Dictionary

nitrosourea One of a group of anticancer drugs that can cross the blood–brain barrier.

nitroglycerin A medication used to dilate blood vessels and improve blood flow. Nitroglycerin has a rapid effect and is used to treat angina pectoris by increasing blood flow to the heart. Nitroglycerin tablets are taken sublingually (under the tongue). Also known as nitro, NTG.

nitrogenous base A molecule that contains nitrogen and has the chemical properties of a base. The nitrogenous bases in DNA are adenine (A), guanine (G), thymine (T), and cytosine (C). The nitrogenous bases in RNA are the same, with one exception: adenine (A), guanine (G), uracil (U), and cytosine (C).

nitrogen narcosis A condition similar to intoxication with alcohol characterized by euphoria, loss of balance and manual dexterity, disorientation, and impaired reasoning. It can occur in scuba divers below 30 meters (100 feet) who breathe compressed air, because of the high nitrogen content of air. Nitrogen narcosis is reversed as the gas pressure decreases and…

nipple, supernumerary An extra nipple. Supernumerary nipples are usually smaller than normal and vestigial (nonfunctional, without accompanying mammary glands). They tend to occur along a roughly curved line that extends from near the armpit, through the center of the normal breast, and down to the lower abdomen. This distribution is very similar to the location…

nipple absence See athelia.

nipple The pigmented projection on the surface of the chest in the male and the breast in the female. In the mature female, ducts that conduct milk from the mammary glands to the surface of the breast exit through the nipple. The surrounding flat area of pigmentation is the areola.

Nipah virus A member of the paramyxovirus family isolated from samples from an outbreak of encephalitis and respiratory illness among adult men in Malaysia and Singapore in 1999 that causes a sometimes fatal form of viral encephalitis. The humans were infected by close contact with infected pigs. Symptoms include high fever and aches, coma, and…

NIH National Institutes of Health.

night sweats Severe hot flashes that occur at night and result in a drenching sweat. Night sweats can have many different causes, including medications, infections, and cancers.

night eating syndrome An eating disorder estimated to affect between 1 percent and 2 percent of adults in which at least 50 percent of the daily food intake is consumed after dinner. Abbreviated NES. The causes of NES have not been understood, but an impaired circadian rhythm of food intake is believed to play a…

night blindness See nyctanopia.