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Chapter 18
Anatomy of the
Cardiovascular System
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 1
Heart

Location of the heart (Figure 18-1)

Lies in the mediastinum, behind the body of the sternum
between the points of attachment of ribs 2 through 6;
approximately two thirds of its mass is to the left of the
midline of the body and one third to the right

Posteriorly the heart rests on the bodies of thoracic
vertebrae 5 through 8

Apex lies on the diaphragm, pointing to the left

Base lies just below the second rib

Boundaries of the heart are clinically important as an aid
in diagnosing heart disorders
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Slide 2
Heart

Size and shape of the heart
(Figures 18-1 and 18-2)

At birth, is transverse and appears large in
proportion to diameter of chest cavity

Between puberty and 25 years of age the heart
attains its adult shape and weight

In adult, shape of the heart tends to resemble that
of the chest
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Slide 3
Heart

Coverings of the heart

Structure of the heart coverings
• Pericardium (Figure 18-4)


Fibrous pericardium—tough, loose-fitting inextensible sac

Serous pericardium—parietal layer lies inside fibrous
pericardium, and visceral layer (epicardium) adheres to
outside of the heart; pericardial space with pericardial fluid
separates the two layers
Function of the heart coverings—provides
protection against friction
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Slide 4
Heart

Structure of the heart

Wall of the heart—made up of three distinct layers
(Figure 18-5):
• Epicardium—outer layer of heart wall
• Myocardium—thick, contractile middle layer of heart wall;
compresses the heart cavities, and the blood within them,
with great force
• Endocardium—delicate inner layer of endothelial tissue
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Slide 5
Heart

Structure of the heart (cont.)

Chambers of the heart—divided into four cavities with the right and left
chambers separated by the septum (Figures 18-6 and 18-7):
• Atria

Two superior chambers, known as “receiving chambers,” because they receive blood
from veins

Atria alternately contract and relax to receive blood and then push it into ventricles

Myocardial wall of each atrium is not very thick, because little pressure is needed to
move blood such a small distance

Auricle—earlike flap protruding from each atrium
• Ventricles

Two lower chambers, known as “pumping chambers,” because they push blood into
the large network of vessels

Ventricular myocardium is thicker than myocardium of the atria, because great force
must be generated to pump blood a large distance; myocardium of left ventricle is
thicker than the right, because it must push blood much further
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Slide 6
Heart

Structure of the heart (cont.)

Valves of the heart—mechanical devices that permit
the flow of blood in one direction only (Figure 18-8)
• Atrioventricular (AV) valves—prevent blood from flowing back
into the atria from the ventricles when the ventricles contract

Tricuspid valve (right AV valve)—guards the right atrioventricular
orifice; free edges of three flaps of endocardium are attached to
papillary muscles by chordae tendineae

Bicuspid, or mitral, valve (left AV valve)—similar in structure to
tricuspid valve except only two flaps present
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Slide 7
Heart

Valves of the heart (cont.)
• Semilunar (SL) valves—half moon–shaped flaps growing out
from the lining of the pulmonary artery and aorta; prevent
blood from flowing back into ventricles from aorta and
pulmonary artery


Pulmonary semilunar valve—at entrance of pulmonary artery
Aortic semilunar valve—at entrance of aorta
• Skeleton of the heart


Set of connected rings that serve as a semirigid support for the
heart valves and for attachment of cardiac muscle of the
myocardium
Serves as an electrical barrier between the myocardium of the
atria and that of the ventricles
• Surface projection (review Figure 18-9)
• Flow of blood through heart (review Figure 18-7)
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Slide 8
Heart

Structure of the heart (cont.)

Blood supply of heart tissue (Figures 18-10 and 18-11)
• Coronary arteries—myocardial cells receive blood from right
and left coronary arteries

First branches to come off aorta

Ventricles receive blood from branches of both right and left
coronary arteries

Each ventricle receives blood only from a small branch of
corresponding coronary artery

Most abundant blood supply goes to myocardium of left ventricle

The right coronary artery is dominant in approximately 50% of all
hearts and the left in about 20%; in approximately 30%, neither
coronary artery is dominant

Few anastomoses exist between the larger branches of the
coronary arteries
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Slide 9
Heart

Blood supply of heart tissue (cont.)
• Veins of the coronary circulation

As a rule, veins follow a course that closely parallels that
of coronary arteries

After going through cardiac veins, blood enters coronary
sinus to drain into right atrium

Several veins drain directly into right atrium
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Slide 10
Heart

Structure of the heart (cont.)

Conduction system of the heart—comprising the sinoatrial (SA)
node, atrioventricular (AV) node, AV bundle, and Purkinje fibers;
made up of modified cardiac muscle (Figure 18-11)
• Sinoatrial node (SA node or pacemaker)— hundreds of cells in right
atrial wall near opening of superior vena cava
• Atrioventricular node (AV node)—small mass of special cardiac muscle
in right atrium along lower part of interatrial septum
• Atrioventricular bundle (AV bundle or bundle of His) and Purkinje fibers

AV bundle originates in AV node, extends by two branches down the two
sides of the interventricular septum, and continues as Purkinje fibers

Purkinje fibers extend out to papillary muscles and lateral walls of
ventricles
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Slide 11
Heart

Structure of the heart (cont.)

Nerve supply of the heart
• Cardiac plexuses—located near arch of aorta, made up
of the combination of sympathetic and parasympathetic
fibers
• Fibers from cardiac plexus accompany right and left
coronary arteries to enter the heart
• Most fibers end in the SA node, but some end in the AV
node and in the atrial myocardium
• Sympathetic nerves—accelerator nerves
• Vagus fibers—inhibitory, or depressor, nerves
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Slide 12
Blood Vessels

Types of blood vessels

Arteries
• Carry blood away from heart—all arteries except
pulmonary artery carry oxygenated blood
• Elastic arteries—largest in body

Examples: aorta and its major branches

Able to stretch without injury

Accommodate surge of blood when heart contracts and
able to recoil when ventricles relax
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Slide 13
Blood Vessels

Arteries (cont.)
• Muscular (distributing) arteries

Smaller in diameter than elastic arteries

Muscular layer is thick
Examples: brachial, gastric, superior mesenteric

• Arterioles (resistance vessels)


Smallest arteries
Important in regulating blood flow to end-organs
• Metarterioles



Short connecting vessel between true arteriole and 20 to 100
capillaries
Encircled by precapillary sphincters
Distal end called thoroughfare channel, which is free
of precapillary sphincters
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Slide 14
Blood Vessels

Types of blood vessels (cont.)

Capillaries—primary exchange vessels
• Microscopic vessels
• Carry blood from arterioles to venules—together, arterioles,
capillaries and venules constitute the microcirculation
(Figure 18-15)
• Not evenly distributed—highest numbers in tissues with high
metabolic rate; may be absent in some “avascular” tissues
such as cartilage
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Slide 15
Blood Vessels
• Types of capillaries (Figure 18-16)

True capillaries—receive blood flowing from metarteriole with input
regulated by precapillary sphincters

Continuous capillaries
– Continuous lining of endothelial cells
– Openings called intercellular clefts exist between adjacent endothelial cells

Fenestrated capillaries
– Have both intercellular clefts and “holes” or fenestrations through plasma
membrane to facilitate exchange functions

Sinusoids
– Large lumen and tortuous course
– Absent or incomplete basement membrane
– Very porous—permit migration of cells into or out of vessel lumen
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Slide 16
Blood Vessels

Types of blood vessels (cont.)

Veins
• Carry blood toward the heart
• Act as collectors and as reservoir vessels; called
capacitance vessels
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Slide 17
Blood Vessels

Structure of blood vessels (Figure 18-14)

Layers
• Tunica adventitia—found in arteries and veins
• Tunica media—found in arteries and veins
• Tunica intima—found in all blood vessels; only layer
present in capillaries
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Slide 18
Blood Vessels

Structure of blood vessels (cont.)

“Building blocks” commonly present
• Lining endothelial cells

Only lining found in capillary

Line entire vascular tree

Provide a smooth luminal surface—protects against
intravascular coagulation

Intercellular clefts, cytoplasmic pores, and fenestrations
allow exchange to occur between blood and tissue fluid

Capable of secreting a number of substances

Capable of reproduction
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Slide 19
Blood Vessels

“Building blocks” commonly present (cont.)
• Collagen fibers

Exhibit woven appearance

Formed from protein molecules that aggregate into fibers

Visible with light microscope

Have only a limited ability to stretch (2% to 3%) under
physiological conditions

Function to strengthen and keep lumen of vessel open
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Slide 20
Blood Vessels

“Building blocks” commonly present (cont.)
• Elastic fibers

Composed of insoluble protein called elastin

Form highly elastic networks

Fibers can stretch over 100% under physiological conditions

Play important role in creating passive tension to help regulate
blood pressure throughout cardiac cycle
• Smooth muscle fibers

Present in all segments of vascular system except capillaries

Most numerous in elastic and muscular arteries

Exert active tension in vessels when contracting
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Slide 21
Major Blood Vessels

Circulatory routes (Figure 18-13)

Systemic circulation—blood flows from the left ventricle
of the heart through blood vessels to all parts of the
body (except gas exchange tissues of lungs) and back
to right atrium

Pulmonary circulation—venous blood moves from right
atrium to right ventricle to pulmonary artery to lung
arterioles and capillaries where gases are exchanged;
oxygenated blood returns to left atrium via pulmonary
veins; from left atrium, blood enters left ventricle
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Slide 22
Major Blood Vessels

Systemic circulation

Systemic arteries
(review Tables 18-2 to 18-6; Figures 18-17 to 18-22)
• Main arteries give off branches, which continue to rebranch,
forming arterioles and then capillaries
• End-arteries—arteries that eventually diverge into capillaries
• Arterial anastomosis—arteries that open into other branches of
the same or other arteries; incidence of arterial anastomoses
increases as distance from the heart increases
• Arteriovenous anastomoses or shunts occur when blood flows
from an artery directly into a vein
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Slide 23
Major Blood Vessels

Systemic circulation (cont.)

Systemic veins (review Figures 18-23 to 18-29)
• Veins are the ultimate extensions of capillaries; unite into vessels
of increasing size to form venules and then veins
• Large veins of the cranial cavity are called dural sinuses
• Veins anastomose as do arteries
• Venous blood from the head, neck, upper extremities, and thoracic cavity (except
lungs) drains into superior vena cava
• Venous blood from thoracic organs drains directly into superior vena cava or
azygos vein
• Hepatic portal circulation (Figure 18-28)

Veins from the spleen, stomach, pancreas, gallbladder, and intestines send their blood
to the liver via the hepatic portal vein

In the liver, venous blood mingles with arterial blood in the capillaries and is eventually
drained from liver by hepatic veins that join the inferior vena cava
• Venous blood from lower extremities and abdomen drains into inferior vena cava
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Slide 24
Major Blood Vessels

Fetal circulation

Basic plan of fetal circulation—additional vessels needed to allow fetal blood
to secure oxygen and nutrients from maternal blood at the placenta
(Figure 18-31)
• Two umbilical arteries—extensions of internal iliac arteries; carry fetal blood to
placenta
• Placenta—attached to uterine wall, where exchange of oxygen and other
substances between the separated maternal and fetal blood occurs (Figure 18-30)
• Umbilical vein—returns oxygenated blood from placenta to fetus; enters body
through umbilicus and goes to undersurface of liver, where it gives off two or three
branches and then continues as ductus venosus
• Ductus venosus—continuation of umbilical vein, drains into inferior vena cava
• Foramen ovale—opening in septum between right and left atria
• Ductus arteriosus—small vessel connecting pulmonary artery with descending
thoracic aorta
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Slide 25
Major Blood Vessels

Fetal circulation (cont.)

Changes in circulation at birth
(compare Figures 18-31 and 18-32)
• When umbilical cord is cut, the two umbilical arteries, the
•
•
•
•
placenta and the umbilical vein no longer function
Umbilical vein within the baby’s body becomes the round
ligament of the liver
Ductus venosus becomes the ligamentum venosum of the liver
Foramen ovale—functionally closed shortly after a newborn’s
first breath and pulmonary circulation is established; structural
closure takes approximately 9 months
Ductus arteriosus—contracts with establishment of respiration,
becomes ligamentum arteriosum
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Slide 26
Cycle of Life:
Cardiovascular Anatomy

Birth—change from placenta-dependent system

Heart and blood vessels maintain basic structure and
function from childhood through adulthood


Exercise thickens myocardium and increases supply of
blood vessels in skeletal muscle tissue
Adulthood through later adulthood—degenerative
changes

Atherosclerosis—blockage or weakening of critical arteries

Heart valves and myocardial tissue degenerate—reduces
pumping efficiency
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Slide 27