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 n., 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]
- blood urea n. (BUN) n., in the form of urea, in the blood; the most prevalent of nonprotein nitrogenous compounds in blood; blood normally contains 10–15 mg of urea/100 mL. Measurements in the laboratory are commonly used as a measure of renal function. SEE ALSO: urea n..
- filtrate n. nonprotein n. in various compounds that normally pass through the glomerular filtration or through a filter in the laboratory (after proteins are precipitated).
- heavy n. SYN: n.-15.
- nonprotein n. (NPN) the n. content of other than protein bodies; e.g., about one-half the nonprotein n. in the blood is contained in urea. SYN: rest n..
- rest n. SYN: nonprotein n..
- undetermined n. the n. of blood, urine, etc., other than urea, uric acid, amino acid s, etc., that can be directly estimated; in blood it amounts to about 25 mg/100 mL.
- urea n. the portion of n. in a biologic sample, such as blood or urine, that derives from its content of urea. SEE ALSO: blood urea n..
- urinary n. n. excreted as urea, amino acid s, uric acid, etc., in the urine; 1 g of urinary n. indicates the breakdown in the body of 6.25 g of protein. SEE ALSO: n. equivalent.

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ni·tro·gen 'nī-trə-jən n a common nonmetallic element that in the free form is normally a colorless odorless tasteless insoluble inert diatomic gas comprising 78 percent of the atmosphere by volume and that in the combined form is a constituent of biologically important compounds (as proteins, nucleic acids, and alkaloids) and hence of all living cells as well as of industrially important substances (as cyanides, fertilizers, dyes, and antibiotics) symbol N see ELEMENT (table)

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a gaseous element and a major constituent of air (79 per cent). Nitrogen is an essential constituent of proteins and nucleic acids and is obtained by animals in the form of protein-containing foods (atmospheric nitrogen cannot be utilized directly). Nitrogenous waste is excreted as urea. Liquid nitrogen is used to freeze some specimens before pathological examination. Symbol: N.

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ni·tro·gen (N) (niґtro-jən) [Gr. nitron niter + -gen] a colorless, gaseous element found free in the air; specific gravity, 0.9713; atomic number, 7; atomic weight, 14.007. It forms about four fifths of common air. Chemically it is almost inert, but it forms by combination of nitric acid and ammonia. It is important biologically, being a constituent of protein and nucleic acids and thus present in all living cells. It will not support respiration; although not a poison, it is fatal if breathed alone, because of the lack of oxygen. It is soluble in the blood and body fluids and when released as bubbles of gas by reduction of atmospheric pressure it causes serious or even fatal symptoms (see decompression sickness, under sickness). [NF] an official preparation, not less than 99 per cent N2 by volume; used to replace air in pharmaceutical preparations.

Medical dictionary. 2011.

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