radical
[rad´ĭ-kal]1. thorough or sweeping; directed to the cause or root of a morbid process.
2. a group of atoms that enters into and goes out of chemical combination without change and that forms one of the fundamental constituents of a molecule.
color radical chromophore.
free radical a radical that carries an unpaired electron; such radicals are extremely reactive, with a very short half-life.
oxygen radical a toxic metabolite of oxygen, such as superoxide or singlet oxygen, capable of damaging microorganisms and normal tissues.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
free rad·i·cal
a radical 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 radical nitric oxide, NO·, plays an important role in vasodilation.
and methyl 
Synonym(s): radical (4)
Free radicals are formed naturally as products of metabolic processes and can also be introduced from outside the body through smoking, inhaling environmental pollutants, or exposure to ultraviolet radiation. They interact readily with nearby molecules and may cause cellular damage, including genetic alterations. It has been theorized that they are involved in degenerative disorders such as Alzheimer dementia and parkinsonism, in plaque formation in atherosclerosis, and in cancer. 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 beta-carotene, also exert an antioxidant effect. see also antioxidant.
Farlex Partner Medical Dictionary © Farlex 2012
free radical
n.
An atom or group of atoms that has at least one unpaired electron and is therefore unstable and highly reactive. In animal tissues, free radicals can damage cells and are believed to accelerate the progression of cancer, cardiovascular disease, and age-related diseases.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
free radical
PhysiologyAny of a family of highly reactive molecules containing an unpaired electron in the outer orbital (e.g., the excited variants of O2). Free radicals cause random damage to structural proteins, enzymes, macromolecules and DNA; they play major roles in inflammation, hyperoxidation, post-ischaemic tissue damage, infarction and possibly also in carcinogenesis and tissue damage induced by organ transplantation. Free radical production is increased by cigarette smoking, radiation, UV light and chemical pollutants.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
free radical
Physiology Any of a family of highly reactive molecules containing an unpaired electron in the outer orbital–eg, the excited variants of O2; FRs cause random damage to structural proteins, enzymes, macromolecules, DNA, playing major roles in inflammation, hyperoxidation, post-ischemic tissue damage, infarction, possibly also CA and tissue damage in transplants. See Antioxidants, Free radical scavenger, Free radical theory Vox populi Freed radical A paroled political polemicist.McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
free rad·i·cal
(frē rad'i-kăl)A radical in its (usually transient) uncombined state; an atom or atom group carrying an unpaired electron and no charge. Free radicals may be involved as short-lived, highly active intermediates in various reactions in living tissue, notably in photosynthesis. The free radical nitric oxide, NO·, plays an important role in vasodilation.
Synonym(s): radical (4) .
Synonym(s): radical (4) .
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
free radical
an atom which has been ionized by radiation and from which electrons have been ejected as a result, leaving one or more unpaired electrons; such atoms react with other molecules e.g. DNA, and may cause damage or mutation.Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
Free radical
An unstable molecule that causes oxidative damage by stealing electrons from surrounding molecules, thereby disrupting activity in the body's cells.
Mentioned in: Smoking
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
free rad·i·cal
(frē rad'i-kăl)A radical in its (usually transient) uncombined state; an atom or atom group carrying an unpaired electron and no charge.
Synonym(s): radical (4) .
Synonym(s): radical (4) .
Medical Dictionary for the Dental Professions © Farlex 2012