Maintenance of the Body
forces the heart to re-
pump the same blood over and over because the valve does not
close properly and blood backﬂows. In valvular
rowing”), the valve ﬂaps become stiﬀ (typically due to calcium
salt deposits or scar tissue that forms following endocarditis) and
constrict the opening. Tis stiﬀness compels the heart to con-
tract more forcibly than normal. Both conditions increase the
heart’s workload and may weaken the heart severely over time.
Te faulty valve (most oFen the mitral valve) can be replaced
with a mechanical valve, a pig or cow heart valve chemically
treated to prevent rejection, or cryopreserved valves from human
cadavers. Heart valves tissue-engineered from a patient’s own cells
grown on a biodegradable scaﬀold are being developed.
Check Your Understanding
What is the function of the papillary muscles and chordae
For answers, see Appendix H.
Pathway of Blood Through the Heart
Trace the pathway of blood through the heart.
blood is pushed
the cusps of
them to close.
(a) Semilunar valves open
(b) Semilunar valves closed
The semilunar (SL) valves.
Having covered the basic anatomy of the heart, we can now
follow the path that blood takes through the heart and its
Focus on Blood Flow Trough the Heart
follows a single “spurt” of blood as it passes
through all four chambers of the heart and both blood cir-
cuits in its ever-repeating journey.
As you work your way through this ﬁgure, keep in mind that
the leF side of the heart is the
systemic circuit pump
right side of the heart is the
pulmonary circuit pump
how unique the pulmonary circuit is. Elsewhere in the body,
veins carry relatively oxygen-poor blood to the heart, and ar-
teries transport oxygen-rich blood from the heart. Exactly the
opposite oxygenation conditions exist in veins and arteries of
the pulmonary circuit.
Equal volumes of blood are pumped to the pulmonary and
systemic circuits at any moment, but the two ventricles have
very unequal workloads. Te pulmonary circuit, served by the
right ventricle, is a short, low-pressure circulation. In contrast,
the systemic circuit, associated with the leF ventricle, takes a
long pathway through the entire body and encounters about ﬁve
times as much friction, or resistance to blood ﬂow.
Tis functional diﬀerence is revealed in the anatomy of the
two ventricles (±igure 18.5e and
). Te walls of
the leF ventricle are three times thicker than those of the right
ventricle, and its cavity is nearly circular. Te right ventricular
cavity is ﬂattened into a crescent shape that partially encloses
the leF ventricle, much the way a hand might loosely grasp
a clenched ﬁst. Consequently, the leF ventricle can generate
much more pressure than the right and is a far more powerful
Name the major branches and describe the distribution of
the coronary arteries.
Although the heart is more or less continuously ﬁlled with
blood, this blood provides little nourishment to heart tissue.
(Te myocardium is too thick to make diﬀusion a practical
means of delivering nutrients.) How, then, does the heart get
, the functional blood
supply of the heart, is the shortest circulation in the body.
right coronary arteries
both arise from the base
of the aorta and encircle the heart in the coronary sulcus.
Tey provide the arterial supply of the coronary circulation
lef coronary artery
runs toward the leF side of the heart
and then divides into two major branches:
anterior interventricular artery
(also known clinically
lef anterior descending artery
) follows the anterior in-
terventricular sulcus and supplies blood to the interventricu-
lar septum and anterior walls of both ventricles.
supplies the leF atrium and the poste-
rior walls of the leF ventricle.