Basics
Of The Heart
Some intriguing facts about the human heart:
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The
heart is a cone-shaped structure which lies
in the middle of the chest, slightly to the left
of centre, behind the breastbone and
between the lungs. |
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The heart of a healthy 70 kg
adult pumps about 7,200 litres of blood daily at
a rate of approximately 5 litres per minute. |
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The heart is enclosed in a sac
called the pericardium. The wall of the heart is
madeup of three layers
known as the epicardium (outer layer), myocardium
(middle layer),and endocardium
(inner layer) respectively. The epicardium and endocardium
are thin protective layers.
In contrast, the myocardium is a thick, muscular
layer which provides the
strength for the heart to function as a pump. |
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The average heart rate is roughly
72 beats per minute, which translates into approximately
100,000 beats per day.
This figure may, however, differ widely among people
of different age groups
. For instance, the heart rate may be as high as
120 beats per minute in infants, and as low as 60
beats per minute in adults. |
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The average adult human heart
is about the size of a clenched fist and weighs
about 300 g. |
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The characteristic “lub-dub”
of a heartbeat is caused by the movement of the
heart valvesduring each
cardiac cycle. In the first phase, which is known
as the systole,the tricuspid andmitral
valves close, producing the “lub” sound.
In the second phase (the diastole), the pulmonaryand
aortic valves close, resulting in the “dub”
sound. |
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