The Heart. C h a p t e r. PowerPoint Lecture Slides prepared by Jason LaPres Lone Star College - North Harris

Introduction to 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

Introduction to Cardiovascular System Three Types of Blood Vessels Arteries Carry blood away from heart Veins Carry blood to heart Capillaries Networks between arteries and veins

Introduction to Cardiovascular System Capillaries Also called exchange vessels Exchange materials between blood and tissues Materials include dissolved gases, nutrients, wastes

Introduction to Cardiovascular System Figure 20 1 An Overview of the Cardiovascular System.

Introduction to Cardiovascular System Four Chambers of the Heart Right atrium Collects blood from systemic circuit Right ventricle Pumps blood to pulmonary circuit Left atrium Collects blood from pulmonary circuit Left ventricle Pumps blood to systemic circuit

Anatomy of 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 Figure 20 2c

Anatomy of the Heart Figure 20 2a The Location of the Heart in the Thoracic Cavity

Anatomy of the Heart The Pericardium Double lining of the pericardial cavity Parietal pericardium Outer layer Forms inner layer of pericardial sac Visceral pericardium Inner layer of pericardium Figure 20 2c

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

Anatomy of the Heart Figure 20 2b The Location of the Heart in the Thoracic Cavity

Anatomy of the Heart Figure 20 c2 The Location of the Heart in the Thoracic Cavity

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 interventricular sulcus and posterior interventricular sulcus: separate left and right ventricles contain blood vessels of cardiac muscle

Anatomy of the Heart Figure 20 3a The Superficial Anatomy of the Heart

Anatomy of the Heart Figure 20 3b The Superficial Anatomy of the Heart

Anatomy of the Heart Figure 20 3c The Superficial Anatomy of the Heart

The Heart Wall Anatomy of the Heart 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

Anatomy of the Heart Figure 20 4 The Heart Wall

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

Anatomy of the Heart Figure 20 5 Cardiac Muscle Cells

Anatomy of the Heart Characteristics of Cardiac Muscle Cells Small size Single, central nucleus Branching interconnections between cells Intercalated discs

Anatomy of the Heart

Anatomy of the Heart Internal Anatomy and Organization Interatrial septum: separates atria Interventricular septum: separates ventricles Atrioventricular (AV) valves Connect right atrium to right ventricle and left atrium to left ventricle The fibrous flaps that form bicuspid (2) and tricuspid (3) valves Permit blood flow in one direction: atria to ventricles The Heart: Valves

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

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

Anatomy of the Heart The Right Atrium Pectinate muscles Contain prominent muscular ridges On anterior atrial wall and inner surfaces of right auricle

Anatomy of the Heart Figure 20 6a-b The Sectional Anatomy of the Heart.

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

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

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

The Left Atrium Anatomy of the Heart 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

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 Systemic circulation Blood leaves left ventricle through aortic valve into ascending aorta Ascending aorta turns (aortic arch) and becomes descending aorta

Anatomy of the Heart Figure 20 6c The Sectional Anatomy of the Heart.

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

Anatomy of the Heart Figure 20 7 Structural Differences between the Left and Right Ventricles

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: prevent valves from swinging into atria Figure 20 8

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 Figure 20 8

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

Anatomy of the Heart Figure 20 8a Valves of the Heart

Anatomy of the Heart Figure 20 8b Valves of the Heart

Anatomy of the Heart Figure 20 8c Valves of the Heart

Anatomy of the Heart Connective Tissues and the Cardiac (Fibrous) Skeleton Physically support cardiac muscle fibers Distribute forces of contraction Add strength and prevent overexpansion of heart Elastic fibers return heart to original shape after contraction

Anatomy of the Heart The Cardiac (Fibrous) Skeleton Four bands around heart valves and bases of pulmonary trunk and aorta Stabilize valves Electrically insulate ventricular cells from atrial cells

Anatomy of the Heart The Blood Supply to the Heart = Coronary Circulation Coronary arteries and cardiac veins Supplies blood to muscle tissue of heart

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

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

Anatomy of the Heart Left Coronary Artery Supplies blood to Left ventricle Left atrium Interventricular septum

Anatomy of the Heart Two main branches of left coronary artery Circumflex artery Anterior interventricular artery Arterial Anastomoses Interconnect anterior and posterior interventricular arteries Stabilize blood supply to cardiac muscle

Anatomy of the Heart The Cardiac Veins Great cardiac vein Drains blood from area of anterior interventricular artery into coronary sinus Anterior cardiac veins Empties into right atrium Posterior cardiac vein, middle cardiac vein, and small cardiac vein Empty into great cardiac vein or coronary sinus

Anatomy of the Heart Figure 20 9a Coronary Circulation

Anatomy of the Heart Figure 20 9b Coronary Circulation

Anatomy of the Heart Figure 20 9c Coronary Circulation

Anatomy of the Heart Figure 20 10 Coronary Circulation and Clinical Testing

The Conducting System Heartbeat A single contraction of the heart The entire heart contracts in series First the atria Then the ventricles

The Conducting System Two Types of Cardiac Muscle Cells Conducting system Controls and coordinates heartbeat Contractile cells Produce contractions that propel blood

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) Electrical events in the cardiac cycle can be recorded on an electrocardiogram (ECG)

The Conducting System Figure 20 11 An Overview of Cardiac Physiology

The Conducting System A system of specialized cardiac muscle cells Initiates and distributes electrical impulses that stimulate contraction Automaticity Cardiac muscle tissue contracts automatically

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

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

The Conducting System Prepotential Also called pacemaker potential Resting potential of conducting cells Gradually depolarizes toward threshold SA node depolarizes first, establishing heart rate

The Conducting System Figure 20 12 The Conducting System of the Heart

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

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)

The Conducting System Figure 20 13 Impulse Conduction through the Heart

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

The Conducting System Figure 20 13 Impulse Conduction through the Heart

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

The Conducting System Figure 20 13 Impulse Conduction through the Heart

The Conducting System Purkinje Fibers Distribute impulse through ventricles (Step 5) Atrial contraction is completed Ventricular contraction begins

The Conducting System Figure 20 13 Impulse Conduction through the Heart

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

The Conducting System Electrocardiogram (ECG or EKG) A recording of electrical events in the heart Obtained by electrodes at specific body locations Abnormal patterns diagnose damage

The Conducting System Features of an ECG P wave Atria depolarize QRS complex Ventricles depolarize T wave Ventricles repolarize

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

The Conducting System Figure 20 14a An Electrocardiogram: Electrode Placement for Recording a Standard ECG

The Conducting System Figure 20 14b An Electrocardiogram: An ECG Printout

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

The Conducting System Figure 20 15 The Action Potential in Skeletal and Cardiac Muscle

The Conducting System Refractory Period Absolute refractory period Long Cardiac muscle cells cannot respond Relative refractory period Short Response depends on degree of stimulus

The Conducting System Timing of Refractory Periods Length of cardiac action potential in ventricular cell 250 300 msecs: 30 times longer than skeletal muscle fiber long refractory period prevents summation and tetany

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

The Conducting System The Role of Calcium Ions in Cardiac Contractions 20% of calcium ions required for a contraction Calcium ions enter plasma membrane during plateau phase Arrival of extracellular Ca 2+ Triggers release of calcium ion reserves from sarcoplasmic reticulum

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

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

The Cardiac Cycle Cardiac cycle = The period between the start of one heartbeat and the beginning of the next Includes both contraction and relaxation

The Cardiac Cycle Phases of the Cardiac Cycle Within any one chamber Systole (contraction) Diastole (relaxation)

The Cardiac Cycle Figure 20 16 Phases of the Cardiac Cycle

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

The Cardiac Cycle Cardiac Cycle and Heart Rate At 75 beats per minute Cardiac cycle lasts about 800 msecs When heart rate increases All phases of cardiac cycle shorten, particularly diastole

The Cardiac Cycle Eight Steps in the Cardiac Cycle 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)

The Cardiac Cycle Figure 20 17 Pressure and Volume Relationships in the Cardiac Cycle

The Cardiac Cycle Eight Steps in the Cardiac Cycle 4. Ventricular systole Isovolumetric ventricular contraction Pressure in ventricles rises AV valves shut 5. Ventricular ejection Semilunar valves open Blood flows into pulmonary and aortic trunks Stroke volume (SV) = 60% of end-diastolic volume

The Cardiac Cycle Figure 20 17 Pressure and Volume Relationships in the Cardiac Cycle

The Cardiac Cycle Eight Steps in the Cardiac Cycle 6. Ventricular pressure falls Semilunar valves close Ventricles contain end-systolic volume (ESV), about 40% of end-diastolic volume 7. Ventricular diastole Ventricular pressure is higher than atrial pressure All heart valves are closed Ventricles relax (isovolumetric relaxation)

The Cardiac Cycle Figure 20 17 Pressure and Volume Relationships in the Cardiac Cycle

The Cardiac Cycle Eight Steps in the Cardiac Cycle 8. Atrial pressure is higher than ventricular pressure AV valves open Passive atrial filling Passive ventricular filling Cardiac cycle ends The Heart: Cardiac Cycle

The Cardiac Cycle Figure 20 17 Pressure and Volume Relationships in the Cardiac Cycle

Heart Sounds S 1 S 2 The Cardiac Cycle Loud sounds Produced by AV valves Loud sounds Produced by semilunar valves S 3, S 4 Soft sounds Blood flow into ventricles and atrial contraction

The Cardiac Cycle Heart Murmur Sounds produced by regurgitation through valves

The Cardiac Cycle Figure 20 18 Heart Sounds

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 Cardiac output (CO) The volume pumped by left ventricle in 1 minute

Cardiodynamics Figure 20 19 A Simple Model of Stroke Volume

Cardiodynamics Cardiac Output CO = HR X SV CO = cardiac output (ml/min) HR = heart rate (beats/min) SV = stroke volume (ml/beat)

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

Cardiodynamics Figure 20 20 Factors Affecting Cardiac Output

Cardiodynamics Factors Affecting the Heart Rate Autonomic innervation Cardiac plexuses: innervate heart Vagus nerves (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)

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

Cardiodynamics Figure 20 21 Autonomic Innervation of the Heart

Cardiodynamics Effects on the SA Node Sympathetic and parasympathetic stimulation Greatest at SA node (heart rate) Membrane potential of pacemaker cells Lower than other cardiac cells Rate of spontaneous depolarization depends on Resting membrane potential Rate of depolarization ACh (parasympathetic stimulation) Slows the heart NE (sympathetic stimulation) Speeds the heart

Cardiodynamics Figure 20 22 Autonomic Regulation of Pacemaker Function

Atrial Reflex Cardiodynamics 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

Cardiodynamics Hormonal Effects on Heart Rate Increase heart rate (by sympathetic stimulation of SA node) Epinephrine (E) Norepinephrine (NE) Thyroid hormone

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

Cardiodynamics Preload The degree of ventricular stretching during ventricular diastole Directly proportional to EDV Affects ability of muscle cells to produce tension

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

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

Cardiodynamics End-Systolic Volume (ESV) The amount of blood that remains in the ventricle at the end of ventricular systole is the ESV

Cardiodynamics Three Factors That Affect ESV Preload Ventricular stretching during diastole Contractility Force produced during contraction, at a given preload Afterload Tension the ventricle produces to open the semilunar valve and eject blood

Cardiodynamics Contractility Is affected by Autonomic activity Hormones

Cardiodynamics Effects of Autonomic Activity on Contractility Sympathetic stimulation NE released by postganglionic fibers of cardiac nerves Epinephrine and NE released by suprarenal (adrenal) medullae Causes ventricles to contract with more force Increases ejection fraction and decreases ESV

Cardiodynamics Effects of Autonomic Activity on Contractility Parasympathetic activity Acetylcholine released by vagus nerves Reduces force of cardiac contractions

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)

Cardiodynamics Afterload Is increased by any factor that restricts arterial blood flow As afterload increases, stroke volume decreases

Cardiodynamics Figure 20 23 Factors Affecting Stroke Volume

Cardiodynamics Heart Rate Control Factors Autonomic nervous system Sympathetic and parasympathetic Circulating hormones Venous return and stretch receptors

Cardiodynamics Stroke Volume Control Factors EDV Filling time Rate of venous return ESV Preload Contractility Afterload

Cardiodynamics Cardiac Reserve The difference between resting and maximal cardiac output

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

Cardiodynamics Figure 20 24 A Summary of the Factors Affecting Cardiac Output