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A Handbook of Biology
The heart is 4 chambered, two upper atria (auricles) and two lower
ventricles. The walls (cardiac muscles) of the ventricles are much thicker
than that of the atria.
The atria are separated by an inter-atrial septum and the ventricles are
separated by inter-ventricular septum.
In between atrium and ventricle there is a thick fibrous atrio-ventricular
septum with an opening.
A tricuspid valve (3 muscular flaps or cusps) guards the opening
between right atrium and right ventricle. A bicuspid (mitral) valve guards
the opening between left atrium and left ventricle. These valves allow
the flow of blood only in one direction, i.e. from atria to ventricles
The openings of right and left ventricles into pulmonary artery and aorta
respectively are provided with the semi-lunar valves. They prevent
backward flow of blood.
Sino atrial node
ÇØÑDÜÇTÏÑG SÝSTËM ØF HËÅRT
It includes nodal tissues, bundles & fibres.
Nodal tissues (specialized cardiac musculature present in heart wall)
are of 2 types:
Sino-atrial node (SAN) in the right upper corner of
the right atrium.
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