611
CHAPTER FIFTEEN
Cardiovascular System
ity to contract in response to cold temperatures and to dilate
in response to heat, contributing to the loss of temperature
control common among the elderly. The extent of change in
arteries may refl
ect stress—that is, not all arteries “age” at
the same rate.
Veins may accumulate collagen and calcify but, in
general, do not change as much with age as do arteries.
Thickened patches may appear in the inner layer, and F bers
in the valves, but venous diameters are large enough that
these changes have little impact on function. The venous
supply to many areas is so redundant that alternate vessels
can often take over for damaged ones.
The once-sleek endothelium changes as the cells become
less uniform in size and shape. The endothelial inner lin-
ings of blood vessels are important to health because these
cells release nitric oxide, which signals the vessels to dilate
to increase blood fl
ow, which counters atherosclerosis and
thrombosis. In addition to the changes in arteries and veins,
the number of capillaries declines with age.
Exercise can help maintain a “young” vascular system.
One study compared the vascular endothelial linings of ath-
letic and sedentary individuals of various ages and found
that the status of the vessels of the exercising elderly were
very similar to those of either athletic or sedentary people in
their twenties. Many studies have correlated regular exercise
to lowered heart disease risk in older people.
Overall, aging-related changes affect many components
of the cardiovascular system. But in the absence of disease,
the system is so F
ne-tuned and redundant that effective oxy-
gen delivery can continue well into the later decades of life.
PRACTICE
66
Explain why the heart may enlarge with age.
67
Describe what happens to resting heart rate with age.
The heart slows down, ever so slightly, with age. A study
of 5,000 healthy people aged forty-F
ve to eighty-four showed
that the cardiac cycle lengthens by 2% to 5% per year. Past
studies that showed a slight increase in ejection fraction per
year were fl awed because this measure represents the ratio
of blood volume pumped with each heartbeat to total blood
volume, and it is the end-diastolic volume that diminishes
over time, due to shrinking cardiac muscle and thickening
heart walls. In actuality, the aging heart pumps about 8 mil-
liliters less per year.
The heart valves thicken and become more rigid after age
sixty, changes that may begin as early as the third decade.
The valves may calcify.
Just as the heart need not falter with age, the cardiac
conduction system may remain functional despite change.
The sinoatrial and atrioventricular nodes and the atrioven-
tricular bundle become more elastic. However, these changes
may alter the ECG pattern.
Systolic blood pressure increases with age; a blood pres-
sure reading of 140/90 is not abnormal in an older person. In
about 40% of the elderly, the systolic pressure exceeds 160.
The increase may be due to the decreasing diameters and
elasticity of arteries. Regular exercise can slow these changes.
Resting heart rate declines from 145 or more beats per minute
in a fetus to 140 beats per minute in a newborn, then levels
out in an adult to about 70 (range of 60–99) beats per minute.
In the vascular system, age-related changes are most
apparent in the arteries. The tunica interna thickens.
Dividing smooth muscle cells in the tunica media may push
up the endothelium in places, and over time, the lumens of
the larger arteries narrow. Rigidity increases as collagen, cal-
cium, and fat are deposited as elastin production declines.
Arterial elasticity at age seventy is only about half of what
it was at age twenty. The arterioles have diminished abil-
4. Heart chambers and valves
a. The heart is divided into four chambers—two atria
and two ventricles—that communicate through
atrioventricular oriF
ces on each side.
b. Right chambers and valves
(1) The right atrium receives blood from the venae
cavae and coronary sinus.
(2) The tricuspid valve guards the right
atrioventricular oriF
ce.
(3) The right ventricle pumps blood into the
pulmonary trunk.
(4) A pulmonary valve guards the base of the
pulmonary trunk.
c. Left chambers and valves
(1) The left atrium receives blood from the
pulmonary veins.
(2) The mitral valve guards the left atrioventricular
oriF
ce.
(3) The left ventricle pumps blood into the aorta.
(4) An aortic valve guards the base of the aorta.
CHAPTER SUMMARY
15.1
INTRODUCTION (PAGE 553)
The cardiovascular system is composed of the heart and
blood vessels, which circulate blood to supply oxygen to,
and remove wastes from, body cells.
15.2
STRUCTURE OF THE HEART (PAGE 553)
1. Size and location of the heart
a. The heart is about 14 centimeters long and
9 centimeters wide.
b. It is located in the mediastinum and rests on the
diaphragm.
2. Coverings of the heart
a. A layered pericardium encloses the heart.
b. The pericardial cavity is a space between the
visceral and parietal layers of the pericardium.
3. Wall of the heart
a. The wall of the heart has three layers.
b. These layers include an epicardium, a
myocardium, and an endocardium.
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