20
UNIT 1
Basic Principles of Cell Structure and Function
Figure 2-7A.
Cell components in light micros-
copy.
H&E,
3
1,075
Only the larger
cell components
can be dis-
tinguished individually by light microscopy.
Examples of such readily identiF
able compo-
nents include the
nucleus
,
nucleoli
, blocks of
heterochromatin
and
euchromatin
, larger
secre-
tory vesicles
, and larger
secondary lysosomes
.
Because of its limited resolution of about 0.2
μ
m,
light microscopy cannot distinguish smaller cel-
lular components, such as
ribosomes
,
centrioles
,
cytoskeletal elements
, and most
primary lyso-
somes
and
mitochondria
, although the presence
of some of these structures can be inferred by
their infl
uence on staining reactions when they
are present in abundance. ±or example, ribo-
somes, whether free or associated with endoplas-
mic reticulum, impart
basophilic
staining to a
region of
cytoplasm
where they are concentrated.
By contrast, mitochondria impart
acidophilic
(
eosinophilic
) staining to regions of cytoplasm
where they are concentrated. In cells with a large
Golgi complex
, its presence can sometimes be
distinguished as an unstained region adjacent to
the nucleus.
Bilobed
Bilobed
nucleus
nucleus
Bilobed
nucleus
Secretory granules
Secretory granules
(contents extracted)
(contents extracted)
Secretory granules
(contents extracted)
Secretory granules
Secretory granules
(contents eosinophilic)
(contents eosinophilic)
Secretory granules
(contents eosinophilic)
Hof (Golgi)
Hof (Golgi)
Hof (Golgi)
Heterochromatin
Heterochromatin
Heterochromatin
Euchromatin
Euchromatin
Euchromatin
Nucleolus
Nucleolus
Nucleolus
Inactive nucleus
Inactive nucleus
(heterochromatin)
(heterochromatin)
Inactive nucleus
(heterochromatin)
Basophilic
Basophilic
cytoplasm (RER)
cytoplasm (RER)
Basophilic
cytoplasm (RER)
Granules of
Granules of
eosinophilic
eosinophilic
leukocyte
leukocyte
Granules of
eosinophilic
leukocyte
A
Cytoplasm of neuronal
Cytoplasm of neuronal
cell body with basophilic
cell body with basophilic
patches of RER
patches of RER
Cytoplasm of neuronal
cell body with basophilic
patches of RER
Euchromatin in nucleus
Euchromatin in nucleus
of neuronal cell body
of neuronal cell body
Euchromatin in nucleus
of neuronal cell body
Nucleolus
Nucleolus
Nucleolus
Nucleus of
Nucleus of
satellite cell
satellite cell
Nucleus of
satellite cell
Shrinkage artifact
B
Figure 2-7B.
Wide range of cell sizes, spinal
ganglion sensory neuron.
H&E,
3
780
Human cells have a wide range of sizes and shapes.
Some of the largest cell types, such as
oocytes
and
megakaryocytes
, can be as much as 100
μ
m in diam-
eter. Similar diameters can be seen in cell bodies of
neurons with long axons such as the sensory neurons
in this illustration. The enormity of the cell body in
the center of the image can be appreciated if its size
is compared with that of the satellite cells that sur-
round it. The
nucleolus
in the nucleus of the neuron
is equal in size to the entire nucleus of the
satellite
cell
. The large volume of cytoplasm that surrounds
the nucleus of the neuron contains large expanses of
RER
and
Golgi complexes
. As large as the cell body
is, it amounts to less than 1% of the total cell volume
because the axon may be over a meter in length. Cell
types with the smallest volumes include
spermato-
zoa
,
lymphocytes
(spherical cells with diameters as
little as 5
μ
m), and
endothelial
and
alveolar
cells
(extremely thin cells that allow exchange of gases
and other materials between compartments).
Cell Structure
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