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The human heart is a
hollow, muscular organ which lies above the diaphragm and just beneath the
sternum in a space between the lungs, called the mediastinum.
The heart, in the
adult, measures about 12 cm. in length, 8 to 9 cm. in breadth at the
broadest part, and 6 cm. in thickness.
Image Link
Its weight, in the
male, varies from 280 to 340 grams; in the female, from 230 to 280 grams.
Heart is enclosed
in the pericardium . The
pericardium is a tough two-layered sac in direct contact with the cardiac
surface and separates the heart from other structures in the mediastinum.
Fibrous pericardium (protective tough outer layer)- attaches to the bases
of the pulmonary artery and aorta, the diaphragm, and sternum.
S erous
pericardium (thin, delicate membrane)- lines the fibrous sac. The outer
layer of this lining is the Parietal pericardium; the inner layer is the
Visceral pericardium.
Friction between the pericardium and the beating heart is reduced to a
minimum by a small amount of lubricating pericardial fluid. Under abnormal
conditions, excess fluid may accumulate in the serous pericardial sac
developing a pericardial effusion.
The wall of the heart is composed of three histologically distinct
tissue layers.
The thin outermost layer is the epicardium.
The dark red muscle of the heart, the myocardium, is located beneath
the epicardium.
Finally, a thin delicate layer of cells called the endocardium lines
the inside surfaces of the myocardium and the valve leaflets within the
heart.
Heart muscle has
the ability to increase its output many fold, as demand requires.
Cardiac myocyte consists of
myofibrils.
Amount of contraction of
myobrils is proportional to the length of the myofibrils within limits
(2 to 2.2 microns).
Contraction power is
diminished if the length is less than 2 or more than 2.2 microns
(Starling's law of Heart).
The heart is composed of
three basic segments - the atriums, the ventricular mass and the
arterial trunks.
Each segment has a
morphologically right and a morphologically left side, although in
congenitally malformed hearts these chambers are not always located in
their usual place. It is essential therefore to decide which
component of the structures gives the best indication of rightness or
leftness.
The atriums are made up of
the venous component, the body of the atrium, the vestibule of the
atrioventricular valve and the appendage.
Detailed notes on the Normal Anatomy of the
Atrium
The ventricles
have inlets, apical trabecular and outlet components. It is the apical
part which is distinctive - coarse in the right but finely
trabeculated in the left ventricle. The arterial trunks are
distinguished on the basis of their patterns of branching, with
coronary and brachiocephalic arteries arising from the aorta as
opposed to the right and left branches of the pulmonary trunk.
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The septal
structures can be considered as atrial ,atrioventricular and
ventricular moieties. The atrial septum is not nearly as extensive as
generally thought, with the so-called "secundum" septum being an
infolding between the caval and pulmonary veins. The atrioventricular
septum has muscular and fibrous parts, with the fibrous part
continuing as the interventricular membranous septum. In the normal
heart it is not possible to distinguish components within the muscular
ventricular septum.
CARDIAC CONDUCTING SYSTEM
The cardiac
valves are crucial structures. When analyzing each valve, it is
important to distinguish the essential component parts, the leaflets,
on the basis of their zones of apposition. Such analysis reveals that
the mitral valve has two leaflets (aortic and mural), whereas the
other valves all have three leaflets.
Detailed notes on the Normal Anatomy of the Ventricle
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