Chapter 19
The Cardiovascular System: Blood Vessels
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19
Note that any vessel with the term
pulmonary
or
lobar
in its
name is part of the pulmonary circulation. All others are part of
the systemic circulation.
Pulmonary arteries carry oxygen-poor, carbon dioxide–rich
blood, and pulmonary veins carry oxygen-rich blood.* Tis is
opposite to the systemic circulation, where arteries carry oxy-
gen-rich blood and veins carry carbon dioxide–rich, relatively
oxygen-poor blood.
Systemic Circulation
Te systemic circulation provides the
functional blood supply
to
all body tissues; that is, it delivers oxygen, nutrients, and other
needed substances while carrying away carbon dioxide and
other metabolic wastes. Freshly oxygenated blood* returning
from the pulmonary circuit is pumped out of the le± ventricle
into the aorta
(Figure 19.20)
.
From the aorta, blood can take various routes, because essen-
tially all systemic arteries branch from this single great vessel.
Te aorta arches upward from the heart and then curves and
runs downward along the body midline to its terminus in the
pelvis, where it splits to form the two large arteries serving the
lower extremities. Te branches of the aorta continue to sub-
divide to produce the arterioles and, finally, the capillaries that
ramify through the organs. Venous blood draining from organs
inferior to the diaphragm ultimately enters the inferior vena
cava.
Except for some coronary and thoracic venous drainage
(which enters the azygos system of veins), the superior vena
cava drains body regions above the diaphragm. Te venae cavae
empty the carbon dioxide–laden blood into the right atrium of
the heart.
²wo important points concerning the two major circula-
tions: (1) Blood passes from systemic veins to systemic arteries
only a±er first moving through the pulmonary circuit (Figure
19.19a), and (2) although the entire cardiac output of the right
ventricle passes through the pulmonary circulation, only a
small fraction of the output of the le± ventricle flows through
any single organ (Figure 19.20). Te systemic circulation can be
viewed as multiple circulatory channels functioning in parallel
to distribute blood to all body organs.
As you examine the tables that follow and locate the various
systemic arteries and veins in the illustrations, be aware of cues
that make your memorization task easier. In many cases, the
name of a vessel reflects the body region traversed (axillary, bra-
chial, femoral, etc.), the organ served (renal, hepatic, gonadal),
or the bone followed (vertebral, radial, tibial). Also, notice that
arteries and veins tend to run side by side and, in many places,
they also run with nerves. Finally, be alert to the fact that the
systemic vessels do not always match on the right and le± sides
of the body. Tus, while almost all vessels in the head and limbs
are bilaterally symmetrical, some of the large, deep vessels of the
trunk region are asymmetrical or unpaired.
*By convention, oxygen-rich blood is shown red and oxygen-poor blood is shown
blue.
Venous blood from the digestive viscera passes through the hepatic portal circula-
tion (liver and associated veins) before entering the inferior vena cava.
RA
RV
LV
LA
Capillary beds of
head and
upper limbs
Common
carotid arteries
to head and
subclavian
arteries to
upper limbs
Aortic
arch
Superior
vena cava
Aorta
Capillary beds of
mediastinal structures
and thorax walls
Azygos
system
Thoracic
aorta
Venous
drainage
Arterial
blood
Diaphragm
Inferior
vena
cava
Inferior
vena
cava
Abdominal
aorta
Capillary beds of
digestive viscera,
spleen, pancreas,
kidneys
Capillary beds of
gonads, pelvis, and
lower limbs
Figure 19.20
Schematic flowchart showing an overview of
the systemic circulation.
The pulmonary circulation is shown
in gray for comparison. RA
5
right atrium, RV
5
right ventricle,
LA
5
left atrium, LV
5
left ventricle.
(continued)
Table 19.3
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