Engineering Chemistry S Datta

562 ENGINEERING CHEMISTRY
Iron
Iron is the most abundant transition element in the Earth’s crust and in general in all
forms of life. The total amount of iron in humans is quite large, averaging 3 to 5 gm for a
healthy adult. Iron is absorbed in its ferrous form (Fe 2+ ). Absorption and excretion of iron are
relatively slow and controlled by different factors. Iron present in different food varies in their
absorption characteristics, such as iron is best absorbed from meat, less absorbed from cereal
grains.
Most of the iron is present in haemoglobin, the plasma oxygen-transport protein, where
iron functions to deliver oxygen for respiration. A much smaller amount is present in
myoglobin—which is a muscle oxygen-transport protein. It is present in cytochromes and
cytochrome oxidase. Iron transport from the storage sites to locations where cells synthesize
iron containing proteins is done by an iron-containing protein called transferrin. In the tissues
it is stored in the form of ferritin, an iron-protein containing ferric hydroxide and ferric
phosphate. The liver, spleen and bone marrow contain much ferritin. Iron is excreted from the
body via bile and faeces and menstrual blood. Since during menstruation, iron loss becomes
double or triple, hence large amount of iron is required for women compared to men.
Food
Intestine
Only 5–10%
of ingested Fe
is absorbed
Transferrin
Intestinal cells
(stored as ferritin)
Blood
Fe carried
by transferrin
Fe in bile
inhibits
absorption
Liver
(Fe stored as
ferritin)
Transferrin
Blood
Bone
marrow
Transferrin
Muscles
(myoglobin;
cytochromes)
Transferrin
Transferrin
Other
tissues
(cytochromes)
Red blood cells
(haemoglobin)
Loss in
menstrual blood
Fig. 26.1 Iron absorption and transport.