Anatomy of the Heart PDF

Anatomy of the Heart Nikolai P Pace MD Faculty of Medicine and Surgery The Heart  A four chambered muscular pump  Consists of a  Right atrium  Left atrium  Right ventricle  Left ventricle  Both atria receive venous blood  The...

Anatomy of the Heart Nikolai P Pace MD Faculty of Medicine and Surgery The Heart  A four chambered muscular pump  Consists of a  Right atrium  Left atrium  Right ventricle  Left ventricle  Both atria receive venous blood  The RV pumps blood to the lungs, the LV pumps blood to the systemic circulation Position and Borders  The heart lies oblique in the thoracic cavity, with its long axis pointing downwards and to the left to the apex  Right border: right atrium  Inferior border: mostly RV and a small portion of LV  The apex is formed at the junction of the inferior and left borders  Left border: mostly left ventricle  Anterior surface: mostly RV, with RA on its right  Posterior surface is the base: made up of the LA with the 4 pulmonary veins 1 Superior vena cava 2 Inferior vena cava 3 Right atrium (blue) 4 Right ventricle (blue) 5 Left ventricle (red) 6 Aorta 7 Pulmonary trunk The Right Atrium  An elongated chamber lying between the SVC and IVC  Forms right border of the heart  Its lower end is formed by the orifice of the IVC  Upper end is prolonged as the right auricle, this overlies the commencement of the aorta  The myocardium forms the pectinate muscles – a series of horizontal ridges in the RA The Right Atrium  The interatrial septum forms the posterior wall of the RA  This contains a shallow saucer shaped depression - the fossa ovalis  The coronary sinus opens into the RA The Right Ventricle  Projects to the left of the right atrium  Separated from the RA by the atrio-ventricular groove in which the Right Coronary Artery runs  Its walls contain a series of muscular ridges – the trabeculae carneae  The papillary muscles connect the ventricular wall to the cusps of the tricuspid valve  The Tricuspid Valve  This valve guards the right atrio-ventricular opening  Its 3 cusps : anterior, posterior, septal  Cusps are attached by the chordae tendinae to the papillary muscles. These are collagenous chords which prevent the cusps from being everted when the ventricle contracts. The Pulmonary Valve  As the cavity of the right ventricle continues upwards it approaches the pulmonary orifice. It narrows and assumes a funnel shape – known as the pulmonary conus.  Separating the pulmonary conus from the pulmonary trunk are the three semilunar cusps of the pulmonary valve.  The Left Atrium  Forms the posterior surface or base of the heart, it lies posterior to the right atrium  The cavity of the left atrium is smooth walled, except for the auricle, which contains muscular ridges – muscoli pectinati  The four pulmonary veins enter the LA symmetrically, one above the other on each side.These are valveless The Mitral Valve  A bicuspid valve (2 cusps), allows blood flow from LA to LV during diastole  Named anterior and posterior The Left Ventricle  Forms the apex of the heart, its walls are three times as thick as those of the RV  It has well developed trabeculae carneae  Has 2 papillary muscles – anterior and posterior Each is connected to the chordae tendinae The Inter-ventricular Septum  This bulges forwards, into the cavity of the right ventricle, so that in cross section the lumen of the LV is circular and that of the RV is crescentic.  The Inter-Ventricular Septum  The upper part of the septum is smooth, thinner and fibrous – this is the membranous part of the septum  The rest of the septum is thick and muscular – this is the muscular part of the septum  The Aortic Valve  Guards the aortic orifice at the entrance to the ascending aorta  Has three semilunar cusps labeled right, left and posterior  During ventricular systole, pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close.  The closure of the aortic valve contributes the A2 component of the second heart sound (S2). About 1-2% of the population have bicuspid aortic valves, although the condition is nearly twice as common in males. It is more common than any other congenital cardiac anomaly. In many cases, the condition will cause no problems. However, especially in later life, a bicuspid aortic valve may become calcified, which may lead to varying degrees of severity of aortic stenosis and aortic regurgitation, which will manifest as murmurs The Ascending Aorta  Immediately above the aortic orifice, the wall of the ascending aorta bulges to form the aortic sinus of Valsalva  There are three aortic sinuses, the left, the right and the posterior.  The left aortic sinus gives rise to the left coronary artery.  The right aortic sinus gives rise to the right coronary artery.  No vessels arise from the posterior aortic sinus, which is therefore known as the non-coronary sinus. The Conducting System  Consists of the 1. Sino-Atrial Node (SAN) 2. Atrio-Ventricular Node (AVN) 3. Atrio-Ventricular bundle of His 4. Right and Left bundle branches 5. Purkinje fibres (subendocardial) The Conducting System  The SAN is the cardiac pacemaker. It is a small mass of myocardial cells, histologically distinct, located subepicardially in the RA wall, just below the SVC.  These cells lack the presence of a stable resting membrane potential and so depolarize frequently.  The AVN is also a small mass of specialized myocardial cells lying in the RA on the interatrial septum The Conducting System  The atrio-ventricular bundle (of His) runs in the inter- ventricular septum.  It divides into the right and left bundle branches  These form the only conduction from the atrium to the ventricles as the fibrous framework of the heart separates the atria and ventricles electrically.