Fundamentals of Anatomy and Physiology - 8e - M20 MART5891 08 SE C20, Angielskie [EN](1)
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20
The Heart
Did you know...?
The first artificial heart was designed by
Robert Jarvik, MD, who implanted it into a
patient in 1982.
Learning Outcomes
After completing this chapter, you should be able to do the following:
20-1
Describe the anatomy of the heart, including vascular supply
and pericardium structure, and trace the flow of blood through
the heart, identifying the major blood vessels, chambers, and
heart valves.
20-2
Explain the events of an action potential in cardiac muscle,
indicate the importance of calcium ions to the contractile
process, describe the conducting system of the heart, and
identify the electrical events associated with a normal
electrocardiogram.
20-3
Explain the events of the cardiac cycle, including atrial and
ventricular systole and diastole, and relate the heart sounds to
specific events in the cycle.
20-4
Define cardiac output, describe the factors that influence heart
rate and stroke volume, and explain how adjustments in stroke
volume and cardiac output are coordinated at different levels of
physical activity.
Clinical Notes
Coronary Artery Disease p. 694
Myocardial Infarction p. 702
Abnormal Conditions Affecting Cardiac Output p. 709
682
Unit 4
Fluids and Transport
An Introduction to the
Cardiovascular System
day, pumping roughly 8000 liters of blood—enough to fill
forty 55-gallon drums, or 8800 quart-sized milk cartons. Try
transferring a gallon of water by using a squeeze pump, and
you’ll appreciate just how hard the heart has to work to keep
you alive. Despite its impressive workload, the heart is a small
organ, roughly the size of a clenched fist.
The heart contains four muscular chambers, two associ-
ated with each circuit. The
right atrium
(A-tre-um; entry
chamber; plural,
atria
) receives blood from the systemic cir-
cuit and passes it to the
right ventricle
(VEN-tri-kl; little
belly), which pumps blood into the pulmonary circuit. The
left atrium
collects blood from the pulmonary circuit and
empties it into the
left ventricle
, which pumps blood into
the systemic circuit. When the heart beats, first the atria con-
tract, and then the ventricles contract. The two ventricles
contract at the same time and eject equal volumes of blood
into the pulmonary and systemic circuits.
This chapter considers the structure and function of the heart.
Blood flows through a network of blood vessels that extend be-
tween the heart and peripheral tissues. Those blood vessels can
be organized into a
pulmonary circuit
, which carries blood to
and from the gas exchange surfaces of the lungs, and a
systemic
circuit
, which transports blood to and from the rest of the body
(
Figure 20–1
). Each circuit begins and ends at the heart, and
blood travels through these circuits in sequence. Thus, blood
returning to the heart from the systemic circuit must complete
the pulmonary circuit before reentering the systemic circuit.
Blood is carried away from the heart by
arteries
,or
efferent
vessels
, and returns to the heart by way of
veins
,or
afferent ves-
sels
. Microscopic thin-walled vessels called
capillaries
inter-
connect the smallest arteries and the smallest veins.
Capillaries are called
exchange vessels
, because their thin
walls permit the exchange of nutrients, dissolved gases, and
waste products between the blood and surrounding tissues.
Unlike most other muscles, the heart never rests. This ex-
traordinary organ beats approximately 100,000 times each
20-1
The heart is a four-chambered
organ, supplied by the coronary
circulation, that pumps oxygen-
poor blood to the lungs and
oxygen-rich blood to the rest of
the body
PULMONARY CIRCUIT
SYSTEMIC CIRCUIT
Systemic arteries
Systemic veins
The heart is located near the anterior chest wall, directly pos-
terior to the sternum (
Figure 20–2a
). The great veins and ar-
teries are connected to the superior end of the heart at the
attached base. The base sits posterior to the sternum at the
level of the third costal cartilage, centered about 1.2 cm
(0.5 in.) to the left side. The inferior, pointed tip of the heart
is the
apex
(A-peks). A typical adult heart measures approx-
imately 12.5 cm (5 in.) from the base to the apex, which
reaches the fifth intercostal space approximately 7.5 cm
(3 in.) to the left of the midline. A midsagittal section
through the trunk does not divide the heart into two equal
halves, because (1) the center of the base lies slightly to the
left of the midline, (2) a line drawn between the center of the
base and the apex points further to the left, and (3) the entire
heart is rotated to the left around this line, so that the right
atrium and right ventricle dominate an anterior view of the
heart.
The heart, surrounded by the
pericardial
(per-i-KAR-de-al)
sac
, sits in the anterior portion of the mediastinum. The
medi-
astinum
, the region between the two pleural cavities, also con-
tains the great vessels (the large arteries and veins linked to the
heart), thymus, esophagus, and trachea.
Figure 20–2b
is a sec-
tional view that illustrates the position of the heart relative to
other structures in the mediastinum.
Pulmonary arteries
Pulmonary veins
Capillaries
in head,
neck, upper
limbs
Capillaries
in lungs
Left
atrium
Right
atrium
Right
ventricle
Left
ventricle
Capillaries
in trunk
and lower
limbs
Figure 20–1
An Overview of the Cardiovascular System.
Driven by the pumping of the heart, blood flows through the
pulmonary and systemic circuits in sequence. Each circuit begins and
ends at the heart and contains arteries, capillaries, and veins.
683
Chapter 20
The Heart
Trachea
Thyroid gland
Right lung
First rib (cut)
Left lung
Esophagus
Posterior
mediastinum
Aorta (arch
segment removed)
Base of
heart
Apex of
heart
Diaphragm
Parietal pericardium (cut)
Left pulmonary
artery
(a) Anterior view of chest cavity
Left pleural
cavity
RIGHT
LUNG
LEFT
LUNG
Right pleural cavity
Left
pulmonary
vein
Bronchus of lung
Right pulmonary artery
Right pulmonary vein
Right phrenic nerve
Aortic
arch
Pulmonary
trunk
Left atrium
Left ventricle
Superior vena cava
Pericardial cavity
Epicardium (visceral
pericardium)
Right atrium
Right ventricle
Parietal pericardium
Anterior mediastinum
Base of
heart
(b) Diagrammatic horizontal section, superior view
Cut edge of
parietal pericardium
Wrist (corresponds
to base of heart)
Fibrous tissue of
pericardial sac
Inner wall
(corresponds
to visceral
pericardium)
Pericardial
cavity
containing
pericardial
fluid
Areolar tissue
Parietal
pericardium
Mesothelium
Air space
(corresponds
to pericardial
cavity)
Balloon
Outer wall
(corresponds
to parietal
pericardium)
Cut edge of epicardium
(visceral pericardium)
Fibrous
attachment
to diaphragm
Apex of heart
(c) Relationship between heart and pericardial cavity
Figure 20–2
The Location of the Heart in the Thoracic Cavity.
(a)
An anterior view of the chest, showing the position of the heart and
major vessels relative to the ribs, sternum, and lungs.
(b)
A superior view of the organs in the mediastinum; portions of the lungs have been
removed to reveal the blood vessels and airways. The heart is situated in the anterior part of the mediastinum, immediately posterior to the
sternum.
(c)
The relationship between the heart and the pericardial cavity; compare with the fist-and-balloon example.
ATLAS:
Plate 47a,b
684
Unit 4
Fluids and Transport
The Pericardium
The lining of the pericardial cavity is called the
pericardium
.
To visualize the relationship between the heart and the peri-
cardial cavity, imagine pushing your fist toward the center of
a large, partially inflated balloon (
Figure 20–2c
). The balloon
represents the pericardium, and your fist is the heart. Your
wrist, where the balloon folds back on itself, corresponds to
the
base
of the heart, to which the
great vessels
, the largest
veins and arteries in the body, are attached. The air space in-
side the balloon corresponds to the pericardial cavity.
The pericardium is lined by a delicate serous membrane
that can be subdivided into the visceral pericardium and the
parietal pericardium. The
visceral pericardium
,or
epicardium
,
covers and adheres closely to the outer surface of the heart; the
parietal pericardium
lines the inner surface of the
pericardial
sac
, which surrounds the heart (
Figure 20–2c
). The pericardial
sac, or
fibrous pericardium
, which consists of a dense network of
collagen fibers, stabilizes the position of the heart and associated
vessels within the mediastinum.
The small space between the parietal and visceral sur-
faces is the pericardial cavity. It normally contains 15–50 mL
of
pericardial fluid
, secreted by the pericardial membranes.
This fluid acts as a lubricant, reducing friction between the
opposing surfaces as the heart beats. Pathogens and inflam-
mation can infect the pericardium, producing the condition
pericarditis
. The inflamed pericardial surfaces rub against
one another, producing a distinctive scratching sound that
can be heard through a stethoscope. The pericardial inflam-
mation also commonly results in an increased production of
pericardial fluid. Fluid then collects in the pericardial cavity,
restricting the movement of the heart. This condition, called
cardiac tamponade
(tam-po-NAD;
tampon
, plug), can also be
caused by traumatic injuries (such as stab wounds) that pro-
duce bleeding into the pericardial cavity.
amounts of fat. In fresh or preserved hearts, this fat must be
stripped away to expose the underlying grooves. These sulci
also contain the arteries and veins that carry blood to and
from the cardiac muscle.
The Heart Wall
A section through the wall of the heart reveals three distinct
layers: an outer epicardium, a middle myocardium, and an in-
ner endocardium.
Figure 20–4a
illustrates these three layers:
1.
The
epicardium
is the visceral pericardium that covers
the outer surface of the heart. This serous membrane con-
sists of an exposed mesothelium and an underlying layer
of loose areolar connective tissue that is attached to the
myocardium.
2.
The
myocardium
, or muscular wall of the heart, forms
both atria and ventricles. This layer contains cardiac
muscle tissue, blood vessels, and nerves. The my-
ocardium consists of concentric layers of cardiac muscle
tissue. The atrial myocardium contains muscle bundles
that wrap around the atria and form figure eights that en-
circle the great vessels (
Figure 20–4b
). Superficial ventric-
ular muscles wrap around both ventricles; deeper muscle
layers spiral around and between the ventricles toward
the apex in a figure-eight pattern.
3.
The inner surfaces of the heart, including those of the
heart valves, are covered by the
endocardium
, a simple
squamous epithelium that is continuous with the endo-
thelium of the attached great vessels.
Cardiac Muscle Tissue
As noted in Chapter 10,
cardiac muscle cells
are intercon-
nected by
intercalated discs
(
Figure 20–5a,c
). At an interca-
lated disc, the interlocking membranes of adjacent cells are
held together by desmosomes and linked by gap junctions
(
Figure 20–5b
). Intercalated discs transfer the force of con-
traction from cell to cell and propagate action potentials.
Table 20–1 provides a quick review of the structural and func-
tional differences between cardiac muscle cells and skeletal
muscle fibers. Among the histological characteristics of car-
diac muscle cells that distinguish them from skeletal muscle
fibers are (1) small size; (2) a single, centrally located nu-
cleus; (3) branching interconnections between cells; and (4)
the presence of intercalated discs.
Superficial Anatomy of the Heart
The four cardiac chambers can easily be identified in a super-
ficial view of the heart (
Figure 20–3
). The two atria have rela-
tively thin muscular walls and are highly expandable. When
not filled with blood, the outer portion of each atrium deflates
and becomes a lumpy, wrinkled flap. This expandable exten-
sion of an atrium is called an
atrial appendage
,oran
auricle
(AW-ri-kl;
auris
, ear), because it reminded early anatomists of
the external ear (
Figure 20–3a
). The
coronary sulcus
, a deep
groove, marks the border between the atria and the ventricles.
The
anterior interventricular sulcus
and the
posterior inter-
ventricular sulcus
, shallower depressions, mark the bound-
ary between the left and right ventricles (
Figure 20–3a,b
).
The connective tissue of the epicardium at the coronary
and interventricular sulci generally contains substantial
Tips
&
Tricks
The term
intercalated
means “inserted between other
elements”; thus, intercalated discs appear to have been
inserted between cardiac muscle cells.
685
Chapter 20
The Heart
Fibrous
pericardium
Pulmonary
trunk
Auricle of
left atrium
Left common
carotid artery
Left subclavian artery
Ascending
aorta
Arch of aorta
Brachiocephalic
trunk
Ligamentum
arteriosum
Parietal
pericardium
Descending
aorta
Superior
vena cava
Ascending
aorta
Left pulmonary
artery
Superior
vena cava
Pulmonary
trunk
Auricle of
right atrium
RIGHT ATRIUM
Auricle
of right
atrium
Auricle of
left atrium
RIGHT
ATRIUM
Right coronary
artery
Fat and vessels
in anterior
interventricular
sulcus
RIGHT
VENTRICLE
Coronary sulcus
RIGHT VENTRICLE
Fat and
vessels in
coronary
sulcus
LEFT
VENTRICLE
Marginal branch
of right coronary artery
Parietal pericardium
fused to diaphragm
Anterior interventricular
sulcus
LEFT
VENTRICLE
(a) Anterior (sternocostal) surface
Base of heart
Arch of aorta
Left pulmonary artery
Right pulmonary
artery
Left pulmonary veins
1
1
Fat and vessels in
coronary sulcus
Superior
vena cava
Ribs
LEFT
ATRIUM
2
2
Coronary
sinus
Right
pulmonary
veins (superior
and inferior)
3
3
4
4
RIGHT
ATRIUM
Apex of
heart
LEFT
VENTRICLE
5
5
6
6
Inferior
vena cava
RIGHT
VENTRICLE
7
7
8
8
9
9
Fat and vessels in posterior
interventricular sulcus
10
10
(b) Posterior (diaphragmatic) surface
(c) Position of heart
Figure 20–3
The Superficial Anatomy of the Heart. (a)
Major anatomical features on the anterior surface.
(b)
Major landmarks on the
posterior surface. Coronary arteries (which supply the heart itself) are shown in red; coronary veins are shown in blue.
(c)
Heart position relative
to the rib cage.
Internal Anatomy and Organization
Next we examine the major landmarks and structures visible
on the interior surface of the heart. In a sectional view, you
can see that the right atrium communicates with the right
ventricle, and the left atrium with the left ventricle (
Figure
20–6a,c
). The atria are separated by the
interatrial septum
(
septum
, wall); the ventricles are separated by the much
thicker
interventricular septum
. Each septum is a muscular
partition.
Atrioventricular (AV) valves
, folds of fibrous tis-
sue, extend into the openings between the atria and ventri-
cles. These valves permit blood flow in one direction only:
from the atria to the ventricles.
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