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The Cardiovascular System: Cardiac Function Outline • • 5/2/2017 • • • • Overview of the Cardiovascular System The Path of Blood Flow Through the Heart and Vasculature Anatomy of the Heart Electrical Activity of the Heart The Cardiac Cycle Cardiac Output and Its Control Dr. C. Gerin -F16 I. Overview of the Cardiovascular System – – – The Heart Blood Vessels Blood Overview of Cardiovascular System Functions Transport of substances 5/2/2017 – Oxygen & nutrients to cells – Wastes from cells to liver & kidneys – Hormones, immune cells, clotting proteins Dr. C. Gerin -F16 to specific target cells The Heart – Four chambers • 2 Atria • 2 Ventricles – Septum • Interatrial • Interventricular – Base – Apex 5/2/2017 Dr. C. Gerin -F16 5/2/2017 Dr. C. Gerin -F16 Blood Vessels Heart Arteries Arterioles Capillaries Venules Veins – Vasculature – Arteries – relatively large, branching vessels that conduct blood away from the heart – Arterioles – small branching vessels with high resistance – Capillaries – site of exchange between blood and tissue 5/2/2017 Dr. C. Gerin -F16 Blood Vessels – Venules – small converging vessels – Veins – relatively large converging vessels that conduct blood to the heart – Closed system 5/2/2017 Dr. C. Gerin -F16 Blood – Erythrocytes – red blood cells • Transports oxygen and carbon dioxide – Leukocytes – white blood cells • Defend body against pathogens – Platelets – cell fragments • Important in blood clotting – Plasma – fluid and solutes 5/2/2017 Dr. C. Gerin -F16 II. The Path of Blood Flow Through the Heart and Vasculature – – 5/2/2017 Series Flow Through the Cardiovascular System Parallel Flow Within the Systemic or Pulmonary Circuit Dr. C. Gerin -F16 Series Flow Through the Cardiovascular System – Pulmonary circuit • Supplied by right heart • Blood vessels from heart to lungs and lungs to heart – Systemic circuit • Supplied by left heart • Blood vessels from heart to systemic tissues and tissues to heart 5/2/2017 Dr. C. Gerin -F16 Oxygenation of Blood – Exchange between blood and tissue takes place in capillaries – Pulmonary capillaries • Blood entering lungs = deoxygenated blood • Oxygen diffuses from tissue to blood • Blood leaving lungs = oxygenated blood – Systemic capillaries • Blood entering tissues = oxygenated blood • Oxygen diffuses from blood to tissue • Blood leaving tissues = deoxygenated blood 5/2/2017 Dr. C. Gerin -F16 Path of Blood Flow – Cardiovascular system = closed system – Flow through systemic and pulmonary circuits are in series – Left ventricle aorta systemic circuit vena cavae right atrium right ventricle pulmonary artery pulmonary circuit pulmonary veins left atrium left ventricle 5/2/2017 Dr. C. Gerin -F16 Path of Blood Flow Through the Cardiovascular System 5/2/2017 Dr. C. Gerin -F16 5/2/2017 Dr. C. Gerin -F16 Parallel Blood Flow Within the Systemic (or Pulmonary) Circuit – Aorta arteries arterioles capillaries – Oxygenated blood enters each capillary bed – Parallel flow allows independent regulation of blood flow to organs – Capillaries venules veins 5/2/2017 Dr. C. Gerin -F16 Parallel Flow Patterns in the Cardiovascular System 5/2/2017 Dr. C. Gerin -F16 5/2/2017 Dr. C. Gerin -F16 III. Anatomy of the Heart – – 5/2/2017 Myocardium and the Heart Wall Valves and Unidirectional Blood Flow Dr. C. Gerin -F16 Location of the Heart 5/2/2017 Dr. C. Gerin -F16 The Heart – Located in thoracic cavity • Diaphragm separates abdominal cavity from thoracic cavity – Size of fist – Weighs approxinately 250 – 350 grams Pericardium – Membranous sac surrounding heart (visceral and parietal serous membrane) – Lubricates heart decreasing friction – Pericarditis = inflammation of pericardium 5/2/2017 Dr. C. Gerin -F16 Figure 18.3 The pericardial layers and layers of the heart wall. Pulmonary trunk Fibrous pericardium Pericardium Parietal layer of serous pericardium Myocardium Pericardial cavity Epicardium (visceral layer of serous pericardium) Myocardium Endocardium Heart chamber © 2013 Pearson Education, Inc. Heart wall Myocardium and the Heart Wall Three layers of the heart wall: – Endocardium (inner) • layer of endothelial cells – Myocardium (middle) • cardiac muscle – Epicardium (outer)= visceral pericardium • external membrane 5/2/2017 Dr. C. Gerin -F16 Cardiac Muscle 5/2/2017 Dr. C. Gerin -F16 Properties of Cardiac Muscle Cells CARDIOMYOCYTES: – Smaller than skeletal – Branches – Sarcomeres • striated 5/2/2017 Dr. C. Gerin -F16 Properties of Cardiac Muscle – Intercalated Disks • Gap junctions (channels between cell cytosol , passage of ions => depolarization) – Contract as unit • Desmosomes – Resist stretch (fill and contraction) – Atria & Ventricles ( Atrium singular) • Separate units 5/2/2017 Dr. C. Gerin -F16 Properties of Cardiac Muscle – Aerobic muscle (primary hypoxia versus primary hypoglycemia) – No cell division after infancy - growth by hypertrophy – 99% contractile cells – 1% autorhythmic cells 5/2/2017 Dr. C. Gerin -F16 Walls of the Heart – Walls of ventricles thicker than walls of atria (why?) – Wall of left ventricle thicker (why??)than wall of right ventricle 5/2/2017 Dr. C. Gerin -F16 Figure 18.5e Gross anatomy of the heart. Aorta Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Frontal section © 2013 Pearson Education, Inc. Left pulmonary artery Left atrium Left pulmonary veins Mitral (bicuspid) valve Aortic valve Pulmonary valve Left ventricle Papillary muscle Interventricular septum Epicardium Myocardium Endocardium Figure 18.5b Gross anatomy of the heart. Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Left common carotid artery Left subclavian artery Aortic arch Ligamentum arteriosum Left pulmonary artery Left pulmonary veins Auricle of left atrium Right atrium Right coronary artery (in coronary sulcus) Anterior cardiac vein Right ventricle Circumflex artery Right marginal artery Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex Small cardiac vein Inferior vena cava Anterior view © 2013 Pearson Education, Inc. Left coronary artery (in coronary sulcus) Left ventricle Thickness of Ventricle Walls 5/2/2017 Dr. C. Gerin -F16 Function of Cardiac Muscle – Rhythmic contraction and relaxation generates heart pumping action – Contraction pushes blood out of heart into vasculature – Relaxation allows heart to fill with blood 5/2/2017 Dr. C. Gerin -F16 Heartbeat – – – – Wave of contraction through cardiac muscle Atria contract as a unit Ventricles contract as a unit Atrial contraction precedes ventricle contraction 5/2/2017 Dr. C. Gerin -F16 Valves and Unidirectional Blood Flow – Pressure within chambers of heart vary with heartbeat cycle – Pressure difference drives blood flow • High pressure to low pressure – Normal direction of flow • Atria to ventricles • Ventricles to arteries – Valves prevent backward flow of blood – All valves open passively based on pressure gradient 5/2/2017 Dr. C. Gerin -F16 Action of the AV Valves 5/2/2017 Dr. C. Gerin -F16 Action of the Semilunar Valves 5/2/2017 Dr. C. Gerin -F16 Heart Valves – Atrioventricular valves = AV valves • Right AV valve = tricuspid valve • Left AV valve = bicuspid valve = mitral valve • Papillary muscles and chordae tendinae – keep AV valves from everting – Semilunar valves • Aortic Valve • Pulmonary Valve 5/2/2017 Dr. C. Gerin -F16 Figure 18.6d Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Opening of inferior vena cava Tricuspid valve Mitral valve Chordae tendineae Myocardium of right ventricle Interventricular septum Papillary © 2013 Pearson Education, Inc. muscles Myocardium of left ventricle Valve Pathology • Two conditions severely weaken heart: – Incompetent valve • Blood backflows so heart repumps same blood over and over – Valvular stenosis • Stiff flaps – constrict opening heart must exert more force to pump blood • Valve replaced with mechanical, animal, or cadaver valve © 2013 Pearson Education, Inc. Pathway of Blood Through the Heart • Pulmonary circuit – Right atrium tricuspid valve right ventricle – Right ventricle pulmonary semilunar valve pulmonary trunk pulmonary arteries lungs – Lungs pulmonary veins left atrium © 2013 Pearson Education, Inc. Pathway of Blood Through the Heart • Systemic circuit – Left atrium mitral valve left ventricle – Left ventricle aortic semilunar valve aorta – Aorta systemic circulation PLAY Animation: © 2013 Pearson Education, Inc. Rotatable heart (sectioned) Pathway of Blood Through the Heart • Equal volumes of blood pumped to pulmonary and systemic circuits • Pulmonary circuit short, low-pressure circulation • Systemic circuit long, high-friction circulation • Anatomy of ventricles reflects differences – Left ventricle walls 3X thicker than right © 2013 Pearson Education, Inc. • Pumps with greater pressure Coronary Circulation • Functional blood supply to heart muscle itself – Delivered when heart relaxed – Left ventricle receives most blood supply • Arterial supply varies among individuals • Contains many anastomoses (junctions) – Provide additional routes for blood delivery – Cannot compensate for coronary artery occlusion © 2013 Pearson Education, Inc. Figure 18.11a Coronary circulation. Superior vena cava Anastomosis (junction of vessels) Aorta Pulmonary trunk Left atrium Left coronary artery Right atrium Right coronary artery Right ventricle Right marginal artery Circumflex artery Posterior interventricular artery The major coronary arteries © 2013 Pearson Education, Inc. Left ventricle Anterior interventricular artery Coronary Circulation: Arteries • Arteries arise from base of aorta • Left coronary artery branches anterior interventricular artery and circumflex artery – Supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle • Right coronary artery branches right marginal artery and posterior interventricular artery – Supplies right atrium and most of right ventricle © 2013 Pearson Education, Inc. Coronary Circulation: Veins • Cardiac veins collect blood from capillary beds • Coronary sinus empties into right atrium; formed by merging cardiac veins – Great cardiac vein of anterior interventricular sulcus – Middle cardiac vein in posterior interventricular sulcus – Small cardiac vein from inferior margin • Several anterior cardiac veins empty directly into right atrium anteriorly © 2013 Pearson Education, Inc. Figure 18.11b Coronary circulation. Superior vena cava Anterior cardiac veins Great cardiac vein Coronary sinus Small cardiac vein The major cardiac veins © 2013 Pearson Education, Inc. Middle cardiac vein Pathology • Angina pectoris – Thoracic pain caused by fleeting deficiency in blood delivery to myocardium – Cells weakened • Myocardial infarction (heart attack) – Prolonged coronary blockage – Areas of cell death repaired with noncontractile scar tissue © 2013 Pearson Education, Inc. IV. Electrical Activity of the Heart 5/2/2017 Dr. C. Gerin -F16 Autorhythmic Cells Autorhythmicity is the ability to generate own rhythm Conduction System Autorhythmic cells that provide pathway to spread excitation through the heart 5/2/2017 Dr. C. Gerin -F16 Conduction System – Pacemaker cells • Spontaneously depolarizing membrane potentials to generate action potentials • Coordinate and provide rhythm to heartbeat – Conduction fibers • Rapidly conduct action potentials initiated by pacemaker cells to myocardium • Conduction velocity = 4 meters/second • Ordinary muscle fibers, CV = 0.4 meter/second 5/2/2017 Dr. C. Gerin -F16 Pacemaker Cells of the Myocardium – Sinoatrial node • Pacemaker of the heart – Atrioventricular node Conduction Fibers of the Myocardium – Internodal pathways – Bundle of His – Purkinje fibers 5/2/2017 Dr. C. Gerin -F16 Autorhythmic Cells Location SA Node (Pacemaker) AV Node Bundle of His Purkinje Fibers Firing Rate at Rest 70-80 APs/min 40-60 APs/min 20-40 APs/min 20-40 APs/min Fastest depolarizing cells drive all other cells (they are linked together by gap junctions) = pacemaker = sets pace for entire heart 5/2/2017 Dr. C. Gerin -F16 Spread of Excitation Between Cells – Atria contract first followed by ventricles – Coordination due to presence of gap junctions and conduction pathways – Intercalated disks • Junctions between adjacent myocardial cells • Desmosomes to resist mechanical stress • Gap junctions for electrical coupling 5/2/2017 Dr. C. Gerin -F16 Electrical Coupling of Cardiac Muscle Cells 5/2/2017 Dr. C. Gerin -F16 5/2/2017 Dr. C. Gerin -F16 Anatomy of the Conduction System 5/2/2017 Dr. C. Gerin -F16 Spread of Excitation – Interatrial Pathway • SA Node right atrium left atrium • Rapid • Simultaneous contraction right and left atria – Internodal Pathway • SA Node AV Node – AV Node Transmission • Only pathway from atria to ventricles • Slow conduction - AV Nodal Delay = 0.1 sec • Atria contract before ventricles 5/2/2017 Dr. C. Gerin -F16 Spread of Excitation Ventricular Excitation – Down Bundle of His – Up Purkinje Fibers • Purkinje Fibers contact ventricle contractile cells • Ventricle contracts from apex up 5/2/2017 Dr. C. Gerin -F16 Spread of Excitation 5/2/2017 Dr. C. Gerin -F16 Control of Heart Beat by Pacemakers – Autorhythmic cells have pacemaker potentials – Spontaneous depolarizations caused by closing K+ channels and opening 2 types of channels • Two channels that open: – If channels: Na+ & K+, net depolarization – Ca2+ channels: further depolarization 5/2/2017 Dr. C. Gerin -F16 Control of Heart Beat by Pacemakers – Depolarize to threshold • Open fast Ca2+ channels- action potential – Repolarization • Open K+ channels 5/2/2017 Dr. C. Gerin -F16 Electrical Activity in Pacemaker Cells 5/2/2017 Dr. C. Gerin -F16 Ionic Bases of the Autorhythmic Cell Action Potential 5/2/2017 Dr. C. Gerin -F16 Contractile Cell Action Potential – Five phases • Phase 0 – increased permeability to sodium • Phase 1 – decreased permeability to sodium • Phase 2 – increased permeability to calcium, decreased permeability to potassium • Phase 3 – increased permeability to potassium, decreased permeability to calcium • Phase 4 – resting membrane potential 5/2/2017 Dr. C. Gerin -F16 Contractile Cell Action Potential – Long duration of action potential = 250-300 msec • (only 1-2 msec in skeletal muscle) 5/2/2017 Dr. C. Gerin -F16 Contractile Cell Action Potential 5/2/2017 Dr. C. Gerin -F16 Ionic Bases of the Contractile Cell Action Potential 5/2/2017 Dr. C. Gerin -F16 Excitation-Contraction Coupling in Cardiac Contractile Cells – Properties similar to skeletal muscle • T tubules • Sarcoplasmic reticulum calcium • Troponin-tropomyosin regulation – Properties similar to smooth muscle • Gap junctions • Extracellular calcium 5/2/2017 Dr. C. Gerin -F16 • Steps of Excitation-Contraction Depolarization Coupling of cardiac contractile cell to threshold via gap junction 2. Opening of calcium channels in plasma membrane 3. AP travels down T tubules 5/2/2017 Dr. C. Gerin -F16 Steps of Excitation-Contraction Coupling • Calcium is released from sarcoplasmic reticulum by - Calcium-induced calcium release Action potentials in T tubules 5. Calcium binds to troponin causing shift in tropomyosin 6. Binding sites for myosin on actin are exposed 7. Crossbridge cycle occurs 5/2/2017 Dr. C. Gerin -F16 Excitation-Contraction Coupling in Cardiac Muscle 5/2/2017 Dr. C. Gerin -F16 5/2/2017 Dr. C. Gerin -F16 Relaxation of Cardiac Muscle – Remove calcium from cytosol • Ca2+ ATPase in sarcoplasmic reticulum • Ca2+ ATPase in plasma membrane • Na+-Ca2+ exchanger in plasma membrane – Troponin and tropomyosin return to position covering myosin binding sites on actin Recording the Electrical Activity of the Heart with an Electrocardiogram – Non-invasive technique – Used to test for clinical abnormalities in conduction of electrical activity in the heart 5/2/2017 Dr. C. Gerin -F16 Electrocardiogram External measure of electrical activity of the heart – Body = conductor • Currents in body can spread to surface (ECG, EMG, EEG) – Distance & amplitude of spread depends on size of potentials and synchronicity of potentials from other cells – Heart electrical activity- synchronized 5/2/2017 Dr. C. Gerin -F16 Einthoven’s Triangle Lead I: LA (+) and RA (-) Lead II: LL (+) and RA (-) Lead III: LL (+) and LA (-) 5/2/2017 Dr. C. Gerin -F16 Standard ECG Trace – P wave – PQ segment • atrial depolarization – QRS complex • AV nodal delay – QT segment • vent. depolarization – T wave • ventricular systole – TQ interval • vent. repolarization 5/2/2017 • ventricular diastole Dr. C. Gerin -F16 ECG Recording 5/2/2017 Dr. C. Gerin -F16 ECG and Ventricular Action Potential Ventricular action potential recorded from a single contractile cell in the ventricle. ECG surface recording of the summed electrical activity of all cells 5/2/2017 Dr. C. Gerin -F16 Abnormal Heart Rates – “Sinus rhythm” = rhythm generated by SA node – Abnormal Heart Rates: • Tachycardia- fast • Bradycardia- slow 5/2/2017 Dr. C. Gerin -F16 Heart Block Slowed/diminished conduction through AV node occurs in varying degrees 1st degree block = slowed conduction through AV node – Increases PQ segment – Increases delay between atrial and ventricular contraction 5/2/2017 Dr. C. Gerin -F16 Heart Block Slowed/diminished conduction through AV node occurs in varying degrees 1st degree block = slowed conduction through AV node – Increases PQ segment – Increases delay between atrial and ventricular contraction 5/2/2017 Dr. C. Gerin -F16 2nd Degree Heart Block Slowed, sometimes stopped conduction through AV node 2nd degree block: – Lose 1-to-1 relationship between P wave and QRS complex – Lose 1-to-1 relationship between atrial and ventricular contraction 5/2/2017 Dr. C. Gerin -F16 3rd Degree Heart Block Loss of conduction through AV node 3rd degree block: – P wave independent of QRS complex – Atrial and ventricular contractions are independent 5/2/2017 Dr. C. Gerin -F16 Extrasystole Extra contraction – PAC = premature atrial contraction – PVC = premature ventricular contraction 5/2/2017 Dr. C. Gerin -F16 Ventricular Fibrillation Loss of coordination of electrical activity – Atrial fibrillation weakness – Ventricular fibrillation - death within minutes 5/2/2017 Dr. C. Gerin -F16