130
UNIT 2
Basic Tissues
Figure 7-13A.
Types of glial cells.
Glial cells
(also called
neuroglia
or
glia
) are nonneuronal cells that
aid in transferring nutrients from capillaries to neurons, main-
tain the blood-brain barrier, regulate the intercellular environ-
ment, provide myelin insulation for axons, provide mechanical
support to neurons, act as phagocytes to remove pathogens and
dead neurons, play a role in presenting antigens in the immune
system, and perform numerous other functions. Recent evidence
suggests that glial cells even participate in some aspects of synap-
tic transmission. It is thought that there are as many as 10 times
the number of glial cells as neurons in the nervous system. The
major types of CNS glial cells are
astrocytes
(described below),
oligodendrocytes
(which produce myelin), and
microglia
(which
act as phagocytes and elements of the immune system). Other
glialike cells include
radial glia cells
and
ependymal cells
in the
CNS and
Schwann cells
and
satellite cells
in the PNS.
J. Lynch
Pia
Astrocyte
Glia limitans
Capillary
Oligodendrocyte
Microglia
Pyramidal
cell
A
Protoplasmic
astrocyte
Protoplasmic astrocyte
Protoplasmic
astrocyte
Pyramidal cells
Cerebral cortex, layer III
Fibrous astrocyte
in cerebellar white matter
B
Figure 7-13B.
Astrocytes.
Golgi preparations, upper left,
3
136; lower right,
3
204
Astrocytes
are found throughout the CNS. Astrocyte processes
called
end-feet
form contacts with capillaries that help produce
the blood-brain barrier and form contacts on neurons that play a
role in supplying nutrients to these cells. Astrocytes regulate the
ionic composition and pH of the extracellular environment and
secrete various neuroactive substances. Astrocyte end-feet form
the
glia limitans
, a coating of the inner surface of the pia mater
that surrounds the brain and spinal cord (Fig. 7-13A). Finally,
astrocytes play an important role in neurotransmitter metabo-
lism and in the modulation of synaptic transmission. There are
two types of astrocytes.
Protoplasmic astrocytes
, in gray matter,
have short, thick processes that are densely clustered and highly
branched, giving them a cloudlike appearance.
Fibrous astro-
cytes
, in white matter, have long, thin processes with relatively
few branchings. The two types of astrocytes have similar func-
tions but differ in some special properties.
CLINICAL CORRELATION
Figure 7-13C.
Glioblastoma.
H&E,
3
68; inset
3
84
Glioblastoma
(a form of
astrocytoma
) is a highly malignant
tumor that arises in the brain from
neoplastic astrocytes
. Sev-
eral features of this tumor help the pathologist arrive at the
diagnosis. In the center of this micrograph, the tumor cells
are necrotic. At the edges of the zone of necrosis, nonnecrotic
tumor cells align themselves in a striking parallel array, like
the pickets of a fence. This con± guration is called
palisading
(
arrows, inset
). Beyond the area of palisading, living tumor
cells commonly surround complex abnormal vascular struc-
tures (
glomeruloid vascular structures
) that resemble the glom-
eruli of the kidney in their tortuous arrangement of capillar-
ies.
Increased mitosis
among the viable tumor cells also aids
in the diagnostic process. Increasing the life span of patients
with glioblastoma is currently an area of intensive research.
Live
Live
tumor cells
tumor cells
Zone of
Zone of
palisading
palisading
Necrotic
Necrotic
tissue
tissue
Necrotic
tissue
Necrotic
tissue
Live
tumor cells
Zone of
palisading
Abnormal
Abnormal
capillaries
capillaries
Abnormal
capillaries
C
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