PRINCIPLES OF TOXICOLOGY

GLOSSARY 567
necrosis Death of one or more cells, or of part of a tissue or organ, generally owing to irreversible
damage.
nematocyst A capsule within specialized cells of certain coelenterates, such as jellyfish, containing
a barbed, threadlike tube that delivers a paralyzing sting when propelled into attackers and prey.
neoplasm Literally, new growth, usually characterized by a random abnormal “immature,” meiosis-type
cell division and proliferation.
nephritis Inflammation of the kidney; a focal or diffuse proliferative or destructive process, which
may involve the glomerulus, tubule, or interstitial renal tissue.
neurodermatitis A nonspecific pruritic skin disorder presumed to result from prolonged vigorous
scratching, rubbing, or pinching, sometimes forming polymorphic lesions.
neuroendocrine Or, relating to, or involving the interaction between the nervous system and the
hormones of the endocrine glands.
neurofibril One of the delicate threads running in every direction through the cytoplasm of the body
of a nerve cell and extending into the axon and dendrites of the cell.
neuromuscular endplate A flattened discoid expansion at the neuromuscular junction, where a
myelinated motor nerve fiber joins a skeletal muscle fiber.
neuropathy General term denoting functional disturbances and/or pathologic changes in the nervous
system.
neutropenia A decrease in the number of neutrophilic leukocytes in the blood.
neutrophil A granular leukocyte having a nucleus with three to five lobes connected by slender
threads of chromatin and cytoplasm, containing fine, inconspicuous granules.
nicotinic effect Poisoning by nicotine or a compound related in structure or action, characterized by
stimulation (low doses) and depression (high doses) of the central and autonomic nervous systems.
In extreme cases, death results from respiratory paralysis. Also referred to as nicotinism.
nitrosamine Any of a group of n-nitroso derivatives of secondary amines. Some show carcinogenic
activity.
NOEL See no-observable-effect level.
noncompetitive inhibition Inhibition of enzyme activity by inhibitors that combine with the enzyme
on a site other than that utilized by the substrate; such inhibition may be irreversible or reversible.
nonspecific chemical action The action of a chemical, such as a strong acid or base or concentrated
solution of organic solvent, which occurs in all cells in direct proportion to the concentration in
contact with the tissue. This is a nonselective effect and its intensity is directly related to the
concentration of the chemical.
nonspecific receptor Secondary receptor within the body, which combine with or react with a
chemical; however, the function of the cell is not influenced by the product that is formed. Such
receptors are usually combining sites on proteins.
no-observable-effect level (NOEL) A measure of the toxicity of a substance, established by the
U.S. Environmental Protection Agency (USEPA); the level of a substance that, when administered
to a group of experimental animals, does not produce those effects observed at higher levels, and
at which no significant differences between the exposed animals and the unexposed or control
animals are observed.
olefin A class of unsaturated aliphatic hydrocarbons having one or more double bonds. Also called
alkene.
oncogenic Giving rise to tumors or causing tumor formation.
opsoclonus A condition characterized by rapid, irregular, nonrhythmic horizontal and vertical
oscillations of the eyes, observed in various disorders of the brainstem or cerebellum.
optic neuritis Inflammation of the optic nerve; it may affect the part of the nerve within the eyeball,
or the portion behind the eyeball.