Chapter 18: The Cardiovascular System: The Heart Heart Anatomy Approximately the size of a fist Location Enclosed in pericardium, a double-walled sac Pericardium Superficial fibrous pericardium Deep two-layered serous pericardium Layers of the Heart Wall Epicardium—visceral layer of the serous pericardium Myocardium Endocardium is continuous with endothelial lining of blood vessels Chambers Four chambers: two atria and two ventricles Atria: The Receiving Chambers Walls are ridged by pectinate muscles Vessels entering right atrium o Superior vena cava o Inferior vena cava o Coronary sinus Vessels entering left atrium o Right and left pulmonary veins Ventricles: The Discharging Chambers Walls are ridged by trabeculae carneae Papillary muscles project into the ventricular cavities Vessel leaving the right ventricle o Pulmonary trunk Vessel leaving the left ventricle o Aorta Pathway of Blood Through the Heart The heart is two side-by-side pumps o Right side is the pump for the pulmonary circuit Vessels that carry blood to and from the lungs o Left side is the pump for the systemic circuit Vessels that carry the blood to and from all body tissues Pathway of Blood Through the Heart Right atrium tricuspid valve right ventricle Right ventricle pulmonary semilunar valve pulmonary trunk pulmonary arteries lungs
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Pathway of Blood Through the Heart Lungs pulmonary veins left atrium Left atrium bicuspid valve left ventricle Left ventricle aortic semilunar valve aorta Aorta systemic circulation Coronary Circulation The functional blood supply to the heart muscle itself Arteries o Right and left coronary, marginal, circumflex, and anterior interventricular arteries Veins o Small cardiac, anterior cardiac, and great cardiac veins Homeostatic Imbalances Angina pectoris o Thoracic pain caused by a fleeting deficiency in blood delivery to the myocardium o Cells are weakened Myocardial infarction (heart attack) o Prolonged coronary blockage o Areas of cell death are repaired with noncontractile scar tissue Heart Valves Ensure unidirectional blood flow through the heart Atrioventricular (AV) valves o Prevent backflow into the atria when ventricles contract o Tricuspid valve (right) o Mitral valve (left) Chordae tendineae anchor AV valve cusps to papillary muscles Heart Valves Semilunar (SL) valves o Prevent backflow into the ventricles when ventricles relax o Aortic semilunar valve o Pulmonary semilunar valve Microscopic Anatomy of Cardiac Muscle Cardiac muscle cells are striated, short, fat, branched, and interconnected Connective tissue matrix (endomysium) connects to the fibrous skeleton T tubules are wide but less numerous; SR is simpler than in skeletal muscle Numerous large mitochondria (25–35% of cell volume) Microscopic Anatomy of Cardiac Muscle Intercalated discs: junctions between cells anchor cardiac cells o Desmosomes prevent cells from separating during contraction o Gap junctions allow ions to pass; electrically couple adjacent cells Heart muscle behaves as a functional syncytium
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Cardiac Muscle Contraction Heart Physiology: Electrical Events Intrinsic cardiac conduction system o A network of noncontractile (autorhythmic) cells that initiate and distribute impulses to coordinate the depolarization and contraction of the heart Heart Physiology: Sequence of Excitation Sinoatrial (SA) node (pacemaker) Atrioventricular (AV) node Atrioventricular (AV) bundle (bundle of His) Right and left bundle branches Purkinje fibers Homeostatic Imbalances Defects in the intrinsic conduction system may result in o Arrhythmias: irregular heart rhythms o Uncoordinated atrial and ventricular contractions o Fibrillation: rapid, irregular contractions; useless for pumping blood Homeostatic Imbalances Defective SA node may result in o Ectopic focus: abnormal pacemaker takes over o If AV node takes over, there will be a junctional rhythm...