in moods may have an affective
disorder. Shallow or reduced affect may
be a sign of schizophreniaor of an
organic brain syndrome.
affective disordersMental illnesses
characterized predominantly by marked
changes in affect. Mood may vary over a
period of time between mania(extreme
elation) and severe depression. (See
also manic–depressive illness.)
affinityA term used to describe the
attraction between chemicals that causes
them to bind together, as, for example,
between an antigen and an antibody
(see immune response). In microbiology,
affinity describes physical similarity
between organisms. In psychology, it
refers to attraction between 2 people.
aflatoxinA poisonous substance pro-
duced by ASPERGILLUS FLAVUS moulds,
which contaminate stored foods, espe-
cially grains, peanuts, and cassava.
Aflatoxin is believed to be one of the
factors responsible for the high inci-
dence of liver cancer in tropical Africa.
afterbirthThe common name for the
tissues that are expelled from the uterus
after delivery of a baby. The afterbirth
includes the placentaand the mem-
branes that surrounded the fetus.
afterpainsContractions of the uterus
that continue after childbirth. Afterpains
are normal and are experienced by
many women, especially during breast-
feeding. They usually disappear a few
days following the birth but may require
treatment with analgesic drugs.
agammaglobulinaemiaA type of im-
munodeficiency disorderin which there
is almost complete absence of B-lympho-
cytesand immunoglobulinsin the blood.
agarAn extract of certain seaweeds
with similar properties to gelatine. It
can be taken for constipation to soften
and give bulk to faeces, and to relieve
indigestion and heartburn. Agar is also
used as a gelling agent in media for
bacterial cultures.
ageThe length of time a person has
existed. Of medical significance in diag-
nosis and in determining treatment, a
person’s age is usually measured
chronologically, but it can also be mea-
sured in terms of physical, mental, or
developmental maturity.
The age of a fetus is measured in terms
of gestational age, which can be
assessed accurately by ultrasound scan-
ning. In children, the most useful
measure of physical development is
bone age (degree of bone maturity as
seen on an X-ray) because all healthy
individuals reach the same adult level
of skeletal maturity, and each bone
passes through the same sequence of
growth. Dental age, another measure
of physical maturity, can be assessed by
the number of teeth that have erupted
(see eruption of teeth) or by the amount
of dental calcification (as seen on an
X-ray) compared with standard values.
In adults, physical age is difficult to
assess other than by physical appear-
ance. It can be estimated after death by
the state of certain organs.
Mental age can be assessed by com-
paring scores on intelligence testswith
standards for chronological age. A young
child’s age can be expressed in terms of
the level of developmental skills, man-
ual dexterity, language, and social skills.
agenesisThe complete absence at birth
of an organ or bodily component, caused
by failure of development in the embryo.
agentAny substance or force capable of
bringing about a biological, chemical, or
physical change. (See also reagent.)
Agent OrangeA herbicide of which
the major constituent is the phenoxy
acid herbicide 2,4,5 T. This substance
may be contaminated in manufacture
with the highly toxic TCDD, commonly
known as dioxin (see defoliant poisoning).
age spotsBlemishes that appear on the
skin with increasing age. Most common
are seborrhoeic keratoses, which are
brown or yellow, slightly raised spots
that can occur at any site. Also common
in elderly people are freckles, solar kera-
toses (small blemishes caused by
overexposure to the sun), and De Mor-
gan’s spots, which are red, pinpoint
blemishes on the trunk. Treatment is
usually unnecessary for any of these,
apart from solar keratoses, which may
eventually progress to skin cancer.
ageusiaThe lack or an impairment of
the sense of taste (see taste,loss of).
aggregation, plateletThe clumping
together of platelets (small, sticky bloodAFFECTIVE DISORDERS AGGREGATION, PLATELET
A