decreased bile ==> decreased fat absorption
  
  • alcoholic cirrhosis
  • primary biliary cirrhosis
  • biliary obstruction
• gastric disorders
  
  • impaired mixing
  • early arrivial of ingested food to small bowel before pancreatic enzymes/bile
• small intestinal bacterial overgrowth (SIBO)

Question 8

Caues/mechanism of small intestinal bacterial overgrowth (SIBO)

Answer 8

• major causes =
  
  • hypomotility (DM, scleroderma)
  • partial obstruction
  • diverticula
  • decreased gastric acid secretion
• bacteria in intestinal lumen ==>
  
  • inactivated bile acids
  • reduced enterokinase effectiveness
  • disrupts small bowel motility

Question 9

Clinical presentation of SIBO

Answer 9

• diarrhea
• steatorrhea
• abdominal pain
• flatulence
• bloating
• weight loss
• later:
  
  • fat-soluble vitamin deficiencies (A,D, E)
  • B12 deficiency
  • serum folate = normal to high

Question 10

Structural diseases that lead to malabsorption

Answer 10

• mechanism: damage ==> decreased absorptive surface area

1. Intestinal inflammation and villus flattening (celiac sprue, infection, tropical sprue, graft vs host disease, Whipple’s disease)
2. Ulceration NSAIDs
3. Crohn’s Disease
4. Ischemia
5. Infiltration (amyloidosis, lymphoma)
6. Other (byapass, extensive small intestine resection)

Question 11

Pathophysiology of Celiac disease

Answer 11

• “celiac sprue” = “gluten-sensitive enteropathy” or “celiac disease”
• inflammatory disease of small intestine due to immune response to peptides of gluten
• presents @ weaning or in adults
• loss of villi due to increased intraepithelial lympthocytes AND
• crypt hyperplasia ==> malabsorption

Question 12

Clinical presentation of celiac disease

Answer 12

• sx of malabsorption
  
  • steatorrhea
  • diarrhea
  • weight loss
  • bloating
  • abdominal pain
• carb/fat/protein malabsorption occur due to villus destruction
• celiac occurs @ proximal small intestine ==> iron and folate malabsorption

Question 13

Dx of celiac disease

Answer 13

• intestinal biopsy:
  
  • villous flattening
  • intraepithelial lymphs
  • crypt hyperplasia
• serologic tests
  
  • anti-endomysial antibodies
  • anti-tissue transglutaminases (tTg) IgA antibodies
  • anti-gliadin IgA and IgG

Question 14

Tx of SIBO

Answer 14

• antibiotics
  
  • e.g. cirprofloxacin

Question 15

Major types of appendix tumors

Answer 15

• carcinoid
  
  • neuroendocrine
  • metastases ==> liver ==> serotonin syndrome
    
    • episodic flushing, diarrhea, wheezing and R-side valvular heart disease
• epithelial tumors
  
  • adenocarcinoma
• secondary tumors (metastases)

Question 16

Definition/major causes of osmotic diarrhea

Answer 16

Osmotic (gap >50mOsm due to unmeasured Osm)

i. Lactose intolerance
ii. Sorbitol
iii. Fructose
iv. Magnesium containing laxatives

Question 17

Definition/major causes of secretory diarrhea

Answer 17

Secretory (gap<50mOsm)

i. Bacterial toxins (V. cholera etc)
ii. Neuroendocrine tumors (Gastrinoma, VIPoma, Carcinoid)
iii. Bile salt (e.g terminal ileal resection)
iv. Stimulant laxatives
v. Motility disorders (Diabetes, IBS)