Small intestinal transit pattern

Intestinal mechanical clearance thus consists of both reflex-mediated contractions (peristalsis) elicited by the stimulatory effect of luminal contents and of periods of spontaneous contractile activity (e.g. the migrating motor complex). During fasting about 50% of intestinal transit has been attributed to phase III of the migrating motor complex, the remaining mostly to the propulsive contractions and motor patterns during phase II [ 108]. Luminal flow can also occur in the absence of propagating contractions of the circular muscle layer, so far considered the motor event mainly responsible for flow in the small intestine. 

A small bowel transit study can be used to evaluate intestinal propulsion and clearance, and the presence of Enterobacteriacea (Gram-negative bacilli) in the small bowel indicates delayed transit [111]. The wide normal variability, however, makes transit tests rather insensitive, and thus less useful clinically [126, 127], It is also a problem that accelerated and delayed transit may coexist in neuropathies and confuse the interpretation. Finally, as nutrients are mostly absorbed in the proximal small bowel, and the rate and pattern of transit vary along the intestine, segmental failure of transit is easily missed by global... 

The small intestinal mucosa tends to maintain a constant morphological appearance, despite the fact that there is a rapid renewal of cells in intestinal crypts and rapid transit of cells up the intestinal villi. Among those factors which are reported to influence morphological structure and the rates of enterocyte proliferation, differentiation and extrusion, are physical trauma[l] changes in gut flora[2] hormones[3] the state of nutrition and feeding patterns [4] and bile acid concentration[5]. 

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