Passive Absorption of Bile Salts in the Lower Gastrointestinal Tract

PASSIVE ABSORPTION OF BILE SALTS IN THE LOWER GASTROINTESTINAL TRACT 

Direct measurement of passive transport in the ileum has not been made because of the presence of the active mechanism. It has been assumed that these processes are quantitatively similar to those in the jejunum. However, there are known differences in permeability characteristics of various parts of the small bowel (40). 

Unlike the normal proximal small intestine, there have been reports of appreciable quantities of unconjugated bile acids in the ileum (41). This is not a uniform finding (42) and may reflect differences in diet or other experimental variables. Insofar as there are appreciable quantities of unconjugated acids, which undoubtedly arise from bacterial hydrolysis, nonionic diffusion plays an important role. 

It is known from the work of Norman and Sjovall (42) that approximately 50 % of bile salts injected into the cecum of a rat is absorbed and re-enters the enterohepatic circulation. In all cases, hydrolysis of conjugated bile salts precedes this absorption. A large fraction of the bile salts are additionally 

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