563
CHAPTER FIFTEEN
Cardiovascular System
The smaller branches of these arteries usually have con-
nections (anastomoses) between vessels that provide alter-
nate pathways for blood, called collateral circulation. These
detours in circulation may supply oxygen and nutrients to
the myocardium when a coronary artery is blocked.
FIGURE 15.14
An angiogram (radiograph) of the coronary arteries
is a diagnostic procedure used to examine speciF
c blood vessels.
Aorta
Cardiac veins
Coronary sinus
Right atrium
Right coronary artery
Left coronary artery
Posterior
interventricular
artery
Anterior
interventricular
artery
Marginal
artery
Circumflex
artery
Myocardial
capillaries in
ventricular
walls
Myocardial
capillaries in
walls of right
atrium and right
ventricle
Myocardial
capillaries in
walls of left
atrium and left
ventricle
Myocardial
capillaries in
ventricular
walls
FIGURE 15.15
±Path±
of blood through the
coronary circulation.
Branches of the
cardiac veins
drain blood that has
passed through the capillaries of the myocardium. Their
paths roughly parallel those of the coronary arteries. As F g-
ure 15.13
b
shows, these veins join the
coronary sinus,
an
enlarged vein on the posterior surface of the heart in the
atrioventricular sulcus. The coronary sinus empties into the
right atrium.
Figure 15.15
summarizes the path of blood that
supplies the tissues of the heart.
In most body parts, blood fl ow in arteries peaks during
ventricular contraction. However, blood fl
ow in the vessels
of the myocardium is poorest during ventricular contrac-
tion. This is because the muscle F
bers of the myocardium
compress nearby vessels as they contract, interfering with
blood flow. Also, the openings into the coronary arteries
are partially blocked as the fl
aps of the aortic valve open.
Conversely, during ventricular relaxation, the myocardial
vessels are no longer compressed, and the aortic valve does
not block the oriF
ces of the coronary arteries. This increases
blood fl
ow into the myocardium.
A thrombus or embolus that blocks or narrows a coronary artery
branch deprives myocardial cells of oxygen, producing ischemia and
painful
angina pectoris.
The pain usually occurs during physical activ-
ity, when oxygen requirements exceed supply. Pain lessens with rest.
Emotional stress may also trigger angina pectoris.
Angina pectoris may cause a heavy pressure, tightening, or
squeezing sensation in the chest. The pain is usually felt behind the
sternum or in the anterior portion of the upper thorax, but may radi-
ate to the neck, jaw, throat, shoulder, upper limb, back, or upper
abdomen. Other symptoms include profuse perspiration (diaphore-
sis), di²
culty breathing (dyspnea), nausea, or vomiting.
A blood clot completely obstructing a coronary artery or one
of its branches (coronary thrombosis) kills part of the heart. This is a
myocardial infarction
(MI), more commonly known as a heart attack.
previous page 593 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 595 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off