Chambers of Heart

Interior of the Heart
The ventricles are separated from each other by the interventricular septum and the atria are separated from each other by the interatrial septum. The interior of the right atrium has a rough anterior part, the atrium proper and a smooth part called the sinus venarum. Also it has an appendage called the auricle. All the large veins open into the smooth part. The opening of the superior vena cava is situated in its upper and posterior part and that of inferior vena cava into its lower part, close to the interatrial septum. The opening of the inferior vena cava is bounded by a fold called the valve of the inferior vena cava. Just to the left of this is the opening of the coronary sinus. Besides these there are small openings called venae cordis minimae for small veins of the heart.

Interior of right side of heart

 The sinus venarum and the atrium proper meet at a muscular ridge called the crista terminalis which corresponds to a groove externally called the sulcus terminalis.Musculi pectinati are the ridges found in the atrium proper. The interatrial septum shows an oval depression called the fossa ovalis in its lower part, the upper margin of which forms a curved ridge called the limbus fossa ovalis. The wall of the fossa ovalis is thin and represents the embryonic septum primum. The limbus fossa ovalis represents the lower curved edge of the septum secundum. The right atrium opens into the right ventricle through the right atrioventricular orifice, which is guarded by the tricuspid nvalve.

Interior of the Left Atrium

The left atrium is a thin walled cavity. Most of the wall is smooth. Musculi pectinati are present only in the auricle of the atrium. The interatrial septum separates the cavity of the right atrium from the left atrium. There may be a depression corresponding to the fossa ovalis in the septum. The four pulmonary veins, two rights and two left from the lungs open into the upper lateral part of the left atrium. The left atrioventricular orifice is situated anteroinferiorly and is guarded by the mitral orifice.

Interior of the Ventricles

Each ventricle has an inflow part beginning just in front of the corresponding atrioventricular orifice and running forwards to the left towards the apex of the heart. The cavity turns upwards to form the outflow part. The inflow part of each ventricle has a rough inner surface because of trabaculae carneae which are bundles of muscle fibers. The wall also has fingerlike processes attached to the ventricular wall at one end and free at the other. These are called papillary muscles. These are functionally related to the atrioventricular valves.

Interior of ventricles

In contrast to the rough wall of the inflow parts, the outflow part of the two ventricles are smooth. The out flow part of the right ventricle is called the infundibulum. It leads to the pulmonary trunk separated by the pulmonary valve. The inflow and outflow parts make an angle of about 90 degrees with each other. The upper part of their junction is marked by a prominent bulging of the myocardium called the supraventricular crest. The outflow part of the left ventricle is called the aortic vestibule. It leads to the ascending aorta separated by the aortic valve. The aortic vestibule forms an acute angle with the inflow path, running sharply upwards and to the right to reach the aortic orifice. It crosses behind the infundibulum from left to right. This explains how the aortic orifice comes to lie to the right of the pulmonary orifice. A large part of the left ventricle is overlapped in front by the right ventricle.

The wall of the left ventricle is much thicker than the wall of the right ventricle. The outline of the left ventricle is roughly circular. In contrast the cavity of the right ventricle is crescentic in outline. This is because of the fact that the interventricular septum bulges into the right ventricle so its right surface is convex, and its left surface is concave.