nitrogen (N) /nī″trəjən/ [Gk, nitron, soda, genein, to produce] , a gaseous nonmetallic element. Its atomic number is 7; its atomic mass is 14.008. It exists as a diatomic molecule, N2. Nitrogen constitutes approximately 78% of the atmosphere and is a component of all proteins and a major component of most organic substances in living cells. Nitrogen is essential to the synthesis of necessary proteins, particularly nitrogen-containing compounds or amino acids derived directly or indirectly from plant food. Nitrogen follows a cycle from atmospheric gas into nitrogen-fixing bacteria, into green vascular plants, into humans and animals, and, by decay or in excreted nitrogenous wastes, as urea, back into the soil. Denitrifying bacteria in the soil break down nitrogenous compounds and release gaseous nitrogen. During a 24-hour period in a healthy individual the nitrogen excreted in the urine, feces, and perspiration, together with the nitrogen retained in dermal structures, such as the skin and hair, equals the nitrogen consumed in food and drink. The process of protein metabolism accounts for this nitrogen balance. When protein catabolism exceeds protein anabolism, the amount of nitrogen in the urine exceeds the amount of nitrogen consumed in foods, producing a negative nitrogen balance or a state of tissue wasting. A positive nitrogen balance exists in the body when the nitrogen intake in foods is greater than that excreted in urine. Conditions usually associated with positive nitrogen balance include those related to growth, pregnancy, and convalescence from a tissue-wasting illness. −nitrogenous, adj.
