noun, plural: polymorphonuclear leukocytes
A type of leukocyte characterized by having nuclei with three or more lobes joined by filamentous connections and perceptible granules in the cytoplasm under a light microscope
Leukocytes (also called white blood cells) are cells of the immune system and one of the cellular elements in blood. Unlike red blood cells, leukocytes lack the hemoglobin pigment (thus, “white”). Similar to red blood cells though, leukocytes also came from a hematopoietic stem cell (hemocytoblast). The hemocytoblast gives rise to progenitor cells of both the myeloid series and the lymphoid series. Leukocytes from the myeloid series include the granulocytes and monocytes whereas those from the lymphoid series include the lymphocytes and lymphoid dendritic cells.
The granulocytes are leukocytes characterized by the observable presence of abundant granules in their cytoplasm under a light microscope. They include the polymorphonuclear leukocytes and the mast cells. The polymorphonuclear leukocytes are characterized by having nuclei with three or more lobes joined by filamentous connections and cytoplasm rich in granules.
In humans, the polymorphonuclear leucocytes are subdivided into eosinophils, basophils and neutrophils (according to the staining properties of the granules using a Romanovsky type stain).
Polymorphonuclear leukocytes are derived from the granulocytic lineage. In the granulocytic series of hematopoiesis, the developmental stages are as follows: hemocytoblast → common myeloid progenitor (or CFU-GEMM) → CFU-GM → CFU-G → myeloblast → promyelocyte → myelocyte → metamyelocyte → band cell → granulocyte, particularly polymorphonuclear leukocytes. Hematopoiesis producing granulocytes, particularly polymophonuclear leukocytes, is referred to as granulopoiesis.
Sometimes, the terms granulocytes and polymorphonuclear lymphocytes are used interchangeably. However, granulocytes are a more-encompassing term for including the mast cells.