PRINCIPLES OF TOXICOLOGY

556 GLOSSARY
aliphatic Organic compounds characterized by a straight- or branched-chain arrangement of the
constituent carbon atoms.
alkane See paraffin.
alkyl A chemical group obtained by removing a hydrogen atom from an alkane or other aliphatic
hydrocarbon.
alkylation The introduction of one or more alkyl radicals (e.g., methyl, CH3–; ethyl, C2H5–; propyl,
CH3CH2CH2–; etc.) by addition or substitution into an organic compound.
allele Either of the pair of alternative characters or genes found at a designated locus on a
chromosome. Chromosome pairing results in expression of a single allele at each locus.
allergy General or local hypersensitive reactions of body tissues of certain persons to certain
substances (allergens) that, in similar amounts and circumstances, are innocuous to other persons.
Allergens can affect the skin (producing urticaria), the respiratory tract (asthma), the gastrointestinal
tract (vomiting and nausea), or may result from injections into the bloodstream (anaphylactic
reaction). See also anaphylactic-type reaction.
alveolar macrophages Actively mobile, phagocytic cells that process particles ingested into the
lung. They originate outside the lungs from precursor cells (promonocytes) in the bone marrow
and from peripheral blood monocytes. They enter the alveolar interstices from the bloodstream and
are able to migrate to terminal bronchioles and lymphatic vessels.
alveolus (pl. alveoli) In the lungs, small outpouchings along the walls of the alveolar sacs, alveolar
ducts, and terminal bronchioles, through the walls of which gas exchange takes place between
alveolar air and pulmonary capillary blood.
amelia The congenital absence of a limb or limbs. See also phocomelia.
amidase An enzyme that catalyzes the breakdown of an amide compound to a carboxylic acid and
ammonia.
Ames assay A screening test capable of revealing mutagenic activity through reverse mutation in
Salmonella typhimurium. Mammalian metabolism can be simulated by addition of S9 liver enzyme
to the bacterial growth medium.
amide A nitrogenous compound with the general formula RNH2C?O, related to or derived from
ammonia. Reaction of an alkali metal with ammonia yields inorganic amides (e.g., sodium amide,
NaNH2)–. Organic amides are closely related to organic acids and are often characterized by the
substitution of one or more acyl groups (RCO) for an H atom of the ammonia molecule (NH3).
amine An organic compound formed from ammonia (NH3) by replacement of one or more of the H
atoms by hydrocarbon radicals.
amyotrophic lateral sclerosis (ALS) A disease marked by progressive degeneration of the neurons
that give rise to the corticospinal tract and of the motor cells of the brainstem and spinal cord,
resulting in a deficit of upper and lower motor neurons; the disease is usually fatal within 2–3 years.
anaphylatic-type reaction One of four types of allergic reaction. A violent allergic reaction to a
second dose of a foreign protein or other antigen to which the body has previously been
hypersensitized. Symptoms include severe vasodilation, urticaria or edema, choking, shock, and
loss of consciousness. Can be fatal.
angiosarcoma Malignant tumor of vascular system arising from endothelial cells.
anoxia A complete reduction in the oxygen concentration supplied to cells or tissues.
anthropogenic Produced or caused by the actions of humans.
antibody An immunoglobulin molecule that has a specific amino acid sequence that causes it to
interact only with the antigen that induced its synthesis, or with antigens closely related to it.
antigen A substance that, when introduced into the body, is capable of inducing the formation of
antibodies and, subsequently, of reacting in a recognizable fashion with the specific induced
antibodies.