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A neutrophil granulocyte is one of the types of granulocyte white blood cells in the human body that specifically acts like armor against bacteria. It was named after its ability to quickly absorb the color of a neutral dye upon staining. Neutrophil granulocytes constitute from 65% to 70% of the total white blood cell count, making them by far the most numerous white blood cells. Like basophils and eosinophils, co-members of neutrophils in the granulocyte group, neutrophils have a divided nucleus, causing it to appear numerous. This is why they are also called polymorphonuclear neutrophils, while the entire granulocyte group is also called polymorphonuclear cell family.
Together with another type of white blood cell called monocytes, granulocytes are also classified as phagocytes, or cells that kill bacteria through phagocytosis. In phagocytosis, materials are absorbed by cells. The term granulocyte is derived from the fact that this white blood cell has many granules in its cytoplasm. Like the other granulocytes, a neutrophil granulocyte has an irregularly shaped nucleus. It is in the bone marrow where neutrophil granulocytes are increased in number.
Bacteria release toxins as soon as they gain access to the body, causing tissue damage and the expansion of blood vessels that are located close to the affected area. As blood flows, neutrophils immediately rush into the area, pass through the blood vessels to attack and consume the bacteria, and ingest pieces of infected cells. During the entire struggle against bacteria, however, a great number of neutrophil granulocytes are destroyed due to the toxins released by the bacteria. Their destruction causes them to release digestive enzymes that can fragment infected cells.
After a time, swelling of the infected area occurs as pus forms. Pus is a thick, semiliquid mixture of blood, dead cells and fragments, tissue fluids, and dead and surviving bacteria. As more and more neutrophils rush into the area to eliminate the bacteria, neutrophil granulocyte formation becomes accelerated, resulting in the condition called neutrophilia, or the increase in the number of neutrophils. This eventually causes the white blood cells to increase in number, resulting in a condition called leukocytosis, which indicates that there is an infection.
Neutrophilia, however, results from other factors such as the use of corticosteroids, or drugs that can counter inflammation. Both large and small blood vessels are allocated with neutrophils. Neutrophils in large blood vessels comprise the circulating neutrophil pool, while those in small blood vessels make up the marginating neutrophil pool. Corticosteroids could trigger neutrophils to transfer from small to large blood vessels. They could also boost the bone marrow to release more neutrophils, thereby causing an increase in the neutrophil granulocyte count.