[Toxicity of oxygen, free radicals and defense mechanisms].

Oxygen is essential for the life of aerobic organisms as the terminal acceptor of electrons. Due to its high affinity for lone electrons it fosters radicular reactions and opposes recombinations of radicals after rupture of covalent linkages. Lipoperoxidation processes then occur, attacking the cellular membranes. These radicular reactions are at the origin of many pathological phenomena. A complex arsenal of endogenous protective agents is normally present in all cells to face up to the danger of lone electron structures in oxygenated media. Food and natural or synthetic pharmacological agents compensate for the deficiencies.