​What is Pathology - What causes oxygen radicals to form?

​What is Pathology - What causes oxygen radicals to form?
During normal cellular respiration, oxygen radicals are generated in minute amounts. Natural antioxidants neutralise the oxygen radicals, which are then destroyed by protecting enzymes. If these natural defensive mechanisms fail, free radicals can build up to dangerous levels. Leukocytes, which utilise these reactive chemicals to destroy bacteria, also produce oxygen radicals.