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Definition

noun

The process of engulfing and ingestion of particles by the cell or a phagocyte (e.g. macrophage) to form a phagosome (or food vacuole), which in turn fuse with lysosome and become phagolysosome where the engulfed material is eventually digested or degraded and either released extracellularly via exocytosis, or released intracellularly to undergo further processing.

Supplement

Phagocytosis is the mechanism used by many protists (e.g. amoeba) to acquire nutrients. In humans and other multicellular animals, phagocytosis is an important defense mechanism against infection by microorganisms (e.g. bacteria) and the process of removing cell debris (e.g. dead tissue cells) and other foreign bodies.

Steps of a macrophage ingesting a pathogen:
a. Ingestion through phagocytosis, a phagosome is formed
b. The fusion of lysosomes with the phagosome creates a phagolysosome; the pathogen is broken down by enzymes
c. Waste material is expelled or assimilated.

Word origin: phago: G, comb. form akin to phageǐn to eat, devour + cyte: G. kutos, hollow vessel + -osis: expressing state or condition.
Related forms: phagocyte (noun), phagocytic (adjective) – as in “a phagocytotic cell”, phagocytose (verb) -- as in “to phagocytose particles”.

Compare: pinocytosis.
See also: endocytosis, plasma membrane.