Johnson LR (1994) Part V Gastrointestinal Physiology in Essential Medical Physiology. New York: Lippincott-Raven Press.
R D'Souza and J Powell-Tuck, Queen Mary's, University of London, London, UK
© 2005 Elsevier Ltd. All rights reserved.
The small intestine is bathed in nutrients derived from food digested by salivary, gastric, and pancreatic enzymes and dispersed by the emulsifying effect of biliary secretions. Its mucosal cells are in intimate relationship with these nutrients, a wide variety of antigens, and the bacterial flora. This relationship is fundamental to small bowel function, which is both secretory and absorptive, providing a defense from bacteria while allowing absorption of both small and large molecules. The relationship is also crucial to the patterns of intestinal motility, which optimize mixing and surface contact during the postprandial phase and revert to a flushing, ''housekeeper'' role postabsorptively. Diseases of the small bowel represent a breakdown in these relationships, which characteristically result in a failure of normal absorption, inflammation, and abnormal secretory responses. The small intestine plays a fundamental role in completing digestion and absorption of carbohydrates, proteins, fats, minerals, and vitamins. Any disorder of the small intestine in its digestive or absorptive capacity or of its immune system may lead to nutritional abnormalities.
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