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CRITICAL ELEMENT IN THE FUNCTION OF ALL CELLS
IRON IS REQUIRED BY EVERY CELL
IRON METABOLISM
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Ferrous (Fe2+) and ferric (Fe3+) forms
Iron can interconvertMakes it a useful component of
Oxygen-binding molecules (i.e., hemoglobin and myoglobin)
Cytochromes Many enzymes
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Free iron
Highly toxicCan generate free radicals
Catalyze the conversion of hydrogen peroxide to free-radical ions
Free-radical ions attack cellular membranes, proteins, and DNA
Proteins bind iron to reduce this toxic effect
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Main role of iron
Carry oxygen Iron is part of the heme protein of hemoglobin Iron deficiency
Hemoglobin synthesis is impaired Anemia - reduced oxygen delivery to tissue
Iron overload Widespread organ damage and death
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How does iron circulate in blood?
Bound to plasma transferrinEach transferrin molecule binds two
atoms of ferric ironNormally one-third saturated (35 %)Responsible for TIBC
250-370 microgram/dl
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How do cells store iron?
In the form of ferritinUp to 4500 atoms of iron can be stored in
a single ferritin molecule
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Storage form of iron (500-1500 mg)
Iron is stored in Reticuloendothelial cells Hepatocytes Skeletal muscle cells
Two-thirds stored as ferritinOne-third as haemosiderin
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Reticuloendothelial macrophages
Degrade hemoglobin in old erythrocytesGive it to transferrin for delivery to cellsProvide most of the usable iron
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Pathway of internal iron exchange
RBC
RE CELLS
PLASMA Tf
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Unidirectional flow
From plasma transferrin to the RBC to the macrophage (RE cells) and back to plasma transferrin
80% of iron passing through the plasma transferrin pool Recycled from broken-down red cells
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Storage iron
Macrophages Liver
Main site of storage Bone marrow Spleen
Derived almost entirely from phagocytosis of senescent erythrocytes or defective developing red cells
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IRON CYCLE
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SUMMARY
80% of iron passing through the plasma transferrin pool is recycled from broken-down red cells
Storage iron in the macrophages of the liver, bone marrow, and spleen is derived almost entirely from phagocytosis of senescent erythrocytes or defective developing red cells
Macrophage takes up little iron from plasma transferrin
Hepatocyte may either donate iron to or receive iron from plasma transferrin
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Most of the iron bound to transferrin comes from
A. Iron absorbed by the intestineB. MacrophagesC. FerritinD. Reticulocytes
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ANSWER
B – MacrophagesMost of the iron bound to transferrin comes
from macrophages in the reticuloendothelial system and not from iron absorbed by the intestine
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