Iron metabolism

Sanjay George

IRON METABOLISM

DISTRIBUTION OF IRON

• Total body iron content is 3 to 5 gm, 75% of which is present in blood. The rest is in liver, bone marrow and muscles.

• 75% of the blood iron is hemoglobin, 5% myoglobin and 15% ferritin.

REQUIREMENT OF IRON

• Daily requirement for an adult Indian is 20mg of iron out of which 1-2mg is absorbed.

• Children between 13-15 years need 20-30 mg/day.

• Pregnant women need 40 mg/day. Transfer of iron and calcium from mother to fetus occurs mainly during last trimester of pregnancy.

• During first three months of life, iron intake is negligible and during this time child is dependent on iron reserve.

• Premature babies are at risk of iron deficiency anemia.

• After 3 months of life, diet supplementation with cereals essential for supplying iron requirement.

SOURCES OF IRON

• Leafy vegetables

• Pulses

• Cereals

• Liver

• Meat

• Jaggery

FACTORS AFFECTING ABSORPTION OF IRON

• Reduced form of iron

• Ascorbic acid – Helps to reduce ferric ions

• Interfering substances – Phytic acid(in cereals) and Oxalic acid(in leafy vegetables) forms insoluble salts.

• Other minerals like calcium, copper, lead and phosphates will inhibit iron absorption.

MUCOSAL BLOCK THEORY

• Duodenum and jejunum are sites of absorption.

• Iron metabolism is maintained by regulation at level of absorption and not by excretion. – One Way Element

• When iron stores in body are depleted absorption is enhanced. Reverse when adequate quantity is present.

ABSORPTION

Fe 2+Divalent metal transporter

Fe 2+ Fe 3+ FerritinFe 2+ crosses membrane

Fe 3+ transferrin in blood stream

REGULATION OF ABSORPTION

• Mucosal Regulation

• Stores Regulation

• Erythropoietic regulation – erythroid cells signal mucosa to increase absorption

IRON TRANSPORT

• Transport form of iron is transferrin, a beta glubulin. Normal plasma level – 250mg/100ml. Increased in iron deficiency.

• Total Iron Binding Capacity in plasma is 400mg/100ml, this is provided by transferrin.

• One third of this capacity is saturated with iron, this protein bound iron(serum iron) is about 120mg/dL.

• Ceruloplasmin is the ferroxidase which oxidises ferrous to ferric state.

• Transferrin receptors are present on most body cells, especially on cells which synthesize heme.

• Iron transferrin complex taken up by body cells by receptor mechanism. The receptor binds 2 molecules of transferrin and is internalized. Iron is taken up by the cells and the receptor molecules are externalized.

• Reticulocyte can internalize 1 million atoms of iron per minute.

STORAGE OF IRON

• The storage form of iron is ferritin.

• Its seen in intestinal mucosal cells, liver, spleen and bone marrow.

• Apoferritin can take up to 4000 atoms of iron per molecule.

IRON IS CONSERVED• When RBC is lysed Hb is released into circulation. Being

low molecular weight, Hb will be lost through urine.

• To prevent this Hb is immediately taken up by haptoglobin an alpha globulin

• Haptoglobin is an acute phase protein and its level is increased in inflammation

• Globin part is removed from Hb, and the heme is released into circulation.

• In order to prevent excretion of haeme through urine, heme is bound with hemopexin.

• Hemopexin is a beta globulin whose levels are enhanced during increased haemolysis.

• Heme-hemopexin complex is taken up by hepatocytes.

• The porphyrin is removed and the free iron is either stored or utilized.

EXCRETION• Iron is a one way element. Regulation of homeostasis is

done at level of absorption.

• Almost no iron is excreted through urine. Feces contains unabsorbed iron as well iron trapped in intestinal cells that are desquamated.

• 30% of intestinal lining cells are replaced every day hence this loss is considerable.

• All cells in skin contain iron. Hence iron is lost by shedding of upper layers of skin.

HEMOGLOBIN

• It’s the chief respiratory pigment in humans. Each Hb molecule consists of 4 heme residues located in globin chains.

• Iron present in Fe 2+ state

• Normal Values:

• Male : 13 – 18 g/dL

• Female : 11.5 – 16.5 g/dL

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