The rapid physiological cascade initiated by the release of the catecholamine norepinephrine (noradrenaline) from sympathetic nerve terminals and the adrenal medulla, serving as a primary effector of the “fight or flight” stress response. This response is characterized by immediate, widespread systemic effects, including increased heart rate, elevated blood pressure, enhanced vigilance, and rapid mobilization of energy substrates. It is a critical component of the body’s acute defense and arousal system, mediated by the Sympathetic-Adreno-Medullar (SAM) axis.
Origin
Norepinephrine was one of the earliest identified neurotransmitters, recognized for its potent and immediate effects on the cardiovascular system and behavioral alertness. The term Norepinephrine Response emphasizes the total physiological effect resulting from its rapid release and widespread action. In endocrinology, it is consistently studied in conjunction with epinephrine and cortisol as a key biomarker of acute and chronic stress load, reflecting the rapid-acting limb of the stress axis.
Mechanism
Upon the perception of a stressor, the hypothalamus rapidly activates the sympathetic nervous system, which immediately releases norepinephrine directly onto target organs via postganglionic neurons. Concurrently, the adrenal medulla releases both norepinephrine and epinephrine into the bloodstream, where they function as systemic hormones. These catecholamines bind to alpha- and beta-adrenergic receptors on target cells, driving immediate physiological changes, such as lipolysis for energy mobilization and peripheral vasoconstriction, preparing the organism for immediate, vigorous action.
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