RESPIRATORY TRACT INFECTION
RETINA
pulmonary vessels for blood transport
to and from the heart.
Air is inhaled and exhaled (see
breath-
ing)
by the action of the dome-shaped
diaphragm and of abdominal and chest
muscles including the intercostal mus-
cles between the ribs.
respiratory tract infection Infection
of the breathing passages, which extend
from the
nose
to the
alveoli.
This type
of infection is divided into upper and
lower respiratory tract infections. Upper
respiratory tract infections affect the
nose, throat, sinuses,
and
larynx.
They
include the common
cold, pharyngitis,
tonsillitis, sinusitis, laryngitis,
and
croup.
Lower respiratory tract infections, which
affect the
trachea
,
bronchi
, and
lungs
,
include acute
bronchitis
, acute
bronchi-
olitis,
and
pneumonia.
restless legs A syndrome characterized
by unpleasant tickling, burning, prickling,
or aching sensations in the leg muscles.
Symptoms tend to come on at night in
bed; they may also be triggered by pro-
longed sitting. The condition tends to
run in families and is common in middle-
aged women, people with
rheumatoid
arthritis
, smokers, and during pregnancy.
The cause is unknown, and there is no
single cure; some patients benefit from
cooling the legs, others from warming
them. Treatment with
levodopa
and
calci-
um channel blockers
can sometimes help.
restoration, dental The reconstruction
of part of a damaged tooth. Restoration
also refers to the material or substitute
part used to rebuild the tooth. Small
repairs are usually made by
filling
the
tooth. For extensive repairs, a dental
inlay
or a
crown
may be used. Chipped
front teeth may be repaired by bonding
(see
bonding, dental).
restricted growth See
short stature.
resuscitation See
artificial respiration;
cardiopulmonary resuscitation
.
retardation See
mental handicap.
reticular formation A network of nerve
cells scattered through the
brainstem
.
reticulocyte The medical term for a
newly formed red
blood cell.
Reticulo-
cytes are made in the bone marrow
from
stem cells.
They remain in the bone
marrow for
1 - 2
days and then pass into
the bloodstream, where they mature
into red blood cells.
reticulosarcoma See
lymphoma, non-
Hodgkin's.
retina The light-sensitive membrane that
lines the back inner surface of the
eye
,
and on which images are cast by the
cornea and lens. The retina contains
specialized nerve cells (rods and cones)
that convert light energy into nerve im-
pulses. The impulses travel from the
rods and cones through other cells in
the retina and along the
optic nerve
to
the
brain.
The rods respond to very dim
light and cones are responsible for
colour vision
.
The retina can be affected by congenital
and genetic disorders, such as
colour vis-
ion deficiency
and
Tay-Sachs disease.
It
can also be infected, injured (see
retinal
detachment
;
retinal tear
), or affected by
tumours such as
retinoblastoma.
Other
disorders affecting the retina include
dia-
betes mellitus
and
retinal vein occlusion.
STRUCTURE OF RETINA
488
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