PRINCIPLES OF TOXICOLOGY

560 GLOSSARY
cytokinesis The division of the cytoplasm of a cell following the division of the nucleus.
cytoplasm The protoplasm of a cell exclusive of the nucleus, consisting of a continuous aqueous
solution (cytosol) and the organelles and inclusions suspended in it (phaneroplasm); the site of most
of the chemical activities of the cell.
cytosol The liquid medium of the cytoplasm (i.e., cytoplasm minus organelles and nonmembranous
insoluble components).
dalton A unit of mass, one-twelfth the mass of the carbon-12 atom. Carbon-12 has a mass of 12.011,
and thus the dalton is equivalent to 1.0009 mass units, or 1.66 × 10 –24 g. Also called the atomic
mass unit (amu).
denaturation The destruction of the usual nature of a substance, usually the change in the physical
properties of proteins caused by heat or certain chemicals.
depolarize Loss of the ionic gradient across a nerve cell membrane, resulting in an action potential
and propagation of a nerve impulse.
dermatitis Inflammation of the skin. Contact dermatitis is a delayed allergic skin reaction resulting
from contact with an allergen. Irritant dermatitis describes irritation of the skin accompanying
exposure to a toxic substance.
detoxification The metabolic process by which the toxic qualities of a poison or toxin are reduced
by the body.
diethylstilbestrol (DES) A synthetic estrogenic compound, C18H20O2, prepared as a white odorless
crystalline powder.
dimethyl sulfoxide (DMSO) An alkyl sulfoxide, C2H6OS, practically colorless in its purified form.
As a highly polar organic liquid, it is a powerful solvent, dissolving most aromatic and unsaturated
hydrocarbons, organic compounds, and many other substances.
diplopia A condition in which a single object is perceived as two objects; double vision.
direct carcinogen See primary carcinogen.
dissociation constant The equilibrium constant for the reaction by which a weak acid compound is
dissociated into hydrogen ions and a conjugate base, in solution. See also pK.
distal alveolar region The part of the lung composed of the alveoli, or tiny air sacs, through which
gas exchange between alveolar air and blood takes place.
DMSO See dimethyl sulfoxide.
dose The amount of a drug needed at a given time to produce a particular biologic effect. In toxicity
studies it is the quantity of a chemical administered to experimental animals at specific time
intervals. The quantity can be further defined in terms of quantity per unit weight or per body surface
area of the test animal. Sometimes the interval of time over which the dose is administered is part
of the dose terminology. Examples are: grams (or milligrams) per kilogram of body weight (or per
square meter of body surface area).
dose–response relationship One of the most basic principles of both pharmacology and toxicology.
It states that the intensity of responses elicited by a chemical is a function of the administered dose
(i.e., a larger dose produces a greater effect than a smaller dose, up to the limit of the capacity of
the biologic system to respond).
drug-induced toxicity Toxicities that are “side effects” to the intended beneficial effect of a drug.
They represent pharmacologic effects that are undesirable but that are known to accompany
therapeutic doses of the drug.
dyscrasia A morbid general state resulting from the presence of abnormal material in the blood.
dysplasia Abnormal development or growth of tissues, organs, or cells.
dyspnea Difficult or labored breathing.
dysrhythmia Disturbances of rhythm, such as speech, brain waves, and heartbeat.