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Lymphocytes are a heterogeneous group of cells that have different origins, lifespans, and functions. They vary markedly in size. Some have a diameter of approximately 7µ, while others are as large as 18µ. The variations in size are mainly due to different amounts of cytoplasm. Therefore, the N:C ratio may range from 5:1 in some lymphocytes to 1:2 in others. The nucleus is about the size of a normal RBC. It is usually round or oval in shape, but may be slightly indented. The chromatin is very dense and clumped.

Small lymphocytes have only a thin rim of clear, homogenous, moderate blue cytoplasm around the nucleus.
Lymphocytes do not contain specific granules. They can occasionally contain cytoplasmic azurophilic granules, also known as non-specific or primary granules.