22
UNIT 1
Basic Principles of Cell Structure and Function
Figure 2-9A.
Exocrine protein–secreting cells, pancreatic acinar cell.
EM,
3
7,000
Rough
endoplasmic
reticulum
Golgi
complex
Lumen
Secretory
granules
Euchromatin
in nucleus
Nucleolus
A
Secretory
Secretory
granules
granules
Secretory
granules
Lumen
Lumen
Lumen
Basophilic
Basophilic
cytoplasm
cytoplasm
Basophilic
cytoplasm
Nucleolus
Nucleolus
Nucleolus
Site of Golgi
Site of Golgi
Site of Golgi
B
There are many examples of glandular epithelial cells that function to
synthesize
and
secrete
proteins
and
glycoproteins
into a
lumen
.
All cells have in common the equipment needed for this function, and all cells are distinctly polarized, with a typical arrangement of
cellular constituents. The necessary organelles are the
RER
,
Golgi complex
, and
secretory vesicles
(often called
secretory granules
).
The
RER
functions to synthesize polypeptides, sequester them, and initiate posttranslational modiF
cations such as glycosylation. The
polypeptides are then shunted by small transport vesicles to the
Golgi
complex
for further modiF
cation and packaging into
secretory
vesicles
, which convey the products to the part of the cell’s plasmalemma that borders a lumen or free surface. The nucleus of an
exocrine protein–secreting cell
can vary in shape and position, but it will typically have
nucleoli
evident and a substantial proportion
of its
chromatin
in the
euchromatin
(transcription-capable) form.
Figure 2-9B.
Light microscopic appearance of an exocrine protein–
secreting cell.
H&E,
3
750
Light microscopic views of
exocrine secretory cells
in sections are consistent
with the structures that can be discerned in electron micrographs. The
nucleus
usually exhibits
nucleoli
and a considerable amount of
euchromatin
. The
cyto-
plasm
at the basal end of the cell is
basophilic
owing to the concentration of
RER
at this location. The position of the
Golgi apparatus
may be evident as a
pale, unstained area of cytoplasm at the apical-facing edge of the nucleus. The
sizes and staining characteristics of the
secretory granules
vary according to
the type of cell and secretory product. In this example, the secretory granules
are
acidophilic
(
eosinophilic
).
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