Figure 2.

Intestinal pathways for calcium, phosphorus, and magnesium absorption. (A) Proposed pathways for calcium (Ca) absorption across the intestinal epithelium. Two routes exist for the absorption of Ca across the intestinal epithelium: the paracellular pathway and the transcellular route. (B) Proposed pathways for phosphorus (Pi) absorption across the intestinal epithelium. NaPi2b mediates active transcellular transport of Pi. A paracellular pathway is also believed to exist. (C) Proposed pathways for magnesium (Mg) absorption across the intestinal epithelium. Apical absorption is mediated by the TRPM6/TRPM7 channel, whereas basolateral exit occurs by an Mg exchanger that is yet to be fully defined. A paracellular pathway is also believed to exist. TRPM, transient receptor potential melastatin.