Gastric juice sequence

In order to determine the approximate sequence and range of molecular sizes of the macromolecular materials contained in native gastric juice, as well as to dissociate some naturally forming large molecular... 

Cooper and Castle have proposed a three-step sequence to explain the vitamin B12 absorption in the gastrointestinal tract. In the first step, vitamin B12 binds with the intrinsic factor in gastric juice. The affinity of the vitamin for the intrinsic factor is thought to be greater than its affinity for proteins in the intestinal content consequently, the intrinsic factor (IF) successfully displaces the vitamin from its weaker bonds with other proteins. Calcium facilitates and EDTA inhibits the absorption of vitamin B12 by the everted intestine. On the basis of these and related findings, workers proposed the second step in vitamin Bi2 absorption. At that stage it is assumed that the intrinsic factor-vitamin B12 complex is trapped in the intestinal wall by the intermediate of calcium bonds and absorbed by pinocytosis. This stage of the absorption process probably is interfered with in sprue and steatorrhea where calcicum soaps are formed in the intestinal lumen. 

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