Phagocytosis is the
cellular process of engulfing solid particles by the
cell membrane to form an internal
phagosome, or "food vacuole." The phagosome is usually delivered to the
lysosome, an
organelle involved in the breakdown of cellular components, which fuses with the phagosome. The contents are subsequently degraded and either released extracellularly via
exocytosis, or released intracellularly to undergo further processing.
Phagocytosis is involved in the acquisition of nutrients for some cells, and in the immune system it is a major mechanism used to remove pathogens and cell debris. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytosed.
Phagocytosis is a specific form of endocytosis involving the vesicular internalization of solid particles, such as bacteria, and is therefore distinct from other forms of endocytosis such as pinocytosis, the vesicular internalization of various liquids.
Phagocytosis is named from Greek roots phago - to eat, kytos - cell, and -osis - a suffix indicating a process; thus it can be translated literally as "the cellular process of eating." It should be noted that the process is only homologous to eating at the level of single-celled organisms; in multicellular animals the process has been adapted to eliminate debris and pathogens, as opposed to taking in fuel for cellular processes, except in the case of the Trichoplax.
