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Free Radical Injury     

  1. Antioxidants: Vit A & C Q, Sulfhydryl containing compounds like cysteine & Glutathione
  2. Serum proteins: Albumin, Ceruloplasmin, TransferrinQ
  3. Enzymes: Superoxide Dismutase, Catalase, Glutathione PeroxidaseQ
  4. Inactivation of free radicals in the body
    1. Free radicals are generated through Fenton's reaction.
    2. In this reaction iron is converted from its ferrous to ferric form and a free radical is generated. i.e. (H2O2 +Fe2+ à Fe3+ + OH+ + OH-)
    3. Note :- H2O2 can also react with copper instead of iron to produce free radicals.
  5. Free radicals
  • Free radicals are chemical species that have a single unpaired electron in the outer orbit.
  • Most of these are partially reduced reactive oxygen forms that are produced as an unavoidable byproduct of mitochondrial respiration also known as reactive oxygen species.
  • The most important are hydrogen peroxide (H2O2), Superoxide anion (O2-) and hydroxyl radical (OH).
  • Free radicals are highly reactive species and toxic they can damage the cell membrane and nucleic acids.
  • Free radicals initiate autocatalytic reactions, whereby molecules with which they react are themselves converted into free radicals to propagate the chain of damage.
  • Free radicals are produced in several ways: -
  1. Ionizing radiations (UV rays, X-rays) can hydrolyze water into hydroxyl (OH) and hydrogen (H) free radicals.
  2. Enzymatic metabolism of exogenous chemicals, e.g., CCL4 can' generate CCL3.
  3. The reduction - oxidation reaction during normal metabolic process.
  • During normal respiration, molecular oxygen is sequentially reduced by addition of electron to generate water.
  • In this process small amount of H2O2 , O2 and OH- are produced.
  • H2O2 generated, can interact with O2 to generate OH through the Haber-weiss reaction.
  • H2O2 + O2 OH- + OH- + O2
  • Rapid burst of superoxide (O2-) occur in activated neutrophils during inflammation with the help of NADPH oxidase.
  • Some intracellular oxidases, e.g., xanthine oxidase generate superoxide radicals.
  1. Transition metal such as iron and copper donate or accept free electrons and catalyze free radical formation (e.g Fenton reaction).
  2. Nitric oxide (NO) generated in endothelium, macrophages and neurons can also act as free radical.
  1. Free radicals cause cell injury by -
    1. Lipid peroxidation and subsequent damage of cellular and mitochondrial membrane.
    2. Oxidative modification and subsequent degradation of intracellular proteins.
    3. DNA strand break.
  2. Following: information have been added in 8th/e of Robbins
  1. The traditional thinking about free radicals was that they cause cell injury and death by necrosis, and in fact, the production of reactive oxygen species (ROS) is a frequent prelude to necrosis.
  2. However, it is now clear that free radicals can trigger apoptosis as well.
Extra Edge :

*Imp. Note : If in a questions all the options are of antioxidants namely vit. c/selenium/ gluthiare and Vitamin. A. Than Vit A is odd one (as its not able to scavenge free radical effectively)


Cell Death


FIGURE 2 : Schematic representation of a normal cell and the changes in reversible and irreversible cell injury.

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