Document Detail

Small intestinal physiology and pathophysiology.
MedLine Citation:
PMID:  2668175     Owner:  NLM     Status:  MEDLINE    
The small intestine, like the rest of the gastrointestinal tract, is an intelligent organ. It generates a wide variety of motor patterns to meet motility requirements in different situations. Its basic motor function after a meal is to mix the chyme with exocrine and intestinal secretions, agitate its contents to uniformly and evenly expose them to the mucosal surface, and to propel them distally at a rate that allows optimal absorption of food components, and reabsorption of bile. Most of these functions are performed by individual phasic contractions. In humans, the phasic contractions are largely disorganized in time and space. These contractions may cause mixing and agitation of luminal contents with slow distal propulsion. Occasionally, an individual contraction of large amplitude and long duration migrates over several centimeters and may rapidly propel the contents over this distance. In general, the spatial and temporal relationships of individual phasic contractions become less organized distally, resulting in a slower propulsion rate in the distal small intestine than in the proximal small intestine. The migrating clustered contractions generated after a meal may also be propulsive, but because of their unpredictable and irregular occurrence, their precise role in postprandial propulsion is incompletely understood. Rapidly migrating contractions may occur when the electrical control activity is obliterated by pharmacologic agents or during parasitic infections. Their effects on motility are not known yet. Between meals, when digestion is complete, the small intestine generates migrating motor complexes that help keep the small intestine clean by dislodging debris from the villi and dumping them into the colon. This may prevent decay of these materials in the small intestine and limit their contribution to bacterial overgrowth. Giant migrating contractions may perform a similar function in the distal small intestine as well as return any refluxed fecal material back to the colon. However, the major role of giant migrating contractions may be, in pathologic states, associated with abdominal cramping and diarrhea. Giant migrating contractions are associated with mass movements. Vomiting is preceded by a retrograde giant contraction. This contraction rapidly empties the contents of the proximal half of small intestine into the stomach in preparation for vomitus expulsion by contraction of abdominal and diaphragmatic muscles. The three basic mechanisms of control of spatial and temporal patterns of contractions are myogenic, neural, and chemical.(ABSTRACT TRUNCATED AT 400 WORDS)
S K Sarna; M F Otterson
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.; Review    
Journal Detail:
Title:  Gastroenterology clinics of North America     Volume:  18     ISSN:  0889-8553     ISO Abbreviation:  Gastroenterol. Clin. North Am.     Publication Date:  1989 Jun 
Date Detail:
Created Date:  1989-09-20     Completed Date:  1989-09-20     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  8706257     Medline TA:  Gastroenterol Clin North Am     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  375-404     Citation Subset:  IM    
Digestive System Research Center, Medical College of Wisconsin, Milwaukee.
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MeSH Terms
Autonomic Nervous System / physiology
Brain / physiology
Digestive System / innervation
Gastrointestinal Motility
Intestine, Small / physiology*,  physiopathology
Muscle Contraction
Muscle, Smooth / physiology
Nervous System Physiological Phenomena
Peptides / metabolism,  physiology
Stimulation, Chemical
Grant Support
Reg. No./Substance:

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