A&P Ch-20 Oct-29-2013
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Transcript of A&P Ch-20 Oct-29-2013
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Ch-20 The Heart
Introduction to Anatomy and Physiology
Chapter 20Heart
1
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Ch-20 The Heart
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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
Three Types of Blood Vessels1) Arteries : Carry blood away fromheart
2) Veins : Carry blood toheart
3) Capillaries : Networks betweenarteries andveins
Also called exchange vessels
Exchange materials between blood and tissues
Materials include dissolved gases, nutrients, wastes
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Introduction to Cardiovascular System
Figure 20
1 An Overview of the Cardiovascular System.
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Anatomy of the Heart
Figure 202a The Location of the Heart in the Thoracic Cavity
Right atrium
Collects blood fromsystemic circuit
Right ventricle
Pumps blood topulmonary circuit
Left atrium
Collects blood frompulmonary circuit
Left ventricle
Pumps blood tosystemic circuit
Four Chambers of the Heart
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Anatomy of the Heart
Figure 20
c2 The Location of the Heart in the Thoracic Cavity
Parietal pericardium
Visceral pericardium Pericardial cavity
Pericardial sac
The Pericardium
Double lining of the pericardial cavity
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Anatomy of the Heart
Figure 20
3a The Superficial Anatomy of the Heart
Atria
Thin-walled
Expandable outer auricle(atrial appendage)
Sulci Coronary sulcus: divides
atria and ventricles
Anterior interventricularsulcusand posteriorinterventricular sulcus:
separate left and rightventricles
contain blood vessels ofcardiac muscle
Superficial Anatomy of the Heart
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Anatomy of the Heart
Figure 204 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 wrapsaround great vessels
Two divisions of ventricularmyocardium
Endocardium(inner layer)
Simple squamous epithelium
The Heart Wall
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Anatomy of the Heart
Figure 20
5 Cardiac Muscle Cells
Cardiac Muscle Tissue
Small size
Single, central nucleus
Branching interconnections
between cells
Intercalated discs
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Anatomy of the Heart
Figure 205 Cardiac Muscle Cells
Interconnect cardiac muscle cells Secured by desmosomes
Linked by gap junctions
Convey force of contraction
Propagate action potentials
Intercalated discs
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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
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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
Foramen ovale
Before birth, is an opening through interatrial septum
Connects the two atria Seals off at birth, forming fossa ovalis
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 20
6a-b The Sectional Anatomy of the Heart
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Anatomy of the Heart
The Right Ventricle
Free edges attach to chordae tendineaefrom papillarymusclesof 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
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) leadsto pulmonary trunk
Pulmonary trunk divides into left andright pulmonaryarteries
Blood flows from right ventricle to pulmonary trunkthrough pulmonary valve
Pulmonary valve has three semilunar cusps
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Anatomy of the Heart
The Left Atrium
Blood gathers into left andright pulmonary veins
Pulmonary veins deliver to left atrium
Blood from left atrium passes to left ventricle through leftatrioventricular (AV) valve
A two-cuspedbicuspid valveor mitral valve
The Left Ventricle Holds same volume as right ventricle
Is larger; muscle is thicker and more powerful
Similar internally to right ventricle but does nothave moderator band
Systemic circulation
Blood leaves left ventricle through aortic valveinto ascendingaorta
Ascending aorta turns (aortic arch) and becomes descending
aorta
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Anatomy of the Heart
Structural Differencesbetween the Left and RightVentricles
Right ventricle wall is thinner, develops less pressure than leftventricle
Right ventricle is pouch-shaped, left ventricle is round
Figure 207 Structural Differences between the Left and Right Ventricles
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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 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
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 208 Valves of the Heart
OCh Th H
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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
The Cardiac (Fibrous) Skeleton
Four bands around heart valves and bases of pulmonary trunkand aorta
Stabilize valves
Electrically insulate ventricular cells from atrial cells
O tCh Th H t
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Anatomy of the Heart
The Blood Supply to the Heart = Coronary Circulation
Coronary arteriesand cardiac veins
Supplies blood to muscle tissue of heart
The Cardiac Veins
Great cardiac vein Drains blood from area of
anterior interventricular arteryinto coronary sinus
Anterior cardiac veins
Empties into right atrium Posterior cardiac vein,
middle cardiac vein, andsmall cardiac vein
Empty into great cardiac veinor coronary sinus
The Coronary Arteries Left and right
Originate at aortic sinuses
High blood pressure, elasticrebound forces blood
through coronary arteriesbetween contractions
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Anatomy of the Heart
2) Left Coronary Artery Supplies blood to
Left ventricle
Left atrium
Interventricular septum
Two main branches of leftcoronary artery Circumflex artery Anterior interventricular artery
Arterial Anastomoses
Interconnect anterior and posteriorinterventricular arteries
Stabilize blood supply to cardiacmuscle
1) Right Coronary Artery
Supplies blood to
Right atrium
Portions of both ventricles
Cells of sinoatrial (SA) andatrioventricular nodes
Marginal arteries(surfaceof right ventricle)
Posterior interventricularartery
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Anatomy of the Heart
Figure 209a Coronary Circulation
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The Conducting System
Heartbeat
A single contraction of the heart
The entire heart contracts in series
First the atria
Then the ventricles
Two Types of Cardiac Muscle Cells Conducting system : Controls and coordinates heartbeat
Contractile cells : Produce contractions that propel blood
A system of specialized cardiac muscle cells
Initiates and distributes electrical impulses that stimulatecontraction
Automaticity
Cardiac muscle tissue contracts automatically
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The Conducting System
Figure 2011 An Overview of Cardiac Physiology
The Cardiac Cycle Begins with action potential at
SA node
Transmitted throughconducting system
Produces action potentials
in cardiac muscle cells(contractile cells)
Electrocardiogram (ECG)
Electrical events in the
cardiac cycle can be recordedon an electrocardiogram(ECG)
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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
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
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 2012 The Conducting System of the Heart
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The Conducting System
Figure 20
13 Impulse Conduction through the Heart
Heart Rate SA node generates
80100 actionpotentials per minute
Parasympathetic
stimulation slowsheart rate
AV node generates4060 actionpotentials per minute
The Sinoatrial (SA) Node In posterior wall of right atrium
Contains pacemaker cells
Connected to AV node byinternodal pathways
Begins atrial activation (Step 1)
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The Conducting System
Figure 2013 Impulse Conduction through the Heart
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 20
13 Impulse Conduction through the Heart
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
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The Conducting System
Figure 20
13 Impulse Conduction through the Heart
Purkinje Fibers Distribute impulse through ventricles (Step 5)
Atrial contraction is completed
Ventricular contraction begins
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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
A recording of electrical events in the heart
Obtained by electrodes at specific body locations
Abnormal patterns diagnose damage
Electrocardiogram (ECG or EKG)
Figure 2014b An Electrocardiogram: An ECG Printout
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The Conducting System
Features of an ECG
P wave :Atria depolarize
QRS complex :Ventricles depolarize
T wave :Ventricles repolarize
Time Intervals Between ECG Waves PR interval
From start of atrial depolarization
To start of QRS complex
Q
T interval From ventricular depolarization
To ventricular repolarization
Figure 2014a An Electrocardiogram: ElectrodePlacement for Recording a Standard ECG
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The Conducting System
Contractile Cells
Purkinje fibers distribute the stimulus to the
contractile cells, which make up most of themuscle cells in the heart
Resting Potential
Of a ventricular cell: about 90 mV
Of an atrial cell: about
80 mV
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The Conducting System
Figure 2015 The Action Potential in Skeletal and Cardiac Muscle
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The Conducting System
Figure 20
15 The Action Potential in Skeletal and Cardiac Muscle
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The Conducting System
Refractory Period Absolute refractory period
Long
Cardiac muscle cells cannot respond
Relative refractory period
Short
Response depends on degree of stimulus
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 andtetany
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The Conducting System
The Role of Calcium Ions in Cardiac Contractions
Contraction of a cardiac muscle cell is produced by anincrease in calcium ion concentration around myofibrils
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 fromsarcoplasmic reticulum
As slow calcium channelsclose
Intracellular Ca2+is absorbed by the SR
Or pumped out of cell
Cardiac muscle tissue
Very sensitive to extracellular Ca2+concentrations
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The Conducting System
The Energy for Cardiac Contractions
Aerobic energy of heart
From mitochondrial breakdown of fatty acids andglucose
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
Phases of the Cardiac Cycle Within any one chamber
Systole(contraction)
Diastole(relaxation)
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
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The Cardiac Cycle
Figure 20
16 Phases of the Cardiac Cycle
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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
EightSteps in the Cardiac Cycle1. 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)
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The Cardiac Cycle
Figure 20
17 Pressure and Volume Relationships in the Cardiac Cycle
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The Cardiac Cycle
Eight Steps in the Cardiac Cycle4. Ventricular systole
Isovolumetric ventricular contraction
Pressure in ventricles rises
AV valves shut5. Ventricular ejection
Semilunar valves open
Blood flows into pulmonary and aortic trunks
Stroke volume (SV) = 60% of end-diastolic volume
6. Ventricular pressure falls Semilunar valves close
Ventricles contain end-systolic volume (ESV), about 40% ofend-diastolic volume
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The Cardiac Cycle
Figure 2017 Pressure and Volume Relationships in the CardiacCycle
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The Cardiac Cycle
Eight Steps in the Cardiac Cycle7. Ventricular diastole
Ventricular pressure is higher than atrial pressure
All heart valves are closed
Ventricles relax (isovolumetric relaxation)
8. Atrial pressure is higher than ventricularpressure
AV valves open
Passive atrial filling
Passive ventricular filling
Cardiac cycle ends
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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 Heart Murmur
Sounds produced by regurgitation through valves
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The Cardiac Cycle
Figure 2018 Heart Sounds
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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
Cardiac Output
CO = HR X SV
CO = cardiac output (mL/min)
HR = heart rate (beats/min)
SV = stroke volume (mL/beat)
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Cardiodynamics
Figure 2019 A Simple Model of Stroke Volume
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Cardiodynamics
Figure 2020 Factors Affecting Cardiac Output
Cardiac output
Adjusted by changes inheart rate or strokevolume
Heart rate
Adjusted by autonomicnervous system orhormones
Stroke volume
Adjusted by changingEDV or ESV
Factors Affecting Cardiac Output
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Cardiodynamics
Factors Affecting the Heart Rate Autonomic innervation
Cardiac plexuses: innervate heart
Vagus nerves (X): carry parasympathetic preganglionic fibersto small ganglia in cardiac plexus
Cardiac centers of medulla oblongata:
cardioacceleratory centercontrols sympathetic
neurons (increases heart rate)
cardioinhibitory centercontrols parasympathetic
neurons (slows heart rate)
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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 byreleasing ACh and NE
Fine adjustments meet needs of other systems
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Cardiodynamics
Figure 20
21 Autonomic Innervation of the Heart
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Cardiodynamics
Effects on the SA Node
Sympathetic andparasympathetic stimulation
Greatest at SA node (heart rate)
Membrane potential ofpacemaker cells
Lower than other cardiac cells
Rate of spontaneousdepolarization depends on
Resting membrane potential
Rate of depolarization
ACh (parasympatheticstimulation)
Slows the heart
NE (sympathetic stimulation)
Speeds the heart
Atrial Reflex
Also called Bainbridge reflex
Adjusts heart rate in responseto venous return
Stretch receptors in rightatrium
Trigger increase in heart rate
Through increasedsympathetic activity
Increase heart rate (by sympatheticstimulation of SA node)
Epinephrine (E)
Norepinephrine (NE)
Thyroid hormone
Hormonal Effectson HR
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Cardiodynamics
Factors Affecting the Stroke Volume
The EDV: amount of blood a ventricle contains at theend of diastole
Filling time:
duration of ventricular diastole
Venous return:
rate of blood flow during ventricular diastole
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
The FrankStarling Principle
As EDV increases, stroke volume increases
Physical Limits Ventricular expansion is limited by
Myocardial connective tissue
The cardiac (fibrous) skeleton
The pericardial sac
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Cardiodynamics
End-Systolic Volume (ESV) The amount of blood that remains in the
ventricle at the end of ventricular systole isthe ESV
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 semilunarvalve and eject blood
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Cardiodynamics
Contractility
Is affected by
Autonomic activity
Hormones
Effects of Autonomic Activity on Contractility
Sympathetic stimulation
NE released by postganglionic fibers of cardiacnerves
Epinephrine and NE released by suprarenal(adrenal) medullae
Causes ventricles to contract with more force
Increases ejection fraction and decreases ESV
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)
Afterload
Is increased by any factor that restricts arterial blood flow
As afterload increases, stroke volume decreases
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Cardiodynamics
Figure 20
23 Factors Affecting Stroke Volume
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Cardiodynamics
Heart Rate Control Factors Autonomic nervous system
Sympathetic andparasympathetic
Circulating hormones
Venous return and stretch receptors
Stroke Volume Control Factors
EDV
Filling time
Rate of venous return
ESV
Preload
Contractility
Afterload
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Cardiodynamics
Figure 2024 A Summary of the Factors Affecting Cardiac Output
Cardiovascular regulation
Ensures adequatecirculation to body tissues
Cardiovascular centers Control heart and
peripheral blood vessels
Cardiovascular systemresponds to
Changing activity patterns
Circulatory emergencies
The Heart and Cardiovascular System