20 The Heart PowerPoint Lecture Presentations prepared by Jason LaPres Lone Star College North Harris
An Introduction to the Cardiovascular System Learning Outcomes Describe the superficial anatomy of the heart, and pericardium structure. Identify the major blood vessels, and chambers. Trace the flow of blood through the heart. Cellular architecture of the heart.
Figure 20-3c The Superficial Anatomy of the Heart Base of heart 1 2 1 2 Ribs 3 3 5 4 4 5 Apex of heart 6 7 8 9 10 6 7 8 9 10 Heart position relative to the rib cage.
Figure 20-2a The Location of the Heart in the Thoracic Cavity Trachea Thyroid gland First rib (cut) Base of heart Right lung Diaphragm 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.
20-1 Anatomy of the Heart Superficial Anatomy of the Heart Adult heart: 12 cm (5 in) in length, 8 cm (3.5 in) wide, and 6 cm (2.5 in) in thickness. Pumps 5 quarts of blood/ minute (4.7 litres) Atria Upper chambers/ thin-walled Expandable outer auricle (atrial appendage) Ventricles Lower chambers/ thick-walled Lack outer appendages
20-1 Anatomy of the Heart The Heart Includes Pointed tip is apex Surrounded by pericardial sac Sits between two pleural cavities in the mediastinum Great veins and arteries at the base
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
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 or cavity Filled with pericardial fluid
Figure 20-2c The Location of the Heart in the Thoracic Cavity Base of heart Cut edge of parietal pericardium Fibrous tissue of pericardial sac Wrist (corresponds to base of heart) Inner wall (corresponds to epicardium) Fibrous attachment to diaphragm Parietal pericardium Areolar tissue Mesothelium Cut edge of epicardium Apex of heart Air space (corresponds to pericardial cavity) Outer wall (corresponds to parietal pericardium) Balloon The relationship between the heart and the pericardial cavity; compare with the fist-and-balloon example.
20-1 Anatomy of the Heart 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
Figure 20-3a The Superficial Anatomy of the Heart Left common carotid artery Brachiocephalic trunk Ascending aorta Superior vena cava Auricle of right atrium RIGHT ATRIUM Left subclavian artery Arch of aorta Ligamentum arteriosum Descending aorta Left pulmonary artery Pulmonary trunk Auricle of left atrium Fat and vessels in coronary sulcus RIGHT VENTRICLE Fat and vessels in anterior interventricular sulcus LEFT VENTRICLE Major anatomical features on the anterior surface.
Figure 20-3b The Superficial Anatomy of the Heart Left pulmonary artery Left pulmonary veins Fat and vessels in coronary sulcus Coronary sinus LEFT VENTRICLE LEFT ATRIUM RIGHT ATRIUM Arch of aorta Right pulmonary artery Superior vena cava Right pulmonary veins (superior and inferior) RIGHT VENTRICLE 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.
20-1 Anatomy of the Heart 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 Also called exchange vessels Exchange materials between blood and tissues Materials include dissolved gases, nutrients, waste products
20-1 Anatomy of the Heart 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
Figure 20-1 An Overview of the Cardiovascular System PULMONARY CIRCUIT Pulmonary arteries Pulmonary veins SYSTEMIC CIRCUIT Systemic arteries Systemic veins Capillaries in lungs Right atrium Capillaries in head, neck, upper limbs Left atrium Right ventricle Left ventricle Capillaries in trunk and lower limbs
20-1 Anatomy of the Heart (External) Epicardium (Outer Layer) Visceral pericardium Covers 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
Figure 20-4a The Heart Wall Parietal pericardium Dense fibrous layer Areolar tissue Mesothelium Myocardium (cardiac muscle tissue) Cardiac muscle cells Connective tissues Pericardial cavity Epicardium (visceral pericardium) Mesothelium Areolar tissue Endocardium Areolar tissue Endothelium
Figure 20-4b The Heart Wall Atrial musculature Ventricular musculature Cardiac muscle tissue forms concentric layers that wrap around the atria or spiral within the walls of the ventricles.
20-1 Anatomy of the Heart Cardiac Muscle Tissue Intercalated discs Interconnect cardiac muscle cells Secured by desmosomes- notches and knots Linked by gap junctions- channels Convey force of contraction Propagate action potentials
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
Figure 20-5a Cardiac Muscle Cells Cardiac muscle cell Mitochondria Intercalated disc (sectioned) Nucleus Cardiac muscle cell (sectioned) Bundles of myofibrils Intercalated discs Cardiac muscle cells
Figure 20-5b Cardiac Muscle Cells Intercalated disc Gap junction Opposing plasma membranes Desmosomes Structure of an intercalated disc
Figure 20-5c Cardiac Muscle Cells Intercalated discs Cardiac muscle tissue LM 575 Cardiac muscle tissue
Figure 20-4b The Heart Wall Atrial musculature Ventricular musculature Cardiac muscle tissue forms concentric layers that wrap around the atria or spiral within the walls of the ventricles.
Internal Anatomy of Heart
20-1 Anatomy of the Heart Internal Anatomy and Organization Interatrial septum separates atria Interventricular septum separates ventricles
20-1 Anatomy of the Heart 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
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
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
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
Figure 20-6a The Sectional Anatomy of the Heart 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 Brachiocephalic trunk Aortic arch LEFT ATRIUM 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 Descending aorta
Figure 20-6c The Sectional Anatomy of the Heart Ascending aorta Cusp of aortic valve Inferior vena cava Fossa ovalis Pectinate muscles Coronary sinus RIGHT ATRIUM Cusps of right AV (tricuspid) valve Trabeculae carneae Left coronary artery branches (red) and great cardiac vein (blue) Cusp of left AV (bicuspid) valve Chordae tendineae Papillary muscles LEFT VENTRICLE Interventricular septum RIGHT VENTRICLE A frontal section, anterior view.
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
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
Figure 20-6b The Sectional Anatomy of the Heart Chordae tendineae Papillary muscles 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.
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
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
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
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
Figure 20-6c The Sectional Anatomy of the Heart Ascending aorta Cusp of aortic valve Inferior vena cava Fossa ovalis Pectinate muscles Coronary sinus RIGHT ATRIUM Cusps of right AV (tricuspid) valve Trabeculae carneae Left coronary artery branches (red) and great cardiac vein (blue) Cusp of left AV (bicuspid) valve Chordae tendineae Papillary muscles LEFT VENTRICLE Interventricular septum RIGHT VENTRICLE A frontal section, anterior view.
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
Figure 20-7a Structural Differences between the Left and Right Ventricles Posterior interventricular sulcus Right ventricle Left 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.
Figure 20-7b Structural Differences between the Left and Right Ventricles Right ventricle Left ventricle Dilated Contracted Diagrammatic views of the ventricles just before a contraction (dilated) and just after a contraction (contracted).
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
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
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
Figure 20-8a Valves of the Heart Transverse Sections, Superior View, Atria and Vessels Removed POSTERIOR Cardiac skeleton Left AV (bicuspid) valve (open) RIGHT VENTRICLE LEFT VENTRICLE Relaxed ventricles Right AV (tricuspid) valve (open) Aortic valve (closed) ANTERIOR Pulmonary valve (closed) 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.
Figure 20-8a Valves of the Heart Frontal Sections through Left Atrium and Ventricle Pulmonary veins Relaxed ventricles Aortic valve (closed) LEFT ATRIUM Left AV (bicuspid) valve (open) Chordae tendineae (loose) Papillary muscles (relaxed) LEFT VENTRICLE (relaxed and filling with blood)
Figure 20-8b Valves of the Heart Right AV (tricuspid) valve (closed) RIGHT VENTRICLE Cardiac skeleton Left AV (bicuspid) valve (closed) LEFT VENTRICLE Contracting ventricles Aortic valve (open) Pulmonary valve (open) Aortic 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.
Figure 20-8b Valves of the Heart Contracting ventricles Aorta Aortic sinus Aortic valve (open) LEFT ATRIUM Left AV (bicuspid) valve (closed) Chordae tendineae (tense) Papillary muscles (contracted) Left ventricle (contracted)
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
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
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
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
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
20-1 Anatomy of the Heart Left Coronary Artery Supplies blood to: Left ventricle Left atrium Interventricular septum
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
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
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.
Figure 20-9b Coronary Circulation Circumflex artery Great cardiac vein Coronary sinus Marginal artery Posterior interventricular artery Posterior cardiac vein Left ventricle Small cardiac vein Right coronary artery Middle cardiac vein Marginal artery Coronary vessels supplying and draining the posterior surface of the heart.
Figure 20-10 Heart Disease and Heart Attacks Normal Artery Narrowing of Artery Tunica externa Lipid deposit of plaque Tunica media Cross-section Cross-section
Figure 20-10 Heart Disease and Heart Attacks Occluded Coronary Artery Damaged Heart Muscle
20-2 The Conducting System Heartbeat A single contraction of the heart The entire heart contracts in series First the atria Then the ventricles
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
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
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
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
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
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
Figure 20-11a The Conducting System of the Heart Sinoatrial (SA) node Internodal pathways Atrioventricular (AV) node AV bundle Purkinje fibers Components of the conducting system Bundle branches
Figure 20-11b The Conducting System of the Heart Threshold Prepotential (spontaneous depolarization) Time (sec) 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.
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
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)
Figure 20-12 Impulse Conduction through the Heart (Step 1) SA node activity and atrial activation begin. SA node Time = 0
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
Figure 20-12 Impulse Conduction through the Heart (Step 2) Stimulus spreads across the atrial surfaces and reaches the AV node. AV node Elapsed time = 50 msec
Figure 20-12 Impulse Conduction through the Heart (Step 3) There is a 100-msec delay at the AV node. Atrial contraction begins. AV bundle Elapsed time = 150 msec Bundle branches
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
Figure 20-12 Impulse Conduction through the Heart (Step 4) 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. Moderator Elapsed time = 175 msec band
20-2 The Conducting System Purkinje Fibers Distribute impulse through ventricles (Step 5) Atrial contraction is completed Ventricular contraction begins
Figure 20-12 Impulse Conduction through the Heart (Step 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 Purkinje fibers
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
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
20-2 The Conducting System Features of an ECG P wave Atria depolarize QRS complex Ventricles depolarize T wave Ventricles repolarize
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
Figure 20-13a An Electrocardiogram Electrode placement for recording a standard ECG.
Figure 20-13b An Electrocardiogram 800 msec R R P wave (atria depolarize) T wave (ventricles repolarize) P R segment S T segment Millivolts P R interval Q S S T interval Q T interval QRS interval (ventricles depolarize)
Figure 20-14 Cardiac Arrhythmias Premature Atrial Contractions (PACs) P P P Paroxysmal Atrial Tachycardia (PAT) P P P P P P Atrial Fibrillation (AF)
Figure 20-14 Cardiac Arrhythmias Premature Ventricular Contractions (PVCs) P T P T P T Ventricular Tachycardia (VT) P Ventricular Fibrillation (VF)
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
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: Ca 2+ entry Duration: ~175 msec Ends with: Closure of slow calcium channels Cause: K + loss Duration: 75 msec Ends with: Closure of slow potassium channels mv Absolute refractory period Relative refractory period Stimulus Time (msec) Events in an action potential in a ventricular muscle cell. KEY Absolute refractory period Relative refractory period
Figure 12-9 The Resting Potential is the Transmembrane Potential of an Undisturbed Cell EXTRACELLULAR FLUID 70 30 0 +30 Cl mv K + leak channel 3 Na + Na + leak channel Plasma membrane Sodium potassium exchange pump CYTOSOL Protein 2 K + Protein Protein
Figure 20-15b The Action Potential in Skeletal and Cardiac Muscle mv Action potential SKELETAL MUSCLE Tension Contraction Time (msec) CARDIAC MUSCLE mv Action potential KEY Absolute refractory period Relative refractory period Tension Contraction Time (msec) Action potentials and twitch contractions in a skeletal muscle (above) and cardiac muscle (below).
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
20-2 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
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
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
20-3 The Cardiac Cycle Two Phases of the Cardiac Cycle Within any one chamber 1. Systole (contraction) 2. Diastole (relaxation) Atrial systole Atrial diastole Ventricular systole Ventricular diastole
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)
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)
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
Figure 20-16 Phases of the Cardiac Cycle
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
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
Figure 20-17 Pressure and Volume Relationships in the Cardiac Cycle ATRIAL DIASTOLE ATRIAL SYSTOLE VENTRICULAR DIASTOLE VENTRICULAR SYSTOLE ATRIAL DIASTOLE Aortic valve opens Aorta Atrial contraction begins. Pressure (mm Hg) Left ventricle Atria eject blood into ventricles. Atrial systole ends; AV valves close. Isovolumetric ventricular contraction. Ventricular ejection occurs. Left atrium Left AV valve closes Semilunar valves close. Isovolumetric relaxation occurs. AV valves open; passive ventricular filling occurs. End-diastolic volume Left ventricular volume (ml) Stroke volume Time (msec)
Figure 20-17 Pressure and Volume Relationships in the Cardiac Cycle VENTRICULAR SYSTOLE ATRIAL DIASTOLE VENTRICULAR DIASTOLE ATRIAL SYSTOLE Aortic valve closes Pressure (mm Hg) Dicrotic notch Left AV valve opens 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. Left ventricular volume (ml) End-systolic volume Time (msec)
20-3 The Cardiac Cycle Heart Sounds S 1 Loud sounds Produced by AV valves S 2 Loud sounds Produced by semilunar valves
20-3 The Cardiac Cycle S 3, S 4 Soft sounds Blood flow into ventricles and atrial contraction Heart Murmur Sounds produced by regurgitation through valves
Figure 20-18a Heart Sounds Sounds heard Valve location Aortic valve Valve location Sounds heard Pulmonary valve Sounds heard Valve location Left AV valve Valve location Sounds heard Right AV valve Placements of a stethoscope for listening to the different sounds produced by individual valves
Figure 20-18b Heart Sounds Semilunar valves open Semilunar valves close Aorta Pressure (mm Hg) Left ventricle Left atrium AV valves close AV valves open Heart sounds S 1 S 4 S 4 S 2 S 3 Lubb Dubb The relationship between heart sounds and key events in the cardiac cycle
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 SV= %EDV
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)
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
Figure 20-20 Factors Affecting Cardiac Output Factors Affecting Heart Rate (HR) Factors Affecting Stroke Volume (SV) Autonomic innervation Hormones End-diastolic volume End-systolic volume HEART RATE (HR) STROKE VOLUME (SV) = EDV ESV CARDIAC OUTPUT (CO) = HR SV
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)
20-4 Cardiodynamics 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
Figure 20-21 Autonomic Innervation of the Heart Cardioinhibitory center Vagal nucleus Cardioacceleratory center Medulla oblongata Vagus (N X) Spinal cord Sympathetic Sympathetic ganglia (cervical ganglia and superior thoracic ganglia [T 1 T 4 ]) Sympathetic preganglionic fiber Sympathetic postganglionic fiber Cardiac nerve Parasympathetic Parasympathetic preganglionic fiber Synapses in cardiac plexus Parasympathetic postganglionic fibers
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
Figure 20-22a Autonomic Regulation of Pacemaker Function Membrane potential (mv) Threshold Normal (resting) Prepotential (spontaneous depolarization) 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.
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
Figure 20-22b Autonomic Regulation of Pacemaker Function Membrane potential (mv) Parasympathetic stimulation Threshold Hyperpolarization Heart rate: 40 bpm Slower depolarization Parasympathetic stimulation releases ACh, which extends repolarization and decreases the rate of spontaneous depolarization. The heart rate slows.
Figure 20-22c Autonomic Regulation of Pacemaker Function Membrane potential (mv) Sympathetic stimulation Threshold Reduced repolarization Heart rate: 120 bpm More rapid depolarization Time (sec) Sympathetic stimulation releases NE, which shortens repolarization and accelerates the rate of spontaneous depolarization. As a result, the heart rate increases.
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
20-4 Cardiodynamics Hormonal Effects on Heart Rate Increase heart rate (by sympathetic stimulation of SA node) Epinephrine (E) Norepinephrine (NE) Thyroid hormone
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
20-4 Cardiodynamics Preload The degree of ventricular stretching during ventricular diastole Directly proportional to EDV Affects ability of muscle cells to produce tension
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
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
20-4 Cardiodynamics End-Systolic Volume (ESV) Is the amount of blood that remains in the ventricle at the end of ventricular systole
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
20-4 Cardiodynamics Contractility Is affected by: Autonomic activity Hormones
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
20-4 Cardiodynamics Effects of Autonomic Activity on Contractility Parasympathetic activity Acetylcholine released by vagus nerves Reduces force of cardiac contractions
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)
20-4 Cardiodynamics Afterload Is increased by any factor that restricts arterial blood flow As afterload increases, stroke volume decreases
Figure 20-23 Factors Affecting Stroke Volume Factors Affecting Stroke Volume (SV) Venous return (VR) Filling time (FT) VR = EDV FT = EDV VR = EDV FT = EDV Increased by sympathetic stimulation Decreased by parasympathetic stimulation Increased by E, NE, glucagon, thyroid hormones Preload Contractility (Cont) of muscle cells Cont = ESV Increased by Cont = ESV vasoconstriction Decreased by vasodilation End-diastolic volume (EDV) End-systolic volume (ESV) Afterload (AL) AL = ESV AL = ESV EDV = EDV = STROKE VOLUME (SV) SV SV ESV = ESV = SV SV
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
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
20-4 Cardiodynamics Cardiac Reserve The difference between resting and maximal cardiac output
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
Figure 20-24 A Summary of the Factors Affecting Cardiac Output Factors affecting heart fate (HR) Factors affecting stroke volume (SV) Skeletal muscle activity Blood volume Changes in peripheral circulation Atrial reflex Venous return Filling time Autonomic innervation Hormones Preload Contractility Vasodilation or vasoconstriction Autonomic innervation Hormones End-diastolic volume End-systolic volume Afterload HEART RATE (HR) STROKE VOLUME (SV) = EDV ESV CARDIAC OUTPUT (CO) = HR SV