DISTRIBUTION OF IRON• Total body iron content is 3 to 5 gm, 75% of which ispresent in blood. The rest is in liver, bone marrow andmuscles.• 75% of the blood iron is hemoglobin, 5% myoglobin and15% ferritin.
REQUIREMENT OF IRON• Daily requirement for an adult Indian is 20mg of iron outof which 1-2mg is absorbed.• Children between 13-15 years need 20-30 mg/day.• Pregnant women need 40 mg/day. Transfer of iron andcalcium from mother to fetus occurs mainly during lasttrimester of pregnancy.
• During first three months of life, iron intake is negligibleand 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 cerealsessential for supplying iron requirement.
FACTORS AFFECTING ABSORPTION OF IRON• Reduced form of iron• Ascorbic acid – Helps to reduce ferric ions• Interfering substances – Phytic acid(in cereals) andOxalic acid(in leafy vegetables) forms insoluble salts.• Other minerals like calcium, copper, lead andphosphates will inhibit iron absorption.
MUCOSAL BLOCK THEORY• Duodenum and jejunum are sites of absorption.• Iron metabolism is maintained by regulation at level ofabsorption and not by excretion. – One Way Element• When iron stores in body are depleted absorption isenhanced. Reverse when adequate quantity is present.
REGULATION OF ABSORPTION• Mucosal Regulation• Stores Regulation• Erythropoietic regulation – erythroid cells signalmucosa to increase absorption
IRON TRANSPORT• Transport form of iron is transferrin, a beta glubulin.Normal plasma level – 250mg/100ml. Increased in irondeficiency.• Total Iron Binding Capacity in plasma is 400mg/100ml,this is provided by transferrin.• One third of this capacity is saturated with iron, thisprotein bound iron(serum iron) is about 120mg/dL.• Ceruloplasmin is the ferroxidase which oxidises ferrousto ferric state.
• Transferrin receptors are present on most body cells,especially on cells which synthesize heme.• Iron transferrin complex taken up by body cells byreceptor mechanism. The receptor binds 2 molecules oftransferrin and is internalized. Iron is taken up by thecells and the receptor molecules are externalized.• Reticulocyte can internalize 1 million atoms of iron perminute.
STORAGE OF IRON• The storage form of iron is ferritin.• Its seen in intestinal mucosal cells, liver, spleen andbone marrow.• Apoferritin can take up to 4000 atoms of iron permolecule.
IRON IS CONSERVED• When RBC is lysed Hb is released into circulation.Being low molecular weight, Hb will be lost throughurine.• To prevent this Hb is immediately taken up byhaptoglobin an alpha globulin• Haptoglobin is an acute phase protein and its level isincreased in inflammation• Globin part is removed from Hb, and the heme isreleased into circulation.
• In order to prevent excretion of haeme through urine,heme is bound with hemopexin.• Hemopexin is a beta globulin whose levels areenhanced during increased haemolysis.• Heme-hemopexin complex is taken up by hepatocytes.• The porphyrin is removed and the free iron is eitherstored or utilized.
EXCRETION• Iron is a one way element. Regulation of homeostasisis done at level of absorption.• Almost no iron is excreted through urine. Fecescontains unabsorbed iron as well iron trapped inintestinal cells that are desquamated.• 30% of intestinal lining cells are replaced every dayhence this loss is considerable.• All cells in skin contain iron. Hence iron is lost byshedding of upper layers of skin.
HEMOGLOBIN• It’s the chief respiratory pigment in humans. Each Hbmolecule consists of 4 heme residues located in globinchains.• Iron present in Fe 2+ state• Normal Values:• Male : 13 – 18 g/dL• Female : 11.5 – 16.5 g/dL