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What are free radicals? How do they cause damage to humans?

Modern science believes that generation of free radicals inside cell is the triggering factor for diseases process in humans.

What are these free radicals?

Free radicals are unstable, free molecules of reactive oxygen species and reactive nitrogen species generated inside the human body. They labelled as incomplete atoms in the sense that they lack an electron attaching to them. Since they are unstable and freely wandering inside the cells, they react quickly with other compounds in their vicinity in order to capture "that" required electron to form a pair and become stable. This inclination and reaction of free radicals with different organelles inside a living cell leads to their structural damage. Once the rate of damage supersedes repair, disease process ensues in the form of depressed immunity, easy susceptibility to viruses and bacteria, cancers, cardio-vascular diseases, nerve degeneration, etc.

Free radical injury inside human cell
Human cell. Note for electron donation from antioxidant molecule.

Types of free radicals

Broadly, free radicals grouped into two major categories; Reactive oxygen species (ROS) and reactive nitrogen species (RNS). Reactive oxygen species comprises peroxides, hydroxyl radical, superoxide, oxybenzone, and hypochlorous molecules. Reactive Nitrogen species include nitric oxide, peroxyntrite, etc. Reactive oxygen species so far are the most powerful free radicals that directly attack cellular structures and DNA.

What triggers free radical production? Sources of free radicals.

In all the living organisms, different kinds of free radicals being produced constantly and spontaneously inside all the metabolically active cells. In fact, free radicals are resulting end product in response to active enzymatic cellular metabolism. They produce constantly inside lysosomes, mitochondria, peroxisoms and other enzymaically active structure inside the cells. Reactive oxygen species lead by hydroxyl radical is the most powerful endogenous oxidants. Apart from regular oxidants produced inside the body, plethora of exogenous agents initiate cascade of oxidation reactions upon gaining entry into the human body and come in contact with tissue cells. Solar radiation, air pollutants such as carbon monoxide, ozone, tobacco smoke, benzene, chlorine, formaldehyde toluene, exposure to ionizing radiation, consumption of medicines, heavy metals in food and water, Inhalation of chemical solvents such as cleaning products, paints, cosmetics, perfumes, pesticides, processed foods containing artificial flavorings, food color agents, trans fats, high levels of lipid peroxides, etc.,

Firstly, these free radicals generated when human body exposed to various stress conditions resulting in splitting up of water molecule to Hydroxyl and hydrogen ion molecules.

H2O= OH+ + H+

This OH+ (Hydroxyl) molecule is the most powerful of ROS.

Role of free radicals in human diseases

Inside the human cells, there is an effective anti-oxidant defence system to counter damaging actions of reactive oxygen species. Oxidative stress happens whenever free radicals take upper hand and shift the tide in their side, resulting in rampant and uncontrolled distress in cellular homeostasis. Most cells can withstand this damage to a limited extent by recognizing and removal of oxidatively damaged particles and repairing the structures.

Free radicals attack all the main cellular components. The extent of tissue damage depends upon the type of reactive species involved. Extensive damage can lead to death of the cell and part or whole of the tissue. Peroxidation of lipids in cell membranes can cause collapse of cell membranes and alter the function of membrane bound proteins such as enzymes and receptors. Direct damage to structural proteins and DNA inside the cells may result in loss of cell architecture and lack of its ability to restore.

What diseases free radicals cause in humans?

Oxidative damage to various structural components inside the cell is the most common reason for development of different disease manifestations in humans. Direct attack on chromosomes and DNA can cause mutation which when continue unregulated may lead to development of cancers. Endothelial damage inside the vessels can cause atherosclerosis, vascular blockade, loss of vessel integrity, bleeding, etc, can cause various cardiovascular diseases. Free radicals have also been attributed for cataracts, Alzheimer's disease, neuro-denerative diseases, kidney tubular dysfunction, connective tissue diseases, age-related eye disease, etc.

Role of anti-oxidants in prevention of Oxidant stress

While ROS continuously attack cell components, numerous natural and synthetic antioxidants engage in taming the oxidant fury by donating an electron and trap them and thereby rescuing organelles and DNA. Antioxidant enzymes like catalase, glutathione peroxidise, superoxide dismutase, etc participate in repair of structural components and restoration of cellular function in the aftermath of oxidant stress.

Several important vitamins like vitamin A, E and C, beta carotene acts as direct antioxidants. Vitamin- C acts at aqueous levels inside the cell.

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Visit here for very informative pages on:-


1. Free radicals, antioxidants and functional foods: Impact on human health.

2. About Free Radical Damage | HOPES - Stanford University.

3. Free Radicals and Their Role in Different Clinical Conditions:an overview. pdf.

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