Bma Illustrated Medical Dictionary

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 infectionInfection

of the breathing passages, which extend

from the noseto 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, andpneumonia.

restless legsA 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 levodopaand calci-

um channel blockerscan sometimes help.

restoration, dentalThe 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

inlayor a crownmay be used. Chipped

front teeth may be repaired by bonding

(see bonding, dental).

restricted growthSee short stature.

resuscitationSee artificial respiration;

cardiopulmonary resuscitation.

retardationSeemental handicap.

reticular formationA 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.

reticulosarcomaSee lymphoma, non-

Hodgkin’s.

retinaThe 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 deficiencyand 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-

betesmellitusand retinal vein occlusion.

RETINA

RESPIRATORY TRACT INFECTION RETINA

R

Retina

Optic nerve

Lens

Connecting nerve cells Nerve fibre Cone Rod

Direction

of light

Direction of

nerve impulse

Electrical signal from

stimulated cell

Pigment

cell

Nerve fibres carry

impulses to brain

Cornea

LOCATION

STRUCTURE OF RETINA

Macula