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 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.
Fe
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.