These are all types of white blood cells (WBC). The normal number of WBCs in the blood is 4,500-10,000 white blood cells per microliter.
There are five types of WBCs:
Neutrophils which make up 50 to 70 % of all circulating WBCs. Their cytoplasm is packed with pale granules containing lysosomal enzymes and bacteria-killing compounds.
Neutrophils are very active and are generally the first to attack bacteria at the site of an injury. The breakdown of used neutrophils in an infected wound forms pus.
Eosinophils which make up about 2-4 percent of circulating WBCs. Their main mode of attack is to excrete toxic compounds
which are effective against parasites that are too large to engulf.
Eosinophils are also sensitive to allergens and increase during allergic reactions.
Basophils are small and make up less than 1% of circulating WBCs. They accumulate in damaged tissue and release histamine, which dilates blood vessels, and heparin, which prevents blood clotting.
Monocytes are large, spherical cells that make up 2 to 8% of circulating WBCs. Monocytes can enter peripheral tissues to become tissue macrophages which can engulf large particles and pathogens.
Lymphocytes , slightly larger than RBCs, make up 20 to 30% of circulating WBCs. They migrate in and out of the blood.
There are 3 functional classes of lymphocytes:
1. T cells (cell-mediated immunity) attack foreign cells directly.
2. B cells (humoral immunity) differentiate into plasma cells which synthesize antibodies
3. Natural killer (NK) cells detect and destroy abnormal tissue cells such as cancers.
All of these cells have a very complex role in the body’s defenses.
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