body iron distribution/stores

Notes: Absorbtion of iron: 1) dietary iron in the form of inorganic or heme iron [3] 2) heme iron is more bioavailable than inorganic iron 3) normal diet contains 14 +/- 4 mg of iron/day, ~6 mg/1000 kcal. 4) iron is absorbed by active transport in the proximal small intestine, especially the duodenum 5) absorbtion is regulated by a single hematopoietic transcription factor (NF-E2) which links intestinal transport of iron to erythropoiesis 6) transport of iron is facilitated by ferroportin within basolateral plasma membrane of duodenal enterocytes, hepatocytes & tissue macrophages 7) ferroportin is regulated (inhibited) by hepcidin which in turn is regulated by plasma iron &/or iron stores 8) ascorbate (by reducing Fe⁺³ to Fe⁺²) & gastric acid increase iron absorption 9) intestinal absorption maximizes at about 1 mg/day Distribution of body iron stores. Iron store male (80 kg) female (60 kg) Hemoglobin: 2500 mg 1700 mg Myoglobin/other Heme: 500 mg 300 mg Transferrin: 3 mg 3 mg Iron stores: 600-1000 mg 0-300 mg Normal total body iron content is 3-4 grams. Causes of iron depletion or deficiency 1) iron store depletion: a) rapid growth (infancy & adolescence) b) menstrual blood loss c) inadequate diet d) malabsorption: -> iron is absorbed by active transport in the proximal small intestine, especially the duodenum e) blood donation 2) iron-deficient erythropoiesis 3) iron-deficiency anemia Iron store measurement: Iron stores marrow iron stain serum ferritin 0 mg 0 < 15 ug/dL 1-300 mg 1+ 15-30 ug/dL 300-800 mg 2+ 30-60 ug/dL 800-1000 mg 3+ 60-150 ug/dL 1000-2000 mg 4+ > 150 ug/dL iron overload - > 500-1000 ug/dL Iron excretion: 1) loss of iron varies from 0.5-2 mg/day in men 2) additional loss of 0.5 mg/day in menstruating women - 10% of women lose up to 2 mg/day during menstruation 3) 67% of iron lost through GI tract as extravasated RBC, iron in the bile & in exfoliated mucosal cells 4) 33% of iron lost indesquamated skin & in urine Pregnancy has its own special considerations. Source Quantity external iron loss 170 mg (150-200) expansion of erythrocyte mass 450 mg (200-600) fetal iron 270 mg (200-370) iron in placenta & umbilical cord 90 mg (30-170) hemorrhage at delivery 150 mg (90-130) total additional iron* * average iron requirements, range in parenthesis requirements in addition to normal daily requirements

General

physiology laboratory analysis

References

Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 640-41
Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998
The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996 pg 1317-1325

Contents

Search