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Small bowel (small intestine)

Infectious disorders

Diarrhea and dysentery

Reviewer: Hanni Gulwani, M.D. (see Reviewers page)
Revised: 16 December 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Usual fluid input into intestines is 9 liters/day (oral intake-2, saliva-1, gastric-2, pancreatic-2, intestinal-1, other-1)
● Most reabsorbed in small bowel and colon
Diarrhea: increase in stool mass, frequency or stool fluidity (3 or more loose stools/day, eMedicine)
Dysentery: low volume, painful, bloody diarrhea
Exudative disease: purulent bloody stools, persists with fasting: due to bacteria (Salmonella, Shigella, Campylobacter), Entamoeba histolytica, idiopathic inflammatory bowel disease, typhlitis
Malabsorption: bulky stools, abates with fasting, due to defective intraluminal digestion, primary mucosal cell abnormalities, reduced small bowel surface area, lymphatic obstruction, Giardia lamblia

Secretory diarrhea:
● >500 ml of fluid stool per day, isotonic with plasma, persists during fasting
● Infectious (viral damage to epithelium): rotavirus, Norwalk virus, enteric adenoviruses, calicivirus, astrovirus
● Infectious (enterotoxin): Vibrio cholera, E. coli, Bacillus cereus, Clostridium perfringens
● Neoplastic: tumor production of peptides, villous adenoma in distal colon
● Excessive laxatives

Osmotic diarrhea:
● Due to luminal solutes, abates with fasting, stool osmolality > electrolyte concentration by 50 mOsm
● Associated with lactase deficiency, lactulose therapy, gut lavage, antacids, primary bile acid malabsorption

Deranged motility:
● Improper gut neuromuscular function causes decreased transit time
● Due to surgical resection of gut, irritable bowel syndrome (neural dysfunction), hyperthyroidism, diabetic neuropathy, carcinoid syndrome
● Decreased motility due to small bowel diverticula, blind loop, bacterial overgrowth


● 12,000 deaths/year from dehydration in developing countries - 50% of all deaths before age 5
● Affects 40% of US population - #2 in attack rates in US after common cold

Micro description

● Patchy lesions with variable villus abnormality, rarely severe
● Increased chronic and acute inflammatory infiltrate in epithelium and lamina propria
● Small intestinal bacterial overgrowth: common cause of chronic diarrhea and malabsorption with either villous blunting or normal duodenal biopsy (Arch Pathol Lab Med 2010;134:264)

Micro images

Small intestinal bacterial overgrowth

End of Small bowel (small intestine) > Infectious disorders > Diarrhea and dysentery

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