ABSENCE
A
TREATMENT
A periapical abscess may be drained by
drilling through the crown of the tooth
into the pulp cavity in order to allow
the pus to escape, followed by
root-canal
treatment
(filling of the pulp cavity with
dental cement). In some cases, extrac-
tion of the tooth (see
extraction, dental)
is necessary.
Antibiotic drugs
are pre-
scribed if the infection has spread.
A periodontal abscess can usually be
treated by careful scraping away of the
infected material by the dentist.
absence
In medical usage, a temporary loss or
impairment
of
consciousness
that
occurs in some forms of
epilepsy,
typi-
cally generalized absence (petit mal)
seizures in childhood.
absorption
The process by which fluids or other
substances are taken up by body tissues.
The
term
absorption
is
commonly
applied to the uptake of nutrients (from
digested food)
into
the
blood and
lymph from the digestive tract.
The major site of absorption is the
small intestine, which is lined with
millions of microscopic fingerlike pro-
jections known as villi (see
villus).
The
villi greatly increase the surface area of
the intestine, thereby increasing the rate
of absorption.
abuse
Maltreatment of a person or misuse of a
substance. (See also
child abuse; drug
abuse; heroin abuse; sexual abuse; solvent
abuse
;
substance abuse
.)
acamprosate
A drug used in the treatment of
alcohol
dependence
.
acanthoma
A noncancerous tumour composed of
cells of the outer layer of skin. There are
various types of acanthoma. They are
most likely to occur on the face, where
they develop in hair follicles, or on the
legs. (See also
keratoacanthoma.)
acanthosis nigricans
A rare, untreatable condition in which
thickened dark patches of skin appear in
the groin, armpits, neck, and other skin
folds. Acanthosis nigricans may occur in
young people as a genetic disorder or as
the result of an endocrine disorder such
as
Cushing’s syndrome.
The
condition
also occurs in people with carcinomas
(cancerous tumours) of the lung and
other organs.
Pseudoacanthosis nigricans is a much
more common condition that is usually
seen in dark-complexioned people who
are overweight. In this form, the skin in
fold areas is both thicker and darker
than the surrounding skin, and exces-
sive sweating usually occurs in affected
areas. Pseudoacanthosis nigricans may
improve with weight loss.
acarbose
A drug that is used in the treatment of
type 2
diabetes mellitus.
Acarbose acts on
enzymes in the intestines, inhibiting the
digestion of starch and therefore slow-
ing the rise in
blood glucose
levels after a
carbohydrate meal.
accessory nerve
The 11th
cranial nerve.
Unlike the other
cranial nerves, most of the accessory
nerve originates from the spinal cord.
The small part of the nerve that origi-
nates from the brain supplies many
muscles of the palate, pharynx (throat),
and larynx (voice-box). Damage to this
part of the nerve may lead to
dysphonia
(difficulty in speaking) and dysphagia
(difficulty in swallowing).
The spinal part of the accessory nerve
supplies large muscles in the neck and
back, most notably the sternomastoid
(which runs from the breastbone to the
side of the skull) and trapezius (the
large, triangular muscle of the upper
back, shoulder, and neck). Damage to
the spinal fibres of the nerve paralyses
these muscles.
accidental death
Death that occurs as a direct result
of an accident. A high proportion of
deaths in
young
adults,
particularly
among males, are accidental. Many of
these deaths are as a result of road traf-
fic
accidents,
drowning,
or
drug
overdose; and alcohol is a significant
contributory factor.
Falls in the home, and burning or
asphyxiation as a result of fires, are
common causes of accidental death in
elderly
people.
Important
causes
of
accidental death in infants are choking
on food or smothering by bedclothes or
other materials such as plastic bags.
Fatal accidents at work have become less
common
with
the
introduction
of
effective safety measures.
acclimatization
Physical or psychological adjustment to
a different climate,
environment,
or
situation.
(See
also
heat
disorders
;
mountain sickness
.)
accommodation
Adjustment, especially the process by
which the eye adjusts itself to focus on
near objects. At rest, the eye is focused
THE MECHANISM OF
ACCOMMODATION
In a normal, healthy eye, light reflected from a near object is brought into focus
on the retina by a process called accommodation. Focusing is achieved by an
automatic change in lens shape.
Focusing on a distant object
The lens focused on a distant object is thin,
flat, and completely relaxed.
Focusing on a near object
To bring a near object into sharp focus, the
ciliary muscles contract and the lens becomes
more convex in shape.
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