body iron distribution/stores
Jump to navigation
Jump to search
Notes
Absorbtion of iron:
- dietary iron in the form of inorganic or heme iron[3]
- heme iron is more bioavailable than inorganic iron
- normal diet contains 14 +/- 4 mg of iron/day, ~6 mg/1000 kcal.
- iron is absorbed by active transport in the proximal small intestine, especially the duodenum
- absorbtion is regulated by a single hematopoietic transcription factor (NF-E2) which links intestinal transport of iron to erythropoiesis
- transport of iron is facilitated by ferroportin within basolateral plasma membrane of duodenal enterocytes, hepatocytes & tissue macrophages
- ferroportin is regulated (inhibited) by hepcidin which in turn is regulated by plasma iron &/or iron stores
- ascorbate (by reducing Fe+3 to Fe+2) & gastric acid increase iron absorption
- 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
- iron store depletion:
- rapid growth (infancy & adolescence)
- menstrual blood loss
- inadequate diet
- malabsorption:
- iron is absorbed by active transport in the proximal small intestine, especially the duodenum
- blood donation
- iron-deficient erythropoiesis
- 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:
- loss of iron varies from 0.5-2 mg/day in men
- additional loss of 0.5 mg/day in menstruating women
- 10% of women lose up to 2 mg/day during menstruation
- 67% of iron lost through GI tract as extravasated RBC, iron in the bile & in exfoliated mucosal cells
- 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
| 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:
- loss of iron varies from 0.5-2 mg/day in men
- additional loss of 0.5 mg/day in menstruating women
- 10% of women lose up to 2 mg/day during menstruation
- 67% of iron lost through GI tract as extravasated RBC, iron in the bile & in exfoliated mucosal cells
- 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
More general terms
Additional terms
- Fe+2/Fe+3 (bioavailable iron)
- ferritin in serum/plasma
- iron (Fe+2/Fe+3) in serum
- iron-deficiency anemia
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
- ↑ 3.0 3.1 The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996 pg 1317-1325