Gastrointestinal tract structural features

The small-intestinal transit flow is a fundamental process for all gastrointestinal absorption phenomena. However, the structure of the gastrointestinal tract is highly complex and it is practically impossible to explicitly write and solve the equations of motion for the drug flow. Instead, numerical computer simulation techniques that incorporate the heterogeneous features of the gastrointestinal wall structure and of the drug flow are used in this section to characterize the intestinal transit process in humans. 

Bethanechol incorporates the stabilizing structural features of both methacholine and carbachol. Thus it is like carbachol in that no appreciable cholinesterase hydrolysis takes place, and like methacholine it does not stimulate ganglia or skeletal muscle. This dmg appears to show some specificity of action in the gastrointestinal and urinary tracts. Thus, it has clinical applications in postoperative distention of the abdomen and bladder in the latter case it relieves the urinary retention that results following surgery. The drug is even orally effective. 

Bile acid metabolism in conventional animals is the activity of a balanced ecological system composed of the host, the associated intestinal microflora, and the diet. The host contributes the bile acids themselves and serves to maintain the homeostasis of the gastrointestinal tract. The intestinal microflora alters the molecular structure of the bile acids which it comes into contact with and also profoundly alters the physiological and, to a degree, the anatomical features of the host. The diet contributes the nutrition for both the host and the intestinal microflora and can cause marked changes in the flora s activity toward the bile acids in vivo (52). In addition, the amount of dietary sterols may cause the host to change its absorption and/or catabolism of cholesterol to bile acid and thus the rate of bile acid excretion (53). 

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