166
UNIT 3
Organ Systems
Erythocytes
Erythocytes
Lumen
Lumen
Endothelium
Endothelium
Erythrocytes
Lumen
Endothelium
External
External
elastic lamina
elastic lamina
External
elastic lamina
Tunica
Tunica
media
media
Tunica
media
Internal
Internal
elastic lamina
elastic lamina
Internal
elastic lamina
Endothelial
Endothelial
cell junction
cell junction
Endothelial
cell junction
Collagen
Collagen
fibers
fibers
Collagen
fibers
Tunica
Tunica
media
media
Dense
Dense
bodies
bodies
Basal lamina
Basal lamina
Tunica
media
Dense
bodies
Basal lamina
Internal
Internal
elastic
elastic
lamina
lamina
Internal
elastic
lamina
A
Figure 9-9B.
Small artery.
SEM,
3
1,300
In this scanning electron micrograph of
a
small artery
, the
endothelial cells
are
extremely squamous, and they are so
closely apposed to the
internal elastic
membrane
that the interface between
the two layers is indistinguishable.
The
smooth muscle cells
of the tunica
media are also closely apposed to each
other so that boundaries between cells
are difF
cult to discern. The ground
substance of the tunica adventitia and
the surrounding connective tissue has
been removed during specimen pro-
cessing so that only some
bundles of
collagen ±
bers
remain.
Smooth muscle
Smooth muscle
Smooth muscle
Erythrocytes
Erythrocytes
Erythrocytes
Collagen
Collagen
fiber
fiber
bundle
bundle
Collagen
fiber
bundle
Internal elastic
Internal elastic
lamina
lamina
Internal elastic
lamina
Endothelial cells
Endothelial cells
Endothelial cells
B
Figure 9-9A.
Medium artery.
TEM,
3
1,000 left;
3
8,700 above
In the wall of the healthy
medium artery
on the left, the layer
of squamous
endothelial cells
adheres closely to the prominent,
highly corrugated,
internal elastic membrane
. The
external elastic
membrane
is also corrugated but thinner. The thick
tunica media
is composed of many layers of closely apposed smooth muscle
cells. In the higher magniF
cation view on the right, the
dense bod-
ies
and
basal laminae
that are characteristic of smooth muscle cells
are readily apparent. The amorphous appearance of the
internal
elastic membrane
is typical of elastic membranes in transmission
electron micrographs.
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