164
UNIT 3
Organ Systems
The Arterial System
Figure 9-7A.
A representation of a large (elastic) artery.
Large arteries
(
elastic arteries
) are also referred to as
conducting arteries
, because of their function in conduct-
ing blood fl
ow out of the heart. There are abundant
elastic
laminae
(thick bundles of elastic F
bers) in the
tunica media
of large arteries, which enable the walls to recoil to resist
pressure as well as to maintain arterial pressure during
diastole when the ventricles are relaxed and pressure is not
generated by the heart. Small vessels located in the
tunica
adventitia
are called
vasa vasorum
; they supply the tissue
of the artery wall with oxygen and nutrients when they are
far from the lumen and diffusion of nutrients is difF
cult.
The aorta, pulmonary arteries, and their main branches
are good examples of elastic arteries.
D. Cui /T. Yang
Vasa vasorum
Nerve
Fibroblast
Elastic lamina
Connective tissue
Smooth
muscle cell
Endothelial cell
Tunica
adventitia
Tunica
media
Tunica
intima
A
Elastic
Elastic
laminae
laminae
Tunica
Tunica
adventitia
adventitia
Tunica
Tunica
media
media
Tunica
Tunica
intima
intima
Elastic
laminae
Tunica
adventitia
Tunica
media
Tunica
intima
B
Figure 9-7B.
Large (elastic) artery, carotid artery.
Elastic
stain,
3
68; inset
3
242
This is an example of a
large artery
(
elastic artery
) from a
portion of the
carotid artery
. The carotid artery generally
has the characteristics of elastic arteries. The
tunica media
of the vessel wall has multiple layers of
elastic lamina
that
are well organized in concentric fashion. These elastic
laminae are sheets of fenestrated elastic material produced
by smooth muscle cells in the tunica media. These cells are
interspersed between the elastic laminae (see ±ig. 4-9B).
The elastic laminae in this specimen are revealed as par-
allel wavy black sheets by a special elastic stain; smooth
muscle cells are not visible here with this type of stain. The
tunica adventitia
of an elastic artery consists of loosely
arranged connective tissue F
bers. These F
bers are mainly
collagen ±
bers
, with a small number of
elastic ±
bers
that
are produced by
± broblasts
.
Tunica
Tunica
adventitia
adventitia
Tunica
Tunica
media
media
Vasa
vasorum
Smooth
Smooth
muscle cells
muscle cells
Elastic
Elastic
laminae
laminae
Tunica
adventitia
Tunica
media
Tunica
intima
C
Smooth
muscle cells
Elastic
laminae
Figure 9-7C.
Large (elastic) artery, aorta.
H&E,
3
68;
insets
3
198
An example of a
large artery
(
aorta
) is shown. The
elastic
laminae
are pink and are more difF
cult to distinguish with
routine H&E stain than they are with elastic stains. The
dark nuclei in the
tunica media
belong to
smooth muscle
cells
(
left inset
), which produce the elastic membrane.
There are some
vasa vasorum
deep in the tunica adven-
titia (
right inset
), which provide oxygen and nutrients for
the tunica media and tunica adventitia of the large artery
wall. Nerves belonging to the autonomic nervous system
may occasionally be found in the
tunica adventitia
(see
±ig. 9-7A).
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