ANATOMY OF THE HEART
The heart is a hollow muscular organ that lies within the pericardium in the mediastinum. The pericardium is a fibroserous sac that encloses the heart and the roots of the great vessels. Its function is to restrict excessive movements of the heart as a whole and to serve as a lubricated container in which the different parts of the heart can contract.
SURFACE OF THE HEART:
The heart has 3 surfaces:
1.Sternocostal surface (anterior): Formed mainly by the right atrium (RA) and right ventricle(RV), which are separated from each other by the atrioventricular (AV)groove.
2.Diaphragmatic surface (inferior): Formed by the right ventricle and the left ventricle(LV), which are separated by the posterior inter ventricular groove. The inferior part of the RA, into which the IVC opens, also forms part of this surface.
3.Base (posterior): Formed by the left atrium (LA), in to which the pulmonary veins open.
Apex of the heart is formed by the left ventricle and is directed downward, forward and to the left. It lies at the level of the fifth intercostal space along the mid clavicular line.
BORDERS OF THE HEART:
Right border formed by RA
Left border formed by LA and LV
Lower border mainly formed by RV, also by RA
Apex formed by LV
CHAMBERS OF THE HEART: the heart is divided by vertical septa into 4 chambers
• Right atrium
• Left atrium
• Right ventricle
• Left ventricle
The walls of the heart composed of cardiac muscle, the myocardium, covered externally with serous pericardium called the epicardium and lined internally with a layer of endothelium, the endocardium.
RIGHT ATRIUM: It consists of a main cavity and a small out pouching, the auricle. On the outside of the heart at the junction between the right atrium and the right auricle is a vertical groove, the sulcus terminalis, which on the inside forms a ridge, the crista terminalis. This part of the RA anterior to this ridge is trabeculated by bundle of muscle fibres, the musculi pectinati, which run from the crista terminalis to the auricle>.
ANTERIOR SURFACE OF THE HEART
POSTERIOR SURFACE OF THE HEART
OPENING INTO RA:
SUPERIOR VENA CAVA (SVC): Opens in to the upper part of the right atrium, drains the upper part of the body and has no valve.
INFERIOR VENA CAVA(IVC): Opens in to the lower part of the RA, drains the lower part of the body. A rudimentary non-functioning valve called the Eustachian valve guards its opening in to the RA.
CORONARY SINUS: Drains blood from the heart walls opens in to RA between the IVC and AV orifice. It is guarded by a rudimentary non-functioning valve.
ATRIO-VENTRICULAR ORIFICE (AV ORIFICE): Lies anterior to the IVC opening and is guarded by the tricuspid valve.
FETAL REMNANTS IN THE RA:
FOSSA OVALIS: It is a shallow depression which is the site of the foramen ovale in the fetus.
ANNULUS OVALIS: It lies on the atrial septum that separates the RA and LA. It forms the upper margin of the fossa ovalis.
The floor of the fossa ovalis represents the persistent primum of the embryo.
INTERIOR SURFACE OF THE HEART
RIGHT VENTRICLE: The RV communicates with the RA through the AV orifice and with the pulmonary trunk through the pulmonary orifice. As the cavity approaches the pulmonary orifice it becomes funnel shapped, at which point it is referred to as the infundibulum. The walls of the RV are much thicker with projecting ridges known as trabeculae carneae. The moderator band is one such trabeculation, which crosses the ventricular cavity from the septal to the anterior wall. It conveys the right branch of the AV bundle, which is the part of the conducting system of the heart. The tricuspid valve guards the atrioventricular orifice and consists of 3 cusps formed by a fold of endocardium. Anterior, septal, inferior (posterior). The bases of these cusps are attached to the fibrous ring of the skeleton of the heart, while the free edges and ventricular surface are attached to the chordae tendinae. The chordae tendinae connect the cusps to the papillary muscles. The pulmonary valve guards the pulmonary orifice and consists of three semilunar cusps. At the root of the pulmonary trunk are 3 dilatations called the sinuses, the 3 cusps are arranged with one posterior and 2 anterior.
LEFT ATRIUM: It consists of a main cavity and a left auricle. The interior of the LA is smooth, but the left auricle possesses muscular ridges as in the right auricle.
OPENINGS INTO THE LA: The four pulmonary veins, two from each lung, open through the posterior wall and have no valves. The left AV orifice is guarded by the mitral valve.
LEFT VENTRICLE: The LV communicates with the LA through the AV orifice and with the aorta through the aortic orifice. The walls of the LV are three times thicker than those of the RV. There are well developed trabeculae carneae and 2 large papillary muscles, but no moderator band. The part of the LV below the aortic orifice is called aortic vestibulae. The Mitral valve (MV) guards the AV orifice. It consists of 2 cusps-anterior mitral leaflet (AML) and posterior mitral leaflet (PML). The attachment of the chordate tendinae to the cusps and the papillary muscles is similar to that of tricuspid valve. The aortic valve guards the aortic orifice and it has 3 cusps.
Right coronary cusps-situated on anterior wall
Left coronary cusps and non-coronary cusps – situated on posterior wall
Behind aortic sinus gives origin to the right coronary artery and the left posterior sinus gives origin to the left main coronary artery.
AORTA: The aorta is the main arterial trunk that delivers oxygenated blood from the left ventricle to the tissues of the body. It is divided in to ascending aorta, arch of aorta, descending thoracic aorta and abdominal aorta.
ARCH OF AORTA: It is the continuation of the ascending aorta. It gives rise to the following branches.
Right brachio cephalic artery: It is the first branch of the arch of the aorta and it divides in to the right subclavian and right common carotid arteries.
Left common carotid
Left subclavian artery