2015 Pearson Education, Inc. Lecture Presentation by Lee Ann Frederick University of Texas at Arlington Chapter 20 The Heart 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System Learning Outcomes 20-1Describe the anatomy of the heart, including vascular supply and pericardium structure, and trace the flow of blood through the heart, identifying the major blood vessels, chambers, and heart valves. 20-2Explain the events of an action potential in cardiac muscle, indicate the importance of calcium ions to the contractile process, describe the conducting system of the heart, and identify the electrical events associated with a normal electrocardiogram. 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System Learning Outcomes 20-3Explain the events of the cardiac cycle, including atrial and ventricular systole and diastole, and relate the heart sounds to specific events in the cycle. 20-4Define cardiac output, describe the factors that influence heart rate and stroke volume, and explain how adjustments in stroke volume and cardiac output are coordinated at different levels of physical activity. 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System The Pulmonary Circuit Carries blood to and from gas exchange surfaces of the lungs The Systemic Circuit Carries blood to and from the rest of the body Blood alternates between pulmonary circuit and systemic circuit 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System Three Types of Blood Vessels 1. Arteries Carry blood away from heart (efferent) 2. Veins Carry blood to heart (afferent) 3. Capillaries Networks between arteries and veins (inter- conection) Microscopic thin-walled exchange vessels between blood and tissues dissolved gases, nutrients, waste products 2015 Pearson Education, Inc. Figure 20-1 An Overview of the Cardiovascular System. Pulmonary arteries Pulmonary veins Systemic arteries Systemic veins PULMONARY CIRCUIT SYSTEMIC CIRCUIT Capillaries in lungs Right atrium Right ventricle Capillaries in trunk and lower limbs Capillaries in head, neck, upper limbs Left atrium Left ventricle 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System Four Muscular Chambers of the Heart 1. Right atrium Collects blood from systemic circuit 2. Right ventricle Pumps blood to pulmonary circuit 3. Left atrium Collects blood from pulmonary circuit 4. Left ventricle Pumps blood to systemic circuit 2015 Pearson Education, Inc Anatomy of the Heart The Heart Surrounded by pericardial sac Sits between two pleural cavities in the mediastinum Near anterior chest wall Directly posterior to the sternum Great veins and arteries at the base Pointed tip is apex 2015 Pearson Education, Inc. Figure 20-2a The Location of the Heart in the Thoracic Cavity. Trachea First rib (cut) Base of heart Right lung Parietal pericardium (cut) Thyroid gland Left lung Apex of heart Diaphragm An anterior view of the chest, showing the position of the heart and major blood vessels relative to the ribs, lungs, and diaphragm. a 2015 Pearson Education, Inc Anatomy of the Heart The Pericardium Double lining of the pericardial cavity Visceral pericardium Inner layer of pericardium Parietal pericardium Outer layer Forms inner layer of pericardial sac 2015 Pearson Education, Inc. Figure 20-2b The Location of the Heart in the Thoracic Cavity. Esophagus b Right pleural cavity Right lung Bronchus of lung Right pulmonary artery Right pulmonary vein Posterior mediastinum Aortic arch Right atrium Anterior mediastinum Right ventricle Superior vena cava Sternum Pericardial sac Epicardium Pericardial cavity Left atrium Left ventricle Pulmonary trunk Left pulmonary vein Left pleural cavity Left lung Left pulmonary artery Aorta (arch segment removed) A superior view of the organs in the mediastinum; portions of the lungs have been removed to reveal blood vessels and airways. The heart is located in the anterior part of the mediastinum, immediately posterior to the sternum. 2015 Pearson Education, Inc Anatomy of the Heart The Pericardium Pericardial cavity Is between parietal and visceral layers Contains pericardial fluid Pericardial sac Fibrous tissue Surrounds and stabilizes heart 2015 Pearson Education, Inc. Figure 20-2c The Location of the Heart in the Thoracic Cavity. Balloon c Base of heart Fibrous attachment to diaphragm Cut edge of parietal pericardium Fibrous tissue of pericardial sac Parietal pericardium Areolar tissue Mesothelium Cut edge of epicardium Apex of heart Wrist (corresponds to base of heart) Inner wall (corresponds to epicardium) Air space (corresponds to pericardial cavity) Outer wall (corresponds to parietal pericardium) The relationship between the heart and the pericardial cavity; compare with the fist-and-balloon example. Pericarditis Cardiac tamponade Pericardioscentesis 2015 Pearson Education, Inc Anatomy of the Heart Superficial Anatomy of the Heart Atria Thin-walled Expandable outer auricle (atrial appendage) Sulci Coronary sulcus divides atria and ventricles Anterior inter-ventricular sulcus Posterior inter-ventricular sulcus Separate left and right ventricles Contain blood vessels of cardiac muscle 2015 Pearson Education, Inc. Figure 20-3a The Position and Superficial Anatomy of the Heart. 1 a Base of heart Ribs Apex of heart Heart position relative to the rib cage. 2015 Pearson Education, Inc. Figure 20-3b The Position and Superficial Anatomy of the Heart. Left ventricle b Fat and vessels in anterior interventricular sulcus Auricle of left atrium Pulmonary trunk Left pulmonary artery Descending aorta Ligamentum arteriosum Arch of aorta Left subclavian artery Right atrium Right ventricle Superior vena cava Left common carotid artery Brachiocephalic trunk Ascending aorta Auricle of right atrium Fat and vessels in coronary sulcus Major anatomical features on the anterior surface. 2015 Pearson Education, Inc. Figure 20-3c The Position and Superficial Anatomy of the Heart. Right ventricle c Left subclavian artery Left common carotid artery Brachiocephalic trunk Ascending aorta Superior vena cava Auricle of right atrium Right atrium Right coronary artery Coronary sulcus Ligamentum arteriosum Left pulmonary artery Pulmonary trunk Auricle of left atrium Left coronary artery (LCA) Anterior interventricular sulcus Left ventricle Anterior interventricular branch of LCA Marginal branch of right coronary artery Anterior surface of the heart, cadaver dissection. 2015 Pearson Education, Inc. Figure 20-3d The Position and Superficial Anatomy of the Heart. Left ventricle d Left atrium Right ventricle Right atrium Left pulmonary artery Left pulmonary veins Fat and vessels in coronary sulcus Coronary sinus Arch of aorta Right pulmonary artery Superior vena cava Right pulmonary veins (superior and inferior) Inferior vena cava Fat and vessels in posterior interventricular sulcus Major landmarks on the posterior surface. Coronary arteries (which supply the heart itself) are shown in red; coronary veins are shown in blue. 2015 Pearson Education, Inc Anatomy of the Heart The Heart Wall Epicardium (Outer layer, serous membrane) Visceral pericardium Covers the heart Myocardium (Middle Layer, muscular) Concentric layers of cardiac muscle tissue Atrial myocardium wraps around great vessels Two divisions of ventricular myocardium Endocardium (Inner Layer) Simple squamous epithelium 2015 Pearson Education, Inc. Figure 20-4a The Heart Wall. Artery a Vein Parietal pericardium Dense fibrous layer Areolar tissue Mesothelium Epicardium (visceral pericardium) Mesothelium Areolar tissue Endocardium Areolar tissue Endothelium Myocardium (cardiac muscle tissue) Cardiac muscle cells Connective tissues Pericardial cavity Heart wall A diagrammatic section through the heart wall, showing the relative positions of the epicardium, myocardium, and endocardium. The proportions are not to scale; the thickness of the myocardial wall has been greatly reduced. The Heart Wall 1. Epicardium 2. Myocardium 3. Endocardium 2015 Pearson Education, Inc. Figure 20-4b The Heart Wall. Cardiac muscle tissue forms -concentric layers that wrap around the atria or -spiral within the walls of the ventricles. Ventricular musculature Atrial musculature b 2015 Pearson Education, Inc Anatomy of the Heart Cardiac Muscle Tissue Intercalated discs Interconnect cardiac muscle cells Secured by desmosomes Linked by gap junctions Transfer the force of contraction from cell to cell Propagate action potentials 2015 Pearson Education, Inc. Figure 20-5a Cardiac Muscle Cells. Nucleus a Cardiac muscle cell (sectioned) Bundles of myofibrils Intercalated discs Cardiac muscle cells Cardiac muscle cell Mitochondria Intercalated disc (sectioned) 2015 Pearson Education, Inc. Figure 20-5b Cardiac Muscle Cells. b Structure of an intercalated disc Desmosomes Intercalated disc Gap junction Z-lines bound to opposing plasma membranes 2015 Pearson Education, Inc. Figure 20-5c Cardiac Muscle Cells. c Intercalated discs LM x 575 Cardiac muscle tissue 2015 Pearson Education, Inc Anatomy of the Heart Characteristics of Cardiac Muscle Cells 1.Small size 2.Single, central nucleus 3.Branching interconnections between cells 4.Intercalated discs 2015 Pearson Education, Inc. Table 20-1 Structural and Functional Differences between Cardiac Muscle Cells and Skeletal Muscle Fibers. 2015 Pearson Education, Inc Anatomy of the Heart Internal Anatomy and Organization Interatrial septum separates atria Interventricular septum separates ventricles 2015 Pearson Education, Inc Anatomy of the Heart Internal Anatomy and Organization Atrioventricular (AV) valves Connect right atrium to right ventricle and left atrium to left ventricle Are folds of fibrous tissue that extend into openings between atria and ventricles Permit blood flow in one direction From atria to ventricles 2015 Pearson Education, Inc Anatomy of the Heart The Right Atrium Superior vena cava Receives blood from head, neck, upper limbs, and chest Inferior vena cava Receives blood from trunk, viscera, and lower limbs Coronary sinus Cardiac veins return blood to coronary sinus Coronary sinus opens into right atrium 2015 Pearson Education, Inc Anatomy of the Heart The Right Atrium Foramen ovale Before birth, is an opening through interatrial septum Connects the two atria Seals off at birth, forming fossa ovalis 2015 Pearson Education, Inc Anatomy of the Heart The Right Atrium Pectinate muscles Contain prominent muscular ridges On anterior atrial wall and inner surfaces of right auricle 2015 Pearson Education, Inc. Figure 20-6a The Sectional Anatomy of the Heart. Aortic arch a Brachiocephalic trunk Superior vena cava Right pulmonary arteries Ascending aorta Fossa ovalis Left common carotid artery Left subclavian artery Ligamentum arteriosum Pulmonary trunk Pulmonary valve Left pulmonary arteries Left pulmonary veins Left atrium Interatrial septum Aortic valve Cusp of left AV (mitral) valve Left ventricle Interventricular septum Opening of coronary sinus Right atrium Pectinate muscles Conus arteriosus Cusp of right AV (tricuspid) valve Chordae tendineae Trabeculae carneae Moderator band Descending aorta Papillary muscles Right ventricle Inferior vena cava A diagrammatic frontal section through the heart, showing major landmarks and the path of blood flow (marked by arrows) through the atria, ventricles, and associated vessels. 2015 Pearson Education, Inc. Figure 20-6c The Sectional Anatomy of the Heart. Right atrium c Left subclavian artery Left common carotid artery Brachiocephalic trunk Superior vena cava Ascending aorta Cusps of right AV (tricuspid) valve Trabeculae carneae Right ventricle Pulmonary trunk Cusp of pulmonary valve Auricle of left atrium Cusp of left AV (bicuspid) valve Chordae tendineae Papillary muscles Left ventricle Interventricular septum Anterior view of a frontally sectioned heart showing internal features and valves. 2015 Pearson Education, Inc Anatomy of the Heart The Right Ventricle Free edges attach to chordae tendineae from papillary muscles of ventricle Prevent valve from opening backward Right atrioventricular (AV) valve Also called tricuspid valve Opening from right atrium to right ventricle Has three cusps Prevents backflow 2015 Pearson Education, Inc Anatomy of the Heart The Right Ventricle Trabeculae carneae Muscular ridges on internal surface of right (and left) ventricle Includes moderator band Ridge contains part of conducting system Coordinates contractions of cardiac muscle cells 2015 Pearson Education, Inc. Figure 20-6b The Sectional Anatomy of the Heart. Chordae tendineae b Papillary muscles The papillary muscles and chordae tendineae support the right AV (tricuspid) valve. The photograph was taken from inside the right ventricle, looking toward a light shining from the right atrium. 2015 Pearson Education, Inc Anatomy of the Heart The Pulmonary Circuit Conus arteriosus (superior end of right ventricle) leads to pulmonary trunk Pulmonary trunk divides into left and right pulmonary arteries Blood flows from right ventricle to pulmonary trunk through pulmonary valve Pulmonary valve has three semilunar cusps 2015 Pearson Education, Inc Anatomy of the Heart The Left Atrium Blood gathers into left and right pulmonary veins Pulmonary veins deliver to left atrium Blood from left atrium passes to left ventricle through left atrioventricular (AV) valve A two-cusped bicuspid valve or mitral valve 2015 Pearson Education, Inc Anatomy of the Heart The Left Ventricle Holds same volume as right ventricle Is larger; muscle is thicker and more powerful Similar internally to right ventricle but does not have moderator band 2015 Pearson Education, Inc Anatomy of the Heart The Left Ventricle Systemic circulation Blood leaves left ventricle through aortic valve into ascending aorta Ascending aorta turns (aortic arch) and becomes descending aorta 2015 Pearson Education, Inc. Figure 20-6c The Sectional Anatomy of the Heart. Right atrium c Left subclavian artery Left common carotid artery Brachiocephalic trunk Superior vena cava Ascending aorta Cusps of right AV (tricuspid) valve Trabeculae carneae Right ventricle Pulmonary trunk Cusp of pulmonary valve Auricle of left atrium Cusp of left AV (bicuspid) valve Chordae tendineae Papillary muscles Left ventricle Interventricular septum Anterior view of a frontally sectioned heart showing internal features and valves. 2015 Pearson Education, Inc Anatomy of the Heart Structural Differences between the Left and Right Ventricles Right ventricle wall is thinner, develops less pressure than left ventricle Right ventricle is pouch-shaped, left ventricle is round 2015 Pearson Education, Inc. Figure 20-7a Structural Differences between the Left and Right Ventricles. Left ventricle a Posterior interventricular sulcus Right ventricle Fat in anterior interventricular sulcus A diagrammatic sectional view through the heart, showing the relative thicknesses of the two ventricles. Notice the pouchlike shape of the right ventricle and the greater thickness of the left ventricle. 2015 Pearson Education, Inc. Figure 20-7b Structural Differences between the Left and Right Ventricles. Left ventricle Right ventricle Dilated Contracted Diagrammatic views of the ventricles just before a contraction (dilated) and just after a contraction (contracted). b 2015 Pearson Education, Inc Anatomy of the Heart The Heart Valves Two pairs of one-way valves prevent backflow during contraction Atrioventricular (AV) valves Between atria and ventricles Blood pressure closes valve cusps during ventricular contraction Papillary muscles tense chordae tendineae to prevent valves from swinging into atria 2015 Pearson Education, Inc Anatomy of the Heart The Heart Valves Semilunar valves Pulmonary and aortic tricuspid valves Prevent backflow from pulmonary trunk and aorta into ventricles Have no muscular support Three cusps support like tripod 2015 Pearson Education, Inc Anatomy of the Heart Aortic Sinuses At base of ascending aorta Sacs that prevent valve cusps from sticking to aorta Origin of right and left coronary arteries 2015 Pearson Education, Inc. Figure 20-8a Valves of the Heart (Part 1 of 2). Cardiac skeleton a Transverse Sections, Superior View, Atria and Vessels Removed POSTERIOR RIGHT VENTRICLE LEFT VENTRICLE Left AV (bicuspid) valve (open) Right AV (tricuspid) valve (open) Aortic valve (closed) Pulmonary valve (closed) ANTERIOR Relaxed ventricles When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are loose, and the papillary muscles are relaxed. Aortic valve closed 2015 Pearson Education, Inc. Figure 20-8a Valves of the Heart (Part 2 of 2). Aortic valve (closed) Pulmonary veins LEFT ATRIUM Left AV (bicuspid) valve (open) Chordae tendineae (loose) Papillary muscles (relaxed) LEFT VENTRICLE (relaxed and filling with blood) Frontal Sections through Left Atrium and Ventricle Relaxed ventricles When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are loose, and the papillary muscles are relaxed. a 2015 Pearson Education, Inc. Figure 20-8b Valves of the Heart (Part 1 of 2). b Contracting ventricles When the ventricles are contracting, the AV valves are closed and the semilunar valves are open. In the frontal section notice the attachment of the left AV valve to the chordae tendineae and papillary muscles. Aortic valve open RIGHT VENTRICLE LEFT VENTRICLE Right AV (tricuspid) valve (closed) Cardiac skeleton Left AV (bicuspid) valve (closed) Aortic valve (open) Pulmonary valve (open) 2015 Pearson Education, Inc. Figure 20-8b Valves of the Heart (Part 2 of 2). b Contracting ventricles When the ventricles are contracting, the AV valves are closed and the semilunar valves are open. In the frontal section notice the attachment of the left AV valve to the chordae tendineae and papillary muscles. Aorta Aortic sinus Aortic valve (open) LEFT ATRIUM Left AV (bicuspid) valve (closed) Chordae tendineae (tense) Papillary muscles (contracted) Left ventricle (contracted) 2015 Pearson Education, Inc Anatomy of the Heart Connective Tissues and the Cardiac Skeleton Connective tissue fibers 1.Physically support cardiac muscle fibers 2.Distribute forces of contraction 3.Add strength and prevent overexpansion of heart 4.Provide elasticity that helps return heart to original size and shape after contraction 2015 Pearson Education, Inc Anatomy of the Heart The Cardiac Skeleton Four bands around heart valves and bases of pulmonary trunk and aorta Stabilize valves Electrically insulate ventricular cells from atrial cells 2015 Pearson Education, Inc Anatomy of the Heart The Blood Supply to the Heart = Coronary circulation Supplies blood to muscle tissue of heart Coronary arteries and cardiac veins 2015 Pearson Education, Inc Anatomy of the Heart The Coronary Arteries Left and right Originate at aortic sinuses High blood pressure, elastic rebound forces blood through coronary arteries between contractions 2015 Pearson Education, Inc Anatomy of the Heart Right Coronary Artery Supplies blood to: Right atrium Portions of both ventricles Cells of sinoatrial (SA) and atrioventricular nodes Marginal arteries (surface of right ventricle) Posterior interventricular artery 2015 Pearson Education, Inc Anatomy of the Heart Left Coronary Artery Supplies blood to: Left ventricle Left atrium Interventricular septum 2015 Pearson Education, Inc Anatomy of the Heart Two Main Branches of Left Coronary Artery 1. Circumflex artery 2. Anterior interventricular artery Arterial Anastomoses Interconnect anterior and posterior interventricular arteries Stabilize blood supply to cardiac muscle 2015 Pearson Education, Inc Anatomy of the Heart The Cardiac Veins Great cardiac vein Drains blood from area of anterior interventricular artery into coronary sinus Anterior cardiac veins Empty into right atrium Posterior cardiac vein, middle cardiac vein, and small cardiac vein Empty into great cardiac vein or coronary sinus 2015 Pearson Education, Inc. Figure 20-9a The Coronary Circulation. Aortic arch Ascending aorta Right coronary artery Atrial arteries Anterior cardiac veins Small cardiac vein Marginal artery Left coronary artery Pulmonary trunk Circumflex artery Anterior interventricular artery Great cardiac vein Coronary vessels supplying and draining the anterior surface of the heart. a 2015 Pearson Education, Inc. Figure 20-9b The Coronary Circulation. b Coronary vessels supplying and draining the posterior surface of the heart. Left ventricle Marginal artery Middle cardiac vein Right coronary artery Small cardiac vein Coronary sinus Circumflex artery Great cardiac vein Marginal artery Posterior interventricular artery Posterior cardiac vein 2015 Pearson Education, Inc. Figure 20-9c The Coronary Circulation. c Auricle of left atrium Circumflex artery Great cardiac vein Marginal artery Posterior cardiac vein Posterior interventricular artery Left pulmonary veins Left pulmonary artery Right pulmonary artery Superior vena cava Right pulmonary veins Left atrium Right atrium Inferior vena cava Coronary sinus Middle cardiac vein Right ventricle A posterior view of the heart; the vessels have been injected with colored latex (liquid rubber). 2015 Pearson Education, Inc. Figure Heart Disease and Heart Attacks (Part 2 of 4). Cross section Tunica externa Tunica media Lipid deposit of plaque Normal Artery Narrowing of Artery 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Coronary artery disease (CAD) Areas of partial or complete blockage of coronary circulation Cardiac muscle cells need a constant supply of oxygen and nutrients Reduction in blood flow to heart muscle produces a corresponding reduction in cardiac performance Reduced circulatory supply, coronary ischemia, results from partial or complete blockage of coronary arteries 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Usual cause is formation of a fatty deposit, or atherosclerotic plaque, in the wall of a coronary vessel The plaque, or an associated thrombus (clot), then narrows the passageway and reduces blood flow Spasms in smooth muscles of vessel wall can further decrease or stop blood flow One of the first symptoms of CAD is commonly angina pectoris 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Angina pectoris In its most common form, a temporary ischemia develops when the workload of the heart increases Although the individual may feel comfortable at rest, exertion or emotional stress can produce a sensation of pressure, chest constriction, and pain that may radiate from the sternal area to the arms, back, and neck 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Myocardial infarction (MI), or heart attack Part of the coronary circulation becomes blocked, and cardiac muscle cells die from lack of oxygen The death of affected tissue creates a nonfunctional area known as an infarct Heart attacks most commonly result from severe coronary artery disease (CAD) 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Myocardial infarction (MI), or heart attack Consequences depend on the site and nature of the circulatory blockage If it occurs near the start of one of the coronary arteries: The damage will be widespread and the heart may stop beating If the blockage involves one of the smaller arterial branches: The individual may survive the immediate crisis but may have many complications such as reduced contractility and cardiac arrhythmias 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Myocardial infarction (MI), or heart attack A crisis often develops as a result of thrombus formation at a plaque (the most common cause of an MI), a condition called coronary thrombosis A vessel already narrowed by plaque formation may also become blocked by a sudden spasm in the smooth muscles of the vascular wall Individuals having an MI experience intense pain, similar to that felt in angina, but persisting even at rest 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Myocardial infarction (MI), or heart attack Pain does not always accompany a heart attack; therefore, the condition may go undiagnosed and may not be treated before a fatal MI occurs A myocardial infarction can usually be diagnosed with an ECG and blood studies Damaged myocardial cells release enzymes into the circulation, and these elevated enzymes can be measured in diagnostic blood tests The enzymes include: Cardiac troponin T, Cardiac troponin I, A special form of creatinine phosphokinase, CK-MB 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Treatment of CAD and myocardial infarction About 25 percent of MI patients die before obtaining medical assistance 65 percent of MI deaths among those under age 50 occur within an hour after the initial infarction 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Treatment of CAD and myocardial infarction Risk factor modification Stop smoking High blood pressure treatment Dietary modification to lower cholesterol and promote weight loss Stress reduction Increased physical activity (where appropriate) 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Treatment of CAD and myocardial infarction Drug treatment Drugs that reduce coagulation and therefore the risk of thrombosis, such as aspirin and coumadin Drugs that block sympathetic stimulation (propranolol or metoprolol) Drugs that cause vasodilation, such as nitroglycerin Drugs that block calcium movement into the cardiac and vascular smooth muscle cells (calcium channel blockers) In a myocardial infarction, drugs to relieve pain, fibrinolytic agents to help dissolve clots, and oxygen 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Treatment of CAD and myocardial infarction Noninvasive surgery Atherectomy Blockage by a single, soft plaque may be reduced with the aid of a long, slender catheter inserted into a coronary artery to the plaque 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Treatment of CAD and myocardial infarction Noninvasive surgery Balloon angioplasty The tip of the catheter contains an inflatable balloon Once in position, the balloon is inflated, pressing the plaque against the vessel walls Because plaques commonly redevelop after angioplasty, a fine tubular wire mesh called a stent may be inserted into the vessel, holding it open 2015 Pearson Education, Inc Anatomy of the Heart Heart Disease Coronary Artery Disease Treatment of CAD and myocardial infarction Coronary artery bypass graft (CABG) In a coronary artery bypass graft, a small section is removed from either a small artery or a peripheral vein and is used to create a detour around the obstructed portion of a coronary artery As many as four coronary arteries can be rerouted this way during a single operation The procedures are named according to the number of vessels repaired, so we speak of single, double, triple, or quadruple coronary bypasses 2015 Pearson Education, Inc. Figure Heart Disease and Heart Attacks (Part 1 of 4). Normal Heart A color-enhanced digital subtraction angiography (DSA) scan of a normal heart. Advanced Coronary Artery Disease A color-enhanced DSA scan showing advanced coronary artery disease. Blood flow to the ventricular myocardium is severely restricted. 2015 Pearson Education, Inc. Figure Heart Disease and Heart Attacks (Part 3 of 4). Occluded Coronary Artery Damaged Heart Muscle 2015 Pearson Education, Inc The Conducting System Heartbeat A single contraction of the heart The entire heart contracts in series First the atria Then the ventricles 2015 Pearson Education, Inc The Conducting System Cardiac Physiology Two types of cardiac muscle cells 1. Conducting system Controls and coordinates heartbeat 2. Contractile cells Produce contractions that propel blood 2015 Pearson Education, Inc The Conducting System The Cardiac Cycle Begins with action potential at SA node Transmitted through conducting system Produces action potentials in cardiac muscle cells (contractile cells) Electrocardiogram (ECG or EKG) Electrical events in the cardiac cycle can be recorded on an electrocardiogram 2015 Pearson Education, Inc The Conducting System The Conducting System A system of specialized cardiac muscle cells Initiates and distributes electrical impulses that stimulate contraction Automaticity Cardiac muscle tissue contracts automatically 2015 Pearson Education, Inc The Conducting System Structures of the Conducting System Sinoatrial (SA) node wall of right atrium Atrioventricular (AV) node junction between atria and ventricles Conducting cells throughout myocardium 2015 Pearson Education, Inc The Conducting System Conducting Cells Interconnect SA and AV nodes Distribute stimulus through myocardium In the atria Internodal pathways In the ventricles AV bundle and the bundle branches 2015 Pearson Education, Inc The Conducting System Prepotential Also called pacemaker potential Resting potential of conducting cells Gradually depolarizes toward threshold SA node depolarizes first, establishing heart rate 2015 Pearson Education, Inc. Figure 20-11a The Conducting System of the Heart. a Sinoatrial (SA) node Internodal pathways Atrioventricular (AV) node AV bundle Bundle branches Purkinje fibers Components of the conducting system. 2015 Pearson Education, Inc. Figure 20-11b The Conducting System of the Heart. Threshold Prepotential Time (sec) mV b +20 mV 20 mV 40 mV 60 mV Changes in the membrane potential of a pacemaker cell in the SA node that is establishing a heart rate of 72 beats per minute. Note the presence of a prepotential, a gradual spontaneous depolarization. 2015 Pearson Education, Inc The Conducting System Heart Rate SA node generates 80100 action potentials per minute Parasympathetic stimulation slows heart rate AV node generates 4060 action potentials per minute 2015 Pearson Education, Inc The Conducting System The Sinoatrial (SA) Node In posterior wall of right atrium Contains pacemaker cells Connected to AV node by internodal pathways Begins atrial activation (Step 1) 2015 Pearson Education, Inc. Figure Impulse Conduction through the Heart (Part 1 of 5). SA node 1 SA node activity and atrial activation begin. Time = 0 2015 Pearson Education, Inc The Conducting System The Atrioventricular (AV) Node In floor of right atrium Receives impulse from SA node (Step 2) Delays impulse (Step 3) Atrial contraction begins 2015 Pearson Education, Inc. Figure Impulse Conduction through the Heart (Part 2 of 5). AV node 2 Stimulus spreads across the atrial surfaces and reaches the AV node. Elapsed time = 50 msec 2015 Pearson Education, Inc. Figure Impulse Conduction through the Heart (Part 3 of 5). AV bundle 3 There is a 100-msec delay at the AV node. Atrial contraction begins. Elapsed time = 150 msec Bundle branches 2015 Pearson Education, Inc The Conducting System The AV Bundle In the septum Carries impulse to left and right bundle branches Which conduct to Purkinje fibers (Step 4) And to the moderator band Which conducts to papillary muscles 2015 Pearson Education, Inc. Figure Impulse Conduction through the Heart (Part 4 of 5). Moderator band 4 The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibers and, by the moderator band, to the papillary muscles of the right ventricle. Elapsed time = 175 msec 2015 Pearson Education, Inc The Conducting System Purkinje Fibers Distribute impulse through ventricles (Step 5) Atrial contraction is completed Ventricular contraction begins 2015 Pearson Education, Inc. Figure Impulse Conduction through the Heart (Part 5 of 5). Purkinje fibers 5 The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed, and ventricular contraction begins. Elapsed time = 225 msec 2015 Pearson Education, Inc The Conducting System Abnormal Pacemaker Function Bradycardia abnormally slow heart rate Tachycardia abnormally fast heart rate Ectopic pacemaker Abnormal cells Generate high rate of action potentials Bypass conducting system Disrupt ventricular contractions 2015 Pearson Education, Inc The Conducting System The Electrocardiogram (ECG or EKG) A recording of electrical events in the heart Obtained by electrodes at specific body locations Abnormal patterns diagnose damage 2015 Pearson Education, Inc The Conducting System Features of an ECG P wave Atria depolarize QRS complex Ventricles depolarize T wave Ventricles repolarize 2015 Pearson Education, Inc The Conducting System Time Intervals between ECG Waves PR interval From start of atrial depolarization To start of QRS complex QT interval From ventricular depolarization To ventricular repolarization 2015 Pearson Education, Inc. Figure 20-13a An Electrocardiogram. a Electrode placement for recording a standard ECG. 2015 Pearson Education, Inc. Figure 20-13b An Electrocardiogram. b P wave (atria depolarize) PR interval R S Q T wave (ventricles repolarize) ST interval QT interval PR segment ST segment QRS interval (ventricles depolarize) R Millivolts 0.5 An ECG printout is a strip of graph paper containing a record of the electrical events monitored by the electrodes. The placement of electrodes on the body surface affects the size and shape of the waves recorded. The example is a normal ECG; the enlarged section indicates the major components of the ECG and the measurements most often taken during clinical analysis. 800 msec 2015 Pearson Education, Inc. Figure Cardiac Arrhythmias (Part 1 of 2). Premature Atrial Contractions (PACs) Paroxysmal Atrial Tachycardia (PAR) Atrial Fibrillation (AF) Premature atrial contractions (PACs) often occur in healthy individuals. In a PAC, the normal atrial rhythm is momentarily interrupted by a surprise atrial contraction. Stress, caffeine, and various drugs may P P P PPPPPP increase the incidence of PACs, presumably by increasing the permeabilities of the SA pacemakers. The impulse spreads along the conduction pathway, and a normal ventricular contraction follows the atrial beat. In paroxysmal (par-ok-SIZ-mal) atrial tachycardia, or PAT, a premature atrial contraction triggers a flurry of atrial activity. The ventricles are still able to keep pace, and the heart rate jumps to about 180 beats per minute. During atrial fibrillation (fib-ri-L-shun), the impulses move over the atrial surface at rates of perhaps 500 beats per minute. The atrial wall quivers instead of producing an organized contraction. The ventricular rate cannot follow the atrial rate and may remain within normal limits. Even though the atria are now nonfunctional, their contribution to ventricular end-diastolic volume (the maximum amount of blood the ventricles can hold at the end of atrial contraction) is so small that the condition may go unnoticed in older individuals. 2015 Pearson Education, Inc. Figure Cardiac Arrhythmias (Part 2 of 2). Premature Ventricular Contractions (PVCs) Ventricular Tachycardia (VT) Ventricular Fibrillation (VF) Premature ventricular contractions (PVCs) occur when a Purkinje cell or ventricular myocardial cell depolarizes to threshold and triggers a premature contraction. Single PVCs are common and not dangerous. The cell PP P P TT T responsible is called an ectopic pacemaker. The frequency of PVCs can be increased by exposure to epinephrine, to other stimulatory drugs, or to ionic changes that depolarize cardiac muscle plasma membranes. Ventricular fibrillation (VF) is responsible for the condition known as cardiac arrest. VF is rapidly fatal, because the ventricles quiver and stop pumping blood. Ventricular tachycardia is defined as four or more PVCs without intervening normal beats. It is also known as VT or V-tach. Multiple PVCs and VT may indicate that serious cardiac problems exist. 2015 Pearson Education, Inc The Conducting System Contractile Cells Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart Resting potential Of a ventricular cell about 90 mV Of an atrial cell about 80 mV 2015 Pearson Education, Inc. Figure 20-15a The Action Potentials in Skeletal and Cardiac Muscle. Stimulus 90 mV Time (msec) Relative refractory period Absolute refractory period KEY Absolute refractory period Relative refractory period Rapid Depolarization Cause: Na + entry Duration: 35 msec Ends with: Closure of voltage-gated fast sodium channels The Plateau Cause: Ca 2+ entry Duration: 175 msec Ends with: Closure of slow calcium channels Repolarization Cause: K + loss Duration: 75 msec Ends with: Closure of slow potassium channels a Events in an action potential in a ventricular muscle cell. 2015 Pearson Education, Inc. Figure 20-15b The Action Potentials in Skeletal and Cardiac Muscle. Contraction Skeletal muscle Action potential Contraction Cardiac muscle Action potential Time (msec) Tension Time (msec) 90 mV 85 mV b Action potentials and twitch contractions in a skeletal muscle (above) and cardiac muscle (below). The shaded areas indicate the durations of the absolute (blue) and relative (beige) refractory periods. KEY Absolute refractory period Relative refractory period 2015 Pearson Education, Inc The Conducting System Refractory Period Absolute refractory period Long Cardiac muscle cells cannot respond Relative refractory period Short Response depends on degree of stimulus 2015 Pearson Education, Inc The Conducting System Timing of Refractory Periods Length of cardiac action potential in ventricular cell 250300 msec 30 times longer than skeletal muscle fiber Long refractory period prevents summation and tetany 2015 Pearson Education, Inc The Conducting System The Role of Calcium Ions in Cardiac Contractions Contraction of a cardiac muscle cell Is produced by an increase in calcium ion concentration around myofibrils 2015 Pearson Education, Inc The Conducting System The Role of Calcium Ions in Cardiac Contractions 1.20 percent of calcium ions required for a contraction Calcium ions enter plasma membrane during plateau phase 2.Arrival of extracellular Ca 2+ Triggers release of calcium ion reserves from sarcoplasmic reticulum (SR) 2015 Pearson Education, Inc The Conducting System The Role of Calcium Ions in Cardiac Contractions As slow calcium channels close Intracellular Ca 2+ is absorbed by the SR Or pumped out of cell Cardiac muscle tissue Very sensitive to extracellular Ca 2+ concentrations 2015 Pearson Education, Inc The Conducting System The Energy for Cardiac Contractions Aerobic energy of heart From mitochondrial breakdown of fatty acids and glucose Oxygen from circulating hemoglobin Cardiac muscles store oxygen in myoglobin 2015 Pearson Education, Inc The Cardiac Cycle The Cardiac Cycle Is the period between the start of one heartbeat and the beginning of the next Includes both contraction and relaxation 2015 Pearson Education, Inc The Cardiac Cycle Two Phases of the Cardiac Cycle Within any one chamber 1.Systole (contraction) 2.Diastole (relaxation) 2015 Pearson Education, Inc. Figure Phases of the Cardiac Cycle. 800 msec a 0 msec 100 msec 370 msec Cardiac cycle Start b c d e f Atrial systole begins: Atrial contraction forces a small amount of additional blood into relaxed ventricles. Atrial systole ends, atrial diastole begins Ventricular systole first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. Ventricular systole second phase: As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. Ventricular diastoleearly: As ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria. Ventricular diastolelate: All chambers are relaxed. Ventricles fill passively. 2015 Pearson Education, Inc. Figure 20-16a Phases of the Cardiac Cycle. 800 msec a 0 msec 100 msec Start Atrial systole begins: Atrial contraction forces a small amount of additional blood into relaxed ventricles. Cardiac cycle 2015 Pearson Education, Inc. Figure 20-16b Phases of the Cardiac Cycle. Cardiac cycle 100 msec b Atrial systole ends, atrial diastole begins 2015 Pearson Education, Inc. Figure 20-16c Phases of the Cardiac Cycle. Cardiac cycle c Ventricular systole first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. 2015 Pearson Education, Inc. Figure 20-16d Phases of the Cardiac Cycle. Cardiac cycle 370 msec d Ventricular systole second phase: As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. 2015 Pearson Education, Inc. Figure 20-16e Phases of the Cardiac Cycle. Cardiac cycle 370 msec e Ventricular diastoleearly: As ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria. 2015 Pearson Education, Inc. Figure 20-16f Phases of the Cardiac Cycle. Cardiac cycle 800 msec f Ventricular diastolelate: All chambers are relaxed. Ventricles fill passively. 2015 Pearson Education, Inc The Cardiac Cycle Blood Pressure In any chamber Rises during systole Falls during diastole Blood flows from high to low pressure Controlled by timing of contractions Directed by one-way valves 2015 Pearson Education, Inc The Cardiac Cycle Cardiac Cycle and Heart Rate At 75 beats per minute (bpm) Cardiac cycle lasts about 800 msec When heart rate increases All phases of cardiac cycle shorten, particularly diastole 2015 Pearson Education, Inc The Cardiac Cycle Phases of the Cardiac Cycle Atrial systole Atrial diastole Ventricular systole Ventricular diastole 2015 Pearson Education, Inc The Cardiac Cycle Atrial Systole 1.Atrial systole Atrial contraction begins Right and left AV valves are open 2.Atria eject blood into ventricles Filling ventricles 3.Atrial systole ends AV valves close Ventricles contain maximum blood volume Known as end-diastolic volume (EDV) 2015 Pearson Education, Inc The Cardiac Cycle Ventricular Systole 4. Ventricles contract and build pressure AV valves close causing isovolumetric contraction 5. Ventricular ejection Ventricular pressure exceeds vessel pressure opening the semilunar valves and allowing blood to leave the ventricle Amount of blood ejected is called the stroke volume (SV) 2015 Pearson Education, Inc The Cardiac Cycle Ventricular Systole 6.Ventricular pressure falls Semilunar valves close Ventricles contain end-systolic volume (ESV), about 40 percent of end-diastolic volume 2015 Pearson Education, Inc. Figure Pressure and Volume Relationships in the Cardiac Cycle (Part 3 of 4). Aorta ATRIAL DIASTOLE ATRIAL SYSTOLE VENTRICULAR DIASTOLE VENTRICULAR SYSTOLE ATRIAL DIASTOLE Aortic valve opens Left ventricle Left atrium Left AV valve closes Pressure (mm Hg) End-diastolic volume Stroke volume Left ventricular volume (mL) Atrial contraction begins. Atria eject blood into ventricles. Atrial systole ends; AV valves close. Isovolumetric ventricular contraction. Ventricular ejection occurs. Semilunar valves close. Isovolumetric relaxation occurs. AV valves open; passive ventricular filling occurs Time (msec) 2015 Pearson Education, Inc The Cardiac Cycle Ventricular Diastole 7.Ventricular diastole Ventricular pressure is higher than atrial pressure All heart valves are closed Ventricles relax (isovolumetric relaxation) 8.Atrial pressure is higher than ventricular pressure AV valves open Passive atrial filling Passive ventricular filling 2015 Pearson Education, Inc. Figure Pressure and Volume Relationships in the Cardiac Cycle (Part 4 of 4). Atrial contraction begins. Atria eject blood into ventricles. Atrial systole ends; AV valves close. Isovolumetric ventricular contraction. Ventricular ejection occurs. Semilunar valves close. Isovolumetric relaxation occurs. AV valves open; passive ventricular filling occurs VENTRICULAR SYSTOLE ATRIAL DIASTOLE VENTRICULAR DIASTOLE ATRIAL SYSTOLE Pressure (mm Hg) Left ventricular volume (mL) End-systolic volume Time (msec) Aortic valve closes Dicrotic notch Left AV valve opens 6 7 8 2015 Pearson Education, Inc The Cardiac Cycle Heart Sounds S 1 Loud sounds Produced by AV valves S 2 Loud sounds Produced by semilunar valves 2015 Pearson Education, Inc The Cardiac Cycle S 3, S 4 Soft sounds Blood flow into ventricles and atrial contraction Heart Murmur Sounds produced by regurgitation through valves 2015 Pearson Education, Inc. Figure 20-18a Heart Sounds. a Aortic valve Sounds heard Valve location Pulmonary valve Valve location Sounds heard Left AV valve Right AV valve Placements of a stethoscope for listening to the different sounds produced by individual valves 2015 Pearson Education, Inc. Figure 20-18b Heart Sounds. Aorta Semilunar valves open Semilunar valves close AV valves close AV valves open Left atrium Left ventricle 120 Pressure (mm Hg) Heart sounds S4S4 Lubb Dupp S4S4 S1S1 S2S2 S3S3 The relationship between heart sounds and key events in the cardiac cycle b 2015 Pearson Education, Inc Cardiodynamics Cardiodynamics The movement and force generated by cardiac contractions End-diastolic volume (EDV) End-systolic volume (ESV) Stroke volume (SV) SV = EDV ESV Ejection fraction The percentage of EDV represented by SV 2015 Pearson Education, Inc. Figure A Simple Model of Stroke Volume. Filling Ventricular diastole End-diastolic volume (EDV) End-systolic volume (ESV) Stroke volume Pumping Ventricular systole Start When the pump handle is raised, pressure within the cylinder decreases, and water enters through a one-way valve. This corresponds to passive filling during ventricular diastole. At the start of the pumping cycle, the amount of water in the cylinder corresponds to the amount of blood in a ventricle at the end of ventricular diastole. This amount is known as the end- diastolic volume (EDV). As the pump handle is pushed down, water is forced out of the cylinder. This corresponds to the period of ventricular ejection. When the handle is depressed as far as it will go, some water will remain in the cylinder. That amount corresponds to the end-systolic volume (ESV) remaining in the ventricle at the end of ventricular systole. The amount of water pumped out corresponds to the stroke volume of the heart; the stroke volume is the difference between the EDV and the ESV. 2015 Pearson Education, Inc. Figure A Simple Model of Stroke Volume (Part 1 of 4). Filling Ventricular diastole Start When the pump handle is raised, pressure within the cylinder decreases, and water enters through a one-way valve. This corresponds to passive filling during ventricular diastole. 2015 Pearson Education, Inc. Figure A Simple Model of Stroke Volume (Part 2 of 4). End-diastolic volume (EDV) At the start of the pumping cycle, the amount of water in the cylinder corresponds to the amount of blood in a ventricle at the end of ventricular diastole. This amount is known as the end- diastolic volume (EDV). 2015 Pearson Education, Inc. Figure A Simple Model of Stroke Volume (Part 3 of 4). Pumping Ventricular systole As the pump handle is pushed down, water is forced out of the cylinder. This corresponds to the period of ventricular ejection. 2015 Pearson Education, Inc. Figure A Simple Model of Stroke Volume (Part 4 of 4). End-systolic volume (ESV) Stroke volume When the handle is depressed as far as it will go, some water will remain in the cylinder. That amount corresponds to the end-systolic volume (ESV) remaining in the ventricle at the end of ventricular systole. The amount of water pumped out corresponds to the stroke volume of the heart; the stroke volume is the difference between the EDV and the ESV. 2015 Pearson Education, Inc Cardiodynamics Cardiac Output (CO) The volume pumped by left ventricle in one minute CO = HR SV CO = cardiac output (mL/min) HR = heart rate (beats/min) SV = stroke volume (mL/beat) 2015 Pearson Education, Inc Cardiodynamics Factors Affecting Cardiac Output Cardiac output Adjusted by changes in heart rate or stroke volume Heart rate Adjusted by autonomic nervous system or hormones Stroke volume Adjusted by changing EDV or ESV 2015 Pearson Education, Inc. Figure Factors Affecting Cardiac Output. Hormones Autonomic innervation End-diastolic volume End-systolic volume Factors Affecting Heart Rate (HR) Factors Affecting Stroke Volume (SV) HEART RATE (HR) STROKE VOLUME (SV) = EDV ESV CARDIAC OUTPUT (CO) = HR SV 2015 Pearson Education, Inc Cardiodynamics Autonomic Innervation Cardiac plexuses innervate heart Vagus nerves (N X) carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus Cardiac centers of medulla oblongata Cardioacceleratory center controls sympathetic neurons (increases heart rate) Cardioinhibitory center controls parasympathetic neurons (slows heart rate) 2015 Pearson Education, Inc Cardiodynamics Autonomic Innervation Cardiac reflexes Cardiac centers monitor: Blood pressure (baroreceptors) Arterial oxygen and carbon dioxide levels (chemoreceptors) Cardiac centers adjust cardiac activity Autonomic tone Dual innervation maintains resting tone by releasing ACh and NE Fine adjustments meet needs of other systems 2015 Pearson Education, Inc. Figure Autonomic Innervation of the Heart. Vagal nucleus Medulla oblongata Vagus (N X) Spinal cord Parasympathetic Parasympathetic preganglionic fiber Synapses in cardiac plexus Parasympathetic postganglionic fibers Cardioinhibitory center Cardioacceleratory center Sympathetic Sympathetic preganglionic fiber Sympathetic ganglia (cervical ganglia and superior thoracic ganglia [T 1 T 4 ]) Sympathetic postganglionic fiber Cardiac nerve 2015 Pearson Education, Inc Cardiodynamics Effects on the SA Node Membrane potential of pacemaker cells Lower than other cardiac cells Rate of spontaneous depolarization depends on: Resting membrane potential Rate of depolarization 2015 Pearson Education, Inc. Figure 20-22a Autonomic Regulation of Pacemaker Function. Threshold a Membrane potential (mV) Spontaneous depolarization Heart rate: 75 bpm Normal (resting) 30 60 0 Pacemaker cells have membrane potentials closer to threshold than those of other cardiac muscle cells (60 mV versus 90 mV). Their plasma membranes undergo spontaneous depolarization to threshold, producing action potentials at a frequency determined by (1) the membrane potential and (2) the rate of depolarization. 2015 Pearson Education, Inc Cardiodynamics Effects on the SA Node Sympathetic and parasympathetic stimulation Greatest at SA node (heart rate) ACh (parasympathetic stimulation) Slows the heart NE (sympathetic stimulation) Speeds the heart 2015 Pearson Education, Inc. Figure 20-22b Autonomic Regulation of Pacemaker Function. Threshold Membrane potential (mV) Heart rate: 40 bpm 30 60 0 Parasympathetic stimulation Hyperpolarization Slower depolarization b Parasympathetic stimulation releases ACh, which extends repolarization and decreases the rate of spontaneous depolarization. The heart rate slows. 2015 Pearson Education, Inc. Figure 20-22c Autonomic Regulation of Pacemaker Function. Threshold Membrane potential (mV) 30 60 0 Heart rate: 120 bpm Sympathetic stimulation Reduced repolarization More rapid depolarization c Sympathetic stimulation releases NE, which shortens repolarization and accelerates the rate of spontaneous depolarization. As a result, the heart rate increases. Time (sec) 2015 Pearson Education, Inc Cardiodynamics Atrial Reflex Also called Bainbridge reflex Adjusts heart rate in response to venous return Stretch receptors in right atrium Trigger increase in heart rate Through increased sympathetic activity 2015 Pearson Education, Inc Cardiodynamics Hormonal Effects on Heart Rate Increase heart rate (by sympathetic stimulation of SA node) Epinephrine (E) Norepinephrine (NE) Thyroid hormone 2015 Pearson Education, Inc Cardiodynamics Factors Affecting the Stroke Volume The EDV amount of blood a ventricle contains at the end of diastole Filling time Duration of ventricular diastole Venous return Rate of blood flow during ventricular diastole 2015 Pearson Education, Inc Cardiodynamics Preload The degree of ventricular stretching during ventricular diastole Directly proportional to EDV Affects ability of muscle cells to produce tension 2015 Pearson Education, Inc Cardiodynamics The EDV and Stroke Volume At rest EDV is low Myocardium stretches less Stroke volume is low With exercise EDV increases Myocardium stretches more Stroke volume increases 2015 Pearson Education, Inc Cardiodynamics The FrankStarling Principle As EDV increases, stroke volume increases Physical Limits Ventricular expansion is limited by: Myocardial connective tissue The cardiac (fibrous) skeleton The pericardial sac 2015 Pearson Education, Inc Cardiodynamics End-Systolic Volume (ESV) Is the amount of blood that remains in the ventricle at the end of ventricular systole 2015 Pearson Education, Inc Cardiodynamics Three Factors That Affect ESV 1. Preload Ventricular stretching during diastole 2. Contractility Force produced during contraction, at a given preload 3. Afterload Tension the ventricle produces to open the semilunar valve and eject blood 2015 Pearson Education, Inc Cardiodynamics Contractility Is affected by: Autonomic activity Hormones 2015 Pearson Education, Inc Cardiodynamics Effects of Autonomic Activity on Contractility Sympathetic stimulation NE released by postganglionic fibers of cardiac nerves Epinephrine and NE released by adrenal medullae Causes ventricles to contract with more force Increases ejection fraction and decreases ESV 2015 Pearson Education, Inc Cardiodynamics Effects of Autonomic Activity on Contractility Parasympathetic activity Acetylcholine released by vagus nerves Reduces force of cardiac contractions 2015 Pearson Education, Inc Cardiodynamics Hormones Many hormones affect heart contraction Pharmaceutical drugs mimic hormone actions Stimulate or block beta receptors Affect calcium ions (e.g., calcium channel blockers) 2015 Pearson Education, Inc Cardiodynamics Afterload Is increased by any factor that restricts arterial blood flow As afterload increases, stroke volume decreases 2015 Pearson Education, Inc. Figure Factors Affecting Stroke Volume. Venous return (VR) VR = EDV Filling time (FT) FT = EDV Contractility (Cont) of muscle cells Cont = ESV Afterload (AL) AL = ESV ESV = SV EDV = SV Preload Increased by sympathetic stimulation Decreased by parasympathetic stimulation Increased by E, NE, glucagon, thyroid hormones Increased by vasoconstriction Decreased by vasodilation End-diastolic volume (EDV) End-systolic volume (ESV) Factors Affecting Stroke Volume (SV) STROKE VOLUME (SV) 2015 Pearson Education, Inc Cardiodynamics Summary: The Control of Cardiac Output Heart rate control factors Autonomic nervous system Sympathetic and parasympathetic Circulating hormones Venous return and stretch receptors 2015 Pearson Education, Inc Cardiodynamics Summary: The Control of Cardiac Output Stroke volume control factors EDV Filling time and rate of venous return ESV Preload, contractility, afterload 2015 Pearson Education, Inc Cardiodynamics Cardiac Reserve The difference between resting and maximal cardiac outputs 2015 Pearson Education, Inc Cardiodynamics The Heart and Cardiovascular System Cardiovascular regulation Ensures adequate circulation to body tissues Cardiovascular centers Control heart and peripheral blood vessels Cardiovascular system responds to: Changing activity patterns Circulatory emergencies 2015 Pearson Education, Inc. Figure 20-24a A Summary of the Factors Affecting Cardiac Output. a Maximum for trained athletes exercising at peak levels Normal range of cardiac output during heavy exercise Average resting cardiac output Heart failure Cardiac output (L/min) Cardiac output varies widely to meet metabolic demands 2015 Pearson Education, Inc. Figure 20-24b A Summary of the Factors Affecting Cardiac Output. Hormones Autonomic innervation End-diastolic volume End-systolic volume Factors affecting heart rate (HR) Factors affecting stroke volume (SV) HEART RATE (HR) STROKE VOLUME (SV) = EDV ESV CARDIAC OUTPUT (CO) = HR SV Hormones Atrial reflex Autonomic innervation Skeletal muscle activity Blood volume Changes in peripheral circulation Venous return Filling time Preload Contractility Vasodilation or vasoconstriction Afterload Factors affecting cardiac output b