Webster's New World Medical Dictionary

NF1
Neurofibromatosis type 1.
NF2
Neurofibromatosis type 2.
NG tube
See 
nasogastric tube.
NHL
Non-Hodgkin’s lymphoma. See 
lymphoma,
non-Hodgkin’s.
niacin
Nicotinic acid, one of the water-soluble B
vitamins. See also Appendix C, “Vitamins.”
niacin deficiency
See 
pellagra.
nicotine
An alkaloid (a nitrogen-containing
chemical) made by the tobacco plant or produced
synthetically. Nicotine has powerful pharmacologic
effects (including increased heart rate, heart stroke
volume, and oxygen consumption by the heart mus-
cle), as well as powerful psychodynamic effects
(such as euphoria, increased alertness, and a sense
of relaxation). Nicotine is also powerfully addictive.
nicotinic acid
See 
niacin.
nictitate
To wink. For example, nictitating spasm
is spasm of the eyelid with continuous winking.
nidus
In medicine, any structure that resembles a
nest in appearance or function. From the Latin for
“nest.” A nidus is a breeding place where bacteria,
parasites, and other agents of a disease lodge and
develop. For example, a nidus of infection is a focus
of infection. A nidus is also the nucleus or origin of
a nerve. The nidus avis cerebelli is a deep sulcus
(groove) on each side of the inferior vermis (a
wormlike structure in the brain), separating it from
the adjacent lobes of the cerebral hemispheres.
Niemann-Pick disease
A group of inherited
biochemical disorders in which lipid (fat) accumu-
lates in the spleen, liver, lungs, bone marrow, and
the brain. Symptoms may include lack of muscle
coordination, brain degeneration, learning prob-
lems, loss of muscle tone, increased sensitivity to
touch, spasticity, feeding and swallowing difficulties,
slurred speech, and an enlarged liver and spleen.
Niemann-Pick disease is inherited in an autosomal
recessive manner. The classical form of the disease
has its onset in very early infancy, and death usually
occurs before age 3. Growth is retarded. Other fea-
tures are jaundice, hepatic (liver) failure, and ascites
(fluid in the abdomen). Eye hallmarks include a
“cherry red spot” in the macula in the center of the
retina and cloudy cornea. In the classic form, accu-
mulation of a substance called sphingomyelin is due
to deficiency of the enzyme sphingomyelinase.