Download Heart Lecture - Berkeley County Schools

Chapter 20
The Heart
Lecture Presentation by
Lee Ann Frederick
University of Texas at Arlington
© 2015 Pearson Education, Inc.
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
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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
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An Introduction to the Cardiovascular
System
• Capillaries
• Also called exchange vessels
• Exchange materials between blood and tissues
• Materials include dissolved gases, nutrients,
waste products
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Figure 20-1 An Overview of the Cardiovascular System.
PULMONARY CIRCUIT
Pulmonary arteries
Pulmonary veins
Capillaries
in lungs
Right
atrium
Right
ventricle
Capillaries
in trunk
and lower
limbs
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SYSTEMIC CIRCUIT
Systemic arteries
Systemic veins
Capillaries
in head,
neck, upper
limbs
Left
atrium
Left
ventricle
An Introduction to the Cardiovascular
System
• 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
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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
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Figure 20-2a The Location of the Heart in the Thoracic Cavity.
Trachea
First rib (cut)
Thyroid
gland
Base of
heart
Right lung
Left lung
Parietal
pericardium
(cut)
Apex of
heart
Diaphragm
a An anterior view of the chest, showing the
position of the heart and major blood vessels
relative to the ribs, lungs, and diaphragm.
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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
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20-1 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
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Figure 20-2b The Location of the Heart in the Thoracic Cavity.
Posterior
mediastinum
Aorta (arch
segment removed)
Esophagus
Left pulmonary artery
Right pleural cavity
Right
lung
Left pleural
cavity
Left
lung
Bronchus of lung
Left pulmonary
vein
Right pulmonary
artery
Pulmonary trunk
Aortic
arch
Right pulmonary
vein
Left atrium
Left ventricle
Superior vena cava
Pericardial cavity
Right atrium
Epicardium
Right ventricle
Anterior mediastinum
Pericardial sac
Sternum
b A superior view of the organs in the mediastinum; portions of the lungs have been removed to reveal
blood vessels and airways. The heart is located in the anterior part of the mediastinum, immediately
posterior to the sternum.
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Figure 20-2c The Location of the Heart in the Thoracic Cavity.
Base of
heart
Cut edge of
parietal pericardium
Fibrous tissue of
pericardial sac
Wrist (corresponds
to base of heart)
Inner wall (corresponds
to epicardium)
Parietal pericardium
Areolar tissue
Mesothelium
Fibrous
attachment to
diaphragm
Air space (corresponds
to pericardial cavity)
Cut edge of epicardium
Outer wall (corresponds
to parietal pericardium)
Apex of heart
Balloon
c The relationship between the heart and the pericardial cavity; compare with the fist-and-balloon example.
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20-1 Anatomy of the Heart
• Superficial Anatomy of the Heart
• Atria
• Thin-walled
• Expandable outer auricle (atrial appendage)
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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
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Figure 20-3a The Position and Superficial Anatomy of the Heart.
Base of heart
1
2
3
4
5
6
7
8
9
10
1
Ribs
2
3
4
5
6
7
8
9
10
a Heart position relative to the rib cage.
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Apex of
heart
Figure 20-3b The Position and Superficial Anatomy of the Heart.
Left subclavian artery
Left common
carotid artery
Arch of aorta
Ligamentum
arteriosum
Brachiocephalic
trunk
Descending
aorta
Ascending
aorta
Left pulmonary
artery
Superior
vena cava
Auricle
of right
atrium
Pulmonary
trunk
Right
atrium
Auricle of
left atrium
Right
ventricle
Fat and
vessels in
coronary
sulcus
Fat and vessels
in anterior
interventricular
sulcus
Left
ventricle
b Major anatomical features on the anterior surface.
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Figure 20-3c The Position and Superficial Anatomy of the Heart.
Left subclavian artery
Left common carotid
artery
Ligamentum
arteriosum
Brachiocephalic trunk
Left pulmonary
artery
Ascending
aorta
Pulmonary
trunk
Superior
vena cava
Auricle of left atrium
Auricle of
right atrium
Left coronary artery
(LCA)
Right atrium
Anterior
interventricular
sulcus
Right
coronary
artery
Coronary sulcus
Marginal branch
of right coronary artery
Right
ventricle
Left
ventricle
Anterior
interventricular
branch of LCA
c Anterior surface of the heart, cadaver dissection.
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Figure 20-3d The Position and Superficial Anatomy of the Heart.
Arch of aorta
Left pulmonary artery
Right pulmonary
artery
Left pulmonary veins
Fat and vessels
in coronary
sulcus
Superior
vena cava
Left
atrium
Coronary
sinus
Right
atrium
Left
ventricle
Right
ventricle
Right
pulmonary
veins
(superior
and inferior)
Inferior
vena cava
Fat and vessels in posterior
interventricular sulcus
d Major landmarks on the posterior surface. Coronary
arteries (which supply the heart itself) are shown in
red; coronary veins are shown in blue.
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20-1 Anatomy of the Heart
• The Heart Wall
1. Epicardium
2. Myocardium
3. Endocardium
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Figure 20-5c Cardiac Muscle Cells.
Intercalated
discs
Cardiac muscle tissue
c Cardiac muscle tissue
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LM x 575
20-1 Anatomy of the Heart
• Internal Anatomy and Organization
• Interatrial septum separates atria
• Interventricular septum separates ventricles
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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
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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
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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
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Figure 20-6a The Sectional Anatomy of the Heart.
Left common carotid artery
Left subclavian artery
Brachiocephalic
trunk
Superior
vena cava
Ligamentum arteriosum
Pulmonary trunk
Aortic arch
Pulmonary valve
Right
pulmonary
arteries
Left pulmonary
arteries
Ascending aorta
Fossa ovalis
Opening of
coronary sinus
Right atrium
Pectinate muscles
Left
atrium
Left pulmonary
veins
Interatrial septum
Aortic valve
Cusp of left AV
(mitral) valve
Conus arteriosus
Left ventricle
Cusp of right AV
(tricuspid) valve
Chordae tendineae
Papillary muscles
Right ventricle
Interventricular
septum
Trabeculae
carneae
Inferior vena cava
Moderator band
Descending aorta
a A diagrammatic frontal section through the heart, showing
major landmarks and the path of blood flow (marked by
arrows) through the atria, ventricles, and associated vessels.
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Figure 20-6c The Sectional Anatomy of the Heart.
Left subclavian artery
Left common carotid artery
Brachiocephalic trunk
Superior vena cava
Ascending aorta
Pulmonary
trunk
Cusp of
pulmonary valve
Auricle of left atrium
Right atrium
Cusp of left AV
(bicuspid) valve
Chordae tendineae
Cusps of right AV
(tricuspid) valve
Papillary muscles
Left ventricle
Trabeculae carneae
Right ventricle
c Anterior view of a frontally sectioned
heart showing internal features and valves.
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Interventricular
septum
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
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Figure 20-6b The Sectional Anatomy of the Heart.
Chordae tendineae
Papillary muscles
b The papillary muscles and chordae
tendineae support the right AV (tricuspid)
valve. The photograph was taken from
inside the right ventricle, looking toward
a light shining from the right atrium.
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20-1 Anatomy of the Heart
• The Pulmonary Circuit
• 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
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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
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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
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Figure 20-6c The Sectional Anatomy of the Heart.
Left subclavian artery
Left common carotid artery
Brachiocephalic trunk
Superior vena cava
Ascending aorta
Pulmonary
trunk
Cusp of
pulmonary valve
Auricle of left atrium
Right atrium
Cusp of left AV
(bicuspid) valve
Chordae tendineae
Cusps of right AV
(tricuspid) valve
Papillary muscles
Left ventricle
Trabeculae carneae
Right ventricle
c Anterior view of a frontally sectioned
heart showing internal features and valves.
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Interventricular
septum
Figure 20-7a Structural Differences between the Left and Right Ventricles.
Posterior
interventricular
sulcus
Left
ventricle
Right
ventricle
Fat in anterior
interventricular sulcus
a
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A diagrammatic sectional view through
the heart, showing the relative thicknesses
of the two ventricles. Notice the pouchlike
shape of the right ventricle and the greater
thickness of the left ventricle.
Figure 20-8a Valves of the Heart (Part 1 of 2).
Transverse Sections, Superior View,
Atria and Vessels Removed
POSTERIOR
Cardiac
skeleton
Relaxed ventricles
RIGHT
VENTRICLE
Left AV (bicuspid)
valve (open)
LEFT
VENTRICLE
Right AV
(tricuspid)
valve (open)
Aortic valve
(closed)
ANTERIOR
a
Aortic valve closed
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Pulmonary
valve (closed)
When the ventricles are relaxed,
the AV valves are open and the
semilunar valves are closed. The
chordae tendineae are loose, and
the papillary muscles are relaxed.
Figure 20-8a Valves of the Heart (Part 2 of 2).
Frontal Sections through Left Atrium and Ventricle
Pulmonary
veins
Relaxed ventricles
LEFT
ATRIUM
Left AV (bicuspid)
valve (open)
Aortic valve
(closed)
Chordae
tendineae (loose)
Papillary muscles
(relaxed)
LEFT VENTRICLE
(relaxed and filling
with blood)
a
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When the ventricles are relaxed, the AV valves are open
and the semilunar valves are closed. The chordae
tendineae are loose, and the papillary muscles are relaxed.
Figure 20-8b Valves of the Heart (Part 1 of 2).
Contracting ventricles
Right AV
(tricuspid) valve
(closed)
RIGHT
VENTRICLE
Cardiac
skeleton
Left AV
(bicuspid) valve
(closed)
LEFT
VENTRICLE
Aortic valve
(open)
Pulmonary
valve (open)
b When the ventricles are contracting,
Aortic valve open
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the AV valves are closed and the
semilunar valves are open. In the
frontal section notice the attachment
of the left AV valve to the chordae
tendineae and papillary muscles.
Contracting ventricles
Figure 20-8b Valves of the Heart (Part 2 of 2).
Aorta
Aortic sinus
Aortic valve
(open)
LEFT
ATRIUM
Left AV (bicuspid)
valve (closed)
Chordae tendineae
(tense)
Papillary muscles
(contracted)
Left ventricle
(contracted)
b When the ventricles are contracting, the AV valves are
closed and the semilunar valves are open. In the frontal
section notice the attachment of the left AV valve to the
chordae tendineae and papillary muscles.
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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
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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
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20-1 Anatomy of the Heart
• Right Coronary Artery
• Supplies blood to:
•
•
•
•
•
Right atrium
Portions of both ventricles
Cells of sinoatrial (SA) and atrioventricular nodes
Marginal arteries (surface of right ventricle)
Posterior interventricular artery
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20-1 Anatomy of the Heart
• Left Coronary Artery
• Supplies blood to:
• Left ventricle
• Left atrium
• Interventricular septum
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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
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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
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Figure 20-9a The Coronary Circulation.
Aortic
arch
Ascending
aorta
Right
coronary
artery
Left coronary
artery
Pulmonary
trunk
Circumflex
artery
Anterior
interventricular
artery
Atrial
arteries
Great
cardiac
vein
Anterior
cardiac
veins
Small
cardiac vein
Marginal
artery
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a Coronary vessels supplying
and draining the anterior
surface of the heart.
Figure 20-9b The Coronary Circulation.
Coronary sinus
Circumflex artery
Great cardiac vein
Marginal artery
Posterior
interventricular
artery
Posterior
cardiac
vein
Small
cardiac
vein
Left
ventricle
Right
coronary
artery
Middle cardiac vein
Marginal artery
b Coronary vessels supplying and draining
the posterior surface of the heart.
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Figure 20-9c The Coronary Circulation.
Auricle of
left atrium
Left pulmonary
veins
Left pulmonary
artery
Right
pulmonary
artery
Circumflex
artery
Superior
vena cava
Great cardiac
vein
Marginal
artery
Right
pulmonary
veins
Posterior
cardiac vein
Left atrium
Right atrium
Inferior
vena cava
Coronary sinus
Middle cardiac vein
Right ventricle
Posterior interventricular artery
c A posterior view of the heart; the vessels have
been injected with colored latex (liquid rubber).
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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 nutrients
• Usual cause is formation of a fatty deposit, or
atherosclerotic plaque, in the wall of a coronary
vessel
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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 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)
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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)
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20-1 Anatomy of the Heart
• Heart Disease – Coronary Artery Disease
• Treatment of CAD and myocardial infarction
• Drug treatment
• Drugs that reduce coagulation and therefore the risk
of thrombosis, such as 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
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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
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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
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20-1 Anatomy of the Heart
• Heart Disease – Coronary Artery Disease
• Treatment of CAD and myocardial infarction
• Coronary artery bypass graft (CABG)
• 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
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Figure 20-10 Heart Disease and Heart Attacks (Part 1 of 4).
Normal Heart
A color-enhanced digital
subtraction angiography (DSA)
scan of a normal heart.
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20-2 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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20-2 The Conducting System
• The Cardiac Cycle
• Begins with action potential at SA node
• Transmitted through conducting system
• Produces action potentials in cardiac muscle cells
(contractile cells)
• Electrocardiogram (ECG or EKG)
• Electrical events in the cardiac cycle can be
recorded on an electrocardiogram
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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
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Figure 20-11a The Conducting System of the Heart.
Sinoatrial
(SA) node
Internodal
pathways
Atrioventricular
(AV) node
AV bundle
Bundle
branches
Purkinje
fibers
a Components of the
conducting system.
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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)
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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
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20-2 The Conducting System
• Purkinje Fibers
• Distribute impulse through ventricles (Step 5)
• Atrial contraction is completed
• Ventricular contraction begins
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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
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20-2 The Conducting System
• The Electrocardiogram (ECG or EKG)
• A recording of electrical events in the heart
• Obtained by electrodes at specific body locations
• Abnormal patterns diagnose damage
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20-2 The Conducting System
• Features of an ECG
• P wave
• Atria depolarize
• QRS complex
• Ventricles depolarize
• T wave
• Ventricles repolarize
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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
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Figure 20-13a An Electrocardiogram.
a Electrode placement for
recording a standard ECG.
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Figure 20-13b An Electrocardiogram.
800 msec
+1
R
P wave
(atria
depolarize)
R
T wave
(ventricles
repolarize)
P–R segment
S–T
segment
+0.5
0
Q S
P–R
interval
S–T
interval
Q–T
interval
b
Millivolts
QRS interval
(ventricles depolarize)
−0.5
An ECG printout is a strip of graph paper containing a record of the electrical events
monitored by the electrodes. The placement of electrodes on the body surface affects
the size and shape of the waves recorded. The example is a normal ECG; the enlarged
section indicates the major components of the ECG and the measurements most often
taken during clinical analysis.
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Figure 20-14 Cardiac Arrhythmias (Part 1 of 2).
Premature Atrial Contractions (PACs)
P
P
P
Paroxysmal Atrial Tachycardia (PAR)
P
P
P
Atrial Fibrillation (AF)
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P
P
P
Premature atrial contractions (PACs)
often occur in healthy individuals. In a PAC,
the normal atrial rhythm is momentarily
interrupted by a “surprise” atrial contraction.
Stress, caffeine, and various drugs may
increase the incidence of PACs, presumably
by increasing the permeabilities of the SA
pacemakers. The impulse spreads along the
conduction pathway, and a normal ventricular
contraction follows the atrial beat.
In paroxysmal (par-ok-SIZ-mal) atrial
tachycardia, or PAT, a premature atrial
contraction triggers a flurry of atrial activity.
The ventricles are still able to keep pace, and the
heart rate jumps to about 180 beats per minute.
During atrial fibrillation (fib-ri-LĀ-shun), the
impulses move over the atrial surface at rates
of perhaps 500 beats per minute. The atrial wall
quivers instead of producing an organized
contraction. The ventricular rate cannot follow
the atrial rate and may remain within normal
limits. Even though the atria are now
nonfunctional, their contribution to ventricular
end-diastolic volume (the maximum amount of
blood the ventricles can hold at the end of atrial
contraction) is so small that the condition may
go unnoticed in older individuals.
Figure 20-14 Cardiac Arrhythmias (Part 2 of 2).
Premature Ventricular Contractions (PVCs)
P
T
P
T
P
Ventricular Tachycardia (VT)
P
Ventricular Fibrillation (VF)
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T
Premature ventricular contractions (PVCs)
occur when a Purkinje cell or ventricular
myocardial cell depolarizes to threshold and
triggers a premature contraction. Single PVCs
are common and not dangerous. The cell
Ventricular tachycardia is defined as four or
more PVCs without intervening normal beats. It
is also known as VT or V-tach. Multiple PVCs
and VT may indicate that serious cardiac
problems exist.
Ventricular fibrillation (VF) is
responsible for the condition known as
cardiac arrest. VF is rapidly fatal,
because the ventricles quiver and
stop pumping blood.
responsible is called an ectopic pacemaker.
The frequency of PVCs can be increased by
exposure to epinephrine, to other stimulatory
drugs, or to ionic changes that depolarize
cardiac muscle plasma membranes.
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)
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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
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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
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20-3 The Cardiac Cycle
• Heart Sounds
• S1
• Loud sounds
• Produced by AV valves
• S2
• Loud sounds
• Produced by semilunar valves
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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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Figure 20-18a Heart Sounds.
Sounds heard
Valve location
Aortic
valve
Valve location Pulmonary
Sounds heard valve
Sounds heard
Valve location
Left
AV
valve
Valve location
Sounds heard
Right
AV
valve
a Placements of a stethoscope for
listening to the different sounds
produced by individual 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
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20-4 Cardiodynamics
• Cardiac Output (CO)
• The volume pumped by left ventricle in one minute
• CO = HR  SV
• CO = cardiac output (mL/min)
• HR = heart rate (beats/min)
• SV = stroke volume (mL/beat)
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