General Characteristics of Leukocytes
Types of White Blood Cells. Six types of white blood cells are normally present inthe blood. They are polymorphonuclear neutrophils, polymorphonucleareosinophils, polymorphonuclear basophils, monocytes, lymphocytes, and, occa-sionally, plasma cells. In addition, there are large numbers of platelets, which are fragments of another type of cell similar to the white blood cells found in the bone marrow, the megakaryocyte. The first three types of cells, the polymor-phonuclear cells, all have a granular appearance, as shown in cell numbers 7, 10, and 12 in Figure 33–1, for which reason they are called granulocytes, or, in clinical terminology, “polys,” because of the multiple nuclei.
The granulocytes and monocytes protect the body against invading organisms mainly by ingesting them—that is, by phagocytosis.The lymphocytes and plasma cells function mainly in connection with the immune system;. Finally, the function of platelets is specifically to activate the blood clotting mechanism.
Concentrations of the Different White Blood Cells in the Blood.
The adult human being has about 7000 white blood cells per microliter of blood (in comparison with 5 million red blood cells). Of the total white blood cells, the normal percentages of the different types are approximately the following:
The number of platelets, which are only cell frag-ments, in each microliter of blood is normally about 300,000.