EXTRINSIC ALLERGIC ALVEOLITIS
extracorporeal circulation
Circulation of blood outside the body
through a machine that temporarily
assumes an organ’s functions. Examples
of extracorporeal
circulation
include
the use of a
heart-lung machine
,
during
open heart surgery, to keep blood mov-
ing around the body and carry out
carbon dioxide-oxygen exchange, and
extracorporeal dialysis
.
extracorporeal dialysis
Haemodialysis performed through an
artificial kidney to remove the sub-
stances that are normally excreted in the
urine (see
dialysis
) .
extracorporeal gas exchange
A technique in w hich blood is diverted
out of the body and through an “artifi-
cial lung” to aid
respiration
.
It involves a
procedure called extracorporeal mem-
brane oxygenation (ECMO), in w hich
blood is passed over an artificial mem-
brane and takes up oxygen, and the
removal of waste carbon dioxide. Extra-
corporeal gas exchange is used to treat
severe
respiratory failure
,
in addition to
mechanical
ventilation
.
extracorpuscular
A term meaning “situated or occurring
outside the
corpuscles
(minute bodies or
cells)” . Extracorpuscular refers particu-
larly to the environment outside the
blood cells
(for example, it may be used
for agents that attack red blood cells
from outside; see
anaemia, haemolytic
) .
extraction, dental
The removal of one or more
teeth
by
a dentist.
WHY IT IS DONE
Dental extraction may be performed
when a tooth is severely decayed or too
badly broken to be repaired or when an
abscess (see
abscess, dental
)
has formed.
Teeth may also be removed if there is
dental crowding
or
malocclusion
(an
incorrect bite); if they are loose due
to severe gum disease; or if they are
preventing another tooth from erupting
through the gum (see
eruption of teeth
).
HOW IT IS DONE
For most extractions, local anaesthesia is
used (see
anaesthesia, dental
) .
A general
anaesthetic (see
anaesthesia, general
)
may
be used to extract badly impacted w is-
dom teeth
(see
impaction, dental
) ,
to
extract several teeth at once, or for
extremely anxious or disabled patients
or young children.
Teeth are usually extracted with dental
forceps, w hich are designed to grasp
the root of the tooth. W hen gentle but
firm pressure is applied, the blades cut
through the periodontal ligaments (the
tough, fibrous membranes supporting
the tooth in its socket), the socket is
gradually
expanded,
and
the
tooth
is removed. Occasionally the root frac-
tures during this procedure and may
need to be removed separately.
In difficult extractions, for example if
the tooth is impacted, if the crown is
missing, or if the roots are very curved,
some gum and bone may need to be
removed from around the tooth before
the tooth is extracted and the gum is
sutured (stitched).
COMPLICATIONS
Most extractions take place without
complications. If bleeding
does
not
stop after extraction of a tooth, sutur-
ing of the tissue around the socket may
be necessary.
Occasionally,
if a blood
clot
(see
blood clotting
) fails to form in the empty
tooth socket, or if the blood clot is dis-
lodged,
dry socket
(infection in the tooth
socket) develops.
extradural haemorrhage
Bleeding into the space between the
inner surface of the skull and the exter-
nal surface of the
dura mater
(the outer
layer of the
meninges
,
the protective
covering of the brain).
CAUSE
Extradural
haemorrhage
most
com-
monly occurs as a result of a heavy
blow
to
the side
of the
head that
fractures the skull (see
skull, fracture of
)
and ruptures an artery running over the
surface of the dura mater.
SYMPTOMS
A
haematoma
(a collection of clotted
blood) forms and enlarges, increasing
pressure inside
the skull.
Symptoms
result several hours or sometimes even
days after the injury These symptoms
may
include
headache,
drowsiness,
vomiting, paralysis affecting one side of
the body, and
seizures
.
If left untreated, extradural haemor-
rhage may be life-threatening.
DIAGNOSIS AND TREATMENT
CTscanning
or
MRI
(techniques that pro-
duce cross-sectional or three-dimensional
images of body structures) are used to
confirm the diagnosis. Treatment may
consist of
craniotomy
(drilling holes in
the skull), draining the blood clot, and
clipping shut the ruptured blood vessel.
extrapyramidal disease
Any of a group of disorders that are the
result of damage to, or degeneration of,
parts of the
extrapyramidal system
(nerve
pathways that link motor nerve nuclei
w ithin the brain). Extrapyramidal dis-
eases disrupt the execution of voluntary
movements; these diseases are charac-
terized by uncontrollable movements,
changes in muscle tone, and postural
disturbances. Examples of extrapyram-
idal disease include
Huntington’s disease,
Parkinson’s disease,
and some types of
cerebral palsy
.
extrapyramidal system
A network of
nerve
pathways that links
the surface of the
cerebrum
(main mass
of the brain) w ith motor nerve nuclei
in the
basal ganglia
,
and parts of the
brainstem
.
This system influences and
modifies electrical impulses sent from
the
brain
to
initiate
movement
in
skeletal muscles.
Damage or degeneration of compo-
nents
in
the
extrapyramidal
system
may be caused by
extrapyramidal disease
.
It may also occur as a side effect of tak-
ing
phenothiazine drugs
.
extrasystole
A contraction of the heart that is inde-
pendent of the heart’s normal rhythm.
Extrasystole arises in response to an
electrical impulse in a part of the heart
other
than
the
sinoatrial
node
(see
ectopic heartbeat
) .
extrauterine pregnancy
An alternative term for an
ectopic preg-
nancy
.
extravasation
The leakage and spread of fluid, usually
from blood vessels or
lymph
vessels, into
the surrounding tissues. Extravasation
has a variety of causes, including injury,
burns, and inflammation.
extravascular
Situated or occurring outside the vessels.
The term refers particularly to the blood
vessels (see
circulatory system
)
and lymph
vessels (see
lymphatic system
) .
Extravascu-
lar fluid is fluid that exists outside the
circulation, in the body tissues.
extrinsic allergic alveolitis
Inflammation and thickening of the
tiny air sacs in the lungs that is caused
by an allergy to inhaled organic dusts
(see
alveolitis
).
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