| 释义 |
oxidative stress
oxidative stressn. A condition of increased oxidant production in animal cells characterized by the release of free radicals and resulting in cellular degeneration.EncyclopediaSeestressoxidative stress
stress [stres] 1. forcibly exerted influence; pressure.2. in dentistry, the pressure of the upper teeth against the lower.3. a state of physiological or psychological strain caused by adverse stimuli, physical, mental, or emotional, internal or external, that tend to disturb the functioning of an organism and which the organism naturally desires to avoid. stress reactions are elicited but should these reactions be inappropriate or inadequate, they may lead to disease states. The term is also used to refer to the stimuli that elicit such a state or stress reactions. Just as a bridge is structurally capable of adjusting to certain physical stresses, the human body and mind are normally able to adapt to the stresses of new situations. However, this ability has definite limits beyond which continued stress may cause a breakdown, although this limit varies from person to person.
Physical Stress. There are many kinds of physical stress, but they can be divided into two principal types, to which the body reacts in different ways. There is emergency stress, a situation that poses an immediate threat, such as a near accident in an automobile, a wound, or an injury. There is also continuing stress, such as that caused by changes in the body during puberty, pregnancy, menopause, acute and chronic diseases, and continuing exposure to excessive noise, vibration, fumes, chemicals, or other agents.
The body's reaction to emergency stress is set off by the adrenal medulla. The medulla of each adrenal gland is directly connected to the nervous system. When an emergency arises, it pours the hormone epinephrine into the bloodstream. This has the effect of speeding up the heart and raising the blood pressure, emptying sugar supplies swiftly into the blood, and dilating the blood vessels in the muscles to give them immediate use of this energy. At the same time, the pupils of the eyes dilate. (See also alarm reaction.)
The reaction of the body to continuing stress is even more complex. Again the principal organs are the adrenal glands, but after the first phase of alarm, the glands continue to produce a steady supply of hormones that apparently increase the body's resistance. This is in addition to specific defenses such as the production of antibodies to fight infection. If the stress is overwhelming, as in the case of an extensive third-degree burn or an uncontrollable infectious disease, the third phase, exhaustion of the adrenal glands, sets in, sometimes with fatal results.Psychologic Stress. The emergency response of the body comes into play when a person merely foresees or imagines danger, as well as in real emergency situations. The thought of danger, or the vicarious experience of it in a thrilling story, play, or film, may be enough to cause the muscles to tense and the heart to start pounding. Psychologic situations can have the same effect. One of the best-known examples of this is “stage fright,” often characterized by tensed muscles and an increased heart rate. At times the person may not even be aware of the unconscious thought that produces this dramatic reaction.Stress and Disease. In recent decades, there have been numerous attempts to find a direct correlation between certain diseases and a stressful environment or a personality type that responds to the environment in a certain way. However, while inappropriate activity and a hectic lifestyle can cause illness in some persons, a busy and productive person can actually be subject to less stress than one who feels trapped in a limited position with no hope for release or a sense of accomplishment.
The diseases most often associated with a stressful environment are, according to some scientists, coronary artery disease and “heart attack,” high blood pressure, and cancer. Studies of laboratory animals have demonstrated a connection between isolated and specific stimuli such as electric shock and separation from mates and the development of heart disease in these animals. The stressful variables in the human environment are, however, much more complex, and a stressful environment can be related to heart disease only as a risk factor (see type a behavior).
The postulated relationship between stress and the development of a malignancy is based on the theory that destructive emotions affect and in some way weaken the body's surveillance system, causing its immune response to fail to recognize and destroy malignant cells.
Although relaxation techniques can reduce blood pressure in persons with mild hypertension, there is no evidence that tension and stress cause the blood pressure to rise and stay at levels above normal.
Other diseases considered by some researchers to be related to stress include asthma, allergies, colitis, migraine headaches, and peptic ulcers. Even though the relationship is not clear and there are currently no hard data to support this, most health care providers are convinced that stress contributes to the worsening of symptoms and influences the impact a disease will have on the lives of some patients while other patients adapt to stress and seem to have no long-term deleterious reaction to it.Coping Mechanisms. Unhealthy ways to cope with psychologic stress include drug abuse and alcoholism, smoking, abusive and violent behavior, and working harder to accomplish unrealistic or poorly defined goals. In order to deal with stress in an effective and healthy way, one must first identify sources of stress, either within oneself or in one's environment.
Job stressors are frequently related to disorganization in the work place, poor time management, and unrealistic or uncommunicated expectations of the employer. Another source of stress for the working person may be the lack of time for family and recreation because of job demands. Once job stressors are identified, some options are to change the stressful situation, modify the way one responds to stressors, or seek another job that is less stressful. In some instances learning to be more assertive and better able to communicate with supervisors and coworkers can reduce job-related stress.
Stressors in the home environment include negative self-concept; inadequate physical, cognitive, or behavioral resources; poor problem-solving skills; marital discord; ineffective parenting or lack of parenting skills; and lack of family support. Effective coping may require strategies to improve self-concept and build self-esteem, develop problem-solving skills, learn effective parenting, and establish a network of people who can give support. Exercise, improving one's nutritional status, making time for recreational activities, and utilizing relaxation techniques to relieve tension can also be healthy ways to cope with stress.oxidative stress any of various pathological changes seen in living organisms in response to excessive levels of cytotoxic oxidants and radicals" >free radicals in the environment.stress reaction any of the biological reactions to adverse stimuli, physical, mental, or emotional, internal or external, that tend to disturb the organism's equilibrium; should these compensating reactions, physiological or psychological, be inadequate or inappropriate, they may lead to disorders. See alarm reaction, acute stress reaction, general adaptation syndrome, acute stress disorder, adjustment disorder, and posttraumatic stress disorder.oxidative stressn. A condition of increased oxidant production in animal cells characterized by the release of free radicals and resulting in cellular degeneration.oxidative stress The presence of oxygen free radicals, which are generated by various stressants–eg, tobacco, alcohol; the primary antioxidant is glutathione; other antioxidants include vitamins A, C, and E; ↑ oxidative stress may be one of the key factors in the early pathogenesis of AIDS in which the production of TNF ↑ the production of free radicals in T cells. See Free radicals. oxidative stress The widespread effects of oxygen FREE RADICALS on any part of the body.oxidative stress A term used to describe the effect of oxidation in which an abnormal level of reactive oxygen species (ROS), such as the free radicals (e.g. hydroxyl, nitric acid, superoxide) or the non-radicals (e.g. hydrogen peroxide, lipid peroxide) lead to damage (called oxidative damage) to specific molecules with consequential injury to cells or tissue. Increased production of ROS occurs as a result of fungal or viral infection, inflammation, ageing, UV radiation, pollution, excessive alcohol consumption, cigarette smoking, etc. Removal or neutralization of ROS is achieved with antioxidants, endogenous (e.g. catalase, glutathione, superoxide dismutase) or exogenous (e.g. vitamins A, C, E, bioflavonoids, carotenoids). Oxidative damage to the eye, particularly the retina and the lens, is a contributing factor to age-related macular degeneration and cataract.MedicalSeeo/s |