Antioxidative System
Oxygen is a double-edged sword. We cannot live without oxygen but at same time we are continuously exposed to oxygen toxicity. However molecular oxygen is neither very reactive nor very toxic. The apparent toxicity of oxygen is actually due to free oxygen radicals formed by partial reduction of molecular oxygen. Moreover, a free radical of any species is capable of independent existence (hence term free). Generally enhanced reactivity of free radicals over more stable molecules result from the fact that more energy is required, for example, to maintain two separate species with an unpaired electron than to allow them to come together and share electrons such that a filled molecular orbital is formed, eventually with formation of a covalent bond. Moreover, the reactivity of free radical is inversely related to stability. Free radicals are produced in the body as by-products of normal cellular metabolic activities such as prostaglandin synthesis, mitochondrial electron transport, endoplasmic reticulum enzyme activity, oxyhaemoglobin, autooxidation and phagocytosis as well as when exposed to environmental pollutants, drugs, pesticides and ionizing radiation producing severe damaging effects on body tissues. Normally a balance is maintained between the oxidative attack of free radicals and the antioxidative defence system prevailing in the cells and tissues of our body, but when the balance is tilted more towards generation of free radicals then degenerative changes set in causing many degenerative diseases. The most important reduction of free radicals in aerobic cells involve molecular oxygen and its radical derivatives (superoxide radical O2-). Moreover rate of univalent pathway and the consequent formation of free radical is significantly increased by uncoupled of oxidative phosphorylation, hyperbaric oxygen treatment and in various pathophysiological conditions such as inflammatory immunologic disorders, metabolism of drugs and alcohol, exposure to UV and...
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