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the first stage of the general adaptation syndrome; the response of the sympathetic nervous system to either physical stress or a strong emotional state (see also stress reaction). It is an automatic and instantaneous response that increases the body's capability to cope with a sudden emergency. The physiologic changes that occur increase physical strength and mental activity. The blood pressure is elevated, the blood glucose level is raised for additional energy, the blood coagulates more readily, and the flow of blood to muscles needed for activity is increased, while those organs not needed for “fight” or “flight” receive a diminished blood supply. One of the most striking manifestations of this reaction is the involution of lymphoid tissues due to the action of adrenal hormones. Called also sympathetic stress reaction and fight-or-flight reaction.
fight-or-flight reactiona defence reaction or alerting response in higher animals, involving an increase in blood pressure and heart rate and a redistribution of the blood away from the viscera towards the STRIATED MUSCLE. These changes result from integrated nerve pathways in the brain known as defence centres, and from the secretion of ADRENALINE.
coordinated result of increased secretion of adrenal medullary hormones and of stimulation and resulting increased activity of the sympathetic nervous system. Creates the optimum situation for the survival of the individual by fighting the adversary or fleeing from it. The reaction comprises constriction of the blood vessels of alimentary tract and skin but dilatation of those to skeletal muscles; increased cardiac rate and output, and coronary dilatation occur; also elevation of the blood sugar levels and metabolic rate, dilatation of the pupils, evacuation of blood from the spleen, bronchodilatation, piloerection and decrease in coagulation time.