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adrenaline a·dren·a·line (ə-drěn'ə-lĭn)
Note: Adrenaline plays a very large role in the fight or flight reaction, which refers to the various processes that occur within the body when it is confronted with some form of mental or physical stress.
Note: Figuratively, the term adrenaline is used in speaking of a high state of excitement: “When the race began, the adrenaline really started pumping.”
two separate but related hormones secreted by the medulla of the adrenal glands. They are also produced at the ends of sympathetic nerve fibres, where they serve as chemical mediators for conveying the nerve impulses to effector organs. Chemically, the two compounds differ only slightly; and they exert similar pharmacological actions, which resemble the effects of stimulation of the sympathetic nervous system. They are, therefore, classified as sympathomimetic agents. The active secretion of the adrenal medulla contains approximately 80 percent epinephrine and 20 percent norepinephrine; but this proportion is reversed in the sympathetic nerves, which contain predominantly norepinephrine.