Chambers Of The Heart

 

       

      Chambers of the heart

Right atrium:

Position:

   It forms the right border, part of the upper border, the sternocostal surface and the base of the heart.

External features:

The chamber is elongated vertically, receiving the superior venacava at the upper end and the inferior venacava at the lower end.

The upper end is prolonged to the left to form the right auricle. The auricle covers the root of the ascending aorta and partly overlaps the infundibulum of the right ventricle.

Along the right border of the atrium there is a shallow vertical groove which passes from the superior venacava above to the inferior venacava below. Thus groove is called the sulcus terminalis. It is produced by an internal muscular ridge part called crista terminalis. The upper part of the sulcus contains the SA node which acts as the pacemaker of the heart.

The right atrioventricular groove separates the right atrium from the right ventricle. It is more or less vertical and lodges the right coronary artery and the small cardiac veins.

Internal features:

The inferior of the right atrium can be broadly divided into the following three parts.

Smooth posterior part ( Sinus venarum):

Developmentally it is derived from the right horn of the sinus venosus.

Tributaries of the right atrium:

Superior venacava

Inferior venacava

Coronary sinus

Anterior cardiac veins

Venae cordis minimi (Thebesian veins)

        The intervenous tubercle of lower is a very small projection, scarcely visible, on the posterior wall of the atrium just below the opening of the superior venacava.

Rough anterior part (pectinate) including auricle:

Developmentally it is derived from the primitive atrial chamber.

It presents a series of transverse muscular ridges called musculi pectinate.

They arise from the crista terminalis and run forwards and downwards towards the atrioventricular orifice, giving the appearance of the teeth of a comb.

Interatrial septum:

Developmentally it is derived from the septum primum and septum secund.

It presents the fossa ovalis, a shallow saucer shaped depression in the lower part. The fossa represents the site of the embryonic septum primum.

The annulus ovalis or limbus fossa ovalis is the prominent margin of the fossa ovalis. It represents the lower free edge of the septum secundum.

The remaining of the foramen ovale are occasionally present. This is a small slit-like valvular opening between the upper part of the fossa and the limbus.

Triangle of Koch is a triangular area behind the septal leaflet of the tricuspid valve and opening of coronary sinus. The AV node is lodged in this area.

Torus aorticus is a bulging produced by the right posterior aortic sinus in the septal wall.

Right ventricle:

Position:

The right ventricle is a triangular chamber which receives blood from right atrium and pumps it to lungs through the pulmonary trunk and pulmonary arteries. It forms the inferior border and large part of sternocostal surface of the heart.

External features:

Externally right ventricle has two surface            Anterior/sternocostal surface                              Inferior/diaphragmatic surface

Inflowing part is rough due to the presence of muscular ridge called trabeculae corneae.

It develops from the proximal part of bulbus cordis of the heart tube.

The outflowing part or infundibulum is smooth and which gives rise to the pulmonary trunk.

It develops from the mid position of the bulbus cordis.

Internal features:

The interior shows two orifice.

The right atrioventricular or tricuspid orifice guarded by tricuspid valve.

The pulmonary orifice is guarded by pulmonary valve.

The interior of inflowing part shows trabeculae corneae or muscular ridges of three types.

Ridges or fixed elevation (Outflowing and inflowing is separated by the muscular ridge called supraventricular crest).

Bridges ( Moderator band is a muscular ridge extending from the ventricular septum to the base of the anterior papillary muscles contain right bundle branch.

Pillars or papillary muscles (Papillary muscles with one end attached to ventricular wall and the other end connected to the cusp of tricuspid valve by cardiac tendonae. There are three papillary muscles in the right ventricle, anterior and posterior septal. The anterior muscle is the largest, the posterior muscle is small and irregular. The septal muscle is divided into number of little nipples. Each papillary muscle is attached by cardiac tendonae.

The wall of right ventricle is thinner than the left ventricle.

Left atrium:

Position:

The left atrium is a quadrangular chamber situated posteriorly. Its appendage, the left auricle projects anteriorly to overlap the infundibulum of the right ventricle.

Features:

The posterior surface of the atrium forms the anterior wall of the oblique sinus of pericardium.

The anterior wall of the atrium is formed by the interatrial septum.

The two pulmonary veins open into the atrium on each side of the posterior wall.

Interventricular septum:

The septum is placed obiquely, its one surface faces forward and to the right and other faces backward and to the left.

The upper part of the septum is thin and membranous.

The lower part of the septum is thick and muscular.

Left ventricle:

Position:

The left ventricle receives oxygenated blood from the left atrium and pumps it into the aorta. It forms apex of the heart, a part of the sternocostal surface, most of the left border and left surface and the left two-thirds of the diaphragmatic surface.

External features:

Externally, the left ventricle has three surfaces - anterior/sternocostal, inferior/diaphragmatic and left lateral surface.

The interior is divisible into two parts.

The lower rough part with trabeculae corneae develops from the primitive ventricle of the heart tube.

The upper smooth part or aortic vestibule gives origin to the ascending aorta. It develops from the mid portion of the bulbus cordis.

Internal features:

The interior of the ventricle shows two orifices.

     The left atrioventricular or bicuspid or mitral orifice, guarded by the bicuspid or mitral valve.

     The aortic orifice, guarded by the aortic valve.

There are two well developed papillary muscles anterior and posterior. 

The cavity of the left ventricle is circular in cross section.

The walls of the left ventricle are three times thicker than those of the right ventricle.

            ***The End***