HBF-II LEC 03 Gross Anatomy Middle Mediastinum Heart Notes 2024 Berger copy.pdf

Middle Mediastinum & Heart - Berger Page 19 of 26 Four rings of dense, fibrous connective tissue (annulus fibrosus) Right and left fibrous trigone – areas of thickened connective tissue between rings Helps to maintain the int...

Middle Mediastinum & Heart - Berger Page 19 of 26 Four rings of dense, fibrous connective tissue (annulus fibrosus) Right and left fibrous trigone – areas of thickened connective tissue between rings Helps to maintain the integrity of the openings it surrounds and provides attachment points for cusps and myocardium Separates atrial from ventricular musculature Serves as a partition of dense connective tissue to electrically isolate the atria from the ventricles, leaving the A/V bundle as the single connection between the two groups of myocardium. 4. Coronary Vasculature Arterial Blood Supply of Heart Right coronary artery  SA nodal branch – supplies SA node  Right marginal branch – supplies right border of heart  AV nodal branch – supplies AV node  Posterior IV artery Typically supplies: Right atrium, most of right ventricle, part of left ventricle, part of IV septum, SA node (60%), AV node (80%) Left coronary artery  SA nodal branch – supplies SA node  Anterior IV artery – supplies ventricle and IV septum  Circumflex branch – supplies posterior surface  Left marginal – branches off of circumflex and supplies left ventricle Typically supplies: Left atrium, most of left ventricle, part of right ventricle, most of IV septum, SA node (40%) Clinical importance: Variations of coronary arteries – - Normally, 50/50 blood supply contribution from LCA & RCA - 15% LCA is dominant  posterior IV branch off of circumflex - Single coronary artery - Circumflex arises directly from right aortic sinus - 4% accessory coronary artery - Branches of coronary arteries are considered end arteries – supply myocardium without functional overlap, BUT, smaller branches do anastomose and functional value of this is apparent in slowly progressive coronary artery disease. Middle Mediastinum & Heart - Berger Page 20 of 26 Figure 32. Clinical importance: Myocardial infarction (MI) – major artery is suddenly occluded by an embolus, myocardium in that region becomes infarcted. MI is an area of myocardium that is necrotic. Atherosclerosis of coronary arteries → coronary insufficiency → ischemic heart disease; often characterized by angina pectoris (pain in substernal region and down medial side of the left arm and forearm). Figure 33. Middle Mediastinum & Heart - Berger Page 21 of 26 Venous Drainage of Heart - Heart drains via coronary sinus (1°) and anterior cardiac veins → right atrium (2°) - Coronary sinus receives great cardiac vein, middle and small cardiac veins - Left posterior vein and left marginal vein → coronary sinus - Smallest cardiac veins – capillary beds of myocardium → atria (provide collateral circulation to musculature) Lymphatic Drainage of Heart - Myocardium and subepicardial connective tissue → subepicardial lymphatic plexus Figure 34. - Travel along coronary groove → ends in inferior tracheobronchial lymph nodes Figure 35. Middle Mediastinum & Heart - Berger Page 22 of 26 5. Conducting System of Heart: - Impulse-conducting system coordinates the cardiac cycle - Consists of cardiac muscle cells & highly specialized conducting fibers for initializing impulses and conducting them through the heart - Nodal tissue initiates heartbeat & coordinates contractions 1. SA node: Impulse 70x/min Pacemaker of heart Located just deep to epicardium, junction of SVC & right atrium 2. AV node: Smaller collection of nodal tissue Just posteroinferior of interatrial septum, near coronary sinus opening Figure 36. Middle Mediastinum & Heart - Berger Page 23 of 26 Figure 37. Figure 38. Cardiac cycle – complete movement of the heart; period from the beginning of one heartbeat to the beginning of the next. Cycle consists of diastole (ventricular filling) and systole (ventricular emptying). 1. Beginning of diastole upon closure of aortic and pulmonary valves 2. Opening of atrio-ventricular valves during early moments of diastole 3. Atrial contraction during final moments of diastole 4. Closure of atrioventricular valves (tricuspid and mitral) very soon after systole begins 5. Opening of aortic and pulmonary valves during systole Figure 39. Summary of cardiac cycle. (Adapted from www.studyblue.com) Middle Mediastinum & Heart - Berger Page 24 of 26 6. Innervation of the Heart: Cardiac plexuses - Anterior to bifurcation of the trachea, posterior to the ascending aorta, superior to the bifurcation of the pulmonary trunk - Autonomic division of the PNS is only in the atria to any specific degree and very little in ventricles; as a result, directly responsible for regulating heart rate and force of atrial contraction and no direct effect on ventricles - Sympathetic stimulation of the nodal tissue increases heart rate and the force of cardiac contractions - Parasympathetic stimulation slows the heart rate, saving energy - Branches from both parasympathetic and sympathetic contribute to the cardiac plexus - Visceral afferents from the heart are also part of the cardiac plexus Figure 40. Middle Mediastinum & Heart - Berger Page 25 of 26 Figure 41. Figure 42. Figure 43. Referred cardiac pain. (Reproduced from https://drsvenkatesan.com/tag/referred-pain/) Clinical importance: The heart is insensitive to touch and temperature; however, ischemia can stimulate pain endings in the myocardium. The axons of afferent pain fibers enter spinal cord segments T1 – T4/5, especially on the left side. Cardiac referred pain is a phenomenon whereby stimuli originating in the heart is perceived as pain arising from a superficial body part – e.g., skin on the medial aspect of left upper limb. Middle Mediastinum & Heart - Berger Page 26 of 26 Auscultatory areas of the heart are shown in Figure 44. Four traditional valve areas are indicated – note that these are not the anatomical positions of the valves, but where they are best heart based on sound projections related to blood flow. Figure 44. Aortic valve area – 2nd right intercostal space Pulmonic valve area – 2nd left intercostal space Mitral valve area – 5th intercostal space Tricuspid valve area – left lower sternal border 7. Great Vessels The pulmonary trunk is contained within the pericardial sac, along with the ascending aorta. The pulmonary trunk arises from the conus arteriosus and divides into left and right pulmonary arteries between TV5-TV6 Ascending aorta originates at the aortic orifice and moves superiorly to the level of the 2nd right costal cartilage, where it enters the superior mediastinum and becomes the arch of the aorta. Figure 45.