Download Chapter 20 The Heart An Introduction to the Cardiovascular System

Chapter 20
The Heart
An Introduction to the Cardiovascular System
• The Pulmonary Circuit
• Carries blood to and from gas exchange surfaces of lungs
• The Systemic Circuit
• Carries blood to and from the body
• Blood alternates between pulmonary circuit and systemic circuit
An Introduction to the Cardiovascular System
• Three Types of Blood Vessels
1. Arteries
•
Carry blood away from heart
2. Veins
• Carry blood to heart
3. Capillaries
• Networks between arteries and veins
An Introduction to the Cardiovascular System
• Capillaries
• Also called exchange vessels
• Exchange materials between blood and tissues
• Materials include dissolved gases, nutrients, waste products
An Introduction to the Cardiovascular System
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• 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
20-1 Anatomy of the Heart
• The Heart
• Great veins and arteries at the base
• Pointed tip is apex
• Surrounded by pericardial sac
• Sits between two pleural cavities in the mediastinum
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
20-1 Anatomy of the Heart
• The Pericardium
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• Pericardial cavity
• Is between parietal and visceral layers
• Contains pericardial fluid
• Pericardial sac
• Fibrous tissue
• Surrounds and stabilizes heart
20-1 Anatomy of the Heart
• Superficial Anatomy of the Heart
• Atria
• Thin-walled
• Expandable outer auricle (atrial appendage)
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 Heart Wall
1. Epicardium
2. Myocardium
3. Endocardium
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20-1 Anatomy of the Heart
• Epicardium (Outer Layer)
• Visceral pericardium
• Covers the heart
20-1 Anatomy of the Heart
• Myocardium (Middle Layer)
• Muscular wall of the heart
• Concentric layers of cardiac muscle tissue
• Atrial myocardium wraps around great vessels
• Two divisions of ventricular myocardium
• Endocardium (Inner Layer)
• Simple squamous epithelium
20-1 Anatomy of the Heart
• Cardiac Muscle Tissue
• Intercalated discs
• Interconnect cardiac muscle cells
• Secured by desmosomes
• Linked by gap junctions
• Convey force of contraction
• Propagate action potentials
20-1 Anatomy of the Heart
• Characteristics of Cardiac Muscle Cells
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1. Small size
2. Single, central nucleus
3. Branching interconnections between cells
4. Intercalated discs
20-1 Anatomy of the Heart
• Internal Anatomy and Organization
• Interatrial septum separates atria
• Interventricular septum separates ventricles
20-1 Anatomy of the Heart
• Internal Anatomy and Organization
• Atrioventricular (AV) valves
• Connect right atrium to right ventricle and left atrium to left ventricle
• Are folds of fibrous tissue that extend into openings between atria and
ventricles
• Permit blood flow in one direction
• From atria to ventricles
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
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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
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
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• 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
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
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• 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
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
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
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• The Heart Valves
• Semilunar valves
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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
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
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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:
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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:
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• 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
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Coronary artery disease (CAD)
• Areas of partial or complete blockage of coronary circulation
• Cardiac muscle cells need a constant supply of oxygen and
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nutrients
• Reduction in blood flow to heart muscle produces a corresponding
reduction in cardiac performance
• Reduced circulatory supply, coronary ischemia, results from partial or
complete blockage of coronary arteries
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Usual cause is formation of a fatty deposit, or atherosclerotic
plaque, in the wall of a coronary vessel
• The plaque, or an associated thrombus (clot), then narrows the
passageway and reduces blood flow
• Spasms in smooth muscles of vessel wall can further decrease
or stop blood flow
• One of the first symptoms of CAD is commonly angina pectoris
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Angina Pectoris
• In its most common form, a temporary ischemia develops when the
workload of the heart increases
• Although the individual may feel comfortable at rest, exertion or
emotional stress can produce a sensation of pressure, chest
constriction, and pain that may radiate from the sternal area to the arms,
back, and neck
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Myocardial infarction (MI), or heart attack
• Part of the coronary circulation becomes blocked, and cardiac muscle
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cells die from lack of oxygen
• The death of affected tissue creates a nonfunctional area known as an
infarct
• Heart attacks most commonly result from severe coronary artery disease
(CAD)
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Myocardial infarction (MI), or heart attack
• Consequences depend on the site and nature of the circulatory blockage
• If it occurs near the start of one of the coronary arteries:
• The damage will be widespread and the heart may stop beating
• If the blockage involves one of the smaller arterial branches:
• The individual may survive the immediate crisis but may have many
complications such as reduced contractility and cardiac arrhythmias
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Myocardial infarction (MI), or heart attack
• A crisis often develops as a result of thrombus formation at a plaque (the
most common cause of an MI), a condition called coronary thrombosis
• A vessel already narrowed by plaque formation may also become
blocked by a sudden spasm in the smooth muscles of the vascular wall
• Individuals having an MI experience intense pain, similar to that felt in
angina, but persisting even at rest
20-1 Anatomy of the Heart
•
Heart Disease - Coronary Artery Disease
•
Myocardial infarction (MI), or heart attack
•
Pain does not always accompany a heart attack, therefore, the condition
may go undiagnosed and may not be treated before a fatal MI occurs
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A myocardial infarction can usually be diagnosed with an ECG and blood
studies
• Damaged myocardial cells release enzymes into the circulation, and
these elevated enzymes can be measured in diagnostic blood tests
• The enzymes include:
•
• Cardiac troponin T,
• Cardiac troponin I,
• A special form of creatinine phosphokinase, CK-MB
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• About 25% of MI patients die before obtaining medical assistance
• 65% of MI deaths among those under age 50 occur within an hour after
the initial infarction
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Risk Factor Modification
• Stop smoking
• High blood pressure treatment
• Dietary modification to lower cholesterol and promote weight loss
• Stress reduction
• Increased physical activity (where appropriate)
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Drug Treatment
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• Drugs that reduce coagulation and therefore the risk of thrombosis, such as
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aspirin and coumadin
Drugs that block sympathetic stimulation (propranolol or metoprolol)
Drugs that cause vasodilation, such as nitroglycerin
Drugs that block calcium movement into the cardiac and vascular smooth
muscle cells (calcium channel blockers)
In a myocardial infarction, drugs to relieve pain, fibrinolytic agents to help
dissolve clots, and oxygen
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Noninvasive Surgery
• Atherectomy
• Blockage by a single, soft plaque may be reduced with the aid of a long,
slender catheter inserted into a coronary artery to the plaque
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Noninvasive Surgery
• Balloon angioplasty
• The tip of the catheter contains an inflatable balloon
• Once in position, the balloon is inflated, pressing the plaque against the vessel
walls
• Because plaques commonly redevelop after angioplasty, a fine tubular wire
mesh called a stent may be inserted into the vessel, holding it open
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Coronary Artery Bypass Surgery (CABG)
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• In a coronary artery bypass graft, a small section is removed from either a
small artery or a peripheral vein and is used to create a detour around the
obstructed portion of a coronary artery
• As many as four coronary arteries can be rerouted this way during a single
operation
• The procedures are named according to the number of vessels repaired, so
we speak of single, double, triple, or quadruple coronary bypasses
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
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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
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• Prepotential
• Also called pacemaker potential
• Resting potential of conducting cells
• Gradually depolarizes toward threshold
• SA node depolarizes first, establishing heart rate
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)
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
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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
20-2 The Conducting System
• Purkinje Fibers
• Distribute impulse through ventricles (Step 5)
• Atrial contraction is completed
• Ventricular contraction begins
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)
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• 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
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
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• Of an atrial cell about –80 mV
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
• Timing of Refractory Periods
• Length of cardiac action potential in ventricular cell
• 250–300 msec
• 30 times longer than skeletal muscle fiber
• Long refractory period prevents summation and tetany
20-2 The Conducting System
• The Role of Calcium Ions in Cardiac Contractions
• Contraction of a cardiac muscle cell
• Is produced by an increase in calcium ion concentration around
myofibrils
20-2 The Conducting System
• The Role of Calcium Ions in Cardiac Contractions
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1. 20% of calcium ions required for a contraction
• Calcium ions enter plasma membrane during plateau phase
2+
2. Arrival of extracellular Ca
• Triggers release of calcium ion reserves from sarcoplasmic reticulum
(SR)
20-2 The Conducting System
• The Role of Calcium Ions in Cardiac Contractions
• As slow calcium channels close
2+
• Intracellular Ca
is absorbed by the SR
• Or pumped out of cell
• Cardiac muscle tissue
2+
• Very sensitive to extracellular Ca 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
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20-3 The Cardiac Cycle
•
Two Phases of the Cardiac Cycle
•
Within any one chamber
1. Systole (contraction)
2. Diastole (relaxation)
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
20-3 The Cardiac Cycle
Phases of the Cardiac Cycle
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•
•
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Atrial systole
Atrial diastole
Ventricular systole
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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 enddiastolic volume
•
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20-3 The Cardiac Cycle
• Ventricular Diastole
7. Ventricular diastole
Ventricular pressure is higher than atrial pressure
• All heart valves are closed
• Ventricles relax (isovolumetric relaxation)
•
8.
Atrial pressure is higher than ventricular pressure
AV valves open
• Passive atrial filling
• Passive ventricular filling
•
20-3 The Cardiac Cycle
• Heart Sounds
• S1
• Loud sounds
• Produced by AV valves
• S2
• Loud sounds
• Produced by semilunar valves
20-3 The Cardiac Cycle
• S3, S4
• Soft sounds
• Blood flow into ventricles and atrial contraction
• Heart Murmur
• Sounds produced by regurgitation through valves
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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
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
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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
•
Autonomic Innervation
•
Cardiac reflexes
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Cardiac centers monitor:
• Blood pressure (baroreceptors)
• Arterial oxygen and carbon dioxide levels (chemoreceptors)
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Cardiac centers adjust cardiac activity
Autonomic tone
Dual innervation maintains resting tone by releasing ACh and NE
• Fine adjustments meet needs of other systems
•
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
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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
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
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• 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
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• 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
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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
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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
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• Circulatory emergencies
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