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Free and bound calcium were determined on intestinal contents of rats maintained on minimal and tolerable calcium diets. The concentration of free calcium was less than the serum value for all intestinal segments and for rats on both diets. The amount of bound calcium was greater when calcium was added to the diet and was greatest in the ileal segment for rats on either diet. The results indicate that the complete absorption of calcium from the duodenum may be followed by a small secretion of calcium back into the lumen of the ileum.
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Sernka et al. (1969) studied this question.
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