L 11 internal features of the heart Lecture notes.pdf

11 Internal features of the heart ILOs By the end of this lecture, students will be able to 1. Correlate the internal features of each chamber of the heart with its function. 2. Differentiate between the inflow and outflow parts of both ventricles in relevance to their structure. 3. Describe the str...

11 Internal features of the heart ILOs By the end of this lecture, students will be able to 1. Correlate the internal features of each chamber of the heart with its function. 2. Differentiate between the inflow and outflow parts of both ventricles in relevance to their structure. 3. Describe the structure and mechanism of closure of the four heart valves. 4. Appraise the integrity of structure of heart valves in relevance to clinical conditions as valve stenosis or incompetence. 5. Identify the structure and importance of the fibrous skeleton of the heart. 6. Differentiate between the different components of the conducting system of the heart relevant to their anatomical location. The cone- shaped heart is internally divided into right and left halves by a longitudinal septum. Again, each half is divided by a transverse septum containing an atrioventricular (AV) valve into: 1. Posterior 1/3 (towards the base): representing the atrium. 2. Anterior 2/3 (towards the apex): representing the ventricle. Thus the chambers of the heart are: right atrium, right ventricle, left atrium as well as left ventricle. [figure 1] The internal anatomy of each chamber is critical to its function. Each plays a role in the process of blood circulation. The right pump receives deoxygenated blood from the body and sends it to the lungs. The left pump receives oxygenated blood from the lungs and sends it to the body. Heart valves permit the passage of blood in one direction and prevent its backflow. Figure 1: Chambers and valves of the heart. Page 1 of 7 The right atrium [figure 2] It forms the right border and right surface of the heart. It is thin (2 mm) It is formed of 2 parts: anterior rough part (pectinate muscles) in the auricle & posterior smooth part. The two parts are separated by a muscular ridge called crista terminalis which corresponds to a faint groove on the outer surface “sulcus terminalis”. Interatrial Septum [figures 2,3] It shows an oval depression called “fossa ovalis” which represents the site of foramen ovale. The fossa ovalis is bounded above and on the sides by a raised margin called “ limbus fossa ovalis”. Figure 2: Interior surface of the right atrium and the interatrial septum. The left atrium [figure 3] It lies behind and to the left of the right atrium forming the greater part of the base of the heart. It is thin (3 mm) It is formed of 2 parts: anterior part (pectinate muscles) including only the left auricle and smooth posterior part formed by entrance of four pulmonary veins. Page 2 of 7 Figure 3: Interior surface of the left atrium. The right ventricle [figure 4] It is semilunar in cross section. Its thickness is about 4-5 mm. It is divided into 2 parts: Inflowing rough part (trabeculae carnae) & outflowing smooth part (conus arteriosus). The tricuspid valve is attached to the papillary muscles of the ventricular wall by the chordae tendinae (heart strings). They are made of fibrous tissue and help to stabilize the valve and prevent blood from flowing back into the right atrium when the ventricle contracts. Figure 4: Interior surface of the right ventricle. Page 3 of 7 The left ventricle [figure 5] It is rounded in cross section. Its thickness is about 8-15 mm. Its wall thickness is 3 times thicker than the right ventricle because it pumps the blood into the systemic circulation. At the tip of the apex the wall of the left ventricle is only about 2 mm thick. It is divided into 2 parts: Inflowing rough part (trabeculae carnae) & outflowing smooth part (Aortic vestibule). Internal muscular ridges throughout except for a small area at the aortic valve opening. The mitral valve is anchored to the left ventricle by papillary muscles and chordae tendinae. Figure 5: Interior surface of the left ventricle. Interventricular septum [figures 5,7] It is the septum separating the 2 ventricles. It is oblique in position being concave towards the left ventricle and convex towards the right ventricle. Page 4 of 7 Its anterior border corresponds to the anterior interventricular groove, while its posterior border corresponds to the posterior interventricular groove. It has 2 parts: - Membranous part: the upper small area. Muscular part: the lower large thick part. Valves of the heart [figure 6] A) Atrioventricular valves: Tricuspid valve & Bicuspid (Mitral valve). B) Semilunar Valves : pulmonary valve & Aortic valve. Figure 6: Valves of the heart. Tricuspid valve [figures 1,4,6] It transmits blood from the right atrium to the right ventricle. It has a fibrous ring and 3 cusps forming the valve (anterior, posterior & septal cusps) Each cusp is attached to the chordae tendinae of the 3 papillary muscles of the right ventricle. Mitral (Bicuspid) valve [figures 1,5,6] It transmits blood from the left atrium to the left ventricle. It has a fibrous ring and 2 cusps forming the valve (anterior& posterior) Page 5 of 7 Each cusp is attached to the chordae tendinae of the 2 papillary muscles of the left ventricle. The chordae tendinae are stronger than those of the right ventricle. Pulmonary valve [figures 1,4,6] It is formed of a fibrous ring guarded by the pulmonary valve that has three semilunar cusps ( one posterior and two anterior) Aortic valve [figures 1,5,6] Its structure is similar to the pulmonary valve but its three semilunar cusps (one anterior and two posterior) There is a dilatation, the sinus of Valsalva, in the aortic wall just above each cusp. These dilatations allow blood to flow behind the cusps at the very beginning of ventricular relaxation in diastole and thus ensure that the aortic valve shuts and that the cusps are not flattened against the side of the aorta. They also allow blood to freely enter the right and left coronary arteries. Fibrous skeleton of the heart [figure 6] The fibrous skeleton of the heart is a framework of dense collagen around the atrioventricular junction and the arterial outflow. It provides structural support for the heart, particularly by stabilizing the heart valves, and it also prevents the heart from being overstretched. Figure 6: Fibrous skeleton of the heart. Page 6 of 7 Cardiac Conduction System [figure 7] The electrical insulation provided by this fibrous skeleton forms the barrier between the atria and the ventricles and ensures that electrical conduction normally only occurs through the bundle of His. 1. 2. 3. 4. The sinu-atrial node (SA node), The atrioventricular node (AV node), The atrioventricular bundle (bundle of His) with its right and left bundle branches, The subendocardial plexus of conduction cells (the purkinje fibers). Figure 7: Conduction system of the heart. Applied Anatomy Valvular Heart Disease Inflammation of a valve can cause the edges of the valve cusps to stick together. Later, fibrous thickening occurs, followed by loss of flexibility and shrinkage. Valve narrowing (stenosis) and valvular incompetence (regurgitation) result, and the heart ceases to function as an efficient pump. This leads to turbulence and vibrations that are heard as heart murmurs. Page 7 of 7