Download 22. Heart

CARDIOVASCUL AR
22
Heart
SYSTEM
O U T L I N E
22.1 Overview of the Cardiovascular System
657
22.1a Pulmonary and Systemic Circulations 657
22.1b Position of the Heart 658
22.1c Characteristics of the Pericardium 659
22.2 Anatomy of the Heart
660
22.2a Heart Wall Structure 660
22.2b External Heart Anatomy 660
22.2c Internal Heart Anatomy: Chambers and Valves
660
22.3 Coronary Circulation 666
22.4 How the Heart Beats: Electrical Properties of
Cardiac Tissue 668
22.4a Characteristics of Cardiac Muscle Tissue
22.4b Contraction of Heart Muscle 669
22.4c The Heart’s Conducting System 670
668
22.5 Innervation of the Heart 672
22.6 Tying It All Together: The Cardiac Cycle
673
22.6a Steps in the Cardiac Cycle 673
22.6b Summary of Blood Flow During the Cardiac Cycle
673
22.7 Aging and the Heart 677
22.8 Development of the Heart 677
MODULE 9: C ARDIOVA SCUL AR SYSTEM
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Chapter Twenty-Two
n chapter 21, we discovered the importance of blood and the
myriad of substances it carries. To maintain homeostasis, blood
must circulate continuously throughout the body. The continual
pumping action of the heart is essential for maintaining blood
circulation. If the heart fails to pump adequate volumes of blood,
cells are deprived of needed oxygen and nutrients, waste products
accumulate, and cell death occurs.
In a healthy, 80-kilogram resting adult, the heart beats about 75
times per minute (about 4500 times per hour or 108,000 times per day).
The amount of blood pumped from one ventricle per minute (about
5.25 liters [L] at rest) is called the cardiac output. When the body is
more active, and the cells need oxygen and nutrients delivered at a
faster pace, the heart can increase its output up to five- or six-fold.
I
22.1 Overview of the Cardiovascular
System
657
which carry blood back to the heart. The differences between
these types of vessels are discussed in chapter 23. Most arteries
carry blood high in oxygen (except for the pulmonary arteries,
as explained later), while most veins carry blood low in oxygen
(except for the pulmonary veins). The arteries and veins entering
and leaving the heart are called the great vessels because of their
relatively large diameter. The heart exhibits several related characteristics and functions:
■
■
■
Learning Objectives:
1. Identify and describe the basic features of the
cardiovascular system.
2. Describe and trace the general patterns of the pulmonary
and systemic circulations.
3. Identify the position and location of the heart.
4. Discuss the structure and function of the pericardium.
Heart
The heart’s anatomy ensures the unidirectional flow of
blood through it. Backflow of blood is prevented by valves
within the heart.
The heart acts like two side-by-side pumps that work at the
same rate and pump the same volume of blood; one directs
blood to the lungs for gas exchange, while the other directs
blood to body tissues for nutrient and respiratory gas delivery.
The heart develops blood pressure through alternate cycles
of heart wall contraction and relaxation. Blood pressure
is the force of the blood pushing against the inside walls
of the vessels. A minimum blood pressure is essential for
pushing blood through the blood vessels.
22.1a Pulmonary and Systemic Circulations
As the center of the cardiovascular system, the heart connects to blood vessels that transport blood between the heart and
all body tissues. The two basic types of blood vessels are arteries
(ar t́ er-ē), which carry blood away from the heart, and veins (vān),
The cardiovascular system consists of two circulations: the pulmonary circulation and the systemic circulation (figure 22.1). The
pulmonary (pŭl m
́ ō-nār-ē; pulmo = lung) circulation consists of the
chambers on the right side of the heart (right atrium and right ventricle) as well as the pulmonary arteries and veins. This circulation
conveys blood to the lungs via pulmonary arteries to reduce carbon
dioxide and replenish oxygen levels in the blood before returning to
Lung
Capillaries
Figure 22.1
Pulmonary veins
Pulmonary Pulmonary arteries
circulation Right atrium
Right ventricle
Vessels transporting
oxygenated blood
Vessels transporting
deoxygenated blood
Left atrium
Left ventricle
Aorta to
systemic
arteries
Systemic
veins
Systemic
circulation
Cardiovascular System. The
cardiovascular system is composed
of the pulmonary circulation and the
systemic circulation. The pulmonary
circulation pumps blood from the right
side of the heart through pulmonary
vessels, to the lungs, and back to the
left side of the heart. The systemic
circulation pumps blood from the left
side of the heart, through systemic
vessels in peripheral tissues, and back
to the right side of the heart.
Capillaries
Vessels involved in
gas exchange
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Chapter Twenty-Two
Heart
Trachea
Sternal angle
Left lung
Right lung
2nd rib
Aortic arch
Left phrenic
nerve
Superior border
Superior
vena cava
Right border
Left
border
Sternum
Right phrenic
nerve
Ascending
aorta
Pulmonary
trunk
Anterior
interventricular
artery
Left ventricle
Diaphragm
Inferior
border
Right atrium
Right coronary
artery
Diaphragm
Right ventricle
(a) Borders of the heart
(b) Heart and lungs, anterior view
Mediastinum
Left lung
Posterior
Ascending aorta
Pleura (cut)
Pericardium
(cut)
Apex of
heart
Diaphragm
(cut)
Thoracic
vertebra
Right lung
Left lung
Aortic
arch (cut)
Heart (in
mediastinum)
Sternum
Anterior
(c) Serous membranes of the heart and lungs
(d) Cross-sectional view
Figure 22.2
Heart Position Within the Thoracic Cavity. The heart is in the mediastinum of the thoracic cavity. (a) An anterior view shows the position
of the heart posterior to the anterior thoracic cage. The borders of the heart are labeled. (b) Cadaver photo of the heart within the mediastinum
(anterior view). (c) Serous membranes (pericardium and pleura) surround the heart and lungs, respectively. (d) A cross-sectional view depicts the
heart’s relationship to the other organs in the thoracic cavity.
the heart in pulmonary veins. Blood returns to the left side of the
heart, where it then enters the systemic circulation.
The systemic (sis-tem ́ i k) circulation consists of the chambers on the left side of the heart (left atrium and left ventricle),
along with all the other named blood vessels. It carries blood
to all the peripheral organs and tissues of the body. Blood that
is high in oxygen (oxygenated) from the left side of the heart is
pumped into the aorta, the largest systemic artery in the body,
and then into smaller systemic arteries. Gas is exchanged with
tissues from the body’s smallest vessels, called capillaries.
Systemic veins then carry blood that is low in oxygen (deoxygenated) and high in carbon dioxide and waste products back to the
heart. Most veins merge and drain into the superior and inferior
venae cavae (vē ́nē ca ́vē; sing., vena cava), which drain blood
into the right atrium. There, the blood enters the pulmonary circulation, and the cycle repeats.
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W H AT D O Y O U T H I N K ?
1
●
We previously mentioned that arteries tend to carry oxygenated
blood, but the pulmonary arteries are the exception. Why are the
pulmonary arteries carrying deoxygenated blood?
22.1b Position of the Heart
The heart is located left of the body midline posterior to the
sternum in the mediastinum (figure 22.2). The heart is slightly
rotated such that its right side or right border (primarily formed
by the right atrium and ventricle) is located more anteriorly, while
its left side or left border (primarily formed by the left atrium
and ventricle) is located more posteriorly. The posterosuperior
surface of the heart, formed primarily by the left atrium, is called
the base. The pulmonary veins that enter the left atrium border
this base. The superior border is formed by the great arterial
trunks (ascending aorta and pulmonary trunk) and the superior
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Chapter Twenty-Two
Fibrous pericardium
Parietal layer of
serous pericardium
Pericardial cavity
Visceral layer of
serous pericardium
(epicardium)
Fibrous pericardium
it beats. The pericardial cavity is a potential space with just a
thin lining of serous fluid. However, it may become a real space
as described in the Clinical View: “Pericarditis.”
W H AT D I D Y O U L E A R N?
1
●
2
●
3
●
4
●
What is the basic distinction between arteries and veins?
Contrast the pulmonary and systemic circulations.
What is the difference between the base of the heart and its apex?
Identify the layers of the pericardium. Why is the pericardial cavity
described as a potential space?
To demonstrate the almost frictionless movement of the heart
within the pericardial sac, try the following demonstration:
Pericardial cavity
Heart wall
Myocardium
Endocardium
Figure 22.3
Pericardium. The pericardium consists of an outer fibrous
pericardium and an inner serous pericardium. The serous pericardium
consists of a parietal layer, which adheres to the fibrous pericardium,
and a visceral layer, which forms the epicardium of the heart. The
space between the parietal and visceral layers of the serous pericardium
is called the pericardial cavity.
vena cava. The inferior, conical end is called the apex (ā ́peks; tip).
It projects slightly anteroinferiorly toward the left side of the body.
The inferior border is formed by the right ventricle.
22.1c Characteristics of the Pericardium
The heart is contained within the pericardium (per-i-kar ́dē-um
̆ ),
a fibrous sac and serous lining (figure 22.3). The pericardium
restricts the heart’s movements so that it doesn’t bounce and move
about in the thoracic cavity, and prevents the heart from overfilling with blood.
The pericardium is composed of two parts. The outer portion is a tough, dense connective tissue layer called the fibrous
pericardium. This layer is attached to both the diaphragm and
the base of the great vessels. The inner portion is a thin, doublelayered serous membrane called the serous pericardium. The
serous pericardium may be subdivided into (1) a parietal layer
of serous pericardium that lines the inner surface of the fibrous
pericardium, and (2) a visceral layer of serous pericardium (also
called the epicardium) that covers the outside of the heart. The
parietal and visceral layers reflect (fold back) along the great
vessels, where these layers become continuous with one another.
The thin space between the parietal and visceral layers of the
serous pericardium is the pericardial cavity, into which serous
fluid is secreted to lubricate the serous membranes and facilitate
the almost frictionless, continuous movement of the heart when
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Study Tip!
Parietal layer of
serous pericardium
Visceral layer of
serous pericardium
(epicardium)
Heart
1. Obtain two glass microscope slides. Place them together and
then try to slide them back-and-forth past each other. You will
find that they stick together (even if they are very clean) and
do not move relative to one another very easily!
2. Now, take two similar glass slides and place a very small drop of
water onto the surface of one slide. Place the slides together, as
before, and then try to slide them back-and-forth past each other.
We predict that you have demonstrated to yourself that glass slides
move easily past each other when a water drop is present between them.
This ease of movement of two opposing surfaces parallels the sliding
movement of the parietal and visceral pericardial surfaces when a thin
layer of serous fluid is present between them.
CLINICAL VIEW
Pericarditis
Pericarditis (per ́ i-kar-dı̄ ́t is; peri = around, kardia = heart, ites =
inflammation) is an inflammation of the pericardium typically
caused by viruses, bacteria, or fungi. Whatever the cause of pericarditis, the pericardium is inflamed. The inflammation causes an
increase in capillary permeability. Thus, the capillaries become
more “leaky,” resulting in fluid accumulation in the pericardial
cavity. At this point, the potential space of the pericardial cavity becomes a real space as it fills with fluid and pus. In severe
cases, the excess fluid accumulation limits the heart’s movement
and keeps it from filling with an adequate amount of blood. The
heart is unable to pump blood, leading to a medical emergency
called cardiac tamponade and resulting in heart failure and death.
Pericarditis typically occurs between the ages of 20 and 50. Fever
and chest pain are frequent symptoms. Pericarditis pain is located
over the center or left side of the chest, and may extend to the
neck or left shoulder. Patients often describe the pain as piercing
or “knifelike,” and say that breathing worsens it. In contrast, pain
from a myocardial infarction typically is described as crushing. But
although the two conditions are different, the diagnosis of myocardial
infarction and pericarditis often may be confused, especially by the
patients experiencing the symptoms. A helpful diagnostic finding
in pericarditis is friction rub, a crackling or scraping sound heard
with a stethoscope that is caused by the movement of the inflamed
pericardial layers against each other. The inflammation results in the
loss of the lubricating action of the serous membranes.
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Chapter Twenty-Two
Heart
22.2 Anatomy of the Heart
Learning Objectives:
1. Describe the external anatomy of the heart and its major
vessels.
2. Observe and identify the internal anatomic characteristics
of each heart chamber.
3. Distinguish how valves regulate blood flow through the heart.
The heart is a relatively small, conical organ approximately
the size of a person’s clenched fist. In the average normal adult,
it weighs about 250 to 350 grams, but certain diseases may cause
heart size to increase dramatically.
22.2a Heart Wall Structure
The heart wall consists of three distinctive layers: an external
epicardium, a middle myocardium, and an internal endocardium
(figure 22.4).
The epicardium (ep-i-kar ́dē-ŭm; epi = upon, kardia = heart) is
the outermost heart layer and is also known as the visceral layer of the
serous pericardium. The epicardium is composed of a serous membrane and areolar connective tissue. As we age, more fat is deposited
in the epicardium, and so this layer becomes thicker and more fatty.
The myocardium (mı̄-ō-kar ́dē-ŭm; mys = muscle) is the middle
layer of the heart wall and is composed of cardiac muscle tissue. The
myocardium is the thickest of the three heart wall layers. It lies deep
to the epicardium and superficial to the endocardium. The myocardial layer is where myocardial infarctions (heart attacks) occur. The
arrangement of cardiac muscle in the heart wall permits the compression necessary to pump large volumes of blood out of the heart.
The internal surface of the heart and the external surfaces of
the heart valves are covered by endocardium (en-dō-kar ́dē-um
̆ ;
endon = within). The endocardium is composed of a simple squamous epithelium, called an endothelium, and a layer of areolar
connective tissue.
Figure 22.4
Organization of the Heart Wall.
The heart wall is composed of an
outer epicardium (visceral layer of
the serous pericardium), a middle
myocardium (cardiac muscle), and an
inner endocardium (composed of areolar
connective tissue and an endothelium).
22.2b External Heart Anatomy
The heart is composed of four hollow chambers: two smaller atria
and two larger ventricles (figure 22.5). The left and right atria
(ā ́trē-ă; sing., atrium; entrance hall) are thin-walled chambers
located superiorly. The anterior part of each atrium is a wrinkled,
flaplike extension, called an auricle (au ́ri-kl; auris = ear) because
it resembles an ear. The atria receive blood returning to the heart
through both circulations: The right atrium receives blood from
the systemic circulation, and the left atrium receives blood from
the pulmonary circulation. Blood that enters an atrium is passed
to the ventricle on the same side of the heart. The left and right
ventricles (ven ́tri-kl; venter = belly) are the inferior chambers. Two
large arteries, the pulmonary trunk and the aorta (ā-ōr ́ta )̆ , exit
the heart at its superior border. The pulmonary trunk carries blood
from the right ventricle into the pulmonary circulation, while the
aorta conducts blood from the left ventricle into the systemic circulation. Both ventricles pump the same volume of blood per minute.
The atria are separated from the ventricles externally by a
relatively deep coronary sulcus (or atrioventricular sulcus) that
extends around the circumference of the heart. The anterior interventricular (in-ter-ven-trik ́ū-lar̆ ) sulcus and the posterior interventricular sulcus are located between the left and right ventricles
on the anterior and posterior surfaces of the heart, respectively.
These sulci extend inferiorly from the coronary sulcus toward the
heart apex. All sulci house blood vessels packed in adipose connective tissue. These vessels supply and drain the heart (discussed
later in this chapter).
22.2c Internal Heart Anatomy: Chambers and Valves
Figure 22.6 depicts the internal anatomy and structural organization of the four heart chambers: the right atrium, right ventricle, left atrium, and left ventricle. Each of these chambers plays
a role in the continuous process of blood circulation. Important to
their function are valves, epithelium-lined dense connective tissue cusps that permit the passage of blood in one direction and
Simple squamous
epithelium
Areolar connective
tissue and fat
Epicardium
(visceral layer of
serous pericardium)
Myocardium (cardiac muscle)
Areolar connective tissue
Endocardium
Endothelium
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Chapter Twenty-Two
Heart
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Aortic arch
Superior vena cava
Ligamentum
arteriosum
Ascending aorta
Left pulmonary artery
Pulmonary trunk
Branches of the
right pulmonary
artery
Left pulmonary veins
Right pulmonary
veins
Auricle of left atrium
Left coronary artery
Auricle of right atrium
Circumflex artery
Right atrium
Great cardiac
vein
Right coronary artery
(in coronary sulcus)
Anterior
interventricular
artery
Marginal artery
Right ventricle
In anterior
interventricular
sulcus
Left ventricle
Small cardiac vein
Inferior vena cava
Apex of heart
Descending aorta
Aortic arch
Branches of the
right pulmonary
artery
Ligamentum arteriosum
Ascending aorta
Left pulmonary vein
Right pulmonary
vein
Pulmonary trunk
Auricle of left atrium
Left coronary artery
Auricle of right atrium
Right atrium
Right coronary artery
(in coronary sulcus)
Anterior
interventricular
artery
Marginal artery
In anterior
interventricular
sulcus
Left ventricle
Right ventricle
Apex of heart
(a) Anterior view
Figure 22.5
External Anatomy and Features of the Heart. (a) An illustration and a cadaver photo show the heart chambers and associated vessels and the
apex of the heart in an anterior view. (continued on next page)
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Chapter Twenty-Two
Heart
Aortic arch
Descending aorta
Superior vena cava
Left pulmonary artery
Right pulmonary artery
Left pulmonary veins
Right pulmonary veins
Left atrium
(forms base of heart)
Coronary sinus
(in coronary sulcus)
Right atrium
Inferior vena cava
Right coronary artery
Left ventricle
Posterior interventricular artery
Middle cardiac vein
Apex of heart
In posterior
interventricular
sulcus
Right ventricle
Aortic arch
Left pulmonary artery
Branches of right pulmonary artery
Left pulmonary veins
(collapsed)
Right pulmonary veins (collapsed)
Left atrium
(forms base of heart)
Right atrium
Coronary sinus
(in coronary sulcus)
Inferior vena cava
Left ventricle
Right coronary artery
Posterior interventricular artery
Middle cardiac vein
Apex of heart
In posterior
interventricular
sulcus
Right ventricle
(b) Posterior view
Figure 22.5
External Anatomy and Features of the Heart. (continued) (b) An illustration and a cadaver photo show the heart chambers and associated
vessels and the base of the heart in a posterior view.
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Chapter Twenty-Two
Heart
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Aortic arch
Ligamentum arteriosum
Ascending aorta
Left pulmonary artery
Superior vena cava
Pulmonary trunk
Right pulmonary artery
Left pulmonary veins
Right pulmonary veins
Left atrium
Right auricle
Aortic semilunar valve
Fossa ovalis
Interatrial septum
Opening for coronary sinus
Left atrioventricular valve
Pulmonary semilunar
valve
Right atrium
Opening for inferior
vena cava
Right atrioventricular valve
Trabeculae carneae
Interventricular septum
Chordae tendineae
Left ventricle
Papillary muscle
Septomarginal trabecula
Right ventricle
Inferior vena cava
Descending aorta
Aortic arch
Ligamentum arteriosum
Ascending aorta
Superior vena cava
Pulmonary trunk
Right auricle
Right atrium
Fossa ovalis
Interatrial septum
Pectinate muscle
Opening for inferior
vena cava
Pulmonary semilunar valve
Right coronary artery
Interventricular septum
Right atrioventricular valve
Left ventricle
Chordae tendineae
Trabeculae carneae
Papillary muscle
Right ventricle
Coronal section, anterior view
Figure 22.6
Internal Anatomy of the Heart. An illustration and a cadaver photo reveal the internal structure of the heart, including the valves and the
musculature of the heart wall.
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Chapter Twenty-Two
Heart
Table 22.1
Heart Valves
Heart Valve
Location
Structure
Function
Right atrioventricular valve
Between right atrium and right
ventricle
Three triangular-shaped cusps of
dense connective tissue covered by
endothelium; chordae tendineae
attached to free edges
Prevents backflow of blood into right
atrium when ventricles contract
Pulmonary semilunar valve
Between right ventricle and
pulmonary trunk
Three semilunar cusps of dense
connective tissue covered by
endothelium; no chordae tendineae
Prevents backflow of blood into right
ventricle when ventricles relax
Left atrioventricular valve
Between left atrium and left ventricle
Two triangular-shaped cusps of
dense connective tissue covered by
endothelium; chordae tendineae
attached to free edges
Prevents backflow of blood into left
atrium when ventricles contract
Aortic semilunar valve
Between left ventricle and ascending
aorta
Three semilunar cusps of dense
connective tissue covered by
endothelium; no chordae tendineae
Prevents backflow of blood into left
ventricle when ventricles relax
prevent its backflow (table 22.1). Valve cusps are the tapering
projection of a cardiac valve, also called flaps or leaflets. When
the flaps of the valves are forced closed during the cardiac cycle,
they produce sounds: “lubb-dupp” heart sounds. The first sound
heard with a stethoscope is the result of the AV valves closing;
producing a “lubb” sound. The second sound is produced when the
semilunar valves close; producing a “dupp” sound. (See Clinical
View, “Heart Sounds,” on page 666 for a more detailed description.)
Fibrous Skeleton
The fibrous skeleton of the heart is located between the atria and
the ventricles, and is formed from dense regular connective tissue
(figure 22.7). The fibrous skeleton performs the following functions:
■
■
■
■
Separates the atria and ventricles.
Anchors heart valves by forming supportive rings at their
attachment points.
Provides electrical insulation between atria and ventricles.
This insulation ensures that muscle impulses are not spread
randomly throughout the heart, and thus prevents all of the
heart chambers from beating at the same time.
Provides a rigid framework for the attachment of cardiac
muscle tissue.
Right Atrium
The right atrium receives venous blood from the systemic circulation and the heart muscle itself. Three major vessels empty into
the right atrium: (1) The superior vena cava drains blood from the
head, neck, upper limbs, and superior regions of the trunk; (2) the
inferior vena cava drains blood from the lower limbs and trunk;
and (3) the coronary sinus drains blood from the heart wall.
The interatrial (in-ter-ā ́trē-a ̆l) septum forms a thin wall
between the right and left atria. The posterior atrial wall is smooth,
but the auricle and anterior wall exhibit obvious muscular ridges,
called pectinate (pek ́ti-nāt; teeth of a comb) muscles. The structural differences in the anterior and posterior walls occur because
the two walls formed from separate structures during embryonic
development. Inspection of the interatrial septum reveals an oval
depression called the fossa ovalis, also called the oval fossa. It
occupies the former location of the fetal foramen ovale, which
shunted blood from the right atrium to the left atrium during fetal
life, as described later in this chapter.
Separating the right atrium from the right ventricle is the
right atrioventricular opening. This opening is covered by a right
atrioventricular (AV) valve (also called the tricuspid valve, since
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Posterior
Left
atrioventricular
valve
Right
atrioventricular
valve
Aortic semilunar
valve
Fibrous
skeleton
Openings to coronary
arteries
Pulmonary semilunar valve
Anterior
Figure 22.7
Fibrous Skeleton of the Heart. Four thick regions of strong dense
regular connective tissue encircle the four heart valves and the origins
of the pulmonary trunk and the aorta. This fibrous skeleton isolates
the atria from the ventricles (so muscle impulses won’t randomly pass
between them), stabilizes the heart valves, and provides an attachment
site for cardiac muscle. This is a superior view of a transverse section.
it has three triangular cusps). Deoxygenated venous blood flows
from the right atrium, through the right atrioventricular opening
when the valve is open, into the right ventricle. The right AV valve
is forced closed when the right ventricle begins to contract, preventing blood from flowing back into the right atrium.
Right Ventricle
The right ventricle receives deoxygenated venous blood from
the right atrium. An interventricular septum forms a thick wall
between the right and left ventricles. The internal wall surface
of each ventricle displays characteristic large, smooth, irregular
muscular ridges, called the trabeculae carneae (tra -̆ bek ́ū-lē; trabs =
beam; kar ́nē-ē; carne = flesh) (see figure 22.6).
The right ventricle typically has three cone-shaped, muscular
projections called papillary (pap ́i-lar̆ -ē; papilla = nipple) muscles,
which anchor numerous thin strands of collagen fibers called
chordae tendineae (kōr ́dē ten ́di-nē-ē). The chordae tendineae
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Chapter Twenty-Two
Heart
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CLINICAL VIEW
Valve Defects and
Their Effects on Circulation
Structural damage to the heart valves can impair blood circulation and
lead to serious health problems. Damage may result from developmental
abnormalities, infection, hypertension, or other cardiovascular problems.
Valvular insufficiency, also termed valvular incompetence, occurs when
one or more of the cardiac valves leaks (called “regurgitant flow”) because
the valve cusps do not close tightly enough. Inflammation or disease may
cause the free edges of the valve cusps to become scarred and constricted,
allowing blood to regurgitate back through the valve. As the heart works
to overcome the effect of the backflow, blood must be forced through the
valve openings and this effort may cause heart enlargement. As a result,
the heart must work harder to circulate the normal amount of blood.
Valvular stenosis (ste-nō ́sis; narrowing) is scarring of the valve
cusps so that they become rigid or partially fused and cannot open
attach to the lower surface of cusps of the right AV valve and prevent
the valve from everting and flipping into the atrium when the right
ventricle is contracting. A muscle bundle called the septomarginal
trabecula (see figure 22.6), or moderator band, connects the base
of the anterior papillary muscle to the interventricular septum. At
its superior end, the right ventricle narrows into a smooth-walled,
conical region called the conus arteriosus. Beyond the conus arteriosus is the pulmonary semilunar valve, which marks the end
of the right ventricle and the entrance into the pulmonary trunk.
The pulmonary trunk divides shortly into right and left pulmonary
arteries, which carry deoxygenated blood to the lungs.
Semilunar valves are located within the walls of both ventricles immediately before the connection of the ventricle to the pulmonary trunk and aorta (see figure 22.6). Each valve is composed
of three thin, half-moon-shaped, pocketlike semilunar cusps. As
blood is pumped into the arterial trunks, it pushes against the
cusps, forcing the valves open. When ventricular contraction ceases,
blood is prevented from flowing back into the ventricles from the
arterial trunk by first entering the pockets of the semilunar valves
between the cusps and the chamber wall. This causes the cusps to
“fill and expand” and meet at the artery center, effectively blocking blood backflow.
completely. A stenotic valve is narrowed and presents resistance to the
flow of blood, so that output from the affected chamber decreases.
Often the affected chamber hypertrophies and dilates—both conditions
that may have deleterious consequences. Heart function may become
so reduced that the rest of the body cannot receive adequate blood
flow. A primary cause of valvular stenosis is rheumatic heart disease.
Rheumatic (roo-mat ́ ik) heart disease may follow a streptococcal infection of the throat. It results when antibodies produced to
kill the bacteria cross-react with the body’s own connective tissue,
thereby initiating an autoimmune disease. All parts of the heart are
subject to injury, but the endocardium, the valve cusps, and the left
AV valve are typically most affected. Significantly scarred and narrow
valves must be surgically repaired or replaced. Patients with a history
of rheumatic heart disease must take antibiotics before undergoing
dental or medical procedures that are likely to introduce bacteria into
the bloodstream.
when the valve is open, into the left ventricle. The left AV valve is
forced closed when the left ventricle begins to contract, preventing
blood backflow into the left atrium.
Left Ventricle
The left ventricular wall is typically three times thicker than the
right ventricular wall (figure 22.8). The left ventricle requires
thicker walls to generate enough pressure to force the oxygenated
blood that has returned to the heart from the lungs into the aorta and
then through the entire systemic circulation. (The right ventricle, in
Left Atrium
Once gas exchange occurs in the lungs, the oxygenated blood
travels through the pulmonary veins to the left atrium (see figure
22.6). The smooth posterior wall of the left atrium contains openings for approximately four pulmonary veins. Sometimes two of
these vessels fuse prior to reaching the left atrium, thus decreasing the number of openings through the atrial wall. Like the right
atrium, the left atrium also has pectinate muscles along its anterior
wall as well as an auricle.
Separating the left atrium from the left ventricle is the left
atrioventricular opening. This opening is covered by the left
atrioventricular (AV) valve (also called the bicuspid valve, since it
has two triangular cusps). This valve is also sometimes called the
mitral (mı̄ ́tra ̆l) valve, because the two triangular cusps resemble
a miter (the headpiece worn by a bishop). Oxygenated blood flows
from the left atrium, through the left atrioventricular opening
mck78097_ch22_656-682.indd 665
Left ventricular
wall
Right ventricular
wall
Figure 22.8
Comparison of Right and Left Ventricular Wall Thickness.
The wall of the left ventricle is about three times thicker than that of the
right ventricle, because the left ventricle must generate a force sufficient
to push blood through the systemic circulation to capillary beds.
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Chapter Twenty-Two
Heart
CLINICAL VIEW
Heart Sounds
By using a stethoscope, a physician can discern four normal heart sounds
with each contraction: the two familiar sounds referred to as “lubb-dupp”
and two minor sounds. The lubb sound signifies the closing of the AV
valves, while the dupp sound signifies the closing of the semilunar valves.
These heart sounds provide clinically important information about heart
activity and the action of heart valves. The minor sounds are caused by
contraction of the atria and flow of blood into the ventricles.
usually the result of turbulence of the blood as it passes through the
heart, and may be caused by valvular leakage, decreased valve flexibility or
a misshapen valve. Sometimes heart murmurs are of little consequence, but
all of them need to be evaluated to rule out a more serious heart problem.
The place where sounds from each AV valve and each semilunar valve
may best be heard does not correspond with the location of the valve
(see figure) because some overlap of valve sounds occurs near their
anatomic locations.
■
■
■
■
The aortic semilunar valve is best heard in the second
intercostal space to the right of the sternum.
The pulmonary semilunar valve is best heard in the second
intercostal space to the left of the sternum.
The right AV valve is best heard by the right side of the
inferior end of the sternum.
The left AV valve is best heard near the apex of the heart
(at the level of the left fifth intercostal space, about 9
centimeters from the midline of the sternum).
Often, abnormal heart sounds, generally called a heart murmur,
are the first indication of heart problems. These sounds may be
heard before, during, or after normal heart sounds. A heart murmur is
contrast, merely has to pump blood to the nearby lungs.) The trabeculae carneae in the left ventricle are more prominent than in the
right ventricle. Typically, two large papillary muscles project from
the ventricle’s inner wall and anchor the chordae tendineae that
attach to the cusps of the left AV valve. At the superior end of the
ventricular cavity, the aortic semilunar valve marks the end of
the left ventricle and the entrance into the aorta (see figure 22.7).
W H AT D I D Y O U L E A R N?
5
●
6
●
7
●
Where is the coronary sulcus located?
What are two similarities and two differences between the right
and left ventricles?
What is the composition and function of the chordae tendineae?
22.3 Coronary Circulation
Learning Objective:
1. Identify and describe the location, origins, and branches of
the coronary blood vessels.
Left and right coronary arteries travel within the coronary
sulcus of the heart to supply the heart wall (figure 22.9a). These
arteries are the only branches of the ascending aorta. The openings for these arteries are located in the wall of the ascending aorta
immediately superior to the aortic semilunar valve.
mck78097_ch22_656-682.indd 666
Pulmonary semilunar valve
Aortic semilunar valve
Left atrioventricular valve
Right atrioventricular valve
Actual location of heart valve
Area where valve sound is best heard
Heart valve locations and auscultation (listening) sites.
The right coronary artery typically branches into the right
marginal artery, which supplies the right border of the heart,
and the posterior interventricular artery, which supplies the
posterior surface of both the left and right ventricles. The left
coronary artery typically branches into the anterior interventricular artery (also called the left anterior descending artery),
which supplies the anterior surface of both ventricles and most
of the interventricular septum, and the circumflex (ser ́ k u m
̆ fleks; around) artery, which supplies the left atrium and ventricle. This arterial pattern can vary greatly among individuals.
For example, some people may have a posterior interventricular
artery that is a branch of the left coronary artery. Knowledge of
this variation is essential when treating individuals for coronary
artery disease.
The coronary arteries are considered functional end
arteries (see chapter 23). In other words, while the left and
right coronary arteries share some tiny connections, called
anastomoses, functionally they act like end arteries, which have
no anastomoses and are the “end of the line” when it comes to
arterial blood flow. The anastomoses allow the coronary arteries to shunt a tiny amount of blood from one artery to another.
However, if one of the arteries becomes blocked, as happens with
coronary artery disease, these anastomoses are too tiny to shunt
sufficient blood from one artery to the other. For example, if a
branch of the left coronary artery becomes blocked, the right
coronary artery cannot shunt enough blood to the part of the
heart supplied by this branch. As a result, the part of the heart
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Chapter Twenty-Two
Heart
667
Aortic arch
Superior vena cava
Pulmonary trunk
Left coronary artery
Aortic semilunar valve
Left atrium
Right atrium
Circumflex artery
Anterior
interventricular
artery
Right coronary artery
Branches of right
coronary artery
Posterior
interventricular artery
Branches of left
coronary artery
Right marginal artery
Right ventricle
Left ventricle
(a) Coronary arteries
Aortic arch
Superior vena cava
Pulmonary trunk
Left atrium
Right atrium
Coronary sinus
Middle cardiac vein
Great cardiac vein
Small cardiac vein
Right ventricle
Left ventricle
(b) Coronary veins
Figure 22.9
Coronary Circulation. Anterior view of (a) coronary arteries and (b) coronary veins that transport blood to and from the cardiac muscle tissue.
wall that was supplied by the branch of the left coronary artery
dies due to lack of blood flow to the tissue.
Venous return occurs through one of several cardiac veins
(figure 22.9b). The great cardiac vein runs alongside the anterior
interventricular artery; the middle cardiac vein runs alongside the
posterior interventricular artery; and the small cardiac vein travels
close to the right marginal artery. These cardiac veins all drain into
the coronary sinus, a large vein that lies in the posterior aspect of
mck78097_ch22_656-682.indd 667
the coronary sulcus. The coronary sinus drains directly into the right
atrium of the heart.
Because the ventricular myocardium is compressed during
contraction, most coronary flow occurs during ventricular
relaxation. Normally, flow is evenly distributed throughout the
thickness of the myocardium. Under certain circumstances, however, coronary flow may be reduced, especially to the regions
immediately external to the endocardium. Situations related to
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Chapter Twenty-Two
CLINICAL VIEW:
IEW:
Heart
In Depth
Angina Pectoris and
Myocardial Infarction
The most common cause of death in the United States is coronary atherosclerosis (ath ́er-ō-skler-ō ́sis; athere = gruel, sclerosis = hardness), or
coronary heart disease (see Clinical View, “Atherosclerosis,” in chapter 23).
This condition is characterized by narrowing of the coronary arteries
that reduces blood flow to the myocardium and gives rise to chest pain.
Coronary atherosclerosis can lead to either angina pectoris or myocardial
infarction.
Angina pectoris (an ́ j ı̄-nă, an-ji ́na) is not a disease, it is actually a
symptom of coronary artery disease caused by narrowing or blockage of
coronary arteries. Generally it results from strenuous activity, when workload demands on the heart exceed the ability of the narrowed coronary
vessels to supply blood. The pain from angina is typically referred along
the sympathetic pathways (T1–T5 spinal cord segments), so an individual
may experience pain in the chest region or down the left arm, where the T1
dermatome is located. The pain diminishes shortly after the person stops
inadequate coronary blood flow include tachycardia (tak ́i-kar ́dē-a ̆;
tachys = quick), an increased heart rate that shortens diastole, and
hypotension (low blood pressure), which reduces the ability of
blood to flow through the ventricular myocardium.
W H AT D O Y O U T H I N K ?
2
●
Do the coronary arteries fill with blood when the ventricles
contract or when they relax?
W H AT D I D Y O U L E A R N?
8
●
Why are coronary arteries considered functional end arteries?
the exertion, and normal blood flow to the heart is restored. Although
many people are successfully treated for years with medications that cause
temporary vascular dilation, such as nitroglycerine, the prognosis and longterm therapy for angina depend on the severity of the vascular narrowing.
Myocardial infarction (in-fark ́shŭn) (MI), commonly called a heart
attack, is a potentially fatal condition resulting from sudden and complete
occlusion (blockage) of a coronary artery. A region of the myocardium
is deprived of oxygen, and some of this tissue may die (necrose). The
symptoms of MI are often different for men and women. Most men experiencing an MI report a sudden, excruciating, and crushing substernal chest
pain, and marked sweating, Many women, however, have relatively little
chest pain. When they experience pain, they describe it as an “aching,”
“tightness,” or “pressure,” rather than pain, and the main locations are
in the back and high chest. In addition, women more often experience
shortness of breath, but because they do not exhibit the traditional or
classic symptoms that some doctors expect, it is likely for a female to
be sent home from the ER with an incorrect diagnosis of heartburn or
anxiety, rather than MI.
cells that usually house one or two central nuclei and numerous
mitochondria for ATP supply (figure 22.10). Cardiac muscle cells
are arranged in spiral bundles and wrapped around and between
the heart chambers. Cardiac muscle tissue exhibits some characteristics that are similar to those of skeletal muscle and others that
are different (table 22.2). For example, the cells in both tissue
types are striated, with extensive capillary networks that supply needed nutrients and oxygen. However, cardiac and smooth
muscle differ in the following ways:
■
■
The sarcoplasmic reticulum in cardiac muscle is less
extensive and not as organized as in skeletal muscle.
Cardiac muscle has no terminal cisternae, while skeletal
muscle does.
22.4 How the Heart Beats: Electrical
Properties of Cardiac Tissue
Table 22.2
Comparison of Cardiac
and Skeletal Muscle
Cardiac Muscle
Skeletal Muscle
Learning Objectives:
Cells are short and branching
Cells are long and cylindrical
One or two nuclei in the center of
the cell
Multiple nuclei at the periphery of
the cell
Cells joined by intercellular
junctions in intercalated discs
Cells do not have specialized
intercellular junctions
The efficient pumping of blood through the heart and blood
vessels requires precisely coordinated contractions of the heart
chambers. These contractions are made possible by the properties of cardiac muscle tissue and by specialized cells in the heart,
known collectively as its conducting system.
Functional contractile unit is the
sarcomere
Functional contractile unit is the
sarcomere
T-tubules overlie Z discs
T-tubules overlie A band/I band
junctions
Composed of thick and thin
filaments
Composed of thick and thin
filaments
22.4a Characteristics of Cardiac Muscle Tissue
Contains sarcoplasmic reticulum
but less than in skeletal muscle
Contains sarcoplasmic reticulum
but more than in cardiac muscle
The myocardium is composed of cardiac muscle, which was
described briefly in chapters 4 (see table 4.14) and 10 (see table
10.6). Recall that cardiac muscle cells are relatively short, branched
More mitochondria than in skeletal
muscle
Fewer mitochondria than in cardiac
muscle
1. Distinguish between, and compare, cardiac muscle and
skeletal muscle.
2. Trace the conduction of muscle impulses along muscle fibers.
3. Describe autorhymicity and the heart’s conducting system.
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Chapter Twenty-Two
Intercalated disc
Openings of
transverse tubules
Heart
669
Intercalated disc
Desmosome
Gap junction
Cardiac muscle cell
Sarcolemma
Nucleus
Mitochondrion
(a) Cross section of cardiac muscle cell
Sarcomere
Intercalated discs
Striations
Sarcolemma
Transverse
tubule
Sarcoplasmic
reticulum
Nucleus
Mitochondrion
Myofibrils
LM 1000x
Z disc
I band
H zone
M line
Z disc
(c) Longitudinal section of cardiac muscle
I band
A band
(b) Cardiac muscle cell, longitudinal view
Figure 22.10
Organization and Histology of Cardiac Muscle. Cardiac muscle cells form the myocardium. (a) Individual cells are relatively short, branched,
and striated. They are connected to adjacent cells by intercalated discs. (b) Transverse tubules are invaginations of the sarcolemma that
surround myofibrils and overlie the Z disc. The sarcoplasmic reticulum is meager in cardiac muscle compared to its abundance in skeletal muscle.
(c) Light micrograph of cardiac muscle in longitudinal section.
■
■
■
Cardiac muscle lacks the extensive association of smooth
endoplasmic reticulum (SER) and transverse tubules
(T-tubules) present in skeletal muscle.
In cardiac muscle, T-tubules overlie Z discs instead
of the junctions of A bands and I bands as seen in
skeletal muscle.
The T-tubules in cardiac muscle have a less extensive
distribution and a reduced association with SER compared
mck78097_ch22_656-682.indd 669
to those in skeletal muscle, allowing for both the delayed
onset and prolonged contraction of cardiac muscle tissue.
22.4b Contraction of Heart Muscle
Cardiac muscle cells contract as a single unit because muscle
impulses (changes in voltage potential across the sarcolemma
[see chapter 10]) are distributed immediately and simultaneously
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Chapter Twenty-Two
Heart
Superior vena cava
Right atrium
Left atrium
Sinoatrial node (pacemaker)
Internodal
pathway
Internodal pathway
Atrioventricular node
Atrioventricular bundle
(bundle of His)
Interventricular
septum
Right bundle
Purkinje fibers
Purkinje fibers
Left bundles
Atrioventricular
node
Atrioventricular
bundle
1 Muscle impulse is generated at the sinoatrial node. It spreads throughout the atria and
to the atrioventricular node by the internodal pathway.
2 Atrioventricular node cells delay the
muscle impulse as it passes to the
atrioventricular bundle.
Atrioventricular
bundle
Interventricular
septum
Left and right
bundle branches
3 The atrioventricular bundle (bundle
of His) conducts the muscle impulse
into the interventricular septum.
Purkinje fibers
4 Within the interventricular septum, the
right and left bundles split from the
atrioventricular bundle.
5 The muscle impulse is delivered to Purkinje
fibers in each ventricle and distributed
throughout the ventricular myocardium.
Figure 22.11
Conducting System of the Heart. Modified cardiac muscle fibers initiate the heartbeat and then spread and conduct the impulse throughout
the heart.
throughout all cells of first the atria and then the ventricles.
Neighboring cardiac muscle cells in the walls of heart chambers
have formed specialized cell–cell contacts called intercalated
discs (in-ter ́ k a -̆ lā-ted disk), which electrically and mechanically link the cells together and permit the immediate passage of
muscle impulses (figure 22.10).
Within the intercalated discs, gap junctions increase the
flow of ions between the cells as the muscle impulse moves
along the sarcolemma. The gap junctions of intercalated
discs provide a low-resistance pathway across the membranes
of adjoining cardiac muscle cells, allowing the unrestricted
passage of ions required for the synchronous beating of cardiac
muscle cells. Numerous desmosomes (see figure 4.1) within
the intercalated discs prevent cardiac muscle cells from pulling apart. Therefore, cardiac muscle cells function as a single,
coordinated unit; the precisely timed stimulation and response
by cardiac muscle cells of both the atria and the ventricles are
dependent upon these structural features.
mck78097_ch22_656-682.indd 670
22.4c The Heart’s Conducting System
The heart exhibits autorhythmicity, meaning that the heart itself
(not external nerves) is responsible for initiating the heartbeat.
Certain cardiac muscle cells are specialized to initiate and conduct
muscle impulses to the contractile muscle cells of the myocardium.
Collectively, these specialized cells are called the heart’s conducting
system (figure 22.11).
The heartbeat is initiated by the specialized cardiac muscle
cells of the sinoatrial (SA) node, which are located in the posterior
wall of the right atrium, adjacent to the entrance of the superior
vena cava. The cells of the SA node act as the pacemaker, the
rhythmic center that establishes the pace for cardiac activity.
Under the influence of parasympathetic innervation, SA node cells
initiate impulses 70 to 80 times per minute.
The muscle impulse travels from the SA node to the atrioventricular (AV) node. The AV node is located in the floor of the right
atrium between the right AV valve and the opening for the coronary
sinus. The AV node normally slows conduction of the impulse as it
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Chapter Twenty-Two
Heart
671
CLINICAL VIEW
The Electrocardiogram
Electrical currents within the heart can be detected during a routine
physical examination using monitoring electrodes attached to the
skin—usually at the wrist, ankles, and six separate locations on the
chest. The electrical signals are collected and charted as an electrocardiogram (ē-lek-trō-kar ́ dē-ō-gram; gramma = drawing), also called an
ECG or EKG. When readings from the different electrodes are compared,
they collectively provide an accurate, comprehensive assessment of
the electrical activity of the heart.
An ECG provides a composite tracing of all muscle impulses generated
by myocardial cells. It records the wave of change in voltage (potential)
across the sarcolemma that (1) originates in the SA node, (2) radiates
through both of the atria to the AV node, (3) passes through the AV node
and the interventricular septum to the heart apex, and (4) stimulates
the Purkinje fibers in the ventricular myocardium.
The progress of impulse transmission through the various parts of the
conducting system is mirrored in an electrocardiogram. A typical ECG
tracing for one heart cycle has three principal deflections: a P wave
above the baseline, a QRS complex that begins (Q) and ends (S) with
small downward deflection from the baseline and has a large deflection
(R) above the baseline, and a T wave above the baseline (see figure).
These waves are indicators of depolarization and repolarization within
specific regions of the heart:
1. The P wave is generated when the impulse originating in the SA
node depolarizes the cells of the atria.
2. The QRS complex identifies the beginning of depolarization
of the ventricles. Simultaneously, the atria repolarize; however,
this repolarization signal is masked by the electrical activity
of the ventricles.
3. The T wave is a small, rounded peak that denotes ventricular
repolarization.
0.8 second
R
Millivolts
+1
1 P wave
3 T wave
0
Q
S
2 QRS complex
-1
The events of a single cardiac cycle as recorded on an electrocardiogram.
travels from the atria to the ventricles, providing a delay between
activation and contraction of the ventricles.
Recall that the fibrous skeleton insulates the atria from the
ventricles to prevent random muscle impulses from spreading
between the atria and the ventricles. There is an opening in the
fibrous skeleton that allows the AV node to communicate with
the next part of the conduction system, the atrioventricular (AV)
bundle. This bundle, also known as the bundle of His, receives
the muscle impulse from the AV node and extends into the interventricular septum before dividing into left and right bundles.
These bundles conduct the impulse to conduction fibers called
Purkinje (pur̆ -kin ́ jē) cells that begin within the apex of the heart
and extend through the walls of the ventricles. Purkinje fibers are
larger than other cardiac muscle cells. Muscle impulse conduction
mck78097_ch22_656-682.indd 671
along the Purkinje fibers is extremely rapid, consistent with
the large size of the cells, and the impulse spreads immediately
throughout the ventricular myocardium.
W H AT D I D Y O U L E A R N?
9
●
10
●
11
●
What are three of the ways in which cardiac muscle differs from
skeletal muscle?
Which component of the conducting system is located in the floor
of the right atrium, between the right AV valve and the coronary
sinus opening?
What is meant by the term autorhythmic when used to describe
the heart?
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Chapter Twenty-Two
Heart
CLINICAL VIEW
Cardiac Arrhythmia
Cardiac arrhythmia (ă-rith ́mē-ă; a = not, rhythmos = rhythm), also called
dysrhythmia, is any abnormality in the rate, regularity, or sequence of
the cardiac cycle. Several common arrhythmias have been described:
■
■
■
Atrial flutter occurs when the atria attempt to beat at a rate
of 200 to 400 times per minute, and as a consequence literally
bombard the AV node with muscle impulses. Abnormal muscle
impulses flow continuously through the atrial conduction
system, thus stimulating the atrial musculature and AV node
over and over. This condition may persist for years, and
frequently degenerates into atrial fibrillation.
Atrial fibrillation (fı̄-bri-lā ́shŭn) differs from atrial flutter
in that the muscle impulses are significantly more chaotic,
leading to an irregular heart rate. The ventricles respond by
increasing and decreasing contraction activities, which may
lead to serious disturbances in the cardiac rhythm.
Premature ventricular contractions (PVCs) often result from
stress, stimulants such as caffeine, or sleep deprivation. They
occur either singly or in rapid bursts due to abnormal impulses
22.5 Innervation of the Heart
Learning Objective:
1. Describe and explain how the sympathetic and
parasympathetic divisions of the autonomic nervous system
regulate heart rate.
The heart is innervated by the autonomic nervous system
(figure 22.12). This innervation consists of sympathetic and
initiated within the AV node or the ventricular conduction
system. All of us experience an occasional PVC, and they are
not detrimental unless they occur in great numbers. Most PVCs
go unnoticed, although occasionally one is perceived as the
heart “skipping a beat” and then “jumping” in the chest.
A more serious arrhythmia is ventricular fibrillation, a rapid,
repetitious movement of the ventricular muscle that replaces normal
contraction. This is a life-threatening condition caused by scattered
impulses originating at different times and places throughout the
entire myocardium. Because the contractions of a heart in fibrillation
are uncoordinated, the heart does not pump blood, and blood circulation stops. This cessation of cardiac activity is called cardiac arrest.
Fibrillation almost certainly results in death unless the normal rhythmic
contractions of the heart are promptly restored. To restore normal heart
contractions, medical personnel apply a strong electrical shock to the
skin of the chest using paddle electrodes. The electrical current passes
through the chest wall to completely and immediately depolarize the
entire myocardium. This procedure is analogous to pushing the reset
button on a computer—and as in rebooting the computer, the hope is
that when the heart begins to function again, it will work as intended.
parasympathetic components, collectively referred to as the coronary plexus. The innervation by autonomic centers in the brainstem doesn’t initiate a heartbeat, but it can increase or decrease the
rate of the heartbeat.
Sympathetic innervation arises from the T1–T5 segments of
the spinal cord. Preganglionic axons enter the sympathetic trunk
and ascend into the thoracic and cervical portions, where they synapse on ganglionic neurons. Postganglionic axons project from the
superior, middle, and inferior cervical ganglia and the T1–T5 ganglia,
Autonomic centers
Parasympathetic
Vagal nucleus
Medulla oblongata
Sympathetic
Figure 22.12
Autonomic Innervation of the Heart.
The amount of blood pumped from the
heart and the heart rate are modified by
autonomic centers in the brainstem.
(Left) Sympathetic stimulation is
carried through the cardiac nerves.
(Right) Parasympathetic stimulation
is carried by vagus nerves.
mck78097_ch22_656-682.indd 672
Cervical sympathetic
ganglion
Vagus nerve (CN X)
Spinal cord
Sympathetic
preganglionic axon
Parasympathetic
preganglionic axon
Sympathetic
postganglionic axon
Cardiac nerve
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Chapter Twenty-Two
and travel directly to the heart through cardiac nerves. Sympathetic
innervation increases the rate and the force of heart contractions.
Parasympathetic innervation comes from the medulla oblongata via the left and right vagus nerves (CN X). As the vagus nerves
descend into the thoracic cavity, they give off branches that supply
the heart. Parasympathetic innervation decreases the heart rate, but
generally tends to have no effect on the force of contractions.
Although there is a particularly rich sympathetic and parasympathetic innervation of the SA and AV nodes, the working myocardial cells are also supplied by both types of autonomic axons.
Study Tip!
Here is one way to help you remember the effects of sympathetic
and parasympathetic innervation on the heart:
Sympathetic innervation Speeds the heart rate.
Parasympathetic innervation does the oPposite (decreases the heart
rate).
W H AT D I D Y O U L E A R N?
12
●
How does the sympathetic division of the autonomic nervous
system affect the heart rate?
22.6 Tying It All Together:
The Cardiac Cycle
Learning Objectives:
1. Identify and describe the events in the cardiac cycle.
2. Trace the pattern of blood flow through the heart.
A cardiac cycle is the time from the start of one heartbeat to
the initiation of the next. During a single cardiac cycle, all chambers within the heart experience alternate periods of contraction
and relaxation. The contraction of a heart chamber is called systole
(sis ́tō-lē). During this period, the contraction of the myocardium
forces blood either into another chamber (from atrium to ventricle)
or into a blood vessel (from a ventricle into the attached large
artery). The relaxation phase of a heart chamber is termed diastole (dı̄-as ́tō-lē; dilation). During this period between contraction
phases, the myocardium of each chamber relaxes, and the chamber
fills with blood.
At the beginning of the cardiac cycle, the left and right
atria contract simultaneously. When the atria contract (atrial
systole), blood is forced into the ventricles through the open AV
valves. During this time, blood is still returning to the atria in the
superior vena cava, inferior vena cava, and coronary sinus (right
atrium) and pulmonary veins (left atrium). After the atria begin
to relax (atrial diastole), left and right ventricular contraction
(ventricular systole) occurs (figure 22.13a). Thus, only two of
the four chambers (either the atria or the ventricles) contract at
the same time. When the ventricles contract, the atrioventricular
openings close as blood pushes against the cusps of the AV valves,
and their edges meet to form a seal. Papillary muscles and the
chordae tendineae prevent these valve cusps from everting. The
semilunar valves are forced open, and blood enters the pulmonary
trunk and the aorta. When the ventricles are relaxing during the
cardiac cycle (ventricular diastole), most of the blood flows passively from the relaxing atria into the ventricles through the open
mck78097_ch22_656-682.indd 673
Heart
673
AV valves (figure 22.13b). Therefore, for the last half of the cardiac
cycle, all four chambers are in diastole together.
W H AT D O Y O U T H I N K ?
3
●
What could happen if the AV valves were to evert into the atria?
22.6a Steps in the Cardiac Cycle
The events in a normal cardiac cycle are shown in figure 22.14
and described here:
1. Atrial systole occurs at the beginning of the cardiac cycle. It
is a brief contraction of the atrial myocardium initiated by the
heart pacemaker. Contraction of the atria finishes filling the
ventricles through the open AV valves while the ventricles are
in diastole. The semilunar valves remain closed.
2. Early ventricular systole is the beginning of the ventricular
contraction. The atria remain in diastole. The AV valves
are forced closed (producing the “lubb” sound), and the
semilunar valves remain closed.
3. Late ventricular systole occurs later in the ventricular
contraction. The atria remain in diastole, and the AV valves
remain closed. Pressure on blood in the ventricles forces
the semilunar valves to open, and blood is ejected into the
arterial trunks.
4. Early ventricular diastole is the start of ventricular
relaxation. The atria remain in diastole. The semilunar
valves close to prevent blood backflow into the ventricles
(producing the “dupp” sound). The AV valves remain closed.
5. Late ventricular diastole is a continuation of ventricular
relaxation and an important time for ventricular filling. The
atria remain in diastole. The AV valve opens, and passive
filling of the ventricle from the atria begins and continues
as most of the ventricular filling occurs. The semilunar
valves remain closed.
22.6b Summary of Blood Flow During the
Cardiac Cycle
As the heart chambers cyclically contract and relax, pressure on
the blood in the chambers alternately increases and decreases.
Table 22.3 illustrates the flow of blood through the four heart
chambers during the cardiac cycle. As you learn this sequence,
keep the following general principles in mind:
■
■
■
Blood flows from veins into the atria under low pressure.
Blood only passes from the atria into the ventricles if
the AV valves are open. Most of the ventricular filling is
passive (about 70%), occurring when both chambers are
relaxing (in diastole) and the atrial pressure is greater than
the ventricular pressure. Filling of the final 30% of the
ventricles occurs when the atria contract (in systole).
Ventricular contraction (systole) increases pressure on the
blood within the ventricles. When ventricular pressure rises
significantly, the AV valves close, and the semilunar valves
are forced open due to increased pressure in the ventricles,
allowing blood to enter the large arterial trunks.
W H AT D I D Y O U L E A R N?
13
●
14
●
Distinguish between systole and diastole.
What events occur in the ventricles during late ventricular diastole?
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Chapter Twenty-Two
Heart
(a) Ventricular Systole (Contraction)
Aortic arch
Blood flow into
ascending aorta
Ascending
aorta
Pulmonary
trunk
Blood flow into
right atrium
Blood flow into
pulmonary trunk
Right
atrium
Left
atrium
Ventricular contraction pushes
blood against the open AV
valves, causing them to close.
Contracting papillary muscles
and the chordae tendineae
prevent valve flaps from
everting into atria.
Ventricles contract, forcing
semilunar valves to open and
blood to enter the pulmonary
trunk and the ascending aorta.
Semilunar valves open
Atrioventricular valves closed
Right ventricle
Cusp of
atrioventricular
valve
Left ventricle
Cusp of
semilunar
valve
Blood in
ventricle
Posterior
Left AV
valve (closed)
Right AV
valve (closed)
Left ventricle
Right
ventricle
Aortic semilunar
valve (open)
Pulmonary
semilunar
valve (open)
Anterior
Transverse
ansverse secti
section
Figure 22.13
Ventricular Systole and Ventricular Diastole. (a) The semilunar valves open during ventricular systole to allow blood to flow into the large
arteries; the AV valves close during ventricular systole to prevent backflow of blood into the atria. (b) During ventricular diastole, the AV valves
open to allow blood to enter the ventricles from the atria; the semilunar valves remain closed to prevent backflow of blood into the ventricles from
the large arteries. Transverse sections in both (a) and (b) show a superior view.
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Chapter Twenty-Two
Heart
675
(b) Ventricular Diastole (Relaxation)
Aortic arch
Blood flow into
right atrium
Blood flow into
left ventricle
Right
atrium
Left
atrium
During ventricular relaxation,
some blood in the ascending
aorta and pulmonary trunk
flows back toward the
ventricles, filling the semilunar
valve cusps and forcing them
to close.
Blood flow into
right ventricle
Ventricles relax and fill with
blood both passively and
then by atrial contraction as
AV valves remain open.
Semilunar valves closed
Atrioventricular valves open
Atrium
Right ventricle
Cusp of
atrioventricular
valve
Left ventricle
Blood
Cusps of
semilunar
valve
Chordae
tendineae
Papillary
muscle
Posterior
Left AV
valve (open)
Right AV
valve (open)
Left ventricle
Right ventricle
Aortic semilunar
valve (closed)
Pulmonary
semilunar
valve (closed)
Anterior
Transverse section
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676
Chapter Twenty-Two
Heart
Atria contract
Atria relax
Atria relax
Semilunar
valves
open
AV
valves
closed
All
valves
closed
AV
valves
open
Ventricles contract
Ventricles contract
2 Early ventricular systole
Atria relax; ventricles begin to contract;
AV valves are forced closed (lubb
sound); semilunar valves still closed
3 Late ventricular systole
Atria continue to relax; ventricles contract;
AV valves remain closed; semilunar
valves are forced open
Ventricles relax
1 Atrial systole
Atria contract; AV valves are open,
semilunar valves are closed
Phase
Atrial
systole
Structure
Atria
Late
ventricular
systole
Early
ventricular
systole
Early
ventricular
diastole
Late
ventricular
diastole
Contract
Relax
Relax
Ventricles
Relax
Contract
Relax
AV valves
Open
Semilunar
valves
Closed
Closed
Time
(seconds) 0.0
0.1
Open
Open
0.2
0.3
Closed
0.4
0.5
Atria relax
0.6
0.7
0.8
Atria relax
Semilunar
valves closed
AV
valves
open
All
valves
closed
Ventricles relax
5 Late ventricular diastole
Atria and ventricles relax; atria continue
passively filling with blood; AV valves
open and ventricles begin to passively fill;
semilunar valves remain closed
Ventricles relax
4 Early ventricular diastole
Atria and ventricles relax; AV valves
remain closed and semilunar valves close
(dupp sound); atria continue passively
filling with blood
Figure 22.14
Cardiac Cycle. The cardiac cycle consists of all of the events that occur with a single heartbeat: contraction (systole) and relaxation (diastole) of all
four heart chambers.
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Chapter Twenty-Two
Table 22.3
Systemic veins
Heart
Blood Flow Through the Heart
Superior
and inferior
venae cavae
Right
atrium
Right
atrioventricular
valve
Right
ventricle
Pulmonary
semilunar
valve
Gas and nutrient
exchange
in peripheral
tissues
Systemic
arteries
677
Pulmonary
trunk and
arteries
Gas exchange
in the lungs
Aortic
semilunar
valve
Aorta
Left
ventricle
Left
atrioventricular
valve
Left
atrium
Pulmonary
veins
Chamber of the Heart
Receives Blood From
Sends Blood To
Valves Through Which Blood
Flows
Right atrium
Superior vena cava, inferior vena
cava, coronary sinus
Right ventricle
Right AV valve
Right ventricle
Right atrium
Pulmonary trunk (blood enters
vessels of pulmonary circulation)
Pulmonary semilunar valve
Left atrium
Pulmonary veins
Left ventricle
Left AV valve
Left ventricle
Left atrium
Ascending aorta (blood enters
vessels of systemic circulation)
Aortic semilunar valve
22.7 Aging and the Heart
22.8 Development of the Heart
Learning Objective:
Learning Objective:
1. Explain how heart function changes as we age.
A healthy heart is capable of quickly and efficiently altering
both the heartbeat rate and the volume of blood pumped during
either an increase or decrease in activity. Consuming a diet low in
saturated fats, abstaining from smoking, and exercising regularly
help maintain a strong, vigorous heart. However, the decreased
flexibility and elasticity of connective tissue that occur with aging
can cause the heart valves to become slightly inflexible. As a result,
a heart murmur may develop, and blood flow through the heart
may be altered. Decreased conducting system efficiency reduces
the heart’s ability to pump the extra blood needed during stress and
exercise. In addition, the muscular wall of the ventricle increases
in thickness when high blood pressure causes the ventricles to
work harder to pump blood into the arterial trunks. Consequently,
the ventricular myocardium undergoes hypertrophy. Hypertrophy
of the heart may have different causes (such as hypertension
or narrowing of vessels connected to the heart), but cardiac
muscle cells always thicken and lose the normal arrangement of
formed cell bundles. Thus, although the heart is enlarged, it works
less efficiently.
W H AT D I D Y O U L E A R N?
15
●
What are some age-related changes that result in altered heart
functions?
mck78097_ch22_656-682.indd 677
1. Trace and describe the formation of postnatal heart
structures from the primitive heart tube.
Development of the heart commences in the third week,
when the embryo becomes too large to receive its nutrients
through diffusion alone. At this time, the embryo needs its own
blood supply, heart, and blood vessels for transporting oxygen and
nutrients through its growing body. The steps involved in heart
development are complex, because the heart must begin working
before its development is complete.
By day 19 (middle of week 3), two heart tubes (or endocardial
tubes) form from mesoderm in the embryo. By day 21, these paired
tubes fuse, forming a single primitive heart tube (figure 22.15). This
tube develops the following named expansions that ultimately give
rise to postnatal heart structures (listed from inferior to superior):
sinus venosus, primitive atrium, primitive ventricle, and bulbus
cordis (bŭl ́bŭs kōr ́dis). The sinus venosus and primitive atrium form
parts of the left and right atria. The primitive ventricle forms most of
the left ventricle. The bulbus cordis may be further subdivided into a
trabeculated part of the right ventricle, which forms most of the right
ventricle; the conus cordis, which forms the outflow tracts for the
ventricles; and the truncus arteriosus, which forms the ascending
aorta and pulmonary trunk. Table 22.4 lists these primitive heart
tube components and the structures they develop into.
By day 22, the primitive heart begins to beat and begins its
process of bending and folding. The heart folding is complete by
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678
Chapter Twenty-Two
Heart
Aortic arch 1
Aortic arch 2
Truncus arteriosus
Truncus arteriosus
Bulbus cordis
Bulbus cordis
Primitive
ventricle
Fusing paired
heart tubes
form a
primitive
heart tube
Primitive
atrium
Sinus venosus
Primitive ventricle
Primitive atrium
Unfused
heart tubes
Sinus venosus
(a) 21 days: Paired heart tubes fuse.
(b) 22 days: Primitive heart tube begins to fold.
(c) 28 days: S-shaped heart tube completes folding.
Figure 22.15
Development of the Heart. The heart develops from mesoderm. By day 19, paired heart tubes are present in the cardiogenic region of the embryo.
(a) These paired tubes fuse by day 21 to form a primitive heart tube. (b) The primitive heart tube bends and folds upon itself, beginning on day 22.
(c) By day 28, the heart tube is S-shaped.
Table 22.4
Primitive Heart Tube Components
and Their Postnatal Structures
Superior vena cava
Heart Tube Component
Postnatal Derivative
Sinus venosus
Superior vena cava, coronary sinus,
smooth posterior wall of right atrium
Primitive atrium
Anterior muscular portions of left and
right atria
Primitive ventricle
Most of left ventricle
Foramen ovale
Trabeculated part of right
ventricle
Most of right ventricle
Endocardial
cushion
Conus cordis
Outflow tracts from ventricles to aorta and
pulmonary trunk
Truncus arteriosus
Ascending aorta, pulmonary trunk
Bulbus cordis
Septum secundum
Blood flow
Right atrium
Septum primum
Left atrium
Left ventricle
Right ventricle
Interventricular
septum
Inferior vena cava
the end of the week (figure 22.15b). The bulbus cordis is pulled
inferiorly, anteriorly, and to the embryo’s right, while the primitive
ventricle moves left to reposition. The primitive atrium and sinus
venosus reposition superiorly and posteriorly. Thus, by day 28 the
heart tube is S-shaped (figure 22.15c).
The next major steps in heart development occur during
weeks 5–8, when the single heart tube becomes partitioned into
four chambers (two atria and two ventricles), and the main vessels
entering and leaving the heart form. The common atrium is subdivided into a left and right atrium by an interatrial septum, which
consists of two parts (septum primum and septum secundum)
that partially overlap. These two parts connect to tissue masses
called endocardial cushions. An opening in the septum secundum
(which is covered by the septum primum) is called the foramen
ovale (ō-val ́ē) (figure 22.16). Because the embryonic lungs are
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Early week 7 (43 days)
Figure 22.16
Interatrial Septum. The interatrial septum is formed by two
overlapping septa (primum and secundum). The foramen ovale is a
passageway that detours blood away from the pulmonary circulation
into the systemic circulation prior to birth.
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Chapter Twenty-Two
not functional, much of the blood is shunted away from the lungs
and to the rest of the body. Since it is the right side of the heart that
sends blood to the lungs, blood is shunted from the right atrium to
the left atrium by traveling through the foramen ovale and pushing the septum primum to the left. Blood cannot flow back from
the left atrium to the right, because the septum primum’s movement to the right is stopped when it comes against the septum
secundum. Thus, the septum primum acts as a unidirectional
flutter valve. When the baby is born and the lungs are fully functional, the blood from the left atrium pushes the septum primum
and secundum together, creating a closed interatrial septum. The
only remnant of the embryonic opening is an oval-shaped depression in the interatrial septum called the fossa (fos ́a ̆; trench) ovalis.
Left and right ventricles are partitioned by an interventricular septum that grows superiorly from the floor of the ventricles. The AV valves, papillary muscles, and chordae tendineae
all form from portions of the ventricular walls as well. The
superior part of the interventricular septum develops from the
Heart
679
aorticopulmonary septum, which is a spiral-shaped mass that
also subdivides the truncus arteriosus into the pulmonary trunk
and the ascending aorta.
Many congenital heart malformations result from incomplete
or faulty development during these early weeks. For example, in
an atrial septal defect the postnatal heart still has an opening
between the left and right atria. Thus, blood from the left atrium
(the higher-pressure system) is shunted to the right atrium (the
lower-pressure system). This can lead to enlargement of the right
side of the heart. Ventricular septal defects can occur if the interventricular septum is incompletely formed. A common malformation called tetralogy of Fallot occurs when the aorticopulmonary
septum divides the truncus arteriosus unevenly. As a result, the
patient has a ventricular septal defect, a very narrow pulmonary
trunk (pulmonary stenosis), an aorta that overlaps both the left
and right ventricles, and an enlarged right ventricle (right ventricular hypertrophy). A good knowledge of heart development is
essential in understanding these congenital heart malformations.
Clinical Terms
bradycardia (brad-ē-kar ́dē-ă; bradys = slow) Slowing of the
heartbeat, usually described as less than 50 beats per minute.
cardiomyopathy (kar ́dē-ō-mı̄-op ́ă-thē) Another term for
disease of the myocardium; causes vary and include
thickening of the ventricular septum (hypertrophy),
secondary disease of the myocardium, or sometimes a
disease of unknown cause.
endocarditis (en ́dō-kar-dı̄ ́tis) Inflammation of the
endocardium. Types include bacterial (caused by
the direct invasion of bacteria), chorditis (affecting
the chordae tendineae), infectious (caused by
microorganisms), mycotic (due to infection by fungi),
and rheumatic (due to endocardial involvement as part of
rheumatic heart disease).
ischemia (is-kē ́mē-ă; ischo = to keep back) Inadequate blood
flow to a structure caused by obstruction of the blood
supply, usually due to arterial narrowing or disruption of
blood flow.
myocarditis (mı̄ ́ō-kar-dı̄ ́tis) Inflammation of the muscular walls
of the heart. This uncommon disorder is caused by viral,
bacterial, or parasitic infections, exposure to chemicals, or
allergic reactions to certain medications.
Chapter Summary
22.1 Overview of
the Cardiovascular
System 657
■
Arteries carry blood away from the heart, and veins return blood to the heart.
■
Heart functions include one-directional blood flow through the cardiovascular system, coordinated side-by-side pumps,
and generation of pressure to drive blood through blood vessels.
22.1a Pulmonary and Systemic Circulations
■
The pulmonary circulation conveys blood to and from the lungs, and the systemic circulation carries blood to and from
all the organs and tissues.
22.1b Position of the Heart
658
■
The heart is located posterior to the sternum in the mediastinum.
■
Its base is the posterosuperior surface formed primarily by the left atrium; the apex is in the conical, inferior end.
22.1c Characteristics of the Pericardium
22.2 Anatomy of
the Heart 660
657
659
■
The pericardium that encloses the heart has an outer fibrous portion and an inner serous portion.
■
The pericardial cavity is a thin space between the layers of the serous pericardium. Pericardial fluid produced by the
serous membranes lubricates the surfaces to reduce friction.
■
The heart is a small, cone-shaped organ.
22.2a Heart Wall Structure
■
660
The heart wall has an epicardium (visceral pericardium), myocardium (thick layer of cardiac muscle), and endocardium
(thin endothelium and areolar connective tissue).
22.2b External Heart Anatomy
660
■
The heart has four chambers: Two smaller atria receive blood returning to the heart, and two larger ventricles pump
blood away from the heart.
■
Around the circumference of the heart, a deep coronary sulcus separates the atria and ventricles. Shallow sulci extend from the
coronary sulcus on the anterior and posterior surfaces between the ventricles. Coronary vessels lie within the sulci.
(continued on next page)
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Chapter Twenty-Two
Heart
Chapter Summary (continued)
22.2 Anatomy of
the Heart 660
(continued)
22.3 Coronary
Circulation 666
22.4 How the Heart
Beats: Electrical
Properties of
Cardiac Tissue 668
22.2c Internal Heart Anatomy: Chambers and Valves
660
■
Dense regular connective tissue forms the fibrous skeleton of the heart that separates the atria and the ventricles. This
skeleton (1) separates atria and ventricles, (2) anchors heart valves, (3) electrically insulates atria and ventricles, and
(4) provides for attachment of cardiac muscle tissue.
■
The right atrium receives blood from the superior vena cava, the inferior vena cava, and the coronary sinus.
■
Atria are separated by an interatrial septum, and ventricles are separated by an interventricular septum.
■
Four pulmonary veins empty into the left atrium.
■
Thick-walled ventricles receive blood from the atria through open AV valves. The free edges of the AV valve cusps are
prevented from everting into the atria by the chordae tendineae.
■
Trabeculae carneae are large, irregular muscular ridges on the inside of the ventricle wall.
■
Papillary muscles are cone-shaped projections on the inner surface of the ventricles that anchor the chordae tendineae.
■
Semilunar valves are located within the wall of each ventricle near its connection to a large artery. The right ventricle
houses the pulmonary semilunar valve, and the left ventricle houses the aortic semilunar valve.
■
The major coronary artery branches are the anterior interventricular and circumflex arteries from the left coronary artery,
and the right marginal and posterior interventricular arteries from the right coronary artery.
■
Venous return is through the cardiac veins into the coronary sinus, which drains into the right atrium of the heart.
22.4a Characteristics of Cardiac Muscle Tissue
668
■
Cardiac muscle cells are small and branched. They form sheets of cardiac muscle tissue arranged into spiral bundles
wrapped around and between the heart chambers.
■
Intercalated discs tightly link the muscle cells together and permit the immediate passage of muscle impulses.
22.4b Contraction of Heart Muscle
669
■
The heart exhibits autorhythmicity. Its stimulus to contract is initiated by cells of the sinoatrial (SA) node in the roof of
the right atrium.
■
Muscle impulses travel to the atrioventricular (AV) node and then through the AV bundle within the interventricular
septum to Purkinje fibers in the heart apex.
22.4c The Heart’s Conducting System
670
22.5 Innervation of
the Heart 672
■
Sympathetic and parasympathetic innervation of the heart have opposing influences on heart rate. Autonomic
innervation increases or decreases the rate of the heartbeat, but does not initiate it.
22.6 Tying It All
Together: The
Cardiac Cycle 673
■
A cardiac cycle is the period of time from the start of one heartbeat to the beginning of the next.
■
All chambers within the heart experience alternate periods of contraction (systole) and relaxation (diastole) during a
single cycle.
22.6a Steps in the Cardiac Cycle
673
22.6b Summary of Blood Flow During the Cardiac Cycle
673
■
Cyclic contraction and relaxation of heart chambers result in the pumping of blood out of the chambers and the
subsequent refilling of the chambers with blood for the next cycle.
22.7 Aging and the
Heart 677
■
Decreased flexibility of heart structures as we age reduces the efficiency of cardiac function. Increased blood pressure
results in hypertrophy of the myocardium.
22.8 Development
of the Heart 677
■
Development of the heart commences in the third week; two heart tubes form and fuse to become a single primitive
heart tube.
■
The primitive heart tube develops expansions that later form postnatal heart structures.
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Chapter Twenty-Two
Heart
681
Challenge Yourself
Matching
Match each numbered item with the most closely related lettered
item.
______ 1. right marginal artery
______ 2. pulmonary veins
______ 3. left AV valve
______ 4. diastole cells
______ 5. SA node
______ 6. venae cavae
______
7. intercalated disc
______ 8. right AV valve
______ 9. circumflex artery
______ 10. systole
a. veins that carry blood to
right atrium
b. period of relaxation
c. contains three cusps; also
known as tricuspid valve
d. specialized junction between
cardiac muscle cells
e. veins that carry blood to
left atrium
f. period of contraction
g. branch of right coronary
artery
h. origin of heartbeat
i. branch of left coronary
artery
j. also known as bicuspid or
mitral valve
Multiple Choice
Select the best answer from the four choices provided.
______ 1. Muscle impulses are spread rapidly between cardiac
muscle cells by
a. sarcomeres.
b. intercalated discs.
c. chemical neurotransmitters.
d. AV valves.
______ 2. Venous blood from the heart wall enters the right
atrium through the
a. superior vena cava.
b. coronary sinus.
c. inferior vena cava.
d. pulmonary veins.
______ 3. How is blood prevented from flowing into the right
ventricle from the pulmonary trunk?
a. closing of the right AV valves
b. opening of the pulmonary semilunar valve
c. contraction of the right atrium
d. closing of the pulmonary semilunar valve
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______ 4. Which of the following is the correct circulatory
sequence for blood to pass through part of the heart?
a. R. atrium → right AV valve → R. ventricle →
pulmonary semilunar valve
b. R. atrium → left AV valve → R. ventricle →
pulmonary semilunar valve
c. L. atrium → right AV valve → L. ventricle →
aortic semilunar valve
d. L. atrium → left AV valve → L. ventricle →
pulmonary semilunar valve
______ 5. The pericardial cavity is located between the
a. fibrous pericardium and the parietal layer of the
serous pericardium.
b. parietal and visceral layers of the serous
pericardium.
c. visceral layer of the serous pericardium and the
epicardium.
d. myocardium and the visceral layer of the serous
pericardium.
______ 6. In the developing heart, the atria form from the
primitive atrium and the
a. sinus venosus.
b. bulbus cordis.
c. primitive ventricle.
d. conus cordis.
______ 7. The irregular muscular ridges in the ventricular
walls are the
a. papillary muscles.
b. trabeculae carneae.
c. chordae tendineae.
d. moderator bands.
______ 8. Sympathetic innervation of cardiac muscle
originates from
a. CN X (vagus nerve).
b. L1–L2 segments of the spinal cord.
c. the AV node.
d. T1–T5 segments of the spinal cord.
______ 9. When the ventricles contract, all of the following
occur except
a. closing of the AV valves.
b. blood ejecting into the pulmonary trunk and aorta.
c. closing of the semilunar valves.
d. opening of the semilunar valves.
______ 10. The thickest part of the heart wall is the
a. pericardium.
b. epicardium.
c. myocardium.
d. endocardium.
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Chapter Twenty-Two
Heart
Content Review
1. What are the differences between the pulmonary and
systemic circulations?
2. What chamber walls primarily form the anterior side of the
heart? What chamber walls form the posterior side of the
heart?
3. Compare the structure, location, and function of the parietal
and visceral layers of the serous pericardium.
4. Where is the fibrous skeleton of the heart located? What are
its functions?
5. Why are the chordae tendineae required for the proper
functioning of the AV valves?
6. Explain why the walls of the atria are thinner than those of
the ventricles, and why the walls of the right ventricle are
relatively thin when compared to the walls of the left ventricle.
7. Identify and compare the branches of the right and left
coronary arteries. In general, what portions of the heart does
each branch supply?
8. Compare cardiac and skeletal muscle. In what ways
are these muscle types similar? In which ways are they
different?
9. Describe the functional differences in the effects of the
sympathetic and parasympathetic divisions of the autonomic
nervous system on the activity of cardiac muscle.
10. What are the phases of the cardiac cycle? Describe each
phase with respect to which heart chambers are in systole
or diastole, which valves are open or closed, and blood flow
into or out of the chambers.
Developing Critical Reasoning
1. It was the end of the semester, and Huang had begun to
prepare for his final examinations. Unfortunately, he still
had to work his full-time job. In order to find sufficient
time to study, he stayed up late and drank large amounts
of coffee to stay alert. One evening during a very late study
session, Huang felt a pounding in his chest and thought he
was having a heart attack. His roommate took Huang to the
emergency room. After an examination and interview by the
physician, Huang was told that he probably had a cardiac
arrhythmia. What was the most probable cause of the
arrhythmia?
2. Josephine is a 55-year-old overweight woman who has a
poor diet and does not exercise. One day while walking
briskly, she experienced pain in her chest and down her
left arm. Her doctor told her she was experiencing angina
due to heart problems. Josephine asks you to explain what
causes angina, and why she was feeling pain in her arm
even though the problem was with her heart. What do you
tell her?
Answers to “What Do You Think?”
1. The pulmonary arteries carry blood low in oxygen to the
lungs because the lungs are responsible for replenishing
the oxygen supplies in the blood. After deoxygenated blood
travels to the lungs, the pulmonary capillaries are involved
in gas exchange—that is, carbon dioxide is removed from
the blood, and oxygen enters the blood. Then the pulmonary
veins carry the newly oxygenated blood back to the heart.
3. If the AV valves were to evert into the atria, some of the
blood from the ventricles would be pushed into the atria,
resulting in inefficient pumping of blood. When the heart
has to work harder to pump the blood out of the heart,
clinical problems result (see Clinical View: “Valve Defects
and Their Effects on Circulation” for further information).
2. When the ventricles contract, they also constrict the
coronary arteries. Thus, the coronary arteries can fill with
blood only when the ventricles are relaxed.
www.mhhe.com/mckinley3
Enhance your study with practice tests and
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