AP-Ch18

Chapter

18 The Heart

PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris

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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 Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

Introduction to Cardiovascular System  Capillaries  Also called exchange vessels  Exchange materials between blood and tissues  Materials include dissolved gases, nutrients, wastes Copyright © 2010 Pearson Education, Inc.

Introduction to Cardiovascular System

Figure 18–1 An Overview of the Cardiovascular System.

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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 Copyright © 2010 Pearson Education, Inc.

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

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Anatomy of the Heart

Figure 18–2a The Location of the Heart in the Thoracic Cavity Copyright © 2010 Pearson Education, Inc.

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

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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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–2b The Location of the Heart in the Thoracic Cavity Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–2c The Location of the Heart in the Thoracic Cavity Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  Superficial Anatomy of the Heart  Atria  Thin-walled  Expandable outer auricle (atrial appendage)

 Sulci  Coronary sulcus: divides atria and ventricles  Anterior interventricular sulcus and posterior interventricular sulcus: – separate left and right ventricles – contain blood vessels of cardiac muscle Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–3a The Superficial Anatomy of the Heart Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–3a The Superficial Anatomy of the Heart Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–3b The Superficial Anatomy of the Heart Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–3c The Superficial Anatomy of the Heart Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Heart Wall  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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–4 The Heart Wall

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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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–5 Cardiac Muscle Cells Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–5 Cardiac Muscle Cells Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–5 Cardiac Muscle Cells Copyright © 2010 Pearson Education, Inc.

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

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Anatomy of the Heart

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Anatomy of the Heart

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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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Right Atrium  Superior vena cava  Receives blood from head, neck, upper limbs, and chest

 Inferior vena cava  Receives blood from trunk, viscera, and lower limbs

 Coronary sinus  Cardiac veins return blood to coronary sinus  Coronary sinus opens into right atrium

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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

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

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Anatomy of the Heart

Figure 18–6a-b The Sectional Anatomy of the Heart.

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Anatomy of the Heart

Figure 18–6a-b The Sectional Anatomy of the Heart.

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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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Right Ventricle  Trabeculae carneae  Muscular ridges on internal surface of right (and left) ventricle  Includes moderator band: – ridge contains part of conducting system – coordinates contractions of cardiac muscle cells

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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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Left Atrium  Blood gathers into left and right pulmonary veins  Pulmonary veins deliver to left atrium  Blood from left atrium passes to left ventricle through left atrioventricular (AV) valve  A two-cusped bicuspid valve or mitral valve Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Left Ventricle  Holds same volume as right ventricle  Is larger; muscle is thicker and more powerful  Similar internally to right ventricle but does not have moderator band  Systemic circulation  Blood leaves left ventricle through aortic valve into ascending aorta  Ascending aorta turns (aortic arch) and becomes descending aorta Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–6c The Sectional Anatomy of the Heart.

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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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–7 Structural Differences between the Left and Right Ventricles Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–7 Structural Differences between the Left and Right Ventricles Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Heart Valves  Two pairs of one-way valves prevent backflow during contraction  Atrioventricular (AV) valves  Between atria and ventricles  Blood pressure closes valve cusps during ventricular contraction  Papillary muscles tense chordae tendineae: prevent valves from swinging into atria Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Heart Valves  Semilunar valves  Pulmonary and aortic tricuspid valves  Prevent backflow from pulmonary trunk and aorta into ventricles  Have no muscular support  Three cusps support like tripod Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  Aortic Sinuses  At base of ascending aorta  Sacs that prevent valve cusps from sticking to aorta  Origin of right and left coronary arteries

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Anatomy of the Heart

Figure 18–8a Valves of the Heart Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–8b Valves of the Heart Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–8c Valves of the Heart

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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 Copyright © 2010 Pearson Education, Inc.

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

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

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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

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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 Copyright © 2010 Pearson Education, Inc.

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

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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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart  The Cardiac Veins  Great cardiac vein  Drains blood from area of anterior interventricular artery into coronary sinus

 Anterior cardiac veins  Empties into right atrium

 Posterior cardiac vein, middle cardiac vein, and small cardiac vein  Empty into great cardiac vein or coronary sinus Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–9a Coronary Circulation Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–9b Coronary Circulation Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–9c Coronary Circulation Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Figure 18–10 Coronary Circulation and Clinical Testing Copyright © 2010 Pearson Education, Inc.

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

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The Conducting System  Two Types of Cardiac Muscle Cells  Conducting system  Controls and coordinates heartbeat

 Contractile cells  Produce contractions that propel blood

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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)

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The Conducting System

Figure 18–11 An Overview of Cardiac Physiology Copyright © 2010 Pearson Education, Inc.

The Conducting System  A system of specialized cardiac muscle cells  Initiates and distributes electrical impulses that stimulate contraction

 Automaticity  Cardiac muscle tissue contracts automatically Copyright © 2010 Pearson Education, Inc.

The Conducting System  Structures of the Conducting System  Sinoatrial (SA) node - wall of right atrium  Atrioventricular (AV) node - junction between atria and ventricles  Conducting cells - throughout myocardium

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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 Copyright © 2010 Pearson Education, Inc.

The Conducting System  Prepotential  Also called pacemaker potential  Resting potential of conducting cells  Gradually depolarizes toward threshold

 SA node depolarizes first, establishing heart rate

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The Conducting System

Figure 18–12 The Conducting System of the Heart Copyright © 2010 Pearson Education, Inc.

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

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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) Copyright © 2010 Pearson Education, Inc.

The Conducting System

Figure 18–13 Impulse Conduction through the Heart Copyright © 2010 Pearson Education, Inc.

The Conducting System  The Atrioventricular (AV) Node  In floor of right atrium  Receives impulse from SA node (Step 2)  Delays impulse (Step 3)  Atrial contraction begins

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The Conducting System

Figure 18–13 Impulse Conduction through the Heart Copyright © 2010 Pearson Education, Inc.

The Conducting System

Figure 18–13 Impulse Conduction through the Heart Copyright © 2010 Pearson Education, Inc.

The Conducting System  The AV Bundle  In the septum  Carries impulse to left and right bundle branches  Which conduct to Purkinje fibers (Step 4)

 And to the moderator band  Which conducts to papillary muscles Copyright © 2010 Pearson Education, Inc.

The Conducting System

Figure 18–13 Impulse Conduction through the Heart Copyright © 2010 Pearson Education, Inc.

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

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The Conducting System

Figure 18–13 Impulse Conduction through the Heart Copyright © 2010 Pearson Education, Inc.

The Conducting System  Abnormal Pacemaker Function  Bradycardia: abnormally slow heart rate  Tachycardia: abnormally fast heart rate  Ectopic pacemaker  Abnormal cells  Generate high rate of action potentials  Bypass conducting system  Disrupt ventricular contractions

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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

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The Conducting System  Features of an ECG  P wave  Atria depolarize

 QRS complex  Ventricles depolarize

 T wave  Ventricles repolarize Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

The Conducting System

Figure 18–14a An Electrocardiogram: Electrode Placement for Recording a Standard ECG Copyright © 2010 Pearson Education, Inc.

The Conducting System

Figure 18–14b An Electrocardiogram: An ECG Printout Copyright © 2010 Pearson Education, Inc.

The Conducting System  Contractile Cells  Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart  Resting Potential  Of a ventricular cell: about –90 mV  Of an atrial cell: about –80 mV Copyright © 2010 Pearson Education, Inc.

The Conducting System

Figure 18–15 The Action Potential in Skeletal and Cardiac Muscle Copyright © 2010 Pearson Education, Inc.

The Conducting System

Figure 18–15 The Action Potential in Skeletal and Cardiac Muscle Copyright © 2010 Pearson Education, Inc.

The Conducting System  Refractory Period  Absolute refractory period  Long  Cardiac muscle cells cannot respond

 Relative refractory period  Short  Response depends on degree of stimulus Copyright © 2010 Pearson Education, Inc.

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

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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

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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 Ca2+  Triggers release of calcium ion reserves from sarcoplasmic reticulum

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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 Copyright © 2010 Pearson Education, Inc.

The Conducting System  The Energy for Cardiac Contractions  Aerobic energy of heart  From mitochondrial breakdown of fatty acids and glucose  Oxygen from circulating hemoglobin  Cardiac muscles store oxygen in myoglobin

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

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

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The Cardiac Cycle

Figure 18–16 Phases of the Cardiac Cycle Copyright © 2010 Pearson Education, Inc.

The Cardiac Cycle  Blood Pressure  In any chamber  Rises during systole  Falls during diastole

 Blood flows from high to low pressure  Controlled by timing of contractions  Directed by one-way valves Copyright © 2010 Pearson Education, Inc.

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

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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

5. Atrial systole ends 

AV valves close



Ventricles contain maximum blood volume



Known as end-diastolic volume (EDV)

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The Cardiac Cycle

Figure 18–17 Pressure and Volume Relationships in the Cardiac Cycle Copyright © 2010 Pearson Education, Inc.

The Cardiac Cycle Eight Steps in the Cardiac Cycle 4. Ventricular systole 

Isovolumetric ventricular contraction



Pressure in ventricles rises



AV valves shut

6. Ventricular ejection 

Semilunar valves open



Blood flows into pulmonary and aortic trunks



Stroke volume (SV) = 60% of end-diastolic volume

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The Cardiac Cycle

Figure 18–17 Pressure and Volume Relationships in the Cardiac Cycle Copyright © 2010 Pearson Education, Inc.

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

8. Ventricular diastole 

Ventricular pressure is higher than atrial pressure



All heart valves are closed



Ventricles relax (isovolumetric relaxation)

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The Cardiac Cycle

Figure 18–17 Pressure and Volume Relationships in the Cardiac Cycle Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

The Cardiac Cycle

Figure 18–17 Pressure and Volume Relationships in the Cardiac Cycle Copyright © 2010 Pearson Education, Inc.

The Cardiac Cycle  Heart Sounds  S1  Loud sounds  Produced by AV valves

 S2  Loud sounds  Produced by semilunar valves

 S3, S4  Soft sounds  Blood flow into ventricles and atrial contraction Copyright © 2010 Pearson Education, Inc.

The Cardiac Cycle  Heart Murmur  Sounds produced by regurgitation through valves

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The Cardiac Cycle

Figure 18–18 Heart Sounds Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

Cardiodynamics

Figure 18–19 A Simple Model of Stroke Volume Copyright © 2010 Pearson Education, Inc.

Cardiodynamics  Cardiac Output  CO = HR X SV  CO = cardiac output (mL/min)  HR = heart rate (beats/min)  SV = stroke volume (mL/beat) Copyright © 2010 Pearson Education, Inc.

Cardiodynamics  Factors Affecting Cardiac Output  Cardiac output  Adjusted by changes in heart rate or stroke volume

 Heart rate  Adjusted by autonomic nervous system or hormones

 Stroke volume  Adjusted by changing EDV or ESV

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Cardiodynamics

Figure 18–20 Factors Affecting Cardiac Output Copyright © 2010 Pearson Education, Inc.

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) Copyright © 2010 Pearson Education, Inc.

Cardiodynamics  Autonomic Innervation  Cardiac reflexes  Cardiac centers monitor: – blood pressure (baroreceptors) – arterial oxygen and carbon dioxide levels (chemoreceptors)

 Cardiac centers adjust cardiac activity  Autonomic tone  Dual innervation maintains resting tone by releasing ACh and NE  Fine adjustments meet needs of other systems Copyright © 2010 Pearson Education, Inc.

Cardiodynamics

Figure 18–21 Autonomic Innervation of the Heart Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

Cardiodynamics

Figure 18–22 Autonomic Regulation of Pacemaker Function Copyright © 2010 Pearson Education, Inc.

Cardiodynamics  Atrial Reflex  Also called Bainbridge reflex  Adjusts heart rate in response to venous return  Stretch receptors in right atrium  Trigger increase in heart rate  Through increased sympathetic activity Copyright © 2010 Pearson Education, Inc.

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

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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

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

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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 Copyright © 2010 Pearson Education, Inc.

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

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

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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

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Cardiodynamics  Contractility  Is affected by  Autonomic activity  Hormones

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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

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

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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)

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

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Cardiodynamics

Figure 18–23 Factors Affecting Stroke Volume Copyright © 2010 Pearson Education, Inc.

Cardiodynamics  Heart Rate Control Factors  Autonomic nervous system  Sympathetic and parasympathetic

 Circulating hormones  Venous return and stretch receptors

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Cardiodynamics  Stroke Volume Control Factors  EDV  Filling time  Rate of venous return

 ESV  Preload  Contractility  Afterload Copyright © 2010 Pearson Education, Inc.

Cardiodynamics  Cardiac Reserve  The difference between resting and maximal cardiac output

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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

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Cardiodynamics

Figure 18–24 A Summary of the Factors Affecting Cardiac Output Copyright © 2010 Pearson Education, Inc.