Iron Absorption

Iron is primarily absorbed in the duodenum and jejunum either as haem (derived from meat) or as free iron. Absorption is related to the total body iron stores and normally the amount absorbed is a small fraction of the amount ingested. Haem is absorbed by pinocytosis and broken down to free iron within the enterocyte. Free iron is absorbed using a specific receptor and once inside the cell it binds with a specific protein, apoferritin, to form ferritin, an intracellular storage complex for iron. Most iron in the form of ferritin is lost in the normal sloughing of epithelial cells. Ferritin-bound iron enters the circulation by cleaving from ferritin and then binding to a intracellular transport protein which then crosses the basal membrane to release iron into the circulation where it is bound to a Prglobulin, transferrin. Iron absorption increases if total body iron is reduced by increasing the number of iron receptors in the intestine, and by increasing the amount of the intracellular carrier protein. Iron absorption is summarized in Figure GI.16.

Dietary fr'Dlycer'dfi

Lpsse

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Fret fuih^ acids

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Fret fuih^ acids

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Figure Gl.15 Lipid digestion and absorption

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