Chapter 2: Leukocytes
Leukocytes in the peripheral blood comprise granulocytes (neutrophils, eosinophils, and basophils), lymphocytes, and monocytes. Plasma cells and mast cells reside in tissues, but may be encountered in the peripheral blood under certain circumstances. In health, the production of leukocytes in the bone marrow and corresponding numbers in the peripheral blood are relatively constant. However, this situation can change both quickly and dramatically as required. Leukocyte status is assessed most commonly on the leukogram, that portion of the CBC that provides total WBC count; differential counts for each leukocyte type; reporting of any morphologic changes/abnormalities involving any leukocyte type; and noting any cells that cannot be identified with certainty or are not normal constituents of peripheral blood.
Mobile leukocyte with the ability to phagocytose, degrade, and/or kill microorganisms (neutrophil, eosinophil, basophil).
Granulocyte with large, round, pink to orange (eosinophilic) cytoplasmic granules and an often bi-lobed nucleus; important in host response to allergens and defense against parasites.
Granulocyte with variably-sized, dark purple (basophilic) cytoplasmic granules and an irregularly lobulated nucleus; important in hypersensitivity reactions.
Mononuclear, non-phagocytic leukocyte responsible for humoral (B lymphocyte) and cell-mediated (T lymphocyte) immune responses.
Mononuclear phagocytic leukocyte that develops into macrophages in tissue.
Terminally differentiated B lymphocyte that secretes specific antibody.
Mononuclear, granular leukocyte important in hypersensitivity reactions.
Organ responsible for production of hemopoietic cells; found in the medullary cavity, especially the ends of long bones (e.g. femur) and flat bones (e.g. the pelvis, sternum.)
All tests on the CBC that evaluate leukocytes. Also, that part of the leukon which is evaluated by examination of a peripheral blood sample (typically does not include leukocyte precursors).
