182
UNIT 3
Organ Systems
Figure 10-1A.
Lymphocytes.
H&E,
3
702; inset,
3
2,176
Lymphocytes
can be found in blood and lymph
circulation
as well as in lymphoid organs. There are many types and
subtypes of lymphocytes, which can be classiF
ed into three
major types based on their immunologic functions:
B lym-
phocytes
(
B cells
)
,
T lymphocytes
(
T cells
)
,
and
null cells
.
Their sizes vary they are morphologically similar to each
other. B and T cells cannot be distinguished from each
other in routine H&E stain. Shown here is an example
of lymphocytes in a blood smear. Lymphocytes have rela-
tively large and round nuclei, and they have a small rim of
cytoplasm surrounding the nucleus. The two
insets
in the
same magniF
cation show the size variation of the lympho-
cytes. A
monocyte
is also seen in this specimen. Monocytes
differentiate into tissue macrophages or special forms of
macrophages
, such as Kupffer cells in the liver, microglia in
the nervous tissue, and osteoclasts in the bone tissue.
Lymphocyte
Larger lymphocyte
Smaller lymphocyte
Monocyte
A
Endothelium
Smooth
muscle
Lumen of the
Lumen of the
central arteriole
central arteriole
Lumen of the
central arteriole
Lymphocytes
Lymphocytes
of PALS
of PALS
Lymphocytes
of PALS
B
Figure 10-1B.
Lymphocytes in spleen.
TEM,
3
8,800.
The
lymphocytes
in the left part of this F
eld are part of the
PALS
that surrounds a
central arteriole
. Part of the wall of the arteriole
occupies the central part of the F
eld, and part of its
lumen
is seen to the right. The lymphocytes here appear to be inactive, judging
from the scant amount of cytoplasm and the small nuclei containing little
euchromatin
. However, one of the lymphocytes does dis-
play a small nucleolus, suggesting at least a basal level of protein synthesis. Although T and B lymphocytes are not distinguishable
morphologically, the location of these lymphocytes in the PALS indicates that they are T lymphocytes.
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