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     169 Ch 20_lecture_presentation 169 Ch 20_lecture_presentation Presentation Transcript

    • © 2012 Pearson Education, Inc. PowerPoint® Lecture Presentations prepared by Jason LaPres Lone Star College—North Harris 20 The Heart
    • © 2012 Pearson Education, Inc. An Introduction to the Cardiovascular System • Learning Outcomes • 20-1 Describe 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. • 20-2 Explain 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.
    • © 2012 Pearson Education, Inc. An Introduction to the Cardiovascular System • Learning Outcomes • 20-3 Explain the events of the cardiac cycle, including atrial and ventricular systole and diastole, and relate the heart sounds to specific events in the cycle. • 20-4 Define 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.
    • © 2012 Pearson Education, Inc. An Introduction to the Cardiovascular System • The Pulmonary Circuit • Carries blood to and from gas exchange surfaces of lungs • The Systemic Circuit • Carries blood to and from the body • Blood alternates between pulmonary circuit and systemic circuit
    • © 2012 Pearson Education, Inc. An Introduction to the Cardiovascular System • Three Types of Blood Vessels 1. Arteries • Carry blood away from heart 2. Veins • Carry blood to heart 3. Capillaries • Networks between arteries and veins
    • © 2012 Pearson Education, Inc. An Introduction to the Cardiovascular System • Capillaries • Also called exchange vessels • Exchange materials between blood and tissues • Materials include dissolved gases, nutrients, waste products
    • © 2012 Pearson Education, Inc. Figure 20-1 An Overview of the Cardiovascular System PULMONARY CIRCUIT SYSTEMIC CIRCUIT Pulmonary arteries Pulmonary veins Systemic veins Systemic arteries Capillaries in lungs Right atrium Right ventricle Capillaries in trunk and lower limbs Capillaries in head, neck, upper limbs Left atrium Left ventricle
    • © 2012 Pearson Education, Inc. An Introduction to the Cardiovascular System • Four 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
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Heart • Great veins and arteries at the base • Pointed tip is apex • Surrounded by pericardial sac • Sits between two pleural cavities in the mediastinum
    • © 2012 Pearson Education, Inc. Figure 20-2a The Location of the Heart in the Thoracic Cavity Trachea First rib (cut) Base of heart Right lung Diaphragm Thyroid gland Left lung Apex of heart Parietal pericardium (cut) An anterior view of the chest, showing the position of the heart and major blood vessels relative to the ribs, lungs, and diaphragm.
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. Figure 20-2b The Location of the Heart in the Thoracic Cavity Right ventricle Aortic arch Posterior mediastinum Aorta (arch segment removed) Left pulmonary artery Left pulmonary vein Pulmonary trunk Left ventricle Epicardium Pericardial sac Anterior mediastinum Pericardial cavity Right atrium Left atrium Right pulmonary artery Right pulmonary vein Superior vena cava Esophagus Right pleural cavity Bronchus of lung Right lung Left lung Left pleural cavity 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 situated in the anterior part of the mediastinum, immediately posterior to the sternum.
    • © 2012 Pearson Education, Inc. Figure 20-2c The Location of the Heart in the Thoracic Cavity Wrist (corresponds to base of heart) Inner wall (corresponds to epicardium) Air space (corresponds to pericardial cavity) Outer wall (corresponds to parietal pericardium) Balloon Cut edge of parietal pericardium Fibrous tissue of pericardial sac Parietal pericardium Areolar tissue Mesothelium Cut edge of epicardium Apex of heart Base of heart Fibrous attachment to diaphragm The relationship between the heart and the pericardial cavity; compare with the fist-and-balloon example.
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Superficial Anatomy of the Heart • Atria • Thin-walled • Expandable outer auricle (atrial appendage)
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Superficial Anatomy of the Heart • Sulci • Coronary sulcus divides atria and ventricles • Anterior interventricular sulcus and posterior interventricular sulcus • Separate left and right ventricles • Contain blood vessels of cardiac muscle
    • © 2012 Pearson Education, Inc. Figure 20-3a The Superficial Anatomy of the Heart Left common carotid artery Brachiocephalic trunk Ascending aorta Superior vena cava Auricle of right atrium Fat and vessels in coronary sulcus Left subclavian artery Arch of aorta Ligamentum arteriosum Descending aorta Left pulmonary artery Pulmonary trunk Auricle of left atrium Fat and vessels in anterior interventricular sulcus LEFT VENTRICLE RIGHT VENTRICLE RIGHT ATRIUM Major anatomical features on the anterior surface.
    • © 2012 Pearson Education, Inc. Figure 20-3a The Superficial Anatomy of the Heart Ascending aorta Parietal pericardium Superior vena cava Auricle of right atrium RIGHT ATRIUM Right coronary artery Coronary sulcus RIGHT VENTRICLE Marginal branch of right coronary artery Auricle of left atrium Pulmonary trunk Fibrous pericardium Parietal pericardium fused to diaphragm Anterior interventricular sulcus LEFT VENTRICLE Major anatomical features on the anterior surface.
    • © 2012 Pearson Education, Inc. Figure 20-3b The Superficial Anatomy of the Heart 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 RIGHT VENTRICLE LEFT VENTRICLE RIGHT ATRIUM LEFT ATRIUM Left pulmonary artery Left pulmonary veins Fat and vessels in coronary sulcus Coronary sinus Major landmarks on the posterior surface. Coronary arteries (which supply the heart itself) are shown in red; coronary veins are shown in blue.
    • © 2012 Pearson Education, Inc. Figure 20-3c The Superficial Anatomy of the Heart Base of heart Apex of heart Ribs Heart position relative to the rib cage. 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Heart Wall 1. Epicardium 2. Myocardium 3. Endocardium
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Epicardium (Outer Layer) • Visceral pericardium • Covers the heart
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Myocardium (Middle Layer) • Muscular wall of the heart • Concentric layers of cardiac muscle tissue • Atrial myocardium wraps around great vessels • Two divisions of ventricular myocardium • Endocardium (Inner Layer) • Simple squamous epithelium
    • © 2012 Pearson Education, Inc. Figure 20-4a The Heart Wall Mesothelium Endocardium Areolar tissue Endothelium Mesothelium Dense fibrous layer Parietal pericardium Pericardial cavity Areolar tissue Areolar tissue Connective tissues Cardiac muscle cells Myocardium (cardiac muscle tissue) Epicardium (visceral pericardium)
    • © 2012 Pearson Education, Inc. Figure 20-4b The Heart Wall Atrial musculature Cardiac muscle tissue forms concentric layers that wrap around the atria or spiral within the walls of the ventricles. Ventricular musculature
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Cardiac Muscle Tissue • Intercalated discs • Interconnect cardiac muscle cells • Secured by desmosomes • Linked by gap junctions • Convey force of contraction • Propagate action potentials
    • © 2012 Pearson Education, Inc. Figure 20-5a Cardiac Muscle Cells Cardiac muscle cells Nucleus Cardiac muscle cell (sectioned) Bundles of myofibrils Cardiac muscle cell Mitochondria Intercalated disc (sectioned) Intercalated discs
    • © 2012 Pearson Education, Inc. Figure 20-5b Cardiac Muscle Cells Intercalated disc Gap junction Opposing plasma membranes Desmosomes Structure of an intercalated disc
    • © 2012 Pearson Education, Inc. Figure 20-5c Cardiac Muscle Cells Intercalated discs Cardiac muscle tissue Cardiac muscle tissue LM × 575
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Characteristics of Cardiac Muscle Cells 1. Small size 2. Single, central nucleus 3. Branching interconnections between cells 4. Intercalated discs
    • © 2012 Pearson Education, Inc. Table 20-1 Structural and Functional Differences between Cardiac Muscle Cells and Skeletal Muscle Fibers
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Internal Anatomy and Organization • Interatrial septum separates atria • Interventricular septum separates ventricles
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Right Atrium • Pectinate muscles • Contain prominent muscular ridges • On anterior atrial wall and inner surfaces of right auricle
    • © 2012 Pearson Education, Inc. Figure 20-6a The Sectional Anatomy of the Heart Descending aorta Left common carotid artery Left subclavian artery Ligamentum arteriosum Pulmonary trunk Pulmonary valve Left pulmonary arteries Left pulmonary veins Interatrial septum Aortic valve Cusp of left AV (mitral) valve LEFT VENTRICLE Interventricular septum Trabeculae carneae Moderator band Aortic arch LEFT ATRIUM Brachiocephalic trunk Superior vena cava Right pulmonary arteries Ascending aorta Fossa ovalis Opening of coronary sinus RIGHT ATRIUM Pectinate muscles Conus arteriosus Cusp of right AV (tricuspid) valve Chordae tendineae Papillary muscles RIGHT VENTRICLE Inferior vena cava
    • © 2012 Pearson Education, Inc. Figure 20-6c The Sectional Anatomy of the Heart A frontal section, anterior view. Inferior vena cava RIGHT VENTRICLE Papillary muscles Cusps of right AV (tricuspid) valve Pectinate muscles RIGHT ATRIUM Fossa ovalis Ascending aorta Cusp of left AV (bicuspid) valve Interventricular septum LEFT VENTRICLE Chordae tendineae Left coronary artery branches (red) and great cardiac vein (blue) Cusp of aortic valve Coronary sinus Trabeculae carneae
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. Figure 20-6b The Sectional Anatomy of the Heart The papillary muscles and chordae tendinae supporting the right AV (tricuspid) valve. The photograph was taken from inside the right ventricle, looking toward a light shining from the right atrium. Chordae tendineae Papillary muscles
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. Figure 20-6c The Sectional Anatomy of the Heart A frontal section, anterior view. Inferior vena cava RIGHT VENTRICLE Papillary muscles Cusps of right AV (tricuspid) valve Pectinate muscles RIGHT ATRIUM Fossa ovalis Ascending aorta Cusp of left AV (bicuspid) valve Interventricular septum LEFT VENTRICLE Chordae tendineae Left coronary artery branches (red) and great cardiac vein (blue) Cusp of aortic valve Coronary sinus Trabeculae carneae
    • © 2012 Pearson Education, Inc. 20-1 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 ANIMATION The Heart: Heart Anatomy
    • © 2012 Pearson Education, Inc. Figure 20-7a Structural Differences between the Left and Right Ventricles Left ventricle Right ventricle Posterior interventricular sulcus 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.
    • © 2012 Pearson Education, Inc. Figure 20-7b Structural Differences between the Left and Right Ventricles Dilated Contracted Diagrammatic views of the ventricles just before a contraction (dilated) and just after a contraction (contracted). Left ventricle Right ventricle
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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 ANIMATION The Heart: Valves
    • © 2012 Pearson Education, Inc. Figure 20-8a Valves of the Heart Relaxedventricles Right AV (tricuspid) valve (open) Transverse Sections, Superior View, Atria and Vessels Removed POSTERIOR RIGHT VENTRICLE Cardiac skeleton Left AV (bicuspid) valve (open) LEFT VENTRICLE Aortic valve (closed) Pulmonary valve (closed)ANTERIOR Aortic valve closed 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.
    • © 2012 Pearson Education, Inc. Figure 20-8a Valves of the Heart Aortic valve (closed) LEFT ATRIUM Left AV (bicuspid) valve (open) Chordae tendineae (loose) Papillary muscles (relaxed) LEFT VENTRICLE (relaxed and filling with blood) Pulmonary veins Frontal Sections through Left Atrium and Ventricle Relaxedventricles
    • © 2012 Pearson Education, Inc. Figure 20-8b Valves of the Heart Contractingventricles Aortic valve open RIGHT VENTRICLE Right AV (tricuspid) valve (closed) Cardiac skeleton Left AV (bicuspid) valve (closed) LEFT VENTRICLE Aortic valve (open) Pulmonary valve (open) 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.
    • © 2012 Pearson Education, Inc. Figure 20-8b Valves of the Heart Contractingventricles Aorta Aortic sinus LEFT ATRIUM Aortic valve (open) Left AV (bicuspid) valve (closed) Chordae tendineae (tense) Papillary muscles (contracted) Left ventricle (contracted)
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Blood Supply to the Heart • = Coronary circulation • Supplies blood to muscle tissue of heart • Coronary arteries and cardiac veins
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Left Coronary Artery • Supplies blood to: • Left ventricle • Left atrium • Interventricular septum
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. Figure 20-9a 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.
    • © 2012 Pearson Education, Inc. Figure 20-9b Coronary Circulation Coronary sinus Circumflex artery Great cardiac vein Marginal artery Posterior interventricular artery Posterior cardiac vein Left ventricle Middle cardiac vein Marginal artery Right coronary artery Small cardiac vein Coronary vessels supplying and draining the posterior surface of the heart.
    • © 2012 Pearson Education, Inc. Figure 20-9c Coronary Circulation Posterior interventricular artery Posterior cardiac vein Marginal artery Great cardiac vein Circumflex artery Auricle of left atrium 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).
    • © 2012 Pearson Education, Inc. Figure 20-10 Heart Disease and Heart Attacks Narrowing of Artery Lipid deposit of plaque Cross-section Tunica externa Tunica media Cross-section Normal Artery
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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)
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease - Coronary Artery Disease • Treatment of CAD and Myocardial Infarction • About 25% of MI patients die before obtaining medical assistance • 65% of MI deaths among those under age 50 occur within an hour after the initial infarction
    • © 2012 Pearson Education, Inc. 20-1 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)
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 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
    • © 2012 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease - Coronary Artery Disease • Treatment of CAD and Myocardial Infarction • Coronary Artery Bypass Surgery (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
    • © 2012 Pearson Education, Inc. Figure 20-10 Heart Disease and Heart Attacks Normal Heart Advanced Coronary Artery Disease A color-enhanced DSA scan showing advanced coronary artery disease. Blood flow to the ven- tricular myocardium is severely restricted. A color-enhanced digital subtraction angiography (DSA) scan of a normal heart.
    • © 2012 Pearson Education, Inc. Figure 20-10 Heart Disease and Heart Attacks Occluded Coronary Artery Damaged Heart Muscle
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Heartbeat • A single contraction of the heart • The entire heart contracts in series • First the atria • Then the ventricles
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Conducting Cells • Interconnect SA and AV nodes • Distribute stimulus through myocardium • In the atrium • Internodal pathways • In the ventricles • AV bundle and the bundle branches
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Prepotential • Also called pacemaker potential • Resting potential of conducting cells • Gradually depolarizes toward threshold • SA node depolarizes first, establishing heart rate ANIMATION The Heart: Conduction System
    • © 2012 Pearson Education, Inc. Figure 20-11a The Conducting System of the Heart AV bundle Components of the conducting system Purkinje fibers Bundle branches Atrioventricular (AV) node Internodal pathways Sinoatrial (SA) node
    • © 2012 Pearson Education, Inc. Figure 20-11b The Conducting System of the Heart 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. Time (sec) Prepotential (spontaneous depolarization) Threshold
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Heart Rate • SA node generates 80–100 action potentials per minute • Parasympathetic stimulation slows heart rate • AV node generates 40–60 action potentials per minute
    • © 2012 Pearson Education, Inc. 20-2 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)
    • © 2012 Pearson Education, Inc. Figure 20-12 Impulse Conduction through the Heart (Step 1) Time = 0 SA node SA node activity and atrial activation begin.
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. Figure 20-12 Impulse Conduction through the Heart (Step 2) Elapsed time = 50 msec AV node Stimulus spreads across the atrial surfaces and reaches the AV node.
    • © 2012 Pearson Education, Inc. Figure 20-12 Impulse Conduction through the Heart (Step 3) Elapsed time = 150 msec Bundle branches AV bundle There is a 100-msec delay at the AV node. Atrial contraction begins.
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. Figure 20-12 Impulse Conduction through the Heart (Step 4) Elapsed time = 175 msec Moderator band The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibers and, via the moderator band, to the papillary muscles of the right ventricle.
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Purkinje Fibers • Distribute impulse through ventricles (Step 5) • Atrial contraction is completed • Ventricular contraction begins
    • © 2012 Pearson Education, Inc. Figure 20-12 Impulse Conduction through the Heart (Step 5) Elapsed time = 225 msec Purkinje fibers The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed, and ventricular contraction begins.
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Features of an ECG • P wave • Atria depolarize • QRS complex • Ventricles depolarize • T wave • Ventricles repolarize
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Time Intervals between ECG Waves • P–R interval • From start of atrial depolarization • To start of QRS complex • Q–T interval • From ventricular depolarization • To ventricular repolarization
    • © 2012 Pearson Education, Inc. Figure 20-13a An Electrocardiogram Electrode placement for recording a standard ECG.
    • © 2012 Pearson Education, Inc. Figure 20-13b An Electrocardiogram 800 msec SQ QRS interval (ventricles depolarize) Millivolts R P–R segment T wave (ventricles repolarize) R P wave (atria depolarize) S–T segment S–T interval Q–T interval P–R interval
    • © 2012 Pearson Education, Inc. Figure 20-14 Cardiac Arrhythmias Premature Atrial Contractions (PACs) Paroxysmal Atrial Tachycardia (PAT) Atrial Fibrillation (AF) PPP PPPPPP
    • © 2012 Pearson Education, Inc. Figure 20-14 Cardiac Arrhythmias Premature Ventricular Contractions (PVCs) Ventricular Tachycardia (VT) Ventricular Fibrillation (VF) PPP P TTT
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. Figure 20-15a The Action Potential in Skeletal and Cardiac Muscle Rapid Depolarization The Plateau Repolarization Cause: Na+ entry Duration: 3–5 msec Ends with: Closure of voltage-gated fast sodium channels Cause: Ca2+ entry Duration: ~175 msec Ends with: Closure of slow calcium channels Cause: K+ loss Duration: 75 msec Ends with: Closure of slow potassium channels Relative refractory period Stimulus Events in an action potential in a ventricular muscle cell. KEY Absolute refractory period Relative refractory period Absolute refractory period Time (msec) mV
    • © 2012 Pearson Education, Inc. Figure 20-15b The Action Potential in Skeletal and Cardiac Muscle mV SKELETAL MUSCLE CARDIAC MUSCLE Action potentialmV Contraction Tension Time (msec) Time (msec) ContractionTension Action potential KEY Absolute refractory period Relative refractory period Action potentials and twitch contractions in a skeletal muscle (above) and cardiac muscle (below).
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Refractory Period • Absolute refractory period • Long • Cardiac muscle cells cannot respond • Relative refractory period • Short • Response depends on degree of stimulus
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • Timing of Refractory Periods • Length of cardiac action potential in ventricular cell • 250–300 msec • 30 times longer than skeletal muscle fiber • Long refractory period prevents summation and tetany
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • The Role of Calcium Ions in Cardiac Contractions 1. 20% of calcium ions required for a contraction • Calcium ions enter plasma membrane during plateau phase 2. Arrival of extracellular Ca2+ • Triggers release of calcium ion reserves from sarcoplasmic reticulum (SR)
    • © 2012 Pearson Education, Inc. 20-2 The Conducting System • The Role of Calcium Ions in Cardiac Contractions • As slow calcium channels close • Intracellular Ca2+ is absorbed by the SR • Or pumped out of cell • Cardiac muscle tissue • Very sensitive to extracellular Ca2+ concentrations
    • © 2012 Pearson Education, Inc. 20-2 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
    • © 2012 Pearson Education, Inc. 20-3 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
    • © 2012 Pearson Education, Inc. 20-3 The Cardiac Cycle • Two Phases of the Cardiac Cycle • Within any one chamber 1. Systole (contraction) 2. Diastole (relaxation)
    • © 2012 Pearson Education, Inc. Figure 20-16 Phases of the Cardiac Cycle Cardiac cycle 370 msec 100 msec 0 msec800 msec Start
    • © 2012 Pearson Education, Inc. Figure 20-16a Phases of the Cardiac Cycle Cardiac cycle 100 msec 0 msec800 msec Atrial systole begins: Atrial contraction forces a small amount of additional blood into relaxed ventricles. Start
    • © 2012 Pearson Education, Inc. Figure 20-16b Phases of the Cardiac Cycle Cardiac cycle 100 msec Atrial systole ends, atrial diastole begins
    • © 2012 Pearson Education, Inc. Figure 20-16c Phases of the Cardiac Cycle Cardiac cycle Ventricular systole— first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves.
    • © 2012 Pearson Education, Inc. Figure 20-16d Phases of the Cardiac Cycle Cardiac cycle 370 msec Ventricular systole— second phase: As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected.
    • © 2012 Pearson Education, Inc. Figure 20-16e Phases of the Cardiac Cycle Cardiac cycle 370 msec Ventricular diastole—early: 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.
    • © 2012 Pearson Education, Inc. Figure 20-16f Phases of the Cardiac Cycle Cardiac cycle Ventricular diastole—late: All chambers are relaxed. Ventricles fill passively. 800 msec
    • © 2012 Pearson Education, Inc. 20-3 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
    • © 2012 Pearson Education, Inc. 20-3 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
    • © 2012 Pearson Education, Inc. 20-3 The Cardiac Cycle • Phases of the Cardiac Cycle • Atrial systole • Atrial diastole • Ventricular systole • Ventricular diastole
    • © 2012 Pearson Education, Inc. 20-3 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)
    • © 2012 Pearson Education, Inc. 20-3 The Cardiac Cycle • Ventricular Systole 4. Ventricles contract and build pressure • AV valves close cause 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)
    • © 2012 Pearson Education, Inc. 20-3 The Cardiac Cycle • Ventricular Systole 6. Ventricular pressure falls • Semilunar valves close • Ventricles contain end-systolic volume (ESV), about 40% of end-diastolic volume
    • © 2012 Pearson Education, Inc. Figure 20-17 Pressure and Volume Relationships in the Cardiac Cycle ATRIAL SYSTOLE ATRIAL DIASTOLE VENTRICULAR DIASTOLE VENTRICULAR SYSTOLE Stroke volume End-diastolic volume Left ventricular volume(mL) Pressure (mmHg) Aortic valve opens Aorta Left ventricle Left atrium Left AV valve closes AV valves open; passive ventricular filling occurs. Isovolumetric relaxation occurs. Semilunar valves close. Ventricular ejection occurs. Isovolumetric ventricular contraction. Atrial systole ends; AV valves close. Atria eject blood into ventricles. Atrial contraction begins. ATRIAL DIASTOLE Time (msec)
    • © 2012 Pearson Education, Inc. 20-3 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
    • © 2012 Pearson Education, Inc. Figure 20-17 Pressure and Volume Relationships in the Cardiac Cycle ATRIAL SYSTOLE ATRIAL DIASTOLE VENTRICULAR SYSTOLE VENTRICULAR DIASTOLE AV valves open; passive ventricular filling occurs. Isovolumetric relaxation occurs. Semilunar valves close. Ventricular ejection occurs. Isovolumetric ventricular contraction. Atrial systole ends; AV valves close. Atria eject blood into ventricles. Atrial contraction begins. Time (msec) End-systolic volume Aortic valve closes Dicrotic notch Left AV valve opens Left ventricular volume(mL) Pressure (mmHg)
    • © 2012 Pearson Education, Inc. 20-3 The Cardiac Cycle • Heart Sounds • S1 • Loud sounds • Produced by AV valves • S2 • Loud sounds • Produced by semilunar valves ANIMATION The Heart: Cardiac Cycle
    • © 2012 Pearson Education, Inc. 20-3 The Cardiac Cycle • S3, S4 • Soft sounds • Blood flow into ventricles and atrial contraction • Heart Murmur • Sounds produced by regurgitation through valves
    • © 2012 Pearson Education, Inc. Figure 20-18a Heart Sounds Aortic valve 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 Valve location Sounds heard Valve location Sounds heard Valve location Sounds heard
    • © 2012 Pearson Education, Inc. Figure 20-18b Heart Sounds Semilunar valves close AV valves open AV valves close “Dubb”“Lubb” The relationship between heart sounds and key events in the cardiac cycle Heart sounds Pressure (mmHg) Aorta Semilunar valves open Left ventricle Left atrium S1 S4S4 S2 S3
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. Figure 20-19 A Simple Model of Stroke Volume Filling Ventricular diastole End-diastolic volume (EDV) Pumping Ventricular systole Stroke volume End-systolic volume (ESV) Start
    • © 2012 Pearson Education, Inc. Figure 20-19 A Simple Model of Stroke Volume Filling Ventricular diastole 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. Start
    • © 2012 Pearson Education, Inc. Figure 20-19 A Simple Model of Stroke Volume 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). End-diastolic volume (EDV)
    • © 2012 Pearson Education, Inc. Figure 20-19 A Simple Model of Stroke Volume Pumping As the pump handle is pushed down, water is forced out of the cylinder. This cor- responds to the period of ventricular ejection. Ventricular systole
    • © 2012 Pearson Education, Inc. Figure 20-19 A Simple Model of 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. Stroke volume End-systolic volume (ESV)
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Cardiac Output (CO) • The volume pumped by left ventricle in 1 minute • CO = HR × SV • CO = cardiac output (mL/min) • HR = heart rate (beats/min) • SV = stroke volume (mL/beat)
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. Figure 20-20 Factors Affecting Cardiac Output End-systolic volume End-diastolic volume Hormones Autonomic innervation STROKE VOLUME (SV) = EDV – ESVHEART RATE (HR) CARDIAC OUTPUT (CO) = HR × SV Factors Affecting Heart Rate (HR) Factors Affecting Stroke Volume (SV)
    • © 2012 Pearson Education, Inc. 20-4 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)
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. Figure 20-21 Autonomic Innervation of the Heart Cardioinhibitory center Cardioacceleratory center Vagal nucleus Medulla oblongata Vagus (N X) Spinal cord Parasympathetic Parasympathetic preganglionic fiber Synapses in cardiac plexus Parasympathetic postganglionic fibers Cardiac nerve Sympathetic postganglionic fiber Sympathetic preganglionic fiber Sympathetic ganglia (cervical ganglia and superior thoracic ganglia [T1–T4]) Sympathetic
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. Figure 20-22a Autonomic Regulation of Pacemaker Function Prepotential (spontaneous depolarization) Normal (resting) Membrane potential (mV) Threshold Heart rate: 75 bpm 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 resting-membrane potential and (2) the rate of depolarization.
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. Figure 20-22b Autonomic Regulation of Pacemaker Function Parasympathetic stimulation releases ACh, which extends repolarization and decreases the rate of spontaneous depolarization. The heart rate slows. Slower depolarization Hyperpolarization Parasympathetic stimulation Heart rate: 40 bpm Membrane potential (mV) Threshold
    • © 2012 Pearson Education, Inc. Figure 20-22c Autonomic Regulation of Pacemaker Function Sympathetic stimulation releases NE, which shortens repolarization and accelerates the rate of spontaneous depolarization. As a result, the heart rate increases. Time (sec) More rapid depolarization Reduced repolarization Sympathetic stimulation Heart rate: 120 bpm Membrane potential (mV) Threshold
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Hormonal Effects on Heart Rate • Increase heart rate (by sympathetic stimulation of SA node) • Epinephrine (E) • Norepinephrine (NE) • Thyroid hormone
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Preload • The degree of ventricular stretching during ventricular diastole • Directly proportional to EDV • Affects ability of muscle cells to produce tension
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • The Frank–Starling Principle • As EDV increases, stroke volume increases • Physical Limits • Ventricular expansion is limited by: • Myocardial connective tissue • The cardiac (fibrous) skeleton • The pericardial sac
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • End-Systolic Volume (ESV) • Is the amount of blood that remains in the ventricle at the end of ventricular systole
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Contractility • Is affected by: • Autonomic activity • Hormones
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Effects of Autonomic Activity on Contractility • Parasympathetic activity • Acetylcholine released by vagus nerves • Reduces force of cardiac contractions
    • © 2012 Pearson Education, Inc. 20-4 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)
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Afterload • Is increased by any factor that restricts arterial blood flow • As afterload increases, stroke volume decreases
    • © 2012 Pearson Education, Inc. Figure 20-23 Factors Affecting Stroke Volume Preload Factors Affecting Stroke Volume (SV) Venous return (VR) VR = EDV FT = EDV Filling time (FT) Increased by sympathetic stimulation Decreased by parasympathetic stimulation Increased by E, NE, glucagon, thyroid hormones Contractility (Cont) of muscle cells Cont = ESV Increased by vasoconstriction Decreased by vasodilation Afterload (AL) AL = ESVEnd-systolic volume (ESV) End-diastolic volume (EDV) STROKE VOLUME (SV) ESV = SV VR = EDV FT = EDV Cont = ESV AL = ESV ESV = SV EDV = SV EDV = SV
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Summary: The Control of Cardiac Output • Heart Rate Control Factors • Autonomic nervous system • Sympathetic and parasympathetic • Circulating hormones • Venous return and stretch receptors
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Summary: The Control of Cardiac Output • Stroke Volume Control Factors • EDV • Filling time, and rate of venous return • ESV • Preload, contractility, afterload
    • © 2012 Pearson Education, Inc. 20-4 Cardiodynamics • Cardiac Reserve • The difference between resting and maximal cardiac output
    • © 2012 Pearson Education, Inc. 20-4 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
    • © 2012 Pearson Education, Inc. Figure 20-24 A Summary of the Factors Affecting Cardiac Output Hormones Factors affecting heart fate (HR) Factors affecting stroke volume (SV) CARDIAC OUTPUT (CO) = HR × SV STROKE VOLUME (SV) = EDV – ESVHEART RATE (HR) Afterload End-systolic volume End-diastolic volume Vasodilation or vasoconstriction ContractilityPreload HormonesAutonomic innervation Filling time Venous return Changes in peripheral circulation Blood volume Skeletal muscle activity Autonomic innervation Atrial reflex