Iron is critical to a number of synthetic and enzymatic
processes. Most of the body iron is part of the hemoglobin
molecule where iron serves a key role in oxygen transport.
Iron is recycled and thus conserved by the body. Daily intake
( 1 mg ) s balanced against small daily losses (1 mg ).
The Fe button below will take you to the iron cycle, allowing
you to see the entire cycle as a whole.
The amounts shown in the Fe Cycle Card are in mg of
iron lost or gained per day. They were derived in the following
manner.
The average blood volume in a 70 kg man is 5,000 ml.
There are 150 grams of hemoglobin in each liter of blood,
therefore there are 750 g of hemoglobin in the body.
Each gram of hemoglobin contains approximately 3.3 mg of
iron or 2475 mg of iron in the body.
Dividing the 2475 mg total by the 120 day average RBC lifespan
results in the iron needed per day or 20.6 mg iron/day.
Hemoglobin Fe
2200 mg
Ferritin & Hemosiderin
1000 mg
Myoglobin Fe
300 mg
Other Fe (cytochromes; enzymes)
100 mg
Total Body Iron
3600 mg
An average adult in the U.S. on a 2,500 calorie diet ( 6 mg
of iron/1,000 kcal) ingests 15 mg of iron daily. Only 5-10
% or about 1.0 mg of dietary iron is absorbed as ferrous iron
(Fe++), mainly in the duodenum and upper jejunum where the
pH is low. The mucosal cells oxidize the ferrous iron to ferric
iron ,
which is then complexed with apoferritin to form ferritin.
Some of the ferritin is transported out of the mucosal cell
into the plasma bound to transferrin. Thus bound, iron can
be transported to the bone marrow or iron storage sites where
it is stored as either ferritin or hemosiderin.
Most cells have transferrin receptors (CD 71) to which
iron ladden transferrin binds. The receptor-transferrin-iron
complex is then incorporated into the cytosol by endocytosis.
In red cells the endocytotic vacuole fuses with a lysozyme,
where at an acid pH the iron (Fe++) is released from transferrin
and transported to mitochondria where it is incorporated
into heme, the ferrous iron complex of protoporphyrin IX.
Although iron is utilized in virtually all cells, the
bulk of body iron is found in erythrocytes with lesser amounts
in myoglobin. Large amounts of iron are required during
growth periods in infant, childhood and teenage years.
Transferrin carries iron to the bone marrow where it is
accepted into RBCs via a transferrin receptor (CD71) and
incorporated into heme for use in hemoglobin.
Not all erythrocytes develop and mature successfully. Some
die in the marrow and their iron is salvaged by macrophages.
This failure to mature resulting in death in the marrow
is known as ineffective erythropoiesis.
Normally only small amounts of iron are lost daily as
hair, skin, urinary bladder,and gastrointestinal cells are
shed. This amount can easily be replaced by dietary intake.
With bleeding, larger amounts of iron can be lost. The
most common normal blood losses are due to menstruation
and pregnancy.
Pathology
> Basic Hematology > Normal
Hematopoiesis > Erythrocyte Review
> Iron Metabolism
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which is then complexed with apoferritin to form ferritin.
Some of the ferritin is transported out of the mucosal cell
into the plasma bound to transferrin. Thus bound, iron can
be transported to the bone marrow or iron storage sites where
it is stored as either ferritin or hemosiderin. 