When bronchioles become narrow
following contraction of the muscle
layer and swelling of the mucous
lining, the passage of air is impeded.
Bronchodilator drugs relax the
muscles surrounding bronchioles by
acting on the nerve signals that govern
muscle activity.
Sympathomimetic and anticholin-
ergic drugs interfere with nerve signals
passed to the muscles through the
autonomic nervous system. Sym-
pathomimetics enhance the action of
neurotransmitters that encourage
muscle relaxation. Anticholinergics
block the neurotransmitters that
trigger muscle contraction. Xanthine
drugs relax muscle in the bronchioles
by a direct effect on the muscle fibres;
however, their precise action is not
fully understood.
Normal bronchioles
The muscle surrounding
the bronchioles is
relaxed, leaving the
airway open.
during an
asthma attack
The muscle contracts
and the lining swells,
narrowing the airway.
After drug treatment
The muscles relax,
opening the airway,
but the mucous lining
remains swollen.
There are two kinds of bronchoscope.
The rigid type is a hollow tube that
is passed into the bronchi via the
mouth and requires a general
anaesthetic. The flexible, fibre-optic
bronchoscope (a narrower tube
formed from light-transmitting fibres)
can be inserted through either the
mouth or nose. It is used after giving
only a mild sedative and/or local
anaesthetic and it reaches farther
into the lungs. Both types of
bronchoscope can be fitted with
forceps for taking tissue samples and
the instrument also has attachments
for performing laser therapy and
cryosurgery. (See also
B r o n c h o s c o p e
T r a c h e a
L u n g
View through
I n s e r t i o n t u b e
F o r c e p s - v a r io u s f o r c e p s c a n
b e a t t a c h e d ; t h is o n e h a s a b a s k e t
f o r r e m o v i n g s m a l l , h a r d o b j e c t s
reaction (see
) .
When the airways
are narrowed, the air is reduced, caus-
ing wheezing or coughing.
is the most common cause of
bronchospasm. Other possible causes
include respiratory infection, chronic
obstructive pulmonary disease (see
monary disease, chronic obstructive
) ,
w hich the lungs are inflamed and dam-
anaphylactic shock
(a potentially
tion), or allergic reaction to chemicals.
A large air passage in a lung. Each lung
has one main bronchus, originating at
the end of the trachea (windpipe). This
divides into
branches known as segmental bronchi,
which further divide into
bronchus, cancer of
lung cancer
bronze diabetes
An outdated term for
a rare genetic disorder in which excess
amounts of
are deposited in tissues.
brown fat
A special type of fat found in infants and
some animals. Located mainly between
and around the shoulderblades, brown
fat provides energy and helps infants to
maintain a constant body temperature.
Brown-Sequard syndrome
A combination of symptoms associated
with damage to a part of the
spinal cord
There is loss of pain and temperature
sensation on the opposite side of the
body below the damage, and weakness
and stiffness of muscles below the dam-
age on the same side of the body.
brow presentation
A rare form of
in w hich
the head of the fetus is bent slightly
backwards and its brow lies against the
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