BERYLLIOSIS
B
berylliosis
An occupational disease that is caused
by the inhalation of dust or fumes con-
taining beryllium, a metallic element
that is used in high-technology indus-
tries such as nuclear energy, electronics,
and aerospace. Short exposure to high
concentrations of beryllium may lead to
an episode of severe
pneumonitis
(lung
inflammation). Exposure over a number
of years to smaller concentrations may
lead to permanent damage to the lungs
and the liver.
Treatment
with
corticosteroid drugs
can reduce damage to the lungs. In
most cases, the introduction of safe
working practices prevents exposure to
dangerous levels of beryllium.
Best’s disease
A
genetic disorder
in which the macula
(part of the light-sensitive retina at the
back of the eye) is abnormal. The disor-
der is congenital (present from birth)
and results in progressive loss of vision.
beta-blocker drugs
COMMON DRUGS
cardioselective
•Atenolol •Betaxolol
• Bisoprolol •Celiprolol •Metoprolol
noncardioselective
•Acebutolol •Carvedilol
• Labetolol •Nadolol •Oxprenolol •Pindolol
• Propranolol •Sotalol •Timolol
A group of drugs, also known as beta-
adrenergic blocking agents, prescribed
principally to treat heart and circulatory
disorders such as
angina pectoris
(pain
in the chest due to an insufficient sup-
ply of blood to the heart muscle) and
hypertension
(high blood pressure). The
drugs block the effects of the
sympathetic
nervous system,
which releases
adrenaline
(epinephrine) and
noradrenaline
(nor-
epinephrine) at nerve endings known
as beta receptors.
There are two types of beta receptor:
beta
1
and beta2. Beta
1
receptors are pre-
sent mainly in the heart and beta
2
are
found in the lungs, blood vessels, and
elsewhere in the body. Certain beta-
blockers (such as atenolol, bisoprolol
and metoprolol)
are termed cardio-
selective and, because they act mostly
on beta
1
receptors, are used principally
to treat heart disease such as angina,
hypertension,
and
cardiac
arrhythmia
(abnormal heartbeat). These drugs are
sometimes given following a
myocardial
infarction
(heart attack)
in order to
reduce the likelihood of further damage
to the heart muscle.
HOW BETA-BLOCKERS WORK
Beta-blockers block specific sites on
body tissues where neurotransmitters
(chemicals released from nerve
endings) bind. These sites are called
beta receptors, and there are two
types: beta2
receptors, found in heart
tissue, and beta2 receptors, found in
the lungs, blood vessels, and other
tissues. At these receptors, two
chemicals, adrenaline (epinephrine)
and noradrenaline (norepinephrine),
are released from nerve endings in the
sympathetic nervous system, the part
of the involuntary nervous system that
enables the body to deal with stress,
anxiety, and exercise. These
neurotransmitters bind to beta
receptors to increase the force and
speed of the heartbeat, to dilate the
airways to increase air flow to the
lungs, and to dilate blood vessels.
Cardioselective beta-blockers bind
predominantly to beta2
receptors;
noncardioselective beta-blockers bind
to both types. Beta-blockers slow the
heart rate and reduce the force of
contraction of heart muscle. These
effects can be used to slow a fast heart
rate and regulate abnormal rhythms.
Beta-blockers prevent attacks of
angina pectoris by reducing the
work performed by the heart muscle
and therefore the heart’s oxygen
requirement. High blood pressure is
reduced because the rate and force at
which the heart pumps blood into the
circulation is lowered.
The effect of blocking beta receptors
on muscles elsewhere in the body is
to reduce the muscle tremor of anxiety
and an overactive thyroid gland.
Beta-blockers may help to reduce
the frequency of migraine attacks by
preventing the dilation of blood vessels
surrounding the brain, which is what
causes the headache. In glaucoma they
lower pressure in the eye by reducing
fluid production in the eyeball.
Normal
Adrenaline (epinephrine) and
noradrenaline (norepinephrine)
can be released either from the
adrenal gland or from sympathetic
nerve endings. They bind to betaj
and beta2 receptors in tissues
around the body.
Cardioselective beta-blockers
Cardioselective beta-blockers
occupy predominantly Bj receptors,
preventing adrenaline and
noradrenaline from binding to them.
This reduces the stimulating action
of adrenaline and noradrenaline on
heart tissue. Cardioselective beta-
blockers do not block B2 receptors,
thereby allowing adrenaline
(epinephrine)/noradrenaline
(norepinephrine) to act on other
tissues around the body.
Noncardioselective beta-blockers
Noncardioselective beta-blockers
occupy both Bj and B2 receptors,
reducing the stimulating action of
adrenaline (epinephrine) and
noradrenaline (norepinephrine)
on tissues around the body.
beta-blocker
vessel cell
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