- 1. In chemistry, a group of elements or atoms usually passing intact from one compound to another, but usually incapable of prolonged existence in a free state ( e.g., methyl, CH3); in chemical formulas, a r. is often distinguished by being enclosed in parentheses or brackets. 2. Thorough or extensive; relating or directed to the extirpation of the root or cause of a morbid process; e.g., a r. operation. 3. Denoting treatment by extreme, drastic, or innovative, as opposed to conservative, measures. 4. SYN: free r.. [L. radix (radic-), root]- free r. a r. in its (usually transient) uncombined state; an atom or atom group carrying an unpaired electron and no charge; e.g., hydroxyl and methyl Free radicals may be involved as short-lived, highly active intermediates in various reactions in living tissue, notably in photosynthesis. The free r. nitric oxide, NO, plays an important role in vasodilation. SYN: r. (4).Free radicals occur naturally within the body as a result of metabolic processes and can also be introduced from without (through smoking, inhaling environmental pollutants, or exposure to UV radiation). They interact readily with nearby molecules and may cause cellular damage, including genetic alterations. It has been theorized that they are involved in plaque formation in atherosclerosis, in cancer, and in degenerative disorders such as Alzheimer dementia and parkinsonism. Natural enzymes such as superoxide dismutase and peroxidase are thought to counteract free radicals, and there is evidence that many nutrients, including vitamins C and E and β-carotene, also exert an antioxidant effect. see also antioxidant.- oxygen-derived free radicals an atom or atom group having an unpaired electron on an oxygen atom, typically derived from molecular oxygen. For example, one-electron reduction of O2 produces the superoxide r., O2·; other examples include the hydroperoxyl r. (HOO·), the hydroxyl r. (HO·), and nitric oxide (NO·). These apparently have a role in reprofusion injury.
* * *rad·i·cal 'rad-i-kəl adj1) designed to remove the root of a disease or all diseased tissue <\radical surgery>2) involving complete removal of an organ <\radical prostatectomy> compare CONSERVATIVErad·i·cal·ly -i-k(ə-)lē advradical n FREE RADICAL also a group of atoms bonded together that is considered an entity in various kinds of reactions
* * *rad·i·cal (radґĭ-kəl) [L. radicalis] 1. directed to the cause; directed to the root or source of a morbid process, as radical surgery. 2. a group of atoms which enters into and goes out of chemical combination without change, and which forms one of the fundamental constituents of a molecule. Organic radicals are symbolized R.
Medical dictionary. 2011.