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Blood and haemopoiesis (sanguis et haemocytopoesis) 141

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7.8 Lymphopoiesis (schematic).

7.9 Scanning electron micrograph of a small lympho- 7.10 Fine structure of a small lymphocyte in the cortex
cyte (x9000). of a lymph node (x4500).

and can be divided into subgroups based on function.
Classification of lymphocytes based on size is of limited · small lymphocytes (5–10 μm), representing the larg-
use as it provides no information about the specific func- est proportion of circulating lymphocytes,
tion of the cell. · medium-sized lymphocytes (10–18 μm) or
With the light microscope, lymphocytes can be catego- · large lymphocytes (up to 25 μm), frequently con-
rised as: sidered to represent immunoblasts (activated
lymphocytes) or natural killer (NK) cells.

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