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TRACE ELEMENTS IRON

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					TRACE ELEMENTS
     IRON
         IRON METABOLISM
• DISTRIBUTION OF IRON IN THE BODY
• Between 50 to 70 mmol (3 to 4 g) of iron
  are distributed between body
  compartments.
• In normal subjects it is all protein-bound; in
  plasma it is bound to Transferrin, in the
  stores to protein in ferritin and
  haemosiderin, and in erythrocytes it is
  incorporated into hemoglobin.
Distribution of Iron in a 70 kg Adult Male
Transferrin                      3-4 mg
Hemoglobin in red                2600 mg
 blood cell
Myoglobin and various 300 mg
 enzymes
Stores (Ferritin and             1000 mg
  Hemosiderin)
Absorption                       1 mg / day
Losses                           1 mg/ day
 In an adult female of similar weight, the amount in stores would
    be generally be less (100-400 mg) and the losses would be
                       greater (1.5 - 2 mg/d).
             IRON METABOLISM
• About 70 per cent of the total iron is
  circulating in erythrocyte hemoglobin.
• Up to 25 per cent of the body iron is stored in
  the reticuloendothelial system, in the liver,
  spleen and bone marrow; bone marrow iron
  is drawn on for hemoglobin synthesis. Iron is
  stored as protein complexes, ferritin and
  haemosiderin. Ferritin iron is more easily
  released from protein than that in
  haemosiderin. Haemosiderin, probably an
  aggregate of ferritin, can be seen by light
  microscopy in unstained tissue preparations.
        RECOMMENDED DAILY DIETARY
           ALLOWANCES OF IRON
Category         Iron (mg ) WHO
                   recommendations
Infants          5-10
Children         5-10
Males            9-18 (5-10)
Females          14-18
Pregnant females 18-28
Lactating females 18-28
        IRON ABSORPTION
• The control of body iron content
  depends upon control of absorption
  by an active process in the upper
  small intestine. Within the intestinal
  cell some of the iron combines with
  the protein apoferritin to form ferritin,
  which, as elsewhere in the body, is a
  storage compound.
        IRON ABSORPTION
• Normally about 18 umol (1 mg) of iron
  is absorbed each day and this just
  replaces loss. This amounts to about
  10 per cent of that taken in the diet,
• Iron absorption seems to be influenced
  by any or all of the following factors:

  – oxygen tension in the intestinal cells;

  – marrow erythropoietic activity;

  – the size of the body iron stores.
          IRON ABSORPTION
• Iron absorption is also increased in
  many non-iron deficiency anaemias.
  – Most normal women taking an adequate
    diet probably absorb slightly more iron
    than men and so replace their higher
    losses in menstrual blood and during
    pregnancy.
  – Iron requirements for growth during
    childhood and adolescence are similar to,
    or slightly higher than, those of
    menstruating women and can be met by
    increased absorption from a normal diet.
Body Iron Compartments
 IRON TRANSPORT IN PLASMA
• Iron is transported in the plasma in the ferric
  form, attached to the specific binding
  protein, transferrin(2molecules/transferrin),
  at a concentration of about 18 umol/L (100
  mg/dl).
• Transferrin is normally capable of binding
  about 54 umol/L (300 mg/dl) of iron and is
  therefore about a third saturated.
• Transferrin-bound iron is carried to stores
  and to bone marrow cells and in the latter
  some iron passes directly into developing
  erythrocytes to form hemoglobin.
      Factors Affecting Plasma Iron
              Concentration
•   Sex and age differences
•   Pregnancy and oral contraceptives
•   Variation within in individual
•   Random variation
•   Circadian (diurnal ) rhythm
•   Monthly variation in women
         IRON EXCRETION
• There is probably no control of iron
  excretion; loss from the body may depend
  on the ferritin iron content of cells lost by
  desquamation, mostly into the intestinal
  tract and from the skin. The total daily loss
  by these routes is about 18 umol (1 mg).
  Urinary loss is negligible, reflecting the fact
  that all circulating iron is protein-bound.
     COMPARISON OF IRON LOSSES IN MEN AND MENSTRUATING/

                                PREGNANT WOMEN
               Source of loss     Extra loss       Daily extra loss   Daily total loss


Men and non    Desquamation       -                -                  18 umol (1 mg)
menstruating
women

Menstruating   Desquamation       290 umol (1 6    9 umol (0.5 mg)    27 umol (1.5 mg)
  women           +menstruati        mg)/month
  (mean value)    on


Pregnancy      Desquamation +     7000 umol (380   27 umol (1.5 mg) 45 umol (2.5 mg)
                  loss to fetus      mg)/9
                  and in             months
                  placenta

Male blood     Desquamation +     4500 umol (250   36 umol (2.0 mg) 54 umol (3.0 mg)
  donors          1 unit of          mg)/4
                  blood              months
     PATHOLOGICAL FACTORS AFFECTING
       PLASMA IRON CONCENTRATION
Iron deficiency and iron overload usually
  cause low and high plasma iron
  concentrations respectively.
• Iron deficiency is associated with a
  hypochromic, microcytic anemia and with
  reduced amounts of stainable bone marrow
  iron. Plasma ferritin concentrations are
  usually, but not always, low.
• Iron overload is associated with increased
  amounts of stainable iron in liver biopsy
  specimens and plasma ferritin conc are
  high.
       PATHOLOGICAL FACTORS
       AFFECTING PLASMA IRON
            CONCENTRATION
Other pathological factors
• Any acute or chronic illness, even a
  bad cold
• Disorders in which the marrow cannot
  use iron, either because it is
  hypoplastic, or because some other
  essential erythropoietic factor, such as
  vitamin B12 or folate, is deficient;
• Hemolytic anemia.
• Acute liver disease.
 Transferrin and Total Iron-binding
          Capacity (TIBC)
• Plasma iron concentrations alone give no
  information about the state of iron stores.
• Diagnostic precision may sometimes be
  improved by measuring both the plasma
  transferrin and iron concentrations.
• The total iron-binding capacity (TIBC). Is
  usually a valid measure of the transferrin
  concentration.
 PHYSIOLOGICAL CHANGES IN THE PLASMA
     TRANSFERRIN CONCENTRATION
• The plasma transferrin concentration is
  less labile than that of iron. However, it
  rises:
   – After about the 28th week of pregnancy
     even if iron stores are normal;
   – In women taking some oral
     contraceptive preparations;
   – In any patient treated with estrogens.
        THE PLASMA TRANSFERRIN
       PATHOLOGICAL CHANGES IN
              CONCENTRATION
Plasma transferrin concentration and TIBC:
• Rise in iron deficiency and fall in iron
  overload
• Fall in those chronic illnesses associated
  with low plasma iron concentrations
• are unchanged in acute illness
• May be very low in the nephrotic
  syndrome
    SYNDROMES OF IRON
        OVERLOAD
• IDIOPATHIC HAEMOCHROMATOSIS

• ANAEMIA AND IRON OVERLOAD

• DIETARY IRON OVERLOAD

• INAPPROPIATE ORAL THERAPY
        IRON OVERLOAD
• CAUSES OF IRON OVERLOAD
• Increased intestinal absorption:
   –idiopathic haemochromatosis;
   –anemia with increased, but
    ineffective, erythropoiesis;
   –liver disease (rare cause);
   –dietary excess;
   –inappropriate oral therapy.
        CONSEQUENCES OF IRON
             OVERLOAD
• Parenchymal iron overload occurs in
  idiopathic haemochromatosis and in
  patients with ineffective erythropoiesis. Iron
  accumulates in the parenchymal cells of the
  liver, pancreas, heart and other organs
  resulting in impairment of these organs &
  diabetes mellitus, hepatic carcinoma.
• Reticuloendothelial iron overload is seen
  after excessive parenteral administration of
  iron or multiple blood transfusions. The iron
  accumulates initially in the R.E cells of the
  liver, spleen and bone marrow.
        CONSEQUENCES OF IRON
               OVERLOAD
• Haemosiderosis is a histological
  definition. An increase in iron stores as
  haemosiderin can be seen. It does not
  necessarily mean that there is an
  increase in total body iron; for example,
  in many types of anemia there is
  reduced hemoglobin iron (less
  hemoglobin) but increased storage
  iron.

• Haemochromatosis describes the
  clinical disorder due to parenchymal
  iron-induced damage.
TRACE ELEMENTS
   CHROMIUM
                     CHROMIUM
RDA      Functions       Metaboli Deficiency Toxicity
                          sm       disease disease
50 –     Trivalent       Not well   Impaired Not
200      chromium, a     defined    tolerance known
ug (1-   constituent                secondary
4u       of “Glucose                to
mol )    Tolerance                  parenteral
         Factor”,                   nutrition,
         helps in                   decrease
         binding of                 sensitivity
         Insulin to                 of tissues
         target tissue              to insulin

				
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posted:7/25/2012
language:English
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