Critical steps in mammalian iron transport. Key iron transport steps are diagrammed, showing the route dietary iron follows from the intestinal lumen to the cytoplasm of an erythroid precursor cell. Nramp2(DCT1) acts as an iron transporter at two steps. It is required for transfer of iron across the intestinal brush border and for export of iron from transferrin cycle endosomes in the bone marrow. The function of Hfe is not well understood, but it appears to regulate basolateral iron transfer from enterocyte to plasma. Transferrin (Tf) chelates circulating iron in plasma.