561
CHAPTER FIFTEEN
Cardiovascular System
Aorta
Part of
aorta
removed
Aortic
valve
cusps
Right coronary
artery
Opening of
left coronary
artery
FIGURE 15.12
The openings of the coronary arteries lie just beyond
the aortic valve.
Blood from systemic circuit
Venae cavae and
coronary sinus
Tricuspid valve
Right atrium
Right ventricle
Pulmonary trunk
Pulmonary arteries
Alveolar capillaries (lungs)
Pulmonary veins
Left atrium
Left ventricle
Aorta
Blood to systemic circuit
Pulmonary valve
Mitral valve
Aortic valve
FIGURE 15.11
Path of blood through the heart and pulmonary circuit.
Blood Supply to the Heart
The f rst two branches oF the aorta, called the right and leFt
coronary arteries,
supply blood to the tissues oF the heart.
Their openings lie just beyond the aortic valve
(f g. 15.12)
.
The right coronary artery passes along the atrioventricu-
lar sulcus between the right atrium and the right ventricle.
It gives oFF two major branches—a
posterior interventricular
artery,
which travels along the posterior interventricular sul-
cus and supplies the walls oF both ventricles, and a
marginal
artery,
which passes along the lower border oF the heart.
Branches oF the marginal artery supply the walls oF the right
atrium and the right ventricle
(f
gs. 15.13
and
15.14)
.
One branch oF the leFt coronary artery, the
circumfl
ex
artery,
Follows the atrioventricular sulcus between the leFt
atrium and the leFt ventricle. Its branches supply blood to
the walls oF the leFt atrium and the leFt ventricle. Another
branch oF the leFt coronary artery, the
anterior interventricu-
lar artery
(or
left anterior descending artery,
) lies in the ante-
rior interventricular sulcus. Its branches supply the walls oF
both ventricles (f
gs. 15.13 and 15.14).
Magnetic resonance imaging
(MRI) can image coronary arteries. Blood
flow appears as a bright signal, and areas of diminished or absent
blood F
ow, or blood turbulence, appear as blank areas. This approach
is less invasive than the standard procedure of
coronary angiography,
in which a catheter is snaked through a blood vessel into the heart
and a contrast agent is used to show heart structure.
The heart must beat continually to supply blood to the
tissues. To do this, myocardial cells require a constant sup-
ply oF Freshly oxygenated blood. The myocardium contains
many capillaries Fed by branches oF the coronary arteries.
When the right ventricular wall contracts, the tricuspid
valve closes the right atrioventricular orif
ce, and the blood
moves through the pulmonary valve into the pulmonary
trunk and its branches (pulmonary arteries). ±rom these ves-
sels, blood enters the capillaries associated with the alveoli
(microscopic air sacs) oF the lungs. Gas exchange occurs
between the blood in the capillaries and the air in the alveoli.
The Freshly oxygenated blood, now relatively low in carbon
dioxide, returns to the heart through the pulmonary veins
that lead to the leFt atrium.
The leFt atrial wall contracts, and the blood moves
through the leFt atrioventricular orif ce and into the chamber
oF the leFt ventricle. When the leFt ventricular wall contracts,
the mitral valve closes the leFt atrioventricular orif
ce, and
the blood passes through the aortic valve into the aorta and
its branches.
Figure 15.11
summarizes the path the blood
takes as it moves through the heart to the alveolar capillaries
and systemic capillaries, then back to the heart.
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