Blood, Heart, and Circulation 447- The flow of blood from arterioles to capillaries is
regulated by precapillary sphincter muscles. - The capillary wall may be continuous, fenestrated, or
discontinuous.
C. Veins have the same three tunics as arteries, but they generally
have a thinner muscular layer than comparably sized arteries. - Veins are more distensible than arteries and can expand
to hold a larger quantity of blood. - Many veins have venous valves that ensure a one-way
flow of blood to the heart. - The flow of blood back to the heart is aided by contraction
of the skeletal muscles that surround veins. The effect of
this action is called the skeletal muscle pump.
13.7 Atherosclerosis and Cardiac
Arrhythmias 436
A. Atherosclerosis of arteries can occlude blood flow to the
heart and brain and is a causative factor in about 50% of all
deaths in the United States, Europe, and Japan.
- Atherosclerosis begins with injury to the endothelium,
the movement of monocytes and lymphocytes into the
tunica interna, and the conversion of monocytes into
macrophages that engulf lipids. Smooth muscle cells
then proliferate and secrete extracellular matrix.
2. Atherosclerosis is promoted by such risk factors as
smoking, hypertension, and high plasma cholesterol
concentration. Low-density lipoproteins (LDLs), which
carry cholesterol into the artery wall, are oxidized
by the endothelium and are a major contributor to
atherosclerosis.
B. Occlusion of blood flow in the coronary arteries by
atherosclerosis may produce ischemia of the heart muscle and
angina pectoris, which may lead to myocardial infarction.
C. The ECG can be used to detect abnormal cardiac rates,
abnormal conduction between the atria and ventricles, and
other abnormal patterns of electrical conduction in the heart.13.8 Lymphatic System 442
A. Lymphatic capillaries are blind-ended but highly permeable.
They drain excess tissue fluid into lymph ducts.
B. Lymph passes through lymph nodes and is returned by way
of the lymph ducts to the venous blood.Test Your Knowledge
- Which of these statements is false?
a. Most of the total blood volume is contained in veins.
b. Capillaries have a greater total surface area than any other
type of vessel.
c. Exchanges between blood and tissue fluid occur across
the walls of venules.
d. Small arteries and arterioles present great resistance to
blood flow.- All arteries in the body contain oxygen-rich blood with the
exception of
a. the aorta. c. the renal artery.
b. the pulmonary artery. d. the coronary arteries. - The “lub,” or first heart sound, is produced by closing of
a. the aortic semilunar valve.
b. the pulmonary semilunar valve.
c. the tricuspid valve.
d. the bicuspid valve.
e. both AV valves.- The first heart sound is produced at
a. the beginning of systole.
b. the end of systole.
c. the beginning of diastole.
d. the end of diastole.- Changes in the cardiac rate primarily reflect changes in the
duration of
a. systole.
b. diastole.
Review Activities
- The QRS wave of an ECG is produced by
a. depolarization of the atria.
b. repolarization of the atria.
c. depolarization of the ventricles.
d. repolarization of the ventricles. - The second heart sound immediately follows the occurrence of
a. the P wave.
b. the QRS wave.
c. the T wave. - The cells that normally have the fastest rate of spontaneous
diastolic depolarization are located in
a. the SA node.
b. the AV node.
c. the bundle of His.
d. the Purkinje fibers. - Which of these statements is true?
a. The heart can produce a graded contraction.
b. The heart can produce a sustained contraction.
c. The action potentials produced at each cardiac cycle
normally travel around the heart in circus rhythms.
d. All of the myocardial cells in the ventricles are normally
in a refractory period at the same time. - An ischemic injury to the heart that destroys myocardial
cells is
a. angina pectoris.
b. a myocardial infarction.
c. fibrillation.
d. heart block.