Science Fair Project Encyclopedia
A phagocyte is a cell that ingests (and destroys) foreign matter, such as microorganisms or debris via a process known as phagocytosis, in which these cells ingest and kill offending cells by cellular digestion. These phagocytes are extremely useful as an initial immune system response to tissue damage.
The two types of phagocytes, polymorphonuclear leukocytes and macrophages, each have an important role in the immune system. While polymorphonuclear leukocytes typically respond swiftly and efficiently to invading pathogens; they are mainly adapted for short term response. Macrophages, on the other hand, are initially slow to react, but are capable of engulfing and digesting almost any foreign agent, and last for a longer period of time.
The polymorphonuclear leukocytes, also known as granulocytes, include neutrophils, eosinophils and basophils. Neutrophils are the most abundant kind of phagocytes. They reduce bacterial cells to their constituent amino acids by ingesting, killing, and digesting them. Eosinophils secrete special enzymes intended to create holes in parasitic worms. Finally, basophils secrete substances such as histamine, in order to extend the period of inflammation.
Macrophages adapted specially for sustained battles against foreign agents. In addition, they help to clean up and remove damaged tissues. Immature macrophages which are circulating in the bloodstream are called monocytes. These macrophages cannot react immediately, but once they have developed, they are often referred to as 'killing machines' they act by phagocytizing and destroying anything that isn't recognized as belonging to the body.
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