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Medical Dictionary


nicotine (nik′o-ten)
1-Methyl-2-(3-pyridyl)pyrrolidine;a poisonous volatile alkaloid derived from tobacco (Nicotiana spp.) and responsible for many of the effects of tobacco; it first stimulates (small doses), then depresses (large doses) at autonomic ganglia and myoneural junctions; its principal urinary metabolite is cotinine. N. is an important tool in physiologic and pharmacologic investigation, is used as an insecticide and fumigant, and forms salts with most acids. SEE ALSO: tobacco. [Nicotiana, genus name of botanical source, + - ine] N. in inhaled tobacco smoke or in smokeless tobacco applied to buccal or nasal mucosa enters the circulation within seconds, causing an increase in heart rate, ventricular stroke volume, and myocardial oxygen consumption, as well as euphoria, heightened alertness, and a sense of relaxation. N. use is powerfully addictive, readily leading to habituation, tolerance, and dependency. Withdrawal from n. causes restlessness, irritability, anxiety, difficulty concentrating, and craving for n.. Addiction to n. is the reason for most tobacco use and is thus directly responsible for the resulting morbidity and mortality.

nicotinehydroxamic acid methiodide (nik′o-ten-hi′drok-sam′ik as′id me-thi′o-did)
An effective cholinesterase reactivator, with actions that are most marked at the skeletal neuromuscular junction; antidotal effects are less striking at autonomic effector sites and insignificant in the central nervous system.

nicotinic (nik-o-tin′ik)
Relating to the stimulating action of acetylcholine and other nicotine-like agents on autonomic ganglia, adrenal medulla, and the motor end-plate of striated muscle.

nicotinic acid
Pyridine-3-carboxylic acid;a part of the vitamin B complex; used in the prevention and treatment of pellagra, as a vasodilator, and in hyperlipidemia, where it lowers cholesterol and acts as an HDL-raising agent. SYN: anti–black-tongue factor, antipellagra factor, niacin, pellagra-preventing factor, vitamin PP.

nicotinic acid amide
SYN: nicotinamide.

nicotinic alcohol
SYN: nicotinyl alcohol.

nicotinomimetic (nik-o-tin′o-mi-met′ik)
Mimicking the action of nicotine.

nicotinyl alcohol (nik-o-tin′il)
Same action and use as nicotinyl tartrate. SYN: nicotinic alcohol.

nicotinyl tartrate
A relatively weak peripheral vasodilator related to nicotinic acid; used in peripheral vascular disorders such as Raynaud disease, acrocyanosis, and chilblains.

nicoumalone (ni-koo′ma-lon)
SYN: acenocoumarol.

nictation (nik-ta′shun)
SYN: nictitation.

nictitate (nik′ti-tat)
To wink. [see nictitation]

nictitation (nik-ti-ta′shun)
Winking. SYN: nictation. [L. nicto, pp. -atus, to wink, fr. nico, to beckon]

nidal (ni′dal)
Relating to a nidus, or nest.

nidation (ni-da′shun)
Embedding of the early embryo in the uterine endometrium. [L. nidus, nest]

Abbreviation for non-insulin-dependent diabetes mellitus.

nidogen (ni′do-jen)
SYN: entactin. [L. nidus, nest, + -gen 1.]

nidus, pl .nidi (ni′dus, ni′di)
1. A nest. 2. The nucleus or central point of origin of a nerve. 3. A focus of infection. 4. The nucleus of a crystal; the coalescence of molecules or small particles that is the beginning of a crystal or similar solid deposit. 5. The focus of reduced density at the center of an osteoid osteoma, on bone radiographs. [L. nest] n. avis a deep depression on each side of the inferior surface of the cerebellum, between the uvula and the biventral lobe, in which the tonsil rests. SYN: n. hirundinis. [L. bird's nest] n. hirundinis SYN: n. avis. [L. swallow's nest]

Albert, German physician, 1880–1921. See N.-Pick cell, N.-Pick disease, N. disease, N. splenomegaly.

Gaston H., 19th century French scientist. See N. rays, under ray.

nifedipine (ni-fed′i-pen)
A calcium channel-blocking agent of the dihydropyridine type; coronary vasodilator.

nifenazone (ni-fen′a-zon)
An analgesic and antipyretic.

nifuraldezone (ni-fur-al′de-zon)
An antibacterial agent.

nifuratel (ni-fu′ra-tel)

nifuroxime (ni-fu-rok′sem, -sim)
A furan derivative, principally effective against Candida albicans.

nigerose (ni′je-ros)
A disaccharide obtained by the hydrolysis of amylopectins, consisting of two d-glucose residues bound in an α1–3 linkage. [fr. nigeran, a polysaccharide synthesized by Aspergillus niger]

nightguard (nit′gard)
A device used to stabilize the teeth and reduce the traumatic effects of bruxism.

Florence, 1820-1910. English nurse; founder of modern nursing.

nightmare (nit′mar)
A terrifying dream, as in which one is unable to cry for help or to escape from a seemingly impending evil. SEE ALSO: incubus, succubus. [A.S. nyht, night, + mara, a demon]

nightshade (nit′shad)
Any of a number of plants of the genus Solanum (family Solanaceae) and of some other genera of the family Solanaceae. deadly n. SYN: belladonna.

night terrors (nit′tar-erz)
A disorder occurring in children, in which the child awakes screaming with fright, the distress persisting for a time during a state of semiconsciousness. SYN: pavor nocturnus, sleep terror.

nigra (ni′gra)
In neuroanatomy, the substantia n.. [L. fr. niger, black]

nigrities (ni-grish′i-ez)
A black pigmentation. [L. blackness, fr. niger, black] n. linguae SYN: black tongue.

nigrosin, nigrosine (ni′gro-sin, -sen) [C.I. 50420]
A variable mixture of blue-black aniline dyes; used as a histologic stain for nervous tissue and as a negative stain for studying bacteria and spirochetes; also used to discriminate between live and dead cells in dye-exclusion staining.

Nigrospora (ni-gros′por-a)
A genus of rapidly growing fungi that produces shiny, black conidia in cultures; it is a common contaminant in laboratory cultures and is nonpathogenic for humans.

nigrostriatal (ni′gro-stri-a′tal)
Referring to the efferent connection of the substantia nigra with the striatum. See substantia nigra.

Abbreviation for National Institutes of Health (U.S. Public Health Service).

nihilism (ni′i-lizm, ni′hi-lizm)
1. In psychiatry, the delusion of the nonexistence of everything, especially of the self or part of the self. 2. Engagement in acts that are totally destructive to one's own purposes and those of one's group. [L. nihil, nothing] therapeutic n. a disbelief in the efficacy or value of therapy, as of drugs, psychotherapy, etc.

nikethamide (ni-keth′a-mid)
Drug that acts mainly on the central nervous system, as a respiratory and cardiovascular stimulant.

Mikhail, Russian dermatologist, 1858–1915. See N. method.

Pyotr V., Russian dermatologist, 1858–1940. See N. sign.

Nile blue A [C.I. 51180]
A basic oxazin dye, used as a fat and vital stain, and in Kittrich stain; as an indicator, it changes from blue to purplish red at pH 10–11.

nimodipine (ni-mo′di-pen)
A calcium channel blocking drug of the dihydropyridine series used as a vasodilator.

nimustine (ni′mus-tin)
A nitrosourea antineoplastic similar to carmustine (BCNU)

ninhydrin (nin-hi′drin)
Reacts with free amino acids to yield CO2, NH3, and an aldehyde, the NH3 produced yielding a colored product (diketohydrindylidene-diketohydrinamine, a bi-indanedione derivative). SEE ALSO: n. reaction.

niobium (Nb) (ni-o′be-um)
A rare metallic element, atomic no. 41, atomic wt. 92.90638, usually found with tantalum. [Niobe, daughter of Tantalus]

nipple (nip′l) [TA]
A wartlike projection at the apex of the breast on the surface of which the lactiferous ducts open; it is surrounded by a circular pigmented area, the areola. SYN: papilla mammae [TA] , mammilla (2) , papilla of breast, teat (1) , thele, thelium (3) . [dim. of A.S. neb, beak, nose (?)] accessory n. a supernumerary n. occurring on the mammary line. aortic n. colloquial term for the radiographic appearance of the left superior intercostal or accessory hemiazygos vein as a bump on the aortic knob.

niridazole (ni-rid′a-zol)
Used for the treatment of schistosomiasis, amebiasis, and dracontiasis.

nisin (ni′sin)
A polypeptide antibiotic produced by Streptococcus lactis; active against certain streptococci, Mycobacterium tuberculosis, Clostridium difficile, and other bacteria.

nisoldipine (ni-sol′di-pen)
A calcium channel blocker of the dihydropyridine series; used as an antihypertensive and antianginal agent.

Rudolf, Swiss surgeon, 1896–1981. See Collis-N. fundoplication, N. fundoplication, N. operation.

Franz, German neurologist, 1860–1919. See N. bodies, under body, N. degeneration, N. granules, under granule, N. substance, N. stain.

nit (nit)
1. The ovum or hatched egg of a body, head, or crab louse; the egg is attached to human hair or clothing by a layer of chitin. 2. A unit of luminance; a luminous intensity of 1 candela per square meter of orthogonally projected surface. [A.S. knitu]

Raissa, 19th century German physician. See N. layer, N. membrane, N. stria.

niter (ni′ter)
SYN: potassium nitrate. [G. nitron, soda, formerly not distinguished from potash] cubic n. SYN: sodium nitrate.

niton (ni′ton)
Archaic term for radon.

nitrate (ni′trat)
A salt of nitric acid.

nitrazepam (ni-tra′ze-pam)
A hypnotic and sedative of the benzodiazepine class.

nitrendipine (ni-tren′-di-pen)
A calcium channel blocker of the dihydropyridine series; used as an antihypertensive.

nitric acid (ni′trik)
A strong acid oxidant and corrosive. fuming n. contains about 91% n.; used as a caustic.

nitric oxide (NO&chmpnt;)
A colorless, radical-free gas that reacts rapidly with O2 to form other nitrogen oxides (e.g., NO2, N2O3, and N2O4) and ultimately is converted to nitrite (NO2−) and nitrate (NO3−); a gaseous mediator of cell-to-cell communication and potent vasodilator, formed from l-arginine in bone, brain, endothelium, granulocytes, pancreatic beta cells, and peripheral nerves by a constitutive n. synthase, and in hepatocytes, Kupffer cells, macrophages, and smooth muscle by an inducible n. synthase (e.g., induced by endotoxin). NO&chmpnt; activates soluble guanylate cyclase, mediates penile erection, and may be the first known retrograde neurotransmitter.The short-lived NO&chmpnt; molecule is a product of various tissues and plays a role in various processes. NO&chmpnt; elaborated by endothelium, which is identical to endothelium-derived relaxing factor, dilates vessels by relaxing vascular smooth muscle; nitrites used in coronary and peripheral vascular disease induce or mimic this action. The 1998 Nobel Prize in Medicine or Physiology was awarded to 3 U.S. pharmacologists, Robert F. Furchgott, Ferid Murad, and Louis J. Ignarro, for their independent discoveries of the role of n. in cardiovascular physiology. In the immune system, macrophages use NO&chmpnt; as a cytotoxic agent. Deficiency or inactivation of NO&chmpnt; may contribute to the pathogenesis of both hypertension and atherosclerosis. An excess of NO&chmpnt;, which is a free radical, is toxic to brain cells, and NO&chmpnt; is also responsible for the precipitate, often fatal, drop in blood pressure accompanying septic shock. Free NO&chmpnt; in the bloodstream is rapidly reduced by the iron of hemoglobin. n. reductase an enzyme oxidizing N2 with some acceptor to 2NO&chmpnt;, a first step in the fixing of atmospheric nitrogen by bacteria. n. synthase (NO synthase) an enzyme that catalyzes the reaction of l-arginine with 2O2 and 1.5NADPH to form NO, l-citrulline, 1.5NADP+, and 2H2O; there are an inducible and two constitutive forms of this enzyme: the constitutive forms play significant roles in regulating vascular tone, tissue blood flow, renal function, etc.; in bone, brain, endothelium, granulocytes, pancreatic Z-cells, and peripheral nerves, the constitutive forms are calcium-calmodulin dependent; in brain, the enzyme is cytosolic; in endothelium, it is membrane bound; the inducible form of the enzyme ( e.g., by endotoxin) in hepatocytes, Kupffer cells, macrophages, and smooth muscle is not calmodulin dependent.

nitridation (ni-tri-da′shun)
Formation of nitrides; formation of nitrogen compounds through the action of ammonia (analogous to oxidation).

nitride (ni′trid)
A compound of nitrogen and one other element, e.g., magnesium n., Mg3N2.

nitrification (ni′tri-fi-ka′shun)
1. Bacterial conversion of nitrogenous matter into nitrates. 2. Treatment of a material with nitric acid.

nitrile (ni′tril)
An alkyl cyanide. Individual nitriles are named for the acid formed on hydrolysis; e.g., CH3CN is acetonitrile rather than methyl cyanide.

Prefix indicating a tervalent nitrogen atom attached to three identical groups; e.g., nitrilotriacetic acid, N(CH2COOH)3.

nitrimuriatic acid (ni′tri-mu-re-at′ik)
SYN: nitrohydrochloric acid.

nitrite (ni′trit)
A salt of nitrous acid.

nitrituria (ni-tri-too′re-a)
The presence of nitrites in the urine, as a result of the action of Escherichia coli, Proteus vulgaris, and other microorganisms that may reduce nitrates.

Prefix denoting the group –NO2. [G. nitron, sodium carbonate.]

nitrocellulose (ni-tro-sel′u-los)
SYN: pyroxylin.


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