Iron Metabolism Overview Quiz

Iron Metabolism Overview

• Iron is a trace element essential for proper growth, development, and physiology.
• It's the most important trace element.

Distribution of Iron in the Body

• 66% is in hemoglobin
• 6% is in myoglobin
• <1% is in Heme enzymes.
• 26% is in transport and storage forms.
• <1% is in iron-sulfur clusters

Biochemical Functions of Iron

• Essential for hemoglobin and myoglobin synthesis.
• Crucial for cytochromes (electron transport chain).
• Necessary for peroxidase synthesis (phagocytosis).
• Important for synthesizing non-heme iron compounds like succinate dehydrogenase and iron-sulfur proteins.
• Associated with effective immune function.

Iron Requirements

• Daily requirement is 15-20 mg.
• Only 2 mg of iron is normally absorbed.

Iron Sources

• Best sources: meat, eggs, salmon, tuna, liver, poultry.
• Lesser amounts are in dark leafy greens, fruits (apples), and whole grains.
• Animal sources are better absorbed than plant sources.

Iron Absorption

• Factors influencing absorption:
  • Facilitators: reducing agents (ascorbic acid, citrate), hydrochloric acid (HCl) in the stomach.
  • Inhibitors: phytates (in cereals), oxalates, tannic acid, antacids.
  • Competitors: calcium, manganese, zinc

Iron Metabolism (Cellular Level)

• Non-heme iron is reduced to ferrous form (Fe2+) for absorption.
• This is facilitated by ferric reductase enzymes like Dcytb1.
• It is then transported into the enterocyte using DMT1.
  • Some iron is stored as ferritin within the enterocyte.
• Hephaestin converts Fe2+ to Fe3+ at the basal surface.
• Fe3+ binds to transferrin for transport out of the enterocyte.

Iron Storage Forms

• Transferrin: protein carrier in circulation (e.g., from gut to bone marrow).
• Apotransferrin: transferrin not bound to iron.
• Ferritin: storage form in hepatocytes and enterocytes.
• Hemosiderin: aggregated ferritin overloaded with iron.

Iron Transport

• Iron is carried in Fe3+ form bound to transferrin.
• Transferrin is a plasma glycoprotein synthesized in the liver; it can carry two Fe3+ ions.
• Normally, 1/3 of circulating transferrin is fully saturated with iron.
• The transferrin-iron complex enters cells via specific receptors, and iron is released for metabolic functions.

Iron Levels in Blood

• Measuring iron and iron-binding capacity is crucial to diagnose deficiencies or overload.
• Serum iron alone isn't conclusive.
• Total Iron Binding Capacity (TIBC), and unsaturated iron-binding capacity (UIBC) are necessary tests.

Ferritin

• Primary iron storage protein in intestinal mucosa, liver, spleen, and bone marrow.
• Apoferritin can bind up to 4000 iron atoms to form ferritin.
• Has the ability to gain and release iron based on body's iron stores.

Hemosiderin

• Formed by partial degradation of ferritin due to iron overload.
• Found in liver, spleen, and bone marrow.
• Accumulates as brown aggregates in tissues when iron levels are high.

Iron Disorders

• Iron deficiency anemia: Causes: inadequate intake, impaired absorption, chronic blood loss, increased demand. Lab findings: decreased serum iron, increased TIBC.
• Iron overload (Hemosiderosis/Hemochromatosis): Causes: repeated attacks of hemolysis, repeated blood transfusions. Lab findings: increased serum iron, decreased TIBC, and increased ferritin.