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norepinephrine
(redirected from levarterenol)

   Also found in: Medical, Wikipedia 0.04 sec.
norepinephrine (nôr'ĕpīnĕf`rən), a neurotransmitter neurotransmitter, chemical that transmits information across the junction ( synapse ) that separates one nerve cell (neuron) from another nerve cell or a muscle. Neurotransmitters are stored in the nerve cell's bulbous end (axon).
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 in the catecholamine catecholamine (kăt'əkôl`əmēn)
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 family that mediates chemical communication in the sympathetic nervous system, a branch of the autonomic nervous system. Like other neurotransmitters, it is released at synaptic nerve endings to transmit the signal from a nerve cell to other cells. Norepinephrine is almost identical in structure to epinephrine epinephrine (ĕp'ənĕf`rīn), hormone important to the body's metabolism, also known as adrenaline.
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, which is released into the bloodstream from the adrenal medulla under sympathetic activation. The sympathetic nervous system functions in response to short-term stress; hence norepinephrine and epinephrine increase the heart rate as well as blood pressure. Other actions of norepinephrine include increased glycogenolysis (the conversion of glycogen glycogen (glī`kəjən)
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 to glucose glucose, dextrose, or grape sugar, monosaccharide sugar with the empirical formula C6H12O6 .
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) in the liver, increased lipolysis (the conversion of fats to fatty acids; see fats and oils fats and oils, group of organic substances that form an important part of the diet and also are useful in many industries. The fats are usually solid, the oils generally liquid at ordinary room temperatures.
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) in adipose (fat) tissue, and relaxation of bronchial smooth muscle to open up the air passages to the lungs. All of these actions represent a mobilization of the body's resources in order to meet the stressful challenge—such a response is often termed the "flight or fight" syndrome.

norepinephrine

 or noradrenaline

One of two catecholamine hormones (epinephrine is the other) secreted by the adrenal glands, as well as at nerve endings, as a neurotransmitter. It resembles adrenaline chemically and in its actions on the body, which mimic sympathetic nervous system stimulation. It constricts most blood vessels and is given for certain types of shock. Norepinephrine is formed from tyrosine and converted to epinephrine. It was discovered by Ulf von Euler-Chelpin (1905–83) in the mid-1940s.


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