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Chapter 18 The Heart Heart Anatomy • Approximately the size of a fist • Location • In the _______________ between _____________________________ • On the superior surface of diaphragm • Two-thirds to the left of the midsternal line • Enclosed in pericardium, a double-walled sac Pericardium • Superficial fibrous pericardium • • Deep two-layered serous pericardium • • • ___________________________ lines the internal surface of the fibrous pericardium Visceral layer (epicardium) on external surface of the heart Layers of the Heart Wall Layers of the Heart Wall • Epicardium— • Myocardium • Spiral bundles of cardiac muscle cells • Layer that contracts • Fibrous skeleton of the heart: crisscrossing, interlacing layer of connective tissue • • • • Supports _____________________ Limits spread of action potentials to specific paths Endocardium ___________________________________ and covers the skeleton of the valves Chambers • Four chambers • Two atria • Separated internally by the __________________________ • Coronary sulcus (_______________________) at the junction of atria • ___________________________ increase atrial volume • Two ventricles • Separated by the _________________________________ • Anterior and posterior interventricular sulci mark the position of the septum externally Chambers Atria: • Walls are ridged by pectinate muscles • Vessels entering right atrium • • • • Vessels entering left atrium • Right and left ____________________________ (2 branches each, total of 4) Ventricles: The Discharging Chambers • Walls are ridged by ________________________________________ • Papillary muscles project into the ventricular cavities • Vessel leaving the right ventricle • • Vessel leaving the left ventricle • Pathway of Blood Through the Heart • The heart is two side-by-side pumps • Right side is the pump for the ______________________________ • Left side is the pump for the _______________________________ • Vessels that carry blood to and from the lungs • Vessels that carry the blood to and from all body tissues Pathway of Blood Through the Heart • • Right ventricle _______________________ pulmonary trunk ___________________________ lungs Pathway of Blood Through the Heart • Lungs ______________ left atrium • Left atrium __________________ left ventricle • Left ventricle _______________________ aorta • Aorta systemic circulation Pathway of Blood Through the Heart • ______________________ of blood are pumped to the pulmonary and systemic circuits • • Systemic circuit blood encounters much resistance in the long pathways • Anatomy of the ventricles reflects these differences Coronary Circulation • The functional blood supply to the heart muscle itself • Arterial supply varies considerably and contains many _____________________ among branches • Collateral routes provide additional routes for blood delivery Coronary Circulation • Arteries • Coronary Circulation • Veins • Coronary sinus • Homeostatic Imbalances • Angina pectoris • • Thoracic pain caused by a __________________________________________ to the myocardium Cells are weakened • Myocardial infarction (heart attack) • • Areas of cell death are repaired with _______________________ Cardiac Catheterization • Procedure used as diagnostic and therapeutic • • • • • Heart Valves • Ensure unidirectional blood flow through the heart • Atrioventricular (AV) valves • ___________________________ into the atria when ventricles contract • ________________________________ (right) • _______________________________ (left) • _____________________________ anchor AV valve cusps to papillary muscles Heart Valves • Mitral Valve Prolapse • • • • • Mitral Valve does not close properly Usually not significant Blood can flow back into atria – “thump-squish” Heart Valves • Semilunar (SL) valves • • • Prevent backflow into the ________________________________when ventricles relax Aortic semilunar valve Pulmonary semilunar valve • Close when _____________________________ is above aorta and pulmonary pressure Microscopic Anatomy of Cardiac Muscle • Cardiac muscle cells are _______________________________ • 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 (____________________of cell volume) Microscopic Anatomy of Cardiac Muscle • Intercalated discs: junctions between cells anchor cardiac cells • • _____________________ prevent cells from separating during contraction ____________________ allow ions to pass; electrically couple adjacent cells • Heart muscle behaves as a __________________________ Cardiac Muscle Contraction • Depolarization of the heart is rhythmic and spontaneous – ______________________ • _______________________________ensure the heart contracts as a unit • Long absolute refractory period (_______________) • Prevents ___________________________from occurring Cardiac Muscle Contraction • Depolarization opens Na+ channels • Allows Na+ to enter cardiac cell • Reverses the membrane potential from ____________________________ • Transmission down the T-tubules causes SR to release Ca2+ into sarcoplasm • ______________________ prolongs the depolarization period briefly – plateau • _________________ are opened which also prolongs the depolarization • Repolarization finally begins from inactivation of Ca2+ and open K+ channels which causes a rapid loss of potassium from cell and restores resting membrane potential Energy Requirements • Heart needs all the basic nutrients muscle does • Large demand for oxygen – ______________________________ • When no oxygen lactic acid is produced • This inhibits ____________________ which in turn can not pump Ca+ into cells • This forces action potentials to find different pathways • If ____________________ area is large it may affect pumping area of heart – ________________! Heart Physiology: Electrical Events • Intrinsic cardiac conduction system • 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 (____________________) • Generates impulses about _______________ times/minute (__________________) • Depolarizes faster than any other part of the myocardium • Atrioventricular (AV) node • Smaller diameter fibers; fewer gap junctions • ______________________ approximately 0.1 second • Depolarizes ______________ times per minute in absence of SA node input Heart Physiology: Sequence of Excitation • Atrioventricular (AV) bundle (______________________) • Only electrical connection between the atria and ventricles • Right and left bundle branches • Two pathways in the ______________________ that carry the impulses toward the apex of the heart • _____________________ • Complete the pathway into the apex and ventricular walls • AV bundle and Purkinje fibers depolarize only __________times per minute in absence of AV node input Homeostatic Imbalances • Defects in the intrinsic conduction system may result in • • • • Arrhythmias: Uncoordinated atrial and ventricular contractions Fibrillation: Cardiomyopathies Arhythmias • Supraventricular arythmias – above the ventricles • Premature atrial contractions • Paroxysmal atrial tachycardia (P.A.T.) • Wolff-Parkinsons-White syndrome • Atrial tachichycardia • Atrial fibrillation • Atrial flutter • Ventricular arythmias • Premature ventricular contractions (PVC’s) • Ventricular tachycardia (V-tach) • Ventricular fibrillation (V-fib) Homeostatic Imbalances • Defective SA node may result in • • Ectopic focus: If AV node takes over, there will be a junctional rhythm (_______________ bpm) • Defective AV node may result in • • Few or no impulses from SA node reach the ventricles Extrinsic Innervation of the Heart • Heartbeat is modified by the ANS • Cardiac centers are located in the _________________ • • _____________________ center innervates SA and AV nodes, heart muscle, and coronary arteries through sympathetic neurons ____________________ center inhibits SA and AV nodes through parasympathetic fibers in the vagus nerves Electrocardiography • Electrocardiogram (________________): a composite of all the _____________________ generated by nodal and contractile cells at a given time • Three waves • P wave: depolarization of SA node (___________________) • QRS complex (0.12 s): ventricular depolarization (________________________) • T wave: ventricular repolarization (_______________________) Heart Sounds • Two sounds (lub-dup) associated with closing of ______________________ • • First sound occurs as ______________ close and signifies beginning of systole Second sound occurs when _______________ close at the beginning of ventricular diastole • __________________________: abnormal heart sounds most often indicative of valve problems Mechanical Events: The Cardiac Cycle • Cardiac cycle: all events associated with blood flow through the heart during one complete heartbeat • • _________________—contraction _________________—relaxation Phases of the Cardiac Cycle • Ventricular filling—takes place in mid-to-late diastole • • • • AV valves are open ____________________ of blood passively flows into ventricles Atrial systole occurs, delivering the remaining 20% __________________________________): volume of blood in each ventricle at the end of ventricular diastole Phases of the Cardiac Cycle • Ventricular systole • __________________ and ventricles begin to contract • Rising ventricular pressure results in closing of AV valves • Isovolumetric contraction phase (all valves are _________________) • In ejection phase, ventricular pressure exceeds pressure in the large arteries, forcing the SL valves open • End systolic volume (ESV): volume of blood remaining in each ventricle Phases of the Cardiac Cycle • Isovolumetric relaxation occurs in early diastole • • Ventricles relax Backflow of blood in aorta and pulmonary trunk closes _______________ and causes dicrotic notch (brief rise in aortic pressure) Cardiac Output (CO) • Volume of blood pumped by each ventricle in one minute • CO = ______________________ • • HR = number of beats per minute SV = Cardiac Output (CO) • At rest • CO (ml/min) = HR (75 beats/min) SV (70 ml/beat) = 5.25 L/min • Maximal CO is 4–5 times resting CO in nonathletic people • Maximal CO may reach 35 L/min in trained athletes • Cardiac reserve: difference between resting and maximal CO Regulation of Stroke Volume • SV = EDV – ESV • Three main factors affect SV • • • Preload Contractility Afterload Regulation of Heart Rate • ___________________________ factors increase heart rate • ________________________ factors decrease heart rate Autonomic Nervous System Regulation • Sympathetic nervous system is activated by emotional or physical stressors • ____________________ causes the pacemaker to fire more ___________________ (and at the same time increases contractility) Autonomic Nervous System Regulation • Parasympathetic nervous system opposes sympathetic effects • __________________ hyperpolarizes pacemaker cells by opening K+ channels • The heart at rest exhibits vagal tone (parasympathetic) Autonomic Nervous System Regulation • ________________________ reflex: a sympathetic reflex initiated by increased venous return • • Stretch of the atrial walls stimulates the SA node Also stimulates atrial stretch receptors activating sympathetic reflexes Chemical Regulation of Heart Rate • • Hormones • • __________________ from adrenal medulla enhances ______________________ ____________________ increases heart rate and enhances the effects of ______________ and _________________ Intra- and extracellular ion concentrations (e.g., Ca2+ and K+) must be maintained for normal heart function Other Factors that Influence Heart Rate • Age • Gender • Exercise • Body temperature Homeostatic Imbalances • ________________________: abnormally fast heart rate (>100 bpm) • If persistent, may lead to fibrillation • _________________________: heart rate slower than 60 bpm • • May result in grossly inadequate blood circulation May be desirable result of endurance training Congestive Heart Failure (CHF) • Progressive condition where the CO is so ______________________ that blood circulation is inadequate to meet tissue needs • Caused by • • • • Coronary atherosclerosis Persistent high blood pressure Multiple myocardial infarcts Dilated cardiomyopathy (DCM) Developmental Aspects of the Heart • Embryonic heart chambers • • • • Sinus venous Atrium Ventricle Bulbus cordis Developmental Aspects of the Heart • Fetal heart structures that bypass pulmonary circulation • • __________________________ connects the two atria ________________________ connects the pulmonary trunk and the aorta Developmental Aspects of the Heart • Congenital heart defects • • Lead to __________________________________________ Involve narrowed valves or vessels that increase the workload on the heart Age-Related Changes Affecting the Heart • Sclerosis and thickening of valve flaps • Decline in cardiac reserve • Fibrosis of cardiac muscle • Atherosclerosis
