HEART VALVE
HEAT EXHAUSTION
H
heart valve
A structure at the exit of a
heart
chamber that allows blood to flow
out of the chamber, but prevents back-
wash. There are 4 heart valves: aortic,
pulmonary, mitral, and tricuspid. Their
opening and closing during each heart
cycle produces
heart sounds
.
Any of the 4 heart valves may be
affected by
stenosis
(narrowing), which
causes the heart to work harder to force
blood through the valve, or by incompe-
tence or insufficiency (leakiness), which
makes the valve unable to prevent back-
wash of blood. These defects cause
characteristic heart
murmurs
.
Heart-valve defects may be present at
birth (see
heart disease, congenital
),
or
they may be acquired later in life. The
most common congenital valve defects
are
aortic stenosis
and
pulmonary stenosis
.
Acquired heart-valve disease is usually
the result of degenerative changes or
ischaemia
affecting part of the heart and
leading to aortic stenosis or
mitral in-
competence
.
Rheumatic fever
can cause
mitral stenosis
, mitral incompetence,
aortic valve defects,
tricuspid stenosis
and
tricuspid incompetence
. The heart
valves may also be damaged by bacteri-
al
endocarditis
.
Heart-valve disorders commonly lead
to
heart failure
,
arrhythmias
, or symp-
toms resulting from
reduced blood
supply to body tissues.
Heart-valve defects may be diagnosed
by
auscultation
,
chest X-ray
,
ECG,
or
echocardiography
and may be corrected
by
heart-valve surgery
.
heart-valve surgery
An operation to
correct a
heart valve
defect or to remove
a diseased or damaged valve. A heart
valve may have to be repaired, widened,
or replaced because it is either incom-
petent (leaky) or stenotic (narrowed).
Widening of a valve may involve
valv-
otomy
or
valvuloplasty
. A damaged valve
can be replaced by a mechanical one
(fashioned from metal and plastic), a
valve constructed from human tissue,
a pig valve, or a valve taken from a
human donor after death. A
heart-lung
machine
is used during replacement.
After heart-valve surgery,
symptoms
such as breathlessness may take weeks
to improve and require medication to
be continued. Some people need long-
term treatment with
anticoagulant drugs
to prevent the formation of blood clots
around the new valve.
heat cramps
Painful contractions in
muscles that are caused by excessive
salt loss as a result of profuse
sweating
.
Heat cramps are usually brought on by
strenuous activity in extreme heat. The
condition may occur independently, or
is sometimes a symptom of
heat ex-
haustion
or
heatstroke
.
Prevention and
treatment consist of taking salt tablets
or drinking weak salt solution.
heat
disorders
The body functions
most efficiently around 37°C, and any
major temperature deviation disrupts
body processes. The malfunctioning or
overloading of the body's mechanisms
for keeping internal temperature con-
stant may cause a heat disorder.
The mechanisms by which the body
loses unwanted heat are controlled by
the
hypothalamus
in the brain. When
blood temperature rises, the hypothal-
amus sends out nerve impulses to
stimulate the
sweat glands
and dilate
blood vessels in the skin, which cools the
body down. However, excessive sweat-
ing may result in an imbalance of salts
and fluids in the body, which may lead
to
heat cramps
or
heat exhaustion
. When
the hypothalamus is disrupted (for ex-
ample, by a
fever
), the body may overheat,
leading to
heatstroke
.
Excessive exter-
nal heat may cause
prickly heat
.
Most heat disorders can be prevented
by gradual acclimatization to hot condi-
tions and taking salt tablets or solution.
A light diet and frequent cool baths or
showers may also help. Alcohol and
strenuous exercise should be avoided.
heat exhaustion
Fatigue
,
culminating in
collapse, caused by overexposure to heat.
There are 3 main causes of heat exhaus-
tion: insufficient water intake, insufficient
salt intake, and a deficiency in
sweat
production. In addition to fatigue, symp-
toms may include faintness, dizziness,
nausea and vomiting, headache, and,
when salt loss is heavy,
heat cramps
. The
skin is usually pale and clammy, breath-
ing is fast and shallow, and the pulse is
rapid and weak. Unless it is treated, heat
exhaustion may develop into
heatstroke
.
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