Cardiac Path Online
Functional Anatomy of the Heart
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 cm to 9 cm in breadth at the broadest part, and 6 cm in thickness.
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.
Serous 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.
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.
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.
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.
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