Calcium transcellular absorption

Calcium is absorbed both actively and passively throughout the small intestine and, to a small extent, in the colon. The active transcellular transport occurs in the duodenum and the passive paracellular process takes place in the jejunum and ileum. The chemical gradient and the sojourn time of the food passing through the intestine determine the movement of calcium that occurs by a passive process. The absorption of calcium in the colon becomes nutritionally significant under conditions of small intestine resection. 

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