IronHepcidinFerroportin, the way outIron from food crosses the gut through one layer of lining cells. It comes in at the top, through DMT1 channels on the brush border, and leaves at the base through ferroportin, the only known way out of the cell, into the blood, where transferrin carries it away. Iron that can't leave is held in ferritin and lost when the cell is shed a few days later.Hepcidin, a hormone from the liver, is the gatekeeper. It docks on ferroportin, plugs it, and makes the cell pull the channel in and break it down. Hepcidin rises after an iron pill and when stores are full, so fewer gates stay open: about 50 % after a week of daily pills and about 45 % two weeks after an IV infusion, against 97 % when iron-hungry.The gate shares come from the model in the IV iron figure (Fig 3). Drawn far larger than life and simplified: a real lining cell carries many more, much finer microvilli, channel and particle counts are a drawing, and time is sped up.