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Introductory Note: Knowledge of the
structure and function of the heart and other aspects
of the vascular system, is part of training in many
therapies, such as Massage (in its many forms, "Indian
Head Massage", "Swedish Massage", "Acupressure
Massage" etc.), Aromatherapy, Acupuncture, Shiatsu,
and others. This page is intended to include the detail
required for most Basic / First Level Courses in these
therapies, and some ITEC Diplomas.
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The physical form and structure of the heart
is described and illustrated on the separate page: The
Structure of the Heart
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The following diagrams are simple summaries of the main parts
of the heart, the functions of which are described
below.
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What are the Functions of the Heart ?
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The main functions of the heart can be summarised as follows:
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Right-Hand Side of the Heart
The right-hand side of the heart receives de-oxygenated blood
from the body tissues (from the upper- and lower-body via
the Superior Vena Cava and the Inferior Vena Cava, respectively)
into the right atrium. This de-oxygenated blood passes through
the tricuspid valve into the right ventricle. This blood is
then pumped under higher pressure from the right ventricle
to the lungs via the pulmonary artery
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Left-Hand Side of the Heart
The left-hand side of the heart receives oxygenated blood
from the lungs (via the pulmonary veins) into the left atrium.
This oxygenated blood then passes through the bicuspid valve
into the left ventricle. It is then pumped to the aorta under
greater pressure (as explained below). This higher pressure
ensures that the oxygenated blood leaving the heart via the
aorta is effectively delivered to other parts of the body
via the vascular system of bllod vessels (incl. arteries,
arterioles, and capillaries).
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How does the heart perform these functions ?
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The pump action performed by the heart is achieved
by a sequence of alternating contraction and relaxation of
the heart muscle (illustrated above).
In this context the term "systole" refers to the
contraction part of the sequence and the term "diastole"
to the relaxation part of the sequence. Hence, the "systolic"
and "diastolic" pressures may be measured and recorded
separately when monitoring blood pressure.
This process is directed by the nervous system,
nerve impluses initiating each sequence. The whole series
of actions that cause alternating contractions and relaxations
may be summarised in five stages:
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1.
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The vagus nerve stimulates the sinoatrial node (SAN),
the pacemaker of the heart.
The sinoatrial node (SAN) is a tiny area of specialised
cardiac (meaning "heart") muscle in the upper
wall of the right atrium, near the vena cava - as shown
above. The fibres of the SAN contract rhythmically approx.
70 times each minute. After each of these contractions,
the impluse is dispersed across the atrial cardiac muscle,
leading to ...
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2.
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... simultaneous contraction of both the right and
left atria. This movement of the cardiac muscle pushes
blood from the atria into the ventricles (via the tricuspid
and bicuspid valves).
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3.
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The contractions of the atria send impulses down the
Purkinje fibers, which in turn stimulate the atrioventricular
node (AVN).
The atrioventricular node is a mass of modified cardiac
muscle located in the lower/central part of the right
atrium of the heart.
The Purkinje fibres are referred to by various
names in different textbooks, so are also known as "Purkyne
Fibres", "Purkynje Fibres", and as the
"Bundle of His". This/these are a bundle of
modified cardiac muscle fibers that transmit impulses
from the atra, via the AVN, to the ventricles.
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4.
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The action potential from the impulse transmitted down
the Purkinje fibers reaches the right and left branches
of the Purkinje fibres - as shown in the diagram on
the right. This causes the ...
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5.
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... ventricles to contract, which pushes blood upwards
into the arteries that take the blood away from the
heart (the pulmonary artery taking blood to the lungs,
and the aorta taking blood to the body).
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Further information about the heart
and the vascular system generally are included
on other pages of this website.
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