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Chapter 18
CIRCULATORY SYSTEM
Blood is ______ not _______
I. The Pulmonary and Systemic Circuits (p. 659;
Fig. 18.1)
A. The right side of the heart receives oxygen-poor blood
returning from body tissues and pumps it to the lungs to
release CO2 and pick up O2 (p. 659; Fig. 18.1).
1. The left side of the heart receives oxygenated blood
from the lungs and pumps it out to the body to supply
oxygen to tissues.
2. The heart has two receiving chambers, the right and
left atria, and two pumping
chambers, the right and left ventricles.
Figure 18.1 The systemic and pulmonary circuits.
Capillary beds of
lungs where gas
exchange occurs
Pulmonary Circuit
Pulmonary
arteries
Aorta and branches
Venae
cavae
Right
atrium
Right
ventricle
Pulmonary veins
Left
atrium
Heart
Left
ventricle
Systemic Circuit
Capillary beds of all
body tissues where
gas exchange occurs
Oxygen-rich,
CO2-poor blood
Oxygen-poor,
CO2-rich blood
© 2013 PEARSON EDUCATION, INC.
II. Heart Anatomy (pp. 659–671; Figs. 18.2–
18.11)
A. Size, Location, and Orientation (p. 659; Fig. 18.2)
1. The heart is the size of a fist and weighs 250–300
grams.
2. The heart is found in the mediastinum and twothirds lies left of the midsternal line.
3. The base is directed toward the right shoulder
and the apex points toward the left hip.
Figure 18.2a Location of the heart in the mediastinum.
Midsternal line
2nd rib
Sternum
Diaphragm
Location of
apical impulse
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Figure 18.2b Location of the heart in the mediastinum.
Mediastinum
Heart
Left lung
Body of T7
vertebra
Posterior
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Figure 18.2c Location of the heart in the mediastinum.
Aorta
Parietal pleura
(cut)
Superior
vena cava
Pulmonary
trunk
Left lung
Pericardium (cut)
Apex of heart
Diaphragm
© 2013 PEARSON EDUCATION, INC.
https://www.youtube.com/watch?v=oHMmtqKgs50&index=
2&list=PLmT5uQC5CzO18gcqU4MLoTaZ1fO7cobX6
B. Coverings of the Heart (pp. 660–661; Fig. 18.3)
1. The heart is enclosed in a double-walled sac called the
pericardium.
a. The superficial pericardium is the fibrous pericardium that
protects the heart, anchors it to surrounding structures, and
prevents the heart from overfilling.
b. Deep to the fibrous pericardium is the serous pericardium,
consisting of a parietal layer that lines the inside of the
pericardium, and a visceral layer (epicardium) that covers the
surface of the heart.
2. Between the visceral and parietal layers is the
pericardial cavity, containing a film of serous fluid
that lubricates their movement against each other.
C. Layers of the Heart Wall (pp. 661–662; Figs. 18.3–18.4)
1. The epicardium is the visceral pericardium of the
serous pericardium.
2. The myocardium is composed mainly of cardiac muscle
and forms the bulk of the heart.
a. Within the myocardium exists a network of connective
tissue fibers, the cardiac skeleton, which reinforces the
myocardium, supports the heart valves and provides
electrical insulation between areas of the heart.
3. The endocardium lines the chambers of the heart
and is continuous with the endothelial linings of
the vascular system.
Figure 18.3 The pericardial layers and layers of the heart wall.
Pulmonary
trunk
Fibrous pericardium
Pericardium
Parietal layer of serous
pericardium
Myocardium
Pericardial cavity
Epicardium (visceral
layer of serous
pericardium)
Myocardium
Endocardium
Heart chamber
© 2013 PEARSON EDUCATION, INC.
Heart
wall
Heart
2.
Coverings of the Heart
a. The heart has its own
special covering called
pericardium
1) Fibrous
pericardium – tough
loose-fitting
Figure 18.4 The circular and spiral arrangement of cardiac muscle bundles in the myocardium of the heart.
Cardiac
muscle
bundles
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D. Chambers and Associated Great Vessels (p. 662; Fig.
18.5)
1. There are partitions that separate the heart
longitudinally: the interatrial septum divides the
atria, and between the ventricles lies the
interventricular septum.
2. The right and left atria are the receiving chambers of
the heart and only minimally contract to propel blood
into the ventricles.
a. There are three veins that enter the right atrium:
the superior and inferior vena cava, which return
blood from the body, and the coronary sinus,
which returns blood from the myocardium.
b. Four pulmonary veins enter the left atrium from
the lungs.
3. The right ventricle pumps blood into the
pulmonary trunk; the left ventricle pumps
blood into the aorta.
Figure 18.5e Gross anatomy of the heart.
Aorta
Left pulmonary artery
Left atrium
Superior vena cava
Right pulmonary artery
Left pulmonary veins
Pulmonary trunk
Right atrium
Mitral (bicuspid) valve
Right pulmonary veins
Fossa ovalis
Pectinate muscles
Tricuspid valve
Right ventricle
Chordae tendineae
Trabeculae carneae
Inferior vena cava
Aortic valve
Pulmonary valve
Left ventricle
Papillary muscle
Interventricular septum
Epicardium
Myocardium
Endocardium
Frontal section
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Figure 18.5a Gross anatomy of the heart.
Left subclavian artery
Left common carotid artery
Brachiocephalic trunk
Aortic arch
Ligamentum arteriosum
Ascending aorta
Pulmonary trunk
Auricle of left atrium
Right atrium
Right coronary artery
(in coronary sulcus)
Anterior interventricular artery
(in anterior interventricular sulcus)
Additional branch off left
coronary artery, normal variation
Right ventricle
Left ventricle
Apex of heart
(left ventricle)
Anterior aspect (pericardium removed)
© 2013 PEARSON EDUCATION, INC.
Figure 18.5f Gross anatomy of the heart.
Ascending aorta (cut open)
Superior vena cava
Pulmonary trunk
Aortic valve
Right ventricle anterior
wall (retracted)
Opening to right
atrium
Pulmonary valve
Interventricular
septum (cut)
Left ventricle
Chordae tendineae
Papillary muscles
Trabeculae carneae
Right ventricle
Photograph; view similar to (e)
© 2013 PEARSON EDUCATION, INC.
E. Heart Valves (pp. 662–668; Figs. 18.5–18.8)
1. There are two atrioventricular (AV) valves between each atrialventricular junction: the tricuspid valve in the right and the mitral
valve in the left.
a. When the heart is relaxed, the AV valves hang loosely down into
the ventricles.
b. When the ventricles contract, blood is forced upward against the
flaps of the AV valves, pushing them closed.
c. Each flap of the AV valves are anchored to papillary muscles in
the ventricles by collagen strings called chordae tendinae, which
prevent eversion of the valves into the atria.
Figure 18.7 The atrioventricular (AV) valves.
1 Blood returning to the heart fills
atria, pressing against the AV valves.
The increased pressure forces AV
valves open.
Direction of
blood flow
Atrium
2 As ventricles fill, AV valve flaps
hang limply into ventricles.
Cusp of
atrioventricular
valve (open)
Chordae
tendineae
3 Atria contract, forcing additional
blood into ventricles.
Ventricle
Papillary
muscle
AV valves open; atrial pressure greater than ventricular pressure
Atrium
Cusps of
atrioventricular
valve (closed)
1 Ventricles contract, forcing
blood against AV valve cusps.
2 AV valves close.
Blood in
ventricle
3 Papillary muscles contract and
chordae tendineae tighten,
preventing valve flaps from everting
into atria.
AV valves closed; atrial pressure less than ventricular pressure
© 2013 PEARSON EDUCATION, INC.
2. Aortic and pulmonary semilunar (SL) valves are located at
the base of the arteries exiting the heart and prevent
backflow of blood into the ventricles.
a. When ventricular pressure rises above aortic and
pulmonary pressure, the SL valves are forced open,
allowing blood to be ejected from the heart.
b. When the ventricles relax, blood flows backward
toward the heart, filling the cusps of the SL valves,
forcing them closed.
Figure 18.8 The semilunar (SL) valves.
Aorta
Pulmonary
trunk
As ventricles contract
and intraventricular
pressure rises, blood
is pushed up against
semilunar valves,
forcing them open.
Semilunar valves open
As ventricles relax
and intraventricular
pressure falls, blood
flows back from
arteries, filling the
cusps of semilunar
valves and forcing
them to close.
Semilunar valves closed
© 2013 PEARSON EDUCATION, INC.
3. There are no valves at the entrances of the vena
cava or pulmonary veins, because the intertia of
blood and the collapse of the atria during
contraction minimizes backflow into these vessels.
Figure 18.6a Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Myocardium
Mitral
(left atrioventricular)
valve
Tricuspid
(right atrioventricular)
valve
Aortic valve
Pulmonary valve
Cardiac
skeleton
Anterior
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Figure 18.6b Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Myocardium
Mitral
(left atrioventricular)
valve
Tricuspid
(right atrioventricular)
valve
Aortic valve
Pulmonary valve
© 2013 PEARSON EDUCATION, INC.
Figure 18.6c Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Chordae tendineae attached
to tricuspid valve flap
© 2013 PEARSON EDUCATION, INC.
Papillary
muscle
https://www.youtube.com/watch?v=7XaftdE_h60&list=PLm
T5uQC5CzO18gcqU4MLoT
https://www.youtube.com/watch?v=qmpd82mpVO4&index
=3&list=PLmT5uQC5CzO18gcqU4MLoTaZ1fO7cobX6aZ1fO7c
obX6&index=1
https://www.youtube.com/watch?v=CsIdppyaPQ&index=4&list=PLmT5uQC5CzO18gcqU4MLoTaZ1fO7cobX
6
Figure 18.6d Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Opening of inferior
vena cava
Tricuspid valve
Mitral valve
Chordae
tendineae
Myocardium
of right
ventricle
Interventricular
septum
Papillary
muscles
Myocardium
of left ventricle
© 2013 PEARSON EDUCATION, INC.
F. Pathway of Blood Through the Heart (p. 668; Figs.
18.9–18.10)
1. The right side of the heart pumps blood into the
pulmonary circuit; the left side of the heart
pumps blood into the systemic circuit.
2. Equal volumes of blood are pumped to the pulmonary
and systemic circuits at the same time, but the two sides
have different workloads.
a. The right ventricle is thinner walled than the left and is
a short, low-pressure circulation.
b. The left ventricle is three times thicker than the right,
enabling it to generate a much higher pressure, so that
the force can overcome the much greater resistance in
the systemic circulation.
Figure 18.10 Anatomical differences between the right and left ventricles.
Left
ventricle
Right
ventricle
Interventricular
septum
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Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Both sides of the heart pump at the same time, but let’s
Oxygen-poor blood
follow one spurt of blood all the way through the
Oxygen-rich blood
Pulmonary
system.
Tricuspid
semilunar
valve
valve
Superior vena cava(SVC)
Right
Right
Pulmonary
Inferior vena cava(IVC)
atrium
ventricle
trunk
Coronary sinus
SVC
Pulmonary
arteries
Tricuspid
valve
Coronary
sinus
Pulmonary
trunk
Right
atrium
Pulmonary
semilunar
valve
Right
ventricle
IVC
To heart
Oxygen-poor blood
returns from the body
tissues back to the heart.
Oxygen-poor blood is carried
in two pulmonary arteries to
To lungs
the lungs (pulmonary circuit)
to be oxygenated.
Systemic
capillaries
To body
Pulmonary
capillaries
Oxygen-rich blood returns
To heart
to the heart via the four
pulmonary veins.
Oxygen-rich blood is
delivered to the body
tissues (systemic circuit).
Aorta
Pulmonary
veins
Aorta
Aortic
semilunar
valve
Left
atrium
Mitral
valve
Left
ventricle
Aortic
semilunar
valve
Left
ventricle
Mitral
valve
Left
atrium
© 2013 PEARSON EDUCATION, INC.
Four
pulmonary
veins
Slide 1
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Slide 2
Oxygen-poor blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
SVC
Coronary
sinus
IVC
© 2013 PEARSON EDUCATION, INC.
Oxygen-rich blood
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
SVC
Slide 3
Right
atrium
Coronary
sinus
Right
atrium
IVC
© 2013 PEARSON EDUCATION, INC.
Oxygen-poor blood
Oxygen-rich blood
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
SVC
Tricuspid
valve
Coronary
sinus
Right
atrium
IVC
Right
atrium
Slide 4
Tricuspid
valve
Right
ventricle
© 2013 PEARSON EDUCATION, INC.
Right
ventricle
Oxygen-poor blood
Oxygen-rich blood
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Tricuspid
valve
Slide 5
Right
ventricle
Pulmonary
semilunar
valve
Pulmonary
arteries
SVC
Coronary
sinus
Right
atrium
IVC
Pulmonary
trunk
Tricuspid
valve
Right
ventricle
© 2013 PEARSON EDUCATION, INC.
Pulmonary
semilunar
valve
Pulmonary
trunk
Oxygen-poor blood
Oxygen-rich blood
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Slide 6
Oxygen-poor blood
Oxygen-rich blood
Superior vena cava (SVC)
Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Tricuspid
valve
Right
ventricle
Pulmonary
semilunar
valve
Pulmonary
trunk
Pulmonary
arteries
SVC
Coronary
sinus
Right
atrium
IVC
Pulmonary
trunk
Tricuspid
valve
Right
ventricle
Pulmonary
semilunar
valve
Oxygen-poor blood is
carried in two pulmonary
arteries to the lungs
(pulmonary circuit) to be
oxygenated.
Pulmonary
capillaries
© 2013 PEARSON EDUCATION, INC.
To lungs
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Slide 7
Oxygen-poor blood
Oxygen-rich blood
Pulmonary
veins
Four
pulmonary
veins
© 2013 PEARSON EDUCATION, INC.
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Slide 8
Oxygen-poor blood
Oxygen-rich blood
Right
ventricle
Pulmonary
veins
Left
atrium
Four
pulmonary
veins
Left
atrium
© 2013 PEARSON EDUCATION, INC.
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Slide 9
Oxygen-poor blood
Oxygen-rich blood
Pulmonary
veins
Left
atrium
Mitral
valve
Left
ventricle
Left
ventricle
Mitral
valve
Left
atrium
© 2013 PEARSON EDUCATION, INC.
Four
pulmonary
veins
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Slide 10
Oxygen-poor blood
Oxygen-rich blood
Right
ventricle
Aorta
Pulmonary
veins
Aortic
semilunar
valve
Left
atrium
Mitral
valve
Left
ventricle
Aorta
Aortic
semilunar
valve
Left
ventricle
Mitral
valve
© 2013 PEARSON EDUCATION, INC.
Left
atrium
Four
pulmonary
veins
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Slide 11
Oxygen-poor blood
Oxygen-rich blood
Systemic
capillaries
To body
Oxygen-rich blood is
delivered to the body
tissues (systemic circuit).
Aorta
Pulmonary
veins
Aortic
semilunar
valve
Aorta
Aortic
semilunar
valve
Left
atrium
Mitral
valve
Left
ventricle
Left
ventricle
Mitral
valve
Left
atrium
© 2013 PEARSON EDUCATION, INC.
Four
pulmonary
veins
Figure 18.9 The heart is a double pump, each side supplying its own circuit.
Both sides of the heart pump at the same time, but let’s
Oxygen-poor blood
follow one spurt of blood all the way through the
Oxygen-rich blood
Pulmonary
system.
Tricuspid
semilunar
valve
valve
Superior vena cava(SVC)
Right
Right
Pulmonary
Inferior vena cava(IVC)
atrium
ventricle
trunk
Coronary sinus
SVC
Pulmonary
arteries
Tricuspid
valve
Coronary
sinus
Pulmonary
trunk
Right
atrium
Pulmonary
semilunar
valve
Right
ventricle
IVC
To heart
Oxygen-poor blood
returns from the body
tissues back to the heart.
Oxygen-poor blood is carried
in two pulmonary arteries to
To lungs
the lungs (pulmonary circuit)
to be oxygenated.
Systemic
capillaries
To body
Pulmonary
capillaries
Oxygen-rich blood returns
To heart
to the heart via the four
pulmonary veins.
Oxygen-rich blood is
delivered to the body
tissues (systemic circuit).
Aorta
Pulmonary
veins
Aorta
Aortic
semilunar
valve
Left
atrium
Mitral
valve
Left
ventricle
Aortic
semilunar
valve
Left
ventricle
Mitral
valve
Left
atrium
© 2013 PEARSON EDUCATION, INC.
Four
pulmonary
veins
Slide 12
Heart
d.
Flow of Blood through
the heart
◦ Right atrium
◦ Tricuspid valve
◦ Right ventricle
◦ Pulmonary semilunar
valve
◦ Plumonary artery
◦ Lungs
◦ Pulmonary veins
◦ Left atrium
◦ Biscuspid (mitral)
◦ Left ventricle
◦ Aortic semilunar valve
◦ Aorta
◦ Body
◦ Superior or inferior
vena cava
◦ Right atrium
G. Coronary Circulation (pp. 668–671; Fig. 18.11)
1. The heart receives no nourishment from the blood as it passes
through the chamber, so a series of vessels, the coronary
circulation, exist to supply blood to the heart itself.
a. The left coronary artery gives rise to the anterior interventricular
artery and the
circumflex artery, which supply blood to the left ventricle and
atrium.
b. The right coronary artery branches into the right marginal artery
and the posterior interventricular artery, which supply blood to
the right ventricle and atrium.
c. Cardiac veins collect blood from the capillary beds of the
myocardium and drain into the coronary sinus, which
empties into the right atrium.
d. The great cardiac vein, middle cardiac vein, and small
cardiac vein all empty into the coronary sinus.
2. In a myocardial infarction, there is prolonged
coronary blockage that leads to cell death.
Figure 18.11a Coronary circulation.
Aorta
Pulmonary
trunk
Left atrium
Superior
vena cava
Anastomosis
(junction of
vessels)
Left
coronary
artery
Right
atrium
Right
coronary
artery
Right
ventricle
Right
marginal
artery
Circumflex
artery
Posterior
interventricular
artery
The major coronary arteries
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Left
ventricle
Anterior
interventricular
artery
Figure 18.11b Coronary circulation.
Superior
vena cava
Great
cardiac
vein
Anterior
cardiac
veins
Coronary
sinus
Small
cardiac vein
The major cardiac veins
© 2013 PEARSON EDUCATION, INC.
Middle cardiac vein
Figure 18.5d Gross anatomy of the heart.
Aorta
Superior vena cava
Left pulmonary artery
Right pulmonary artery
Right pulmonary veins
Left pulmonary veins
Right atrium
Auricle of left atrium
Left atrium
Inferior vena cava
Great cardiac vein
Coronary sinus
Right coronary artery
(in coronary sulcus)
Posterior interventricular
artery (in posterior
interventricular sulcus)
Middle cardiac vein
Right ventricle
Posterior vein of
left ventricle
Left ventricle
Apex
Posterior surface view
© 2013 PEARSON EDUCATION, INC.
III. Cardiac Muscle Fibers (pp. 671–674;
Figs. 18.12–18.13)
A. Microscopic Anatomy (p. 671; Fig. 18.12
1. Cardiac muscle cells have large mitochondria that
occupy 25–35% of the total cell volume, have
myofibrils arranged in sarcomeres (contains skeletal
muscles), but have a less extensive sarcoplasmic
(striated muscle fibers) reticulum, when compared to
skeletal muscle.
B. Energy Requirements (pp. 673–674)
1. Cardiac muscle has more mitochondria than
skeletal muscle, indicating reliance on exclusively
aerobic respiration for its energy demands.
2. Cardiac muscle is capable of switching nutrient
pathways to use whatever nutrient supply is
available, including lactic acid.
IV. Heart Physiology (pp. 674–685; Figs.
18.14–18.23)
A. Electrical Events (pp. 674–678; Figs. 18.14–18.19)
1. The heart does not depend on the nervous system to
provide stimulation; it relies on gap junctions to
conduct impulses throughout the heart and the
intrinsic conduction system, which are specialized
cardiac cells that initiate and distribute impulses to
ensure that the heart depolarizes in an orderly fashion.
2. The cardiac pacemaker cells have an unstable resting
potential and produce pacemaker potentials that
continuously depolarize, initiating the action potentials
that are conducted throughout the heart.
Membrane potential (mV)
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.
+10
0
–10
–20
–30
–40
–50
–60
–70
Action
potential
2
Slide 1
1 Pacemaker potential This
slow depolarization is due to both
opening of Na+ channels and
closing of K+ channels. Notice
that the membrane potential is
never a flat line.
Threshold
2 Depolarization The action
potential begins when the
pacemaker potential reaches
threshold. Depolarization is due
to Ca2+ influx through Ca2+
channels.
2
3
3
1
1
Pacemaker
potential
Time (ms)
© 2013 PEARSON EDUCATION, INC.
3 Repolarization is due to
Ca2+ channels inactivating and
K+ channels opening. This allows
K+ efflux, which brings the
membrane potential back to its
most negative voltage.
Membrane potential (mV)
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.
Action
potential
+10
0
–10
–20
–30
–40
–50
–60
–70
Slide 2
1 Pacemaker potential This
slow depolarization is due to both
opening of Na+ channels and
closing of K+ channels. Notice
that the membrane potential is
never a flat line.
Threshold
1
1
Pacemaker
potential
Time (ms)
© 2013 PEARSON EDUCATION, INC.
Membrane potential (mV)
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.
+10
0
–10
–20
–30
–40
–50
–60
–70
Action
potential
2
Slide 3
1 Pacemaker potential This
slow depolarization is due to both
opening of Na+ channels and
closing of K+ channels. Notice
that the membrane potential is
never a flat line.
Threshold
2 Depolarization The action
potential begins when the
pacemaker potential reaches
threshold. Depolarization is due
to Ca2+ influx through Ca2+
channels.
2
1
1
Pacemaker
potential
Time (ms)
© 2013 PEARSON EDUCATION, INC.
Membrane potential (mV)
Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.
+10
0
–10
–20
–30
–40
–50
–60
–70
Action
potential
2
Slide 4
1 Pacemaker potential This
slow depolarization is due to both
opening of Na+ channels and
closing of K+ channels. Notice
that the membrane potential is
never a flat line.
Threshold
2 Depolarization The action
potential begins when the
pacemaker potential reaches
threshold. Depolarization is due
to Ca2+ influx through Ca2+
channels.
2
3
3
1
1
Pacemaker
potential
Time (ms)
© 2013 PEARSON EDUCATION, INC.
3 Repolarization is due to
Ca2+ channels inactivating and
K+ channels opening. This allows
K+ efflux, which brings the
membrane potential back to its
most negative voltage.
3. Impulses pass through the cardiac pacemaker cells in the
following order: sinoatrial node, atrioventricular node,
atrioventricular bundle, right and left bundle branches,
and the subendocardial conducting network.
a. The sinoatrial node is located in the right atrium and is
the primary pacemaker for the heart.
b. The atrioventricular (AV) node, in the interatrial
septum, delays firing slightly, in order to allow the atria
to finish contracting before the ventricles contract.
c. The atrioventricular (AV) bundle is the only electrical
connection between the atria and the ventricles and
conducts impulses into the ventricles from the AV node.
d. The right and left bundle branches conduct impulses
down the interventricular septum to the apex.
e. The subendocardial conducting network penetrates
throughout the ventricular walls, distributing impulses
throughout the ventricles.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Superior vena cava
Slide 1
Right atrium
1 The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
2 The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
Left atrium
3 The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
Subendocardial
conducting
network
(Purkinje fibers)
4 The bundle branches
conduct the impulses
through the
interventricular septum.
Interventricular
septum
5 The subendocardial
conducting network
depolarizes the contractile
cells of both ventricles.
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
© 2013 PEARSON EDUCATION, INC.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Superior vena cava
Slide 2
Right atrium
1 The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Interventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
© 2013 PEARSON EDUCATION, INC.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Superior vena cava
Slide 3
Right atrium
1 The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
2 The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Interventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
© 2013 PEARSON EDUCATION, INC.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Superior vena cava
Slide 4
Right atrium
1 The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
2 The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
Left atrium
3 The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
Subendocardial
conducting
network
(Purkinje fibers)
Interventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
© 2013 PEARSON EDUCATION, INC.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Superior vena cava
Slide 5
Right atrium
1 The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
2 The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
Left atrium
3 The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
Subendocardial
conducting
network
(Purkinje fibers)
4 The bundle branches
conduct the impulses
through the
interventricular septum.
Interventricular
septum
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
© 2013 PEARSON EDUCATION, INC.
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Superior vena cava
Slide 6
Right atrium
1 The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
2 The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
Left atrium
3 The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
Subendocardial
conducting
network
(Purkinje fibers)
4 The bundle branches
conduct the impulses
through the
interventricular septum.
Interventricular
septum
5 The subendocardial
conducting network
depolarizes the contractile
cells of both ventricles.
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
© 2013 PEARSON EDUCATION, INC.
Figure 18.15b Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Pacemaker potential
SA node
Atrial muscle
AV node
Ventricular
muscle
Pacemaker
potential
Plateau
0
100
200
300
400
Milliseconds
Comparison of action potential shape at
various locations
© 2013 PEARSON EDUCATION, INC.
4. The autonomic nervous system modifies the heartbeat
through cardiac centers in the medulla oblongata:
a. The cardioacceleratory center projects to sympathetic neurons
throughout the heart, increasing both heart rate and
contractile force.
b. The cardioinhibitory center sends impulses to the
parasympathetic dorsal vagus nucleus in the medulla
oblongata, which stimulates the vagus nerve to the heart,
slowing the heartbeat.
Figure 18.16 Autonomic innervation of the heart.
The vagus nerve
(parasympathetic)
decreases heart rate.
Dorsal motor nucleus
of vagus
Cardioinhibitory
center
Cardioacceleratory center
Medulla oblongata
Sympathetic
trunk
ganglion
Thoracic spinal cord
Sympathetic trunk
Sympathetic cardiac
nerves increase heart rate
and force of contraction.
AV
node
SA
node
Parasympathetic fibers
Sympathetic fibers
© 2013 PEARSON EDUCATION, INC.
Interneurons
5. An electrocardiograph monitors and amplifies the
electrical signals of the heart and records it as an
electrocardiogram (ECG).
a. A typical ECG has three deflections: a P wave,
indicating depolarization of the atria; a QRS complex,
resulting from ventricular contraction; and a T wave,
caused by ventricular repolarization.
Figure 18.17 An electrocardiogram (ECG) tracing.
Sinoatrial
node
Atrioventricular
node
QRS complex
R
Ventricular
depolarization
Ventricular
repolarization
Atrial
depolarization
T
P
Q
P-R
Interval
0
S
S-T
Segment
Q-T
Interval
0.2
0.4
Time (s)
© 2013 PEARSON EDUCATION, INC.
0.6
0.8
Slide 1
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing.
SA node
R
R
T
P
Q
Q
S
S
4 Ventricular depolarization is
complete.
R
1 Atrial depolarization, initiated by
the SA node, causes the P wave.
R
AV node
Q
Q
S
5 Ventricular repolarization begins
at apex, causing the T wave.
S
2 With atrial depolarization
complete, the impulse is delayed at
the AV node.
R
R
T
P
T
P
Q
T
P
T
P
T
P
Q
S
6
3 Ventricular depolarization begins at
apex, causing the QRS complex. Atrial
repolarization occurs.
Depolarization
© 2013 PEARSON EDUCATION, INC.
S
Ventricular repolarization is complete.
Repolarization
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection
waves of an ECG tracing.
SA node
Depolarization
Slide 2
R
Repolarization
T
P
Q
S
1 Atrial depolarization, initiated
by the SA node, causes the P
wave.
© 2013 PEARSON EDUCATION, INC.
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection
waves of an ECG tracing.
SA node
Depolarization
Slide 3
R
Repolarization
T
P
Q
S
1 Atrial depolarization, initiated
by the SA node, causes the P
wave.
R
AV node
T
P
Q
S
2 With atrial depolarization
complete, the impulse is delayed
at the AV node.
© 2013 PEARSON EDUCATION, INC.
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection
waves of an ECG tracing.
SA node
Depolarization
Slide 4
R
Repolarization
T
P
Q
S
1 Atrial depolarization, initiated
by the SA node, causes the P
wave.
R
AV node
T
P
Q
S
2 With atrial depolarization
complete, the impulse is delayed
at the AV node.
R
T
P
Q
S
3 Ventricular depolarization
begins at apex, causing the QRS
complex. Atrial repolarization
© 2013
PEARSON EDUCATION, INC.
occurs.
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection
waves of an ECG tracing.
Slide 5
Depolarization R
Repolarization
T
P
Q
S
4 Ventricular depolarization is complete.
© 2013 PEARSON EDUCATION, INC.
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection
waves of an ECG tracing.
Slide 6
Depolarization R
Repolarization
T
P
Q
S
4 Ventricular depolarization is complete.
R
T
P
Q
S
5 Ventricular repolarization
begins at apex, causing the T
wave.
© 2013 PEARSON EDUCATION, INC.
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection
waves of an ECG tracing.
Slide 7
Depolarization R
Repolarization
T
P
Q
S
4 Ventricular depolarization is complete.
R
T
P
Q
S
5 Ventricular repolarization
begins at apex, causing the T
wave.
R
T
P
Q
S
6 Ventricular repolarization is
complete.
© 2013 PEARSON EDUCATION, INC.
Slide 8
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing.
SA node
R
R
T
P
Q
Q
S
S
4 Ventricular depolarization is
complete.
R
1 Atrial depolarization, initiated by
the SA node, causes the P wave.
R
AV node
Q
Q
S
5 Ventricular repolarization begins
at apex, causing the T wave.
S
2 With atrial depolarization
complete, the impulse is delayed at
the AV node.
R
R
T
P
T
P
Q
T
P
T
P
T
P
Q
S
6
3 Ventricular depolarization begins at
apex, causing the QRS complex. Atrial
repolarization occurs.
Depolarization
© 2013 PEARSON EDUCATION, INC.
S
Ventricular repolarization is complete.
Repolarization
Figure 18.19 Normal and abnormal ECG tracings.
Normal sinus rhythm.
Junctional rhythm. The SA node is nonfunctional, P waves are
absent, and the AV node paces the heart at 40–60 beats/min.
Second-degree heart block. Some P waves are not conducted
through the AV node; hence more P than QRS waves are seen. In
this tracing, the ratio of P waves to QRS waves is mostly 2:1.
Ventricular fibrillation. These chaotic, grossly irregular ECG
deflections are©
seen
acute heart
attack INC.
and electrical shock.
2013inPEARSON
EDUCATION,
B. Heart Sounds (pp. 678–679; Fig. 18.20)
1. Normal
a. The first heart sound, lub, corresponds to closure
of the AV valves, and occurs
during ventricular systole.
b. The second heart sound, dup, corresponds to the
closure of the aortic and
pulmonary valves and occurs during ventricular
diastole.
Figure 18.20 Areas of the thoracic surface where the sounds of individual valves can best be detected.
Aortic valve sounds
heard in 2nd intercostal
space at right sternal
margin
Pulmonary valve
sounds heard in 2nd
intercostal space at left
sternal margin
Mitral valve sounds
heard over heart apex
(in 5th intercostal space)
in line with middle of
clavicle
Tricuspid valve sounds
typically heard in right
sternal margin of 5th
intercostal
space
© 2013 PEARSON EDUCATION, INC.
2. Abnormal
a. Heart murmurs are extraneous heart sounds due to
turbulent backflow of blood through a valve that does
not close tightly.
https://www.youtube.com/watch?v=6YY3OOPmUDA
C. Mechanical Events: The Cardiac Cycle (pp. 679–681; Fig.
18.21)
1. Systole is the contractile phase of the cardiac cycle and
diastole is the relaxation phase of the cardiac cycle.
2. A cardiac cycle consists of a series of pressure and
volume changes in the heart during one heartbeat.
a. Ventricular filling occurs during mid-to-late ventricular
diastole, when the AV valves are open, semilunar
valves are closed, and blood is flowing passively into
the ventricles.
b. The atria contract during the end of ventricular diastole,
propelling the final volume of blood into the ventricles.
c. The atria relax and the ventricles contract during
ventricular systole, causing closure of the AV valves and
opening of the semilunar valves, as blood is ejected from
the ventricles to the great arteries.
d. Isovolumetric relaxation occurs during early
diastole, resulting in a rapid drop in ventricular
pressure, which then causes closure of the
semilunar valves and opening of the AV valves.
Figure 18.20 Areas of the thoracic surface where the sounds of individual valves can best be detected.
Aortic valve sounds
heard in 2nd intercostal
space at right sternal
margin
Pulmonary valve
sounds heard in 2nd
intercostal space at left
sternal margin
Mitral valve sounds
heard over heart apex
(in 5th intercostal space)
in line with middle of
clavicle
Tricuspid valve sounds
typically heard in right
sternal margin of 5th
intercostal
space
© 2013 PEARSON EDUCATION, INC.
D. Cardiac Output (pp. 681–685; Figs. 18.22–18.23)
1. Cardiac output is defined as the amount of blood pumped
out of a ventricle per beat and is calculated as the product
of stroke volume and heart rate.
a. Stroke volume is the volume of blood pumped out of a
ventricle per beat, and roughly equals 70 ml.
b. The average adult heart rate is 75 beats per minute.
c. Cardiac output changes with demand; cardiac reserve is
the difference between the resting and maximal cardiac
output.
2. Regulation of Stroke Volume
a. Stroke volume represents the difference between the
end diastolic volume (EDV), the amount of blood that
collects in the ventricle during diastole, and end
systolic volume (ESV), the volume of blood that
remains in the ventricle after contraction is complete.
b. The Frank-Starling law of the heart states that the critical
factor controlling stroke volume is preload, the degree of
stretch of cardiac muscle cells immediately before they
contract.
c. The most important factor determining the degree of
stretch of cardiac muscle is venous return to the heart.
d. Contractility is the contractile strength achieved at a
given muscle length; contractile strength increases if
there is an increase in cytoplasmic calcium ion
concentration.
e. Afterload is the ventricular pressure that must be
overcome before blood can be ejected from the heart
and does not become a significant determinant of stroke
volume except in hypertensive individuals.
3. Regulation of Heart Rate
a. Sympathetic stimulation of pacemaker cells increases
heart rate and contractility by increasing Ca++
movement into the cell.
b. Parasympathetic inhibition of cardiac pacemaker cells
decreases heart rate by increasing membrane
permeability to K+.
c. Hormones such as epinephrine and thyroxine
increase heart rate.
d. Ion imbalances can interfere with the normal
function of the heart.
e. Age, gender, exercise, and body temperature all
influence heart rate.
4. Homeostatic Imbalance of Cardiac Output
a. Congestive heart failure occurs when the
pumping efficiency of the heart is so low that
blood circulation cannot meet tissue needs.
b. Pulmonary congestion occurs when one side of
the heart fails, resulting in
pulmonary edema.
V. Developmental Aspects of the Heart (pp.
685–687; Figs. 18.24–18.25)
A. Before Birth (pp. 685–686; Figs. 18.24–18.25)
1. The heart begins as a pair of endothelial tubes
that fuse to make a single heart tube with four
bulges representing the four chambers.
2. The foramen ovale is an opening in the interatrial
septum that allows blood returning to the
pulmonary circuit to be directed into the atrium of
the systemic circuit.
3. The ductus arteriosus is a vessel extending
between the pulmonary trunk and the aortic arch
that allows blood in the pulmonary trunk to be
shunted to the aorta.
Figure 18.24 Development of the human heart.
Arterial end
4a
4
Arterial end
Superior
vena cava
Tubular
heart
Ventricle
2
Ductus
arteriosus
Pulmonary
trunk
Foramen
ovale
Atrium
3
Ventricle
1
Venous end
Day 20:
Endothelial
tubes begin
to fuse.
Aorta
Day 22:
Heart starts
pumping.
Day 24: Heart
continues to
elongate and
starts to bend.
Venous end
Day 28: Bending
continues as ventricle
moves caudally and
atrium moves cranially.
© 2013 PEARSON EDUCATION, INC.
Inferior
vena cava
Day 35: Bending is
complete.
Ventricle
Figure 18.25 Three examples of congenital heart defects.
Narrowed
aorta
Occurs in
about 1 in every
500 births
Ventricular septal defect.
The superior part of the
inter-ventricular septum fails
to form, allowing blood to mix
between the two ventricles.
More blood is shunted from
left to right because the left
ventricle is stronger.
Occurs in
about 1 in every
1500 births
Coarctation of the aorta.
A part of the aorta is
narrowed, increasing the
workload of the left ventricle.
© 2013 PEARSON EDUCATION, INC.
Occurs in
about 1 in every
2000 births
Tetralogy of Fallot.
Multiple defects (tetra =
four): (1) Pulmonary trunk
too narrow and pulmonary
valve stenosed, resulting in
(2) hypertrophied right
ventricle; (3) ventricular
septal defect; (4) aorta
opens from both ventricles.
B. Heart Function Throughout Life (pp. 686–687)
1. Regular exercise causes the heart to enlarge and
become more powerful and efficient.
2. Sclerosis and thickening of the valve flaps occurs
over time, in response to constant pressure of
the blood against the valve flaps.
3. Decline in cardiac reserve occurs due to a decline in
efficiency of sympathetic stimulation.
4. Fibrosis of cardiac muscle may occur in the nodes
of the intrinsic conduction system, resulting in
arrhythmias.
5. Atherosclerosis is the gradual deposit of fatty
plaques in the walls of the systemic
vessels.
https://www.youtube.com/watch?v=vZNa_I4xBnk
https://www.youtube.com/watch?v=ns0aQ1wgPmM (no)
https://www.youtube.com/watch?v=6B3Lwq65XRw