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 (N) [ni´tro-jen]
a chemical element, atomic number 7, atomic weight 14.007. (See Appendix 6.) It is a gas constituting about four-fifths of common air; chemically it is almost inert. It is not poisonous but is fatal if breathed alone because of oxygen deprivation. It is soluble in the blood and body fluids, and can cause serious symptoms when released as bubbles of gas by rapid decompression (see bends). Nitrogen occurs in proteins and amino acids and is thus present in all living cells.
nitrogen 13 a radioactive isotope of nitrogen having a half-life of 9.97 minutes and decaying by positron emission; it is used as a tracer in positron emission tomography.
nitrogen balance the state of the body in regard to the rate of protein intake and protein utilization. When protein is metabolized, about 90 per cent of its nitrogen is excreted in the urine in the form of urea, uric acid, creatinine, and other nitrogen end-products. The remaining 10 per cent of the nitrogen is eliminated in the feces. A negative nitrogen balance occurs when more protein is used by the body than is taken in. A positive nitrogen balance implies a net gain of protein in the body. Negative nitrogen balance can be caused by such factors as malnutrition, debilitating diseases, blood loss, and glucocorticoids. A positive balance can be caused by exercise, growth hormone, and testosterone.
liquid nitrogen nitrogen in liquid form, i.e., below −195.79°C; used as a coolant, such as in thermographic equipment.
nitrogen mustards a group of toxic, blistering alkylating agents that are cell cycle phase nonspecific; it includes nitrogen mustard itself (mechlorethamine hydrochloride), chlorambucil, cyclophosphamide, ifosfamide, and melphalan. Some have been used as antineoplastic agents in certain forms of cancer; they do not cure these conditions, but ease their effects by destroying mitotic cells (those newly formed by division), thereby affecting malignant tissue in its early stage of development, and leaving normal tissue unaffected. They are especially useful in treatment of leukemia, in which they reduce the leukocyte count, and in cases in which the malignant disease is widespread throughout the body and therefore cannot be effectively treated locally by surgery or radiotherapy. In cases of lung cancer, mechlorethamine hydrochloride is usually injected directly into the lungs via the pulmonary circulation. Side effects, which tend to limit the usefulness of these drugs, include nausea, vomiting, and a decrease in bone marrow production.
nonprotein nitrogen (NPN) the nitrogenous constituents of the blood exclusive of the protein bodies, consisting of the nitrogen of urea, uric acid, creatine, creatinine, amino acids, polypeptides, and an undetermined part known as rest nitrogen. Measurement of this is used as a test of renal function, but has been largely replaced by measurement of specific substances, such as urea and creatinine.
nitrogen washout test a test for vital capacity of lungs; with the patient inhaling pure oxygen, the volume of exhaled nitrogen is obtained for each breath until it falls below 1 per cent of the gas being exhaled (usually about seven minutes' time); the total volume of nitrogen that has been exhaled at this point is assumed to be 0.8 of the vital capacity.
nitrogen washout test, single breath the patient inhales a vital capacity's volume of pure oxygen and then slowly exhales. The nitrogen content of the exhalation is measured over the entire breath and a curve is generated; different parts of the curve represent nitrogen concentrations of gas in different components of the total lung capacity, and can be analyzed for irregularities. Called also single breath test.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

ni·tro·gen (N),

1. A gaseous element, atomic no. 7, atomic wt. 14.00674; N2 forms about 78.084% by volume of the dry atmosphere.
2. The molecular form of nitrogen, N2.
3. Pharmaceutical grade N2, containing not less than 99.0% by volume of N2; used as a diluent for medicinal gases, and for air replacement in pharmaceutical preparations.
[L. nitrum, niter, + -gen, to produce]
Farlex Partner Medical Dictionary © Farlex 2012


A gaseous element (atomic number 7; atomic weight 14.01) that is present in biological systems either as the molecular form, N2, or bound to other elements, such as oxygen (i.e., nitric oxide, a neurotransmitter). Nitrogen is critical to all biological systems and is present in proteins and DNA.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


1. A gaseous element; atomic no. 7, atomic wt. 14.00674; forms about 78.084% by volume of the dry atmosphere.
2. The molecular form of nitrogen, N2.
3. Pharmaceutical grade N2, containing not less than 99.0% by volume of N2; used as a diluent for medicinal gases, and for air replacement in pharmaceutical preparations.
[L. nitrum, niter, + -gen, to produce]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(ni'tro-jen) [ nitro- + -gen] N
A colorless, odorless, tasteless, gaseous chemical element, atomic weight (mass) 14.0067, atomic number 7. It occurs free in the atmosphere and forms approx. 80% of the volume of the atmosphere.
CAS # 7727-37-9

A component of all proteins, nitrogen is essential to plant and animal life for tissue building. Generally it is found organically only in the form of compounds such as ammonia, nitrites, and nitrates. These are transformed by plants into proteins and, being consumed by animals, are converted into animal proteins of the blood and tissues.

nitrogen dioxide

NO2, a toxic greenhouse gas, produced primarily by the combustion of fossil fuels. It is a powerful oxidant that can cause lung injury when inhaled at high concentrations.
CAS # 10102-44-0
Enlarge picture

liquid nitrogen

Nitrogen cooled to 77K (77°C above absolute zero). Liquid nitrogen is used to cool or freeze body parts, esp. the skin, in anesthesia and some surgeries. See: illustration

nitrogen monoxide

Nitric oxide.

nonprotein nitrogen

Compounds in animal nutrition that can be converted to nitrogen sources in ruminant animals. Urea, biuret, and ammonia are three examples.
Medical Dictionary, © 2009 Farlex and Partners


An inert, colourless and odourless gas constituting about 80% of the atmosphere. The element is present in all proteins and occurs in the urine in the form of urea. Under pressure, considerable nitrogen will dissolve in the blood. The release of gaseous nitrogen in the blood in bubbles that can block small arteries is the chief danger in too sudden decompression in divers.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


A gaseous element that makes up the base pairs in DNA.
Mentioned in: Gene Therapy
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


(N) (nī'trŏ-jĕn)
A gaseous element that forms about 78.084% by volume of dry atmosphere; used as a diluent for medicinal gases, and for air replacement in pharmaceutical preparations.
[L. nitrum, niter, + -gen, to produce]
Medical Dictionary for the Dental Professions © Farlex 2012
References in periodicals archive ?
With the state's environment burdened by noxious air and noise pollution emitted from the continually increasing volume of traffic on its highways, the New Jersey Department of Transportation (NJ DOT), Office of Transportation Technologies, with considerable support from Rutgers, The State University of New Jersey, set out to pursue the long-term goal of solving its air quality problems through the development and employment of advanced vehicle and power technologies.
The "get-government-off-our-backs" types have brought us noxious air, acid rain, toxic dump sites, tainted meats, poisonous water.
Many residents have been wounded by the noxious air, enduring bloody noses, respiratory wheezes, even cancer.
The noxious air, the noise, and the heat are all health hazards that further justify people's apprehensions.
One sure way to foment a border dispute is to complain that your neighbor is sending noxious air pollutants in your direction.