Norepinephrine, also known as noradrenaline, is a potent catecholamine that functions as both a hormone and a neurotransmitter within the central and peripheral nervous systems. As a hormone, it is primarily released from the adrenal medulla, playing a central role in the body’s sympathetic “fight-or-flight” response by increasing heart rate and mobilizing energy stores. As a neurotransmitter, it is essential for regulating vigilance, arousal, mood, and attention.
Origin
The name is derived from its chemical structure, being the N-demethylated form of epinephrine (adrenaline). The term is a key component of physiological and pharmacological nomenclature, defining one of the principal monoamines in the human body. Its discovery was integral to understanding the mechanisms of the autonomic nervous system.
Mechanism
Norepinephrine is synthesized from the amino acid tyrosine and acts by binding to various adrenergic receptors (α1, α2, β1, β2, β3) located on target cells throughout the body. In the adrenal medulla, its release is triggered by acetylcholine from preganglionic sympathetic fibers. This binding initiates a G-protein coupled signaling cascade that mediates physiological effects, such as vasoconstriction and increased glycogenolysis, thereby preparing the body for immediate action and maintaining cardiovascular homeostasis.
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