Pathophysiology of Small Intestine Flashcards
Mechanism/cause of diarrhea (general)
- occurs when colonic water load exceeds absorptive capacity
- A) small intestinal output substatantially increases
- B) colonic absorptive ability decreases/overwhelmed
Major types of diarrhea
- watery stool
- osmotic
- secretory
- steatorrhea (fecal fat +)
- malabsorption
- maldigestion
- inflammatory/exudative (often bloody)
- crohn’s
- ischemia
- invasive infection
- function (Irritable Bowel Syndrome)
Definition/type of watery stool
- Watery = Stool osm gap= 290- 2(stool Na + stool K
- Osmotic (gap >50mOsm due to unmeasured Osm)
- Secretory (gap<50mOsm)
Major causes of steatorrhea
- 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
Major causes of inflammatory/exudative diarrhea
- Crohn’s disease
- Ischemia
- Invasive infections (colon)
- i.C. difficile
- ii.EHEC
- iii.Amebiasis
- iv.Shigella
Characteristics of Functional Diarrhea
- Functional = Irritable Bowel Syndrome
- Usually watery diarrhea
- Diagnosis of exclusion
Major causes of fat malabsorption
- 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)
Caues/mechanism of small intestinal bacterial overgrowth (SIBO)
- 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
Clinical presentation of SIBO
- diarrhea
- steatorrhea
- abdominal pain
- flatulence
- bloating
- weight loss
- later:
- fat-soluble vitamin deficiencies (A,D, E)
- B12 deficiency
- serum folate = normal to high
Structural diseases that lead to malabsorption
- mechanism: damage ==> decreased absorptive surface area
- Intestinal inflammation and villus flattening (celiac sprue, infection, tropical sprue, graft vs host disease, Whipple’s disease)
- Ulceration NSAIDs
- Crohn’s Disease
- Ischemia
- Infiltration (amyloidosis, lymphoma)
- Other (byapass, extensive small intestine resection)
Pathophysiology of Celiac disease
- “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
Clinical presentation of celiac disease
- 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
Dx of celiac disease
- intestinal biopsy:
- villous flattening
- intraepithelial lymphs
- crypt hyperplasia
- serologic tests
- anti-endomysial antibodies
- anti-tissue transglutaminases (tTg) IgA antibodies
- anti-gliadin IgA and IgG
Tx of SIBO
- antibiotics
- e.g. cirprofloxacin
Major types of appendix tumors
- carcinoid
- neuroendocrine
- metastases ==> liver ==> serotonin syndrome
- episodic flushing, diarrhea, wheezing and R-side valvular heart disease
- epithelial tumors
- adenocarcinoma
- secondary tumors (metastases)
Definition/major causes of osmotic diarrhea
Osmotic (gap >50mOsm due to unmeasured Osm)
i. Lactose intolerance
ii. Sorbitol
iii. Fructose
iv. Magnesium containing laxatives
Definition/major causes of secretory diarrhea
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)
