Page 312 - Textbook of Pathology, 6th Edition

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SECTION II

Figure 12.11 Daily iron cycle. Iron on absorption from upper small intestine circulates in plasma bound to transferrin and is transported to the
bone marrow for utilisation in haemoglobin synthesis. The mature red cells are released into circulation, which on completion of their lifespan of 120
days, die. They are then phagocytosed by RE cells and iron stored as ferritin and haemosiderin. Stored iron is mobilised in response to increased
demand and used for haemoglobin synthesis, thus completing the cycle (M = males; F = females).

tract, from excretion in the urine and sweat, and loss via hair cells of the spleen, liver and bone marrow and in the
and nails. Iron excreted in the faeces mainly consists of parenchymal cells of the liver.
Haematology and Lymphoreticular Tissues
unabsorbed iron and desquamated mucosal cells.
Pathogenesis
DISTRIBUTION. In an adult, iron is distributed in the body
as under: Iron deficiency anaemia develops when the supply of iron is
inadequate for the requirement of haemoglobin synthesis.
1. Haemoglobin—present in the red cells, contains most of Initially, negative iron balance is covered by mobilisation
the body iron (65%). from the tissue stores so as to maintain haemoglobin
2. Myoglobin—comprises a small amount of iron in the synthesis. It is only after the tissue stores of iron are exhausted
muscles (3.5%). that the supply of iron to the marrow becomes insufficient
3. Haem and non-haem enzymes—e.g. cytochrome, for haemoglobin formation and thus a state of iron deficiency
catalase, peroxidases, succinic dehydrogenase and anaemia develops. The development of iron deficiency
flavoproteins constitute a fraction of total body iron (0.5%). depends upon one or more of the following factors:
4. Transferrin-bound iron—circulates in the plasma and 1. Increased blood loss
constitutes another fraction of total body iron (0.5%). 2. Increased requirements
3. Inadequate dietary intake
All these forms of iron are in functional form.
4. Decreased intestinal absorption.
5. Ferritin and haemosiderin—are the storage forms of excess The relative significance of these factors varies with the
iron (30%). They are stored in the mononuclear-phagocyte age and sex of the patient (Table 12.4). Accordingly, certain