Chapter 18 The Cardiovascular System: The Heart PDF

Chapter 18 The Cardiovascular System: The Heart  Outline The Pulmonary and Systemic Circuits Heart Anatomy Cardiac Muscle Fibers Heart Physiology  Outline The Pulmonary and Systemic Circuits Heart Anatomy Cardiac Muscle Fibe...

Chapter 18 The Cardiovascular System: The Heart  Outline The Pulmonary and Systemic Circuits Heart Anatomy Cardiac Muscle Fibers Heart Physiology  Outline The Pulmonary and Systemic Circuits Heart Anatomy Cardiac Muscle Fibers Heart Physiology  The Pulmonary and Systemic Circuits Heart is transport system; two side-by-side pumps – Right side receives oxygen-poor blood from tissues Pumps to lungs to get rid of CO2, pick up O2, via pulmonary circuit – Left side receives oxygenated blood from lungs Pumps to body tissues via systemic circuit  The Pulmonary and Systemic Circuits Receiving chambers of heart: – Right atrium Receives blood returning from systemic circuit – Left atrium Receives blood returning from pulmonary circuit  The Pulmonary and Systemic Circuits Pumping chambers of heart: – Right ventricle Pumps blood through pulmonary circuit – Left ventricle Pumps blood through systemic circuit  Figure 18.1 The systemic and pulmonary circuits. Capillary beds of lungs where gas exchange occurs Pulmonary Circuit Pulmonar y Pulmonary arteries veins Aorta and Venae branches cavae Left atrium Left Right ventricle atrium Heart Right ventricle Systemic Circuit Capillary beds of all Oxygen-rich, body tissues where gas exchange occurs CO2-poor blood Oxygen-poor, CO2-rich blood © 2013 Pearson Education, Inc.  Outline The Pulmonary and Systemic Circuits Heart Anatomy Cardiac Muscle Fibers Heart Physiology  Heart Anatomy Approximately size of fist Location: – In mediastinum between second rib and fifth intercostal space – On superior surface of diaphragm – Two-thirds of heart to left of midsternal line – Anterior to vertebral column, posterior to sternum  Heart Anatomy Base (posterior surface) leans toward right shoulder Apex points toward left hip Apical impulse palpated between fifth and sixth ribs, just below left nipple  Figure 18.2a Location of the heart in the mediastinum. Midsternal line 2nd rib Sternum Diaphrag Location of m apical impulse © 2013 Pearson Education, Inc.  Figure 18.2b Location of the heart in the mediastinum. Mediastinum Hear t eft L lung Body of T7 vertebra Posterior © 2013 Pearson Education, Inc.  Figure 18.2c Location of the heart in the mediastinum. Superior Aorta vena cava Parietal pleura (cut) Pulmonary Left lung trunk Pericardium (cut) Apex of heart Diaphragm © 2013 Pearson Education, Inc. Coverings of the Heart: Pericardium Double-walled sac Superficial fibrous pericardium – Protects, anchors to surrounding structures, and prevents overfilling  Pericardium Deep two-layered serous pericardium – Parietal layer lines internal surface of fibrous pericardium – Visceral layer (epicardium) on external surface of heart – Two layers separated by fluid-filled pericardial cavity (decreases friction)  Figure 18.3 The pericardial layers and layers of the heart wall. Pulmonar y Fibrous trunk pericardium Pericardiu Parietal layer of serous pericardium m Myocardium Pericardial cavity Epicardium (visceral layer of serous Heart pericardium) Myocardium wall Endocardiu m Heart chamber © 2013 Pearson Education, Inc.  Homeostatic Imbalance Pericarditis – Inflammation of pericardium – Roughens membrane surfaces 🡪 pericardial friction rub (creaking sound) heard with stethoscope – Cardiac tamponade Excess fluid sometimes compresses heart 🡪 limited pumping ability  Layers of the Heart Wall Three layers of heart wall: – Epicardium – Myocardium – Endocardium Epicardium – Visceral layer of serous pericardium  Layers of the Heart Wall Myocardium – Spiral bundles of contractile cardiac muscle cells – Cardiac skeleton: crisscrossing, interlacing layer of connective tissue Anchors cardiac muscle fibers Supports great vessels and valves Limits spread of action potentials to specific paths  Layers of the Heart Wall Endocardium continuous with endothelial lining of blood vessels – Lines heart chambers; covers cardiac skeleton of valves  Figure 18.3 The pericardial layers and layers of the heart wall. Pulmonar y Fibrous trunk pericardium Pericardiu Parietal layer of serous pericardium m Myocardium Pericardial cavity Epicardium (visceral layer of serous Heart pericardium) wall Myocardium Endocardiu m Heart chamber © 2013 Pearson Education, Inc.  Figure 18.4 The circular and spiral arrangement of cardiac muscle bundles in the myocardium of the heart. Cardiac muscle bundles © 2013 Pearson Education, Inc.  Chambers Four chambers: – Two superior atria – Two inferior ventricles Interatrial septum – separates atria – Fossa ovalis – remnant of foramen ovale of fetal heart Interventricular septum – separates ventricles  Figure 18.5e Gross anatomy of the heart. Aorta Left pulmonary Superior vena cava artery Right pulmonary Left atrium artery Left pulmonary veins Pulmonary trunk Right atrium Mitral (bicuspid) valve Right pulmonary veins Fossa ovalis Aortic valve Pectinate muscles Pulmonary valve Tricuspid valve Right ventricle Left ventricle Chordae tendineae Papillary muscle Interventricular septum Trabeculae carneae Epicardium Inferior vena cava Myocardium Endocardium Frontal section  Chambers and Associated Great Vessels Coronary sulcus (atrioventricular groove) – Encircles junction of atria and ventricles Anterior interventricular sulcus – Anterior position of interventricular septum Posterior interventricular sulcus – Landmark on posteroinferior surface Atria: The Receiving Chambers Auricles – Appendages that increase atrial volume Right atrium – Pectinate muscles – Posterior and anterior regions separated by crista terminalis Left atrium – Pectinate muscles only in auricles Atria: The Receiving Chambers Small, thin-walled Contribute little to propulsion of blood Three veins empty into right atrium: – Superior vena cava, inferior vena cava, coronary sinus Four pulmonary veins empty into left atrium  Ventricles: The Discharging Chambers Most of the volume of heart Right ventricle - most of anterior surface Left ventricle – posteroinferior surface Trabeculae carneae – irregular ridges of muscle on walls Papillary muscles – anchor chordae tendineae  Ventricles: The Discharging Chambers Thicker walls than atria Actual pumps of heart Right ventricle – Pumps blood into pulmonary trunk Left ventricle – Pumps blood into aorta (largest artery in body)  Figure 18.5b Gross anatomy of the heart. Left common carotid Brachiocephalic trunk artery Left subclavian artery Superior vena cava Aortic arch Right pulmonary Ligamentum arteriosum Left pulmonary artery Ascending artery Left pulmonary Pulmonary aorta veins trunk Auricle of left atrium Right pulmonary veins Circumflex Right atrium artery Right coronary Left coronary artery artery (in coronary (in coronary sulcus) sulcus) Anterior cardiac vein Left ventricle Right ventricle Right marginal Great cardiac vein artery cardiac Small Anterior interventricular vein artery (in anterior Inferior vena cava interventricular sulcus) Apex Anterior view © 2013 Pearson Education, Inc.  Figure 18.5a Gross anatomy of the heart. Aortic arch (fat covered) Pulmonary trunk Auricle of right atrium Auricle of left atrium Anterior interventricular artery Right ventricle Apex of heart (left ventricle) Anterior aspect (pericardium removed) © 2013 Pearson Education, Inc.  Figure 18.5f Gross anatomy of the heart. Ascending aorta (cut Superior vena cava open) Pulmonary trunk Aortic valve Right ventricle anterior wall (retracted) Pulmonary Trabeculae carneae valve Interventricula r Opening to right septum (cut) atrium Left ventricle Chordae Papillary tendineae muscles Right ventricle Photograph; view similar to (e) © 2013 Pearson Education, Inc.  Heart Valves Ensure unidirectional blood flow through heart Open and close in response to pressure changes Two atrioventricular (AV) valves – Prevent backflow into atria when ventricles contract – Tricuspid valve (right AV valve) – Mitral valve (left AV valve, bicuspid valve) – Chordae tendineae anchor cusps to papillary muscles Hold valve flaps in closed position  Figure 18.7 The atrioventricular (AV) valves. 1 Blood returning to the heart fills atria, pressing against the AV valves. Direction of The increased pressure forces AV blood flow valves open. Atrium Cusp of 2 As ventricles fill, AV valve flaps atrioventricular hang limply into ventricles. valve (open) Chordae tendinea 3 Atria contract, forcing additional e blood into ventricles. Papillar y Ventricle muscle AV valves open; atrial pressure greater than ventricular pressure Atrium Cusps of 1 Ventricles contract, forcing atrioventricular blood against AV valve cusps. valve (closed) 2 AV valves close. Blood in ventricle 3 Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria. AV valves closed; atrial pressure less than ventricular pressure © 2013 Pearson Education, Inc.  Heart Valves Two semilunar (SL) valves – Prevent backflow into ventricles when ventricles relax – Open and close in response to pressure changes – Aortic semilunar valve – Pulmonary semilunar valve  Figure 18.8 The semilunar (SL) valves. Aort a Pulmonar y trunk As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open. Semilunar valves open As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close. Semilunar © 2013 Pearson Education, valves closed Inc.  Figure 18.6a Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Myocardium Mitral (left atrioventricular) valve Tricuspid (right atrioventricular) valve Aortic valve Pulmonary valve Cardiac skeleton Anterior © 2013 Pearson Education, Inc.  Figure 18.6b Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Myocardium Mitral (left atrioventricular) valve Tricuspid (right atrioventricular) valve Aortic valve Pulmonary valve © 2013 Pearson Education, Inc.  Figure 18.6c Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Chordae tendineae attached Papillary to tricuspid valve flap muscle © 2013 Pearson Education, Inc.  Figure 18.6d Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Opening of inferior Mitral valve vena cava Chordae Tricuspid valve tendineae Myocardium of right ventricle Interventricular septum Papillary Myocardium muscles © 2013 Pearson Education, of left ventricle Inc.  Homeostatic Imbalance 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  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  Pathway of Blood Through the Heart Systemic circuit – Left atrium  mitral valve  left ventricle – Left ventricle  aortic semilunar valve  aorta – Aorta  systemic circulation  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide Both sides of the heart pump at the same time, but let’s follow one Oxygen-poor blood 1 spurt of blood all the way through the system. Oxygen-rich blood Pulmonary Tricuspid Semilunar Superior vena cava (SVC) Right valve Right valve Pulmonary Inferior vena cava (IVC) Coronary sinus atrium ventricle trunk Pulmonary Tricuspid arteries SVC Coronary valve Pulmonary sinus trunk Right atrium Pulmonary Right semilunar IVC ventricle valve Oxygen-poor blood is carried Oxygen-poor blood To heart in two pulmonary arteries to To lungs returns from the body tissues back to the heart. the lungs (pulmonary circuit) to be oxygenated. Systemic Pulmonary capillaries capillaries Oxygen-rich blood is Oxygen-rich blood returns To body delivered to the body to the heart via the four To heart tissues (systemic circuit). pulmonary veins. Aorta Pulmonary veins Mitral Left Aortic semilunar valve atrium valve Left ventricle Aortic Semilunar Mitral Left valve Left Four © 2013 Pearson Education,Aorta valve ventricle atrium pulmonary Inc. veins  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 2 Superior vena cava (SVC) Oxygen-poor blood Inferior vena cava (IVC) Coronary sinus Oxygen-rich blood SVC Coronar y sinus IVC © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 3 Superior vena cava (SVC) Oxygen-poor blood Right Inferior vena cava (IVC) atrium Oxygen-rich blood Coronary sinus SVC Coronar y sinus Right atrium IVC © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 4 Tricuspid Superior vena cava (SVC) Right valve Right Oxygen-poor blood Inferior vena cava (IVC) Coronary sinus atrium ventricle Oxygen-rich blood SVC Tricuspid Coronary valve sinus Right atrium Right IVC ventricle © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 5 Pulmonary Tricuspid Semilunar Superior vena cava (SVC) Right valve Right valve Pulmonary Oxygen-poor blood Inferior vena cava (IVC) trunk atrium ventricle Oxygen-rich blood Coronary sinus Pulmonary arteries SVC Tricuspid Coronary sinus valve Pulmonary trunk Right atrium Pulmonary Right semilunar ventricle valve IVC © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 6 Oxygen-poor blood Pulmonary Oxygen-rich blood Tricuspid Semilunar Superior vena cava (SVC) valve Right valve Pulmonary Inferior vena cava (IVC) Right Coronary sinus atrium ventricle trunk Pulmonary arteries SVC Coronary Tricuspid sinus valve Pulmonary trunk Right atrium Pulmonary semilunar Right valve IVC ventricle Oxygen-poor blood is carried in two pulmonary arteries to the To lungs lungs (pulmonary circuit) to be oxygenated. Pulmonary capillaries © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide Oxygen-poor 7 Pulmonar blood Oxygen-rich blood y veins Four pulmonary © 2013 Pearson Education, veins Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide Oxygen-poor blood 8 Blood Flow Through the Heart Oxygen-rich blood Pulmonar y Right veins ventricle Left atrium Left Four atrium pulmonary veins © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 9 Oxygen-poor blood Oxygen-rich blood Pulmonar y veins Mitra Left l atrium valve Left ventricle Mitra Left l Left Four ventricle valve atrium pulmonary veins © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 10 Oxygen-poor blood Oxygen-rich blood Right ventricle Aort Pulmonar a y veins Aortic Mitra Left semiluna l r atrium valve valve Left ventricle Aortic Semiluna Mitra r l Four Left Left Aorta valve valve pulmonary ventricle atrium veins © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide 11 Blood Flow Through the Heart Oxygen-poor blood Oxygen-rich blood Systemic capillarie s Oxygen-rich blood is delivered to the body To body tissues (systemic circuit). Aort Pulmonar a y veins Aortic Mitra semiluna Left l atrium r valve valve Left ventricle Aortic Semiluna Mitra r l Left Four valve Left Aorta ventricle valve atrium pulmonary veins © 2013 Pearson Education, Inc.  Figure 18.9 The heart is a double pump, each side supplying its own circuit. Slide Both sides of the heart pump at the same time, but let’s follow one Oxygen-poor blood 12 spurt of blood all the way through the system. Oxygen-rich blood Pulmonary Tricuspid Semilunar Superior vena cava (SVC) Right valve Right valve Pulmonary Inferior vena cava (IVC) Coronary sinus atrium ventricle trunk Pulmonary Tricuspid arteries SVC Coronary valve Pulmonary sinus trunk Right atrium Pulmonary Right semilunar IVC ventricle valve Oxygen-poor blood is carried Oxygen-poor blood To heart in two pulmonary arteries to To lungs returns from the body tissues back to the heart. the lungs (pulmonary circuit) to be oxygenated. Systemic Pulmonary capillaries capillaries Oxygen-rich blood is Oxygen-rich blood returns To body delivered to the body to the heart via the four To heart tissues (systemic circuit). pulmonary veins. Aorta Pulmonary veins Mitral Left Aortic semilunar valve atrium valve Left ventricle Aortic Semilunar Mitral Left valve Left Four © 2013 Pearson Education,Aorta valve ventricle atrium pulmonary Inc. veins  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 Pumps with greater pressure  Figure 18.10 Anatomical differences between the right and left ventricles. Left ventricle Right ventricle Interventricular septum © 2013 Pearson Education, Inc.  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  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  Figure 18.11a Coronary circulation. Aorta Pulmonar Superior y vena cava trunkLeft Anastomosis atrium (junction of vessels) Left coronary Right artery atrium Right Circumflex coronary artery artery Left Right ventricle ventricle Anterior Right interventricular marginal Posterior artery artery interventricular artery The major coronary arteries © 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  Figure 18.11b Coronary circulation. Superior vena cava Anterior Great cardiac cardiac veins vein Coronary sinus Small cardiac vein Middle cardiac vein The major cardiac veins © 2013 Pearson Education, Inc.  Figure 18.5d Gross anatomy of the heart. Aort a Superior vena cava Left pulmonary Right pulmonary artery arterypulmonary Right Left pulmonary veins veins Auricle of left atrium Right atrium Left atrium Inferior vena cava Great cardiac Coronary vein sinus Right coronary Posterior vein of artery left ventricle (in coronary sulcus) Posterior interventricular Left ventricle artery (in posterior interventricular sulcus) Middle cardiac vein Right ventricle Apex Posterior surface view © 2013 Pearson Education, Inc.  Homeostatic Imbalances 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  Outline The Pulmonary and Systemic Circuits Heart Anatomy Cardiac Muscle Fibers Heart Physiology  Microscopic Anatomy of Cardiac Muscle Cardiac muscle cells striated, short, branched, fat, interconnected, 1 (perhaps 2) central nuclei Connective tissue matrix (endomysium) connects to cardiac skeleton – Contains numerous capillaries T tubules wide, less numerous; SR simpler than in skeletal muscle Numerous large mitochondria (25–35% of cell volume)  Figure 18.12a Microscopic anatomy of cardiac muscle. Intercalated Cardiac Nucleus discs muscle cell Gap junctions Desmosomes © 2013 Pearson Education, Inc.  Microscopic Anatomy of Cardiac Muscle Intercalated discs - junctions between cells - anchor cardiac cells – Desmosomes prevent cells from separating during contraction – Gap junctions allow ions to pass from cell to cell; electrically couple adjacent cells Allows heart to be functional syncytium – Behaves as single coordinated unit  Figure 18.12b Microscopic anatomy of cardiac muscle. Cardiac muscle cell Mitochondrion Nucleus Intercalated disc Mitochondrion T tubule Sarcoplasmi c Z disc reticulum Nucleus Sarcolemm a I band I band A band © 2013 Pearson Education, Inc.  Cardiac Muscle Contraction Three differences from skeletal muscle: 1)~1% of cells have automaticity (autorhythmicity) Do not need nervous system stimulation Can depolarize entire heart 2)All cardiomyocytes contract as unit, or none do 3)Long absolute refractory period (250 ms) Prevents tetanic contractions  Cardiac Muscle Contraction Three similarities with skeletal muscle: 1. Depolarization opens few voltage-gated fast Na+ channels in sarcolemma  Reversal of membrane potential from –90 mV to +30 mV Brief; Na channels close rapidly 2. Depolarization wave down T tubules  SR to release Ca2+  3. Excitation-contraction coupling occurs Ca2+ binds troponin  filaments slide  Cardiac Muscle Contraction More differences – Depolarization wave also opens slow Ca2+ channels in sarcolemma 🡪 SR to release its Ca2+ – Ca2+ surge prolongs the depolarization phase (plateau)  Cardiac Muscle Contraction More differences – Action potential and contractile phase last much longer Allow blood ejection from heart – Repolarization result of inactivation of Ca2+ channels and opening of voltage-gated K+ channels Ca2+ pumped back to SR and extracellularly  Figure 18.13 The action potential of contractile cardiac muscle cells. Slide 2 Action potential 1 Depolarization is due to Na+ influx 20 Plateau through fast voltage-gated Na+ Membrane potential (mV) channels. A positive feedback cycle 0 Tension rapidly opens many Na+ channels, development reversing the membrane potential. Channel inactivation ends this phase. Tension (g) –20 (contraction) 1 –40 –60 Absolute refractory –80 period 0 150 300 Time (ms) © 2013 Pearson Education, Inc.  Figure 18.13 The action potential of contractile cardiac muscle cells. Slide 3 Action potential 1 Depolarization is due to Na+ influx 20 Plateau through fast voltage-gated Na+ Membrane potential (mV) channels. A positive feedback cycle 0 2 rapidly opens many Na+ channels, Tension development reversing the membrane potential. Channel inactivation ends this phase. Tension (g) –20 (contraction) 1 2 Plateau phase is due to Ca2+ –40 influx through slow Ca2+ channels. This keeps the cell depolarized –60 because few K+ channels are open. Absolute refractory –80 period 0 150 300 Time (ms) © 2013 Pearson Education, Inc.  Figure 18.13 The action potential of contractile cardiac muscle cells. Slide 4 Action potential 1 Depolarization is due to Na+ influx 20 Plateau through fast voltage-gated Na+ Membrane potential (mV) channels. A positive feedback cycle 0 2 rapidly opens many Na+ channels, Tension development reversing the membrane potential. Channel inactivation ends this phase. Tension (g) –20 (contraction) 1 3 2 Plateau phase is due to Ca2+ –40 influx through slow Ca2+ channels. This keeps the cell depolarized –60 because few K+ channels are open. Absolute refractory 3 Repolarization is due to Ca2+ –80 period channels inactivating and K+ channels opening. This allows K+ 0 150 300 efflux, which brings the membrane Time (ms) potential back to its resting voltage. © 2013 Pearson Education, Inc.  Energy Requirements Cardiac muscle – Has many mitochondria Great dependence on aerobic respiration Little anaerobic respiration ability – Readily switches fuel source for respiration Even uses lactic acid from skeletal muscles  Homeostatic Imbalance Ischemic cells  anaerobic respiration  lactic acid  – High H+ concentration  high Ca2+ concentration Mitochondrial damage  decreased ATP production  Gap junctions close  fatal arrhythmias  Outline The Pulmonary and Systemic Circuits Heart Anatomy Cardiac Muscle Fibers Heart Physiology  Heart Physiology: Electrical Events Heart depolarizes and contracts without nervous system stimulation – Rhythm can be altered by autonomic nervous system  Heart Physiology: Setting the Basic Rhythm Coordinated heartbeat is a function of – Presence of gap junctions – Intrinsic cardiac conduction system Network of noncontractile (autorhythmic) cells Initiate and distribute impulses 🡪 coordinated depolarization and contraction of heart Pacemaker (Autorhythmic) Cells Have unstable resting membrane potentials (pacemaker potentials or prepotentials) due to opening of slow Na+ channels – Continuously depolarize At threshold, Ca2+ channels open Explosive Ca2+ influx produces the rising phase of the action potential Repolarization results from inactivation of Ca2+ channels and opening of voltage-gated K+ channels Action Potential Initiation by Pacemaker Cells Three parts of action potential: – Pacemaker potential Repolarization closes K+ channels and opens slow Na+ channels  ion imbalance  – Depolarization Ca2+ channels open  huge influx rising phase of action potential – Repolarization K+ channels open  efflux of K+  Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 2 1 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is Action Threshold never a flat line. +10 potential Membrane potential (mV) 0 –10 –20 –30 –40 –50 1 1 –60 Pacemaker –70 potential Time (ms) © 2013 Pearson Education, Inc.  Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 3 1 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is Action Threshold never a flat line. +10 potential Membrane potential (mV) 0 2 Depolarization The action –10 potential begins when the 2 2 pacemaker potential reaches –20 threshold. Depolarization is due –30 to Ca2+ influx through Ca2+ –40 channels. –50 1 1 –60 Pacemaker –70 potential Time (ms) © 2013 Pearson Education, Inc.  Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart. Slide 4 1 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is Action Threshold never a flat line. +10 potential Membrane potential (mV) 0 2 Depolarization The action –10 potential begins when the 2 2 pacemaker potential reaches –20 threshold. Depolarization is due –30 3 3 to Ca2+ influx through Ca2+ –40 channels. –50 1 3 Repolarization is due to Ca2+ 1 –60 Pacemaker channels inactivating and potential K+ channels opening. This allows –70 K+ efflux, which brings the membrane potential back to its Time (ms) most negative voltage. © 2013 Pearson Education, Inc.  Sequence of Excitation Cardiac pacemaker cells pass impulses, in order, across heart in ~220 ms – Sinoatrial node  – Atrioventricular node – Atrioventricular bundle  – Right and left bundle branches : – Subendocardial conducting network (Purkinje fibers)  Heart Physiology: Sequence of Excitation Sinoatrial (SA) node – Pacemaker of heart in right atrial wall Depolarizes faster than rest of myocardium – Generates impulses about 75X/minute (sinus rhythm) Inherent rate of 100X/minute tempered by extrinsic factors Impulse spreads across atria, and to AV node  Heart Physiology: Sequence of Excitation Atrioventricular (AV) node – In inferior interatrial septum – Delays impulses approximately 0.1 second Because fibers are smaller diameter, have fewer gap junctions Allows atrial contraction prior to ventricular contraction – Inherent rate of 50X/minute in absence of SA node input  Heart Physiology: Sequence of Excitation Atrioventricular (AV) bundle (bundle of His) – In superior interventricular septum – Only electrical connection between atria and ventricles Atria and ventricles not connected via gap junctions  Heart Physiology: Sequence of Excitation Right and left bundle branches – Two pathways in interventricular septum – Carry impulses toward apex of heart  Heart Physiology: Sequence of Excitation Subendocardial conducting network – Complete pathway through interventricular septum into apex and ventricular walls – More elaborate on left side of heart – AV bundle and subendocardial conducting network depolarize 30X/minute in absence of AV node input Ventricular contraction immediately follows from apex toward atria  Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 2 Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway Left atrium Subendocardial conducting network (Purkinje fibers) Inter- ventricular septum Anatomy of the intrinsic conduction system showing the sequence of electrical © 2013 Pearson excitation Education, Inc.  Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 3 Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway Left 2 The impulses pause (0.1 s) at atrium the atrioventricular (AV) node. Subendocardial conducting network (Purkinje fibers) Inter- ventricular septum Anatomy of the intrinsic conduction system showing the sequence of electrical © 2013 Pearson excitation Education, Inc.  Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 4 Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway Left 2 The impulses pause (0.1 s) at atrium the atrioventricular (AV) node. 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje to the ventricles. fibers) Inter- ventricular septum Anatomy of the intrinsic conduction system showing the sequence of electrical © 2013 Pearson excitation Education, Inc.  Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 5 Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway Left 2 The impulses pause (0.1 s) at atrium the atrioventricular (AV) node. 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje to the ventricles. fibers) 4 The bundle branches conduct the impulses Inter- through the ventricular interventricular septum. septum Anatomy of the intrinsic conduction system showing the sequence of electrical © 2013 Pearson excitation Education, Inc.  Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat. Slide 6 Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway Left 2 The impulses pause (0.1 s) at atrium the atrioventricular (AV) node. 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje to the ventricles. fibers) 4 The bundle branches conduct the impulses Inter- through the ventricular interventricular septum. septum 5 The subendocardial conducting network depolarizes the contractile cells of both ventricles. Anatomy of the intrinsic conduction system showing the sequence of electrical © 2013 Pearson excitation Education, Inc.  Figure 18.15b Intrinsic cardiac conduction system and action potential succession during one heartbeat. Pacemaker potential SA node Atrial muscle AV node Pacemaker Ventricular potential muscle Plateau 10 20 30 40 0 0 0 0 0 Milliseconds Comparison of action potential shape at © 2013 Pearson Education, various locations Inc.  Homeostatic Imbalances Defects in intrinsic conduction system may cause – Arrhythmias - irregular heart rhythms – Uncoordinated atrial and ventricular contractions – Fibrillation - rapid, irregular contractions; useless for pumping blood 🡪 circulation ceases 🡪 brain death Defibrillation to treat  Homeostatic Imbalances Defective SA node may cause – Ectopic focus - abnormal pacemaker – AV node may take over; sets junctional rhythm (40–60 beats/min) Extrasystole (premature contraction) – Ectopic focus sets high rate – Can be from excessive caffeine or nicotine  Homeostatic Imbalance To reach ventricles, impulse must pass through AV node Defective AV node may cause – Heart block Few (partial) or no (total) impulses reach ventricles – Ventricles beat at intrinsic rate – too slow for life – Artificial pacemaker to treat  Extrinsic Innervation of the Heart Heartbeat modified by ANS via cardiac centers in medulla oblongata – Sympathetic  ↑ rate and force – Parasympathetic  ↓ rate – Cardioacceleratory center – sympathetic – affects SA, AV nodes, heart muscle, coronary arteries – Cardioinhibitory center – parasympathetic – inhibits SA and AV nodes via vagus nerves  Figure 18.16 Autonomic innervationDorsal of the heart. motor The vagus nerve (parasympathetic) nucleus decreases heart of vagus Cardioinhibitor rate. y center Cardioaccele Medulla - oblongata Sympatheti ratory center c trunk ganglion Thoracic spinal Sympathetic cord trunk Sympathetic cardiac nerves increase heart rate and force of contraction. AV node SA node © 2013 Pearson Education, Sympathetic Parasympathetic fibers Interneurons Inc. fibers  Electrocardiography Electrocardiogram (ECG or EKG) – Composite of all action potentials generated by nodal and contractile cells at given time Three waves: – P wave – depolarization SA node - atria – QRS complex - ventricular depolarization and atrial repolarization – T wave - ventricular repolarization  Figure 18.17 An electrocardiogram (ECG) tracing. Sinoatria l node Atrioventricular node QRS complex R Ventricular depolarization Ventricular Atrial repolarizatio depolarization n P T Q S-T P-R Interva Segmen l t Q-T S Interva l 0 0.2 0.4 0.6 0.8 © 2013 Pearson Education, Inc. Time (s) Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection waves of an Slide ECG tracing. 1 SA node R R P T P T Q S Q S 1 Atrial depolarization, initiated by 4 Ventricular depolarization is the SA node, causes the P wave. complete. R AV node R P T P T Q Q S S 2 With atrial depolarization 5 Ventricular repolarization complete, the impulse is delayed at begins at apex, causing the T wave. the AV node. R R P T P T Q Q S S 6 Ventricular repolarization is 3 Ventricular depolarization begins at complete. apex, causing the QRS complex. Atrial Depolarizatio repolarization occurs. Repolarization n © 2013 Pearson Education, Inc.  Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection Slide waves of an ECG tracing. 2 SA node R Depolarization Repolarization P T Q S 1 Atrial depolarization, initiated by the SA node, causes the P wave. © 2013 Pearson Education, Inc.  Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection Slide waves of an ECG tracing. 3 SA node R Depolarization Repolarization P T Q S 1 Atrial depolarization, initiated by the SA node, causes the P wave. AV node R P T Q S 2 With atrial depolarization complete, the impulse is delayed at the AV node. © 2013 Pearson Education, Inc.  Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection Slide waves of an ECG tracing. 4 SA node R Depolarization Repolarization P T Q S 1 Atrial depolarization, initiated by the SA node, causes the P wave. AV node R P T Q S 2 With atrial depolarization complete, the impulse is delayed at the AV node. R P T Q S 3 Ventricular depolarization begins at apex, causing the QRS © 2013 Pearson Education, complex. Atrial repolarization Inc. occurs.  Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection Slide waves of an ECG tracing. 5 Depolarization R Repolarization P T Q S 4 Ventricular depolarization is complete. © 2013 Pearson Education, Inc.  Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection Slide waves of an ECG tracing. 6 Depolarization R Repolarization P T Q S 4 Ventricular depolarization is complete. R P T Q S 5 Ventricular repolarization begins at apex, causing the T wave. © 2013 Pearson Education, Inc.  Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection Slide waves of an ECG tracing. 7 Depolarization R Repolarization P T Q S 4 Ventricular depolarization is complete. R P T Q S 5 Ventricular repolarization begins at apex, causing the T wave. R P T Q