Cardiac structures

Myocardial anatomy and physiology

The heart wall consists of three major tissue layers. These are the endocardium, a thin layer of endothelial cells in direct contract with the blood, the myocardium, the middle layer of the heart and the epicardium, the outer layer of the heart comprised of the visceral pericardium.

The heart is divided into the right and left side by a muscular structure known as the septum. The function of the right heart is to deliver unoxygenated blood from the body to the lungs. The left heart delivers oxygenated blood from the lungs to the body.

Blood enters the right side of the heart via the superior vena cava and the inferior vena cava. Blood leaves the right heart via the pulmonary artery. Blood enters the left heart via four pulmonary veins and leaves via the aorta. The right side of the heart has thinner musculature because it protects its volume against minimal resistance in the pulmonary circulation (PVR) The left side of the heart has thicker musculature because it protects its volume against greater resistance in the peripheral circulation (SVR).

Each side of the heart has two sets of valves. These valves separate and further divide each side of the heart into the receiving chamber (atrium) and the ejecting chamber (ventricle).

On the right we have the atrioventricular (tricuspid) and the semilunar (pulmonary)

valves. On the left we have the atrioventricular (mitral/bicuspid) and the semilunar

(aortic) valves. Both atrioventricular valves are supported by chordae tendonae which are attached to papillary muscles. The papillary muscles extend from the ventricular wall and contract with the ventricular wall allowing valve closure. The semilunar valves separate the ventricles from their outflow vessels. The semilunar valves appear cup like, each possessing three cusps, without any supporting structures. The aortic valve contains the origin of the coronary arteries.