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Small bowel (small intestine)



Reviewer: Hanni Gulwani, M.D. (see Reviewers page)
Revised: 14 December 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Standard site for biopsies is proximal jejunum, just distal to ligament of Trietz
● Mount specimen mucosal side up on solid substance, then embed perpendicular to mounting material; then step section or serial section
● Small bowel is important for absorption of fats, fat-soluble vitamins, proteins, carbohydrates, electrolytes, minerals, water
● In US, most common malabsorption disorders are celiac sprue, pancreatic insufficiency and Crohn’s disease
● Steatorrhea: bulky, greasy stools associated with weight loss, anorexia, muscle wasting

Symptoms associated with specific deficiencies

● Diarrhea, flatus, abdominal pain, weight loss, mucositis, anemia (iron, folate, Vitamins B6, B12)
● Bleeding / purpura (Vitamin K)
● Osteopenia, tetany (calcium, magnesium, vitamin D)
● Amenorrhea / impotence / infertility (generalized malnutrition)
● Hyperparathyroidism (calcium, vitamin D)
● Edema (albumin)
● Dermatitis (zinc, vitamin A, fatty acids, niacin)
● Peripheral neuropathy (vitamins A, B12)

Physiologic classification of malabsorption

Disturbances related to:
● (a) Intraluminal digestion: saliva, gastric peptic digestion, small bowel, bile salts
● (b) Terminal digestion: hydrolysis of carbohydrates and peptides by disaccharidases and peptidases in brush border of small bowel
● (c) Transepithelial transport: across small bowel epithelium to intestinal vasculature; fatty acids to triglycerides, cholesterol to chylomicrons

(a) Causes of defective intraluminal digestion
● Digestion of fats/proteins: pancreatic insufficiency due to pancreatitis or cystic fibrosis, Zollinger-Ellison syndrome
● Defective bile secretion (fat solubilization): ileal dysfunction or resection with decreased bile salt uptake, cessation of bile flow (obstruction, hepatic dysfunction), nutrient preabsorption or modification by bacterial overgrowth

(b/c) Causes of abnormalities in terminal digestion or transepithelial transport
● Disaccharidase deficiency (lactose intolerance), bacterial overgrowth, abetalipoproteinemia, defects in ileal bile acid transporter

End of Small bowel (small intestine) > Malabsorption > Malabsorption-general

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