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Glossary
Mutagen
Any chemical or physical agent that induces
a genetic mutation (an unusual change in form,
quality, or some other characteristic) or increases the
mutation rate by causing changes in DNA.
Mydriasis
Physiologic dilatation of the pupil of the eye.
Myoclonus
A spasm of a portion of a muscle, an entire
muscle, or a group of muscles.
Myoglobin
The oxygen-transporting pigment of
muscle consisting of one heme molecule containing
one iron molecule attached to a single globin chain.
Myopathy
Any disease or abnormal condition of skel-
etal muscle, usually characterized by muscle weak-
ness, wasting, and histologic changes within muscle
tissue.
Myotome
The muscle plate or portion of an embry-
onic somite that develops into a voluntary muscle;
or a group of muscles innervated by a single spinal
segment.
Necrosis
Localized tissue death that occurs in groups
of cells or part of a structure or an organ in response
to disease or injury.
Neutropenia
An abnormal decrease in the number of
neutrophilic leukocytes in the blood.
Nidus
The point where a morbid process originates,
develops, or is located.
Nociception
The reception of painful stimuli from the
physical or mechanical injury to body tissues by
nociceptors (receptors usually found in either the
skin or the walls of the viscera).
Nosocomial
Pertaining to or originating in a hospital,
such as a nosocomial infection; an infection acquired
during hospitalization.
Nystagmus
Involuntary, rapid, rhythmic movements of
the eyeball.
Oncogene
A gene that is capable of causing the initial
and continuing conversion of normal cells into
cancer cells.
Oncotic
Relating to, caused by, or marked by edema
or any swelling.
Oocyte
A primordial or incompletely developed ovum.
Oogenesis
The process of the growth and maturation
of the female gametes, or ova.
Opacification
An act or process of becoming or ren-
dering impenetrable to light rays, x-rays, or other
electromagnetic radiations.
Opsonization
The process of making cells, such as bac-
teria, more susceptible to the action of phagocytes.
Organelle
Any one of the various membrane-bound
particles of distinctive morphology and function
present within most cells, such as the mitochondria,
Golgi complex, and lysosomes.
Orthopnea
An abnormal condition in which a person
must be in an upright position in order to breathe
deeply or comfortably.
Orthosis
An external orthopedic appliance or appa-
ratus, as a brace or splint, used to support, align,
prevent, or correct deformities, or to improve the
function of movable parts of the body.
Osmolality
The concentration of osmotically active
particles in solution expressed in osmols or millios-
mols per kilogram of solvent.
Osmolarity
The concentration of osmotically active
particles in solution expressed in osmols or millios-
mols per liter of solution.
Osmosis
The movement or passage of a pure solvent,
such as water, through a semipermeable membrane
from a solution that has a lower solute concentra-
tion to one that has a higher solute concentration.
Osteophyte
A bony project or outgrowth.
Palpable
Perceptible by touch.
Pandemic
A sudden outbreak, or epidemic, of a disease
occurring over a widespread geographic area and
affecting a high proportion of the population.
Papilla
A small, nipple-shaped projection, elevation, or
structure, such as the conoid papillae of the tongue.
Papule
A small, circumscribed, solid elevation of the
skin less than one centimeter in diameter. (Adjective:
papular)
Paracrine
A mode of hormone action in which a
chemical messenger that is synthesized and released
from a cell acts on nearby cells of a different type
and affects their function.
Paralysis
An abnormal condition characterized by the
impairment or loss of motor function due to a lesion
of the neural or muscular mechanism.
Paraneoplastic
Relating to alterations produced in
tissue remote from a tumor or its metastases.
Parenchyma
The basic tissue or elements of an organ
as distinguished from supporting or connective
tissue or elements. (Adjective: parenchymal)
Paresis
Slight or partial paralysis.
Paresthesia
Any abnormal touch sensation, which can
be experienced as numbness, tingling, or a “pins
and needles” feeling, often in the absence of external
stimuli.
Parietal
Pertaining to the outer wall of a cavity or
organ; or pertaining to the parietal bone of the skull
or the parietal lobe of the brain.
Parous
Having borne one or more viable offspring.
Pathogen
Any microorganism capable of producing
disease.
Pedigree
A systematic presentation, such as in a table,
chart, or list, of an individual’s ancestors that is used
in human genetics in the analysis of inheritance.
Peptide
Any of a class of molecular chain compounds
composed of two or more amino acids joined by
peptide bonds.
Perfusion
The process or act of pouring over or
through, especially the passage of a fluid through a
specific organ or an area of the body.
Peripheral
Pertaining to the outside, surface, or sur-
rounding area of an organ or other structure; or
located away from a center or central structure.
Permeable
A condition of being pervious, or per-
mitting passage, so that fluids and certain other
substances can pass through, as in a permeable
membrane.
Pervasive
Pertaining to something that becomes diffused
throughout every part.
Petechia
A tiny, perfectly round, purplish-red spot that
appears on the skin as a result of minute intradermal
or submucous hemorrhage. (Plural: petechiae)
