CHAPTER 2
Cell Structure and Function
21
Basophilic
Basophilic
cytoplasm (RER)
cytoplasm (RER)
Basophilic
cytoplasm (RER)
Nucleus
Nucleus
Nucleus
Site of Golgi
Site of Golgi
complex (hof)
complex (hof)
Site of Golgi
complex (hof)
Nucleolus
Nucleolus
Nucleolus
B
Figure 2-8B.
Light microscopic appearance of plasma cells.
H&E,
3
1,200
The appearance of
plasma cells
in light microscopy is consistent with the
ultrastructure of these antibody-secreting cells. The nucleus has a mixture of
heterochromatin
and
euchromatin
in an arrangement that is variously described
as a “clock face” or checkerboard pattern. A large
nucleolus
or two occupy the
center of the nucleus. The
cytoplasm
is
basophilic
as a result of the ribonucleic
acid associated with the extensive RER. Depending upon the orientation of the
cell in the section, a pale area, called the
hof
, can be seen adjacent to the nucleus.
This unstained area is the location of the
Golgi complex
.
Cell Structure Correlates with Function
Plasma cells
function to synthesize and secrete
immunoglobulin
, a
glycoprotein
. Once these cells have differentiated from stimulated
B lymphocytes, they secrete the antibodies as fast as they are generated for 1 to 2 weeks before they die. The major structures
required for this process are
RER
, the
Golgi complex
, and
secretory vesicles
. The
RER
is the site of synthesis and sequestering of the
polypeptides of the antibody. Posttranslational modiF cation and packaging occur in the
Golgi complex
, and the
secretory
vesicles
convey the product to the cell surface. Because plasma cells do not store the immunoglobulin, few, if any, secretory vesicles are seen
in the cytoplasm. Rather, the cytoplasm is packed with RER, and there is a large Golgi complex (
not visible in this section
) located
adjacent to the nucleus. The nucleus has one or more well-developed
nucleoli
, but there is a considerable amount of
heterochroma-
tin
, considering that this is an active protein-secreting cell. The explanation may be that only one protein, an antibody molecule,
is secreted, and the cell is terminally differentiated, so it will never divide. The immunoglobulin is secreted into the surrounding
interstitial compartment
, from which it can enter circulation through walls of small blood or lymph vessels. Even though the cell is
not sharply polarized, the nucleus tends to occupy an eccentric position, with the Golgi complex near the center of the cell.
Figure 2-8A.
Protein-secreting cells, plasma cell.
EM,
3
17,000
Rough
endoplasmic
reticulum
Heterochromatin
Nucleolus
Euchromatin
Nuclear
envelope
Secretory
vesicle
A
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