Expand|article|date=July 2007 (the latter not pictured)Parts:
4. Waste material
Phagocytosis is the cellular process of engulfing solid particles by the
cell membraneto form an internal phagosome, or "food vacuole." The phagosome is usually delivered to the lysosome, an organelleinvolved 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 systemit 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
endocytosisinvolving 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 "-oasis" - 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
Process [The Immune System, Peter Parham, Garland Science, 2nd edition]
Phagocytosis is activated by attachment to Pathogen-associated molecular patterns (PAMPS), which leads to
NF-κBactivation. Opsonins such as C3band antibodies can act as attachment sites and aid phagocytosis of pathogens.
Engulfment of material is facilitated by the actin-myosin contractile system. The phagosome of ingested material is then fused with the lysosome, leading to degradation
Degradation can be oxygen-dependent or oxygen-independent. Oxygen-dependent degradation depends on NADPH and the production of
reactive oxygen species. Hydrogen peroxide and myeloperoxidase activate a halogenating system which leads to the destruction of bacteria. Oxygen-independent degradation depends on the release of granules, containing proteolytic enzymes such as defensins, lysozyme and cationic proteins. Other antimicrobial peptides are present in these granules, including lactoferrin which sequesters iron to provide unfavourable growth conditions for bacteria.
protists are able to phagocytose particles; however, in animals phagocytosis is performed by specialized cells called phagocytes, which are able to remove foreign bodies and thus fight infection. In humans and many other animals, phagocytes include macrophages, monocytes, dendritic cells, and granulocytesPrescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3] . The term "professional phagocytes" can be used to describe both macrophages and neutrophils, as these cells are considered to have phagocytosis as their primary function [GeorgiaImmunology|1/phagocyt] .
A great body of evidence continues to mount showing that neighbouring cells in a tissue will phagocytize their apoptotic neighbours, thus maintaining tissue homeostasis.Clarifyme|date=March 2008 This clearance can, depending on the location, facilitate greater clearance than that achieved by resident macrophages.Fact|date=May 2007
In humans, the most important facet of phagocytosis is its control of inflammation. Its most important function is the transport of cells into the blood. Depending on the phagocytosed particle, phagocytosis can induce inflammation or, as is the case with apoptotic cells,Clarifyme|date=March 2008 induce resolution of inflammation. Phagocytosis is also involved in immune tolerance, which prevents inflammation against normal components of the bodyFact|date=May 2007.
For the activation of the adaptive immune response, phagocytosis is a necessary activation step. A
T helper cellmust be presented with foreign particles bound to the major histocomptability complex class II (MHC II) receptor to become activated.
protists, phagocytosis is used as a means of feeding, providing part or all of their nourishment. This is called phagotrophic nutrition, as distinguished from osmotrophic nutrition, which takes place by absorption. In some, such as amoeba, phagocytosis takes place by surrounding the target object with pseudopods, as in animal phagocytes. In other protozoa, for instance, ciliates, there is a specialized groove or chamber in the cell where phagocytosis takes place, called the cytostomeor mouth. The resulting phagosomemay be merged with lysosomes containing digestive enzymes, forming a phagolysosome. The food particles will then be digested, and the released nutrients are diffused or transported into the cytosolfor use in other metabolic processes.
Resistance to phagocytosis
A substance or process which impedes or prevents the action of phagocytes is termed antiphagocytic (for example,
Yersinia pestis, the bacteriumcausing the plague). Additionally, some bacteria may need to be opsonizedbefore they are recognised as particles to be phagocytosedFact|date=May 2007.
Certain intracellular pathogens, such the bacterial agents of
leprosyand tuberculosis, are resistant to lysosomal degradation once internalised via phagocytosis.
conidia" over an imaging time of 2 h with one frame every 30 s interferon-γone night before filming with conidia. The observation was made over a period of 2.5 h every 30 s
Antigen presenting cell
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Look at other dictionaries:
phagocytosis — phagocytosis. См. фагоцитоз. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
phagocytosis — [fag΄ə sī tō′sis] n. [ModL: see PHAGOCYTE & OSIS] the ingestion and destruction by phagocytes of cells, microorganisms, foreign particles, etc.: see ENDOCYTOSIS phagocytotic [fag΄ō sītät′ik] adj … English World dictionary
phagocytosis — /fag euh suy toh sis/, n. Physiol. the ingestion of a smaller cell or cell fragment, a microorganism, or foreign particles by means of the local infolding of a cell s membrane and the protrusion of its cytoplasm around the fold until the material … Universalium
phagocytosis — The process of ingestion and digestion by cells of solid substances, e.g., other cells, bacteria, bits of necrosed tissue, foreign particles. SEE ALSO: endocytosis. [phagocyte + G. osis, condition] induced p. p. occurring when bacteria are… … Medical dictionary
phagocytosis — noun (plural phagocytoses) Etymology: New Latin Date: 1889 the engulfing and usually the destruction of particulate matter by phagocytes • phagocytotic adjective … New Collegiate Dictionary
phagocytosis — n. [Gr. phagein, to eat; kytos, container] The ingestion of solid particles by a cell; phagocytic adj … Dictionary of invertebrate zoology
phagocytosis — (fag o si to sis) The endocytotic process in which a cell encloses large particles in a membrane delimited phagocytic vacuole or phagosome and engulfs them … Dictionary of microbiology
phagocytosis — Uptake of particulate material by a cell (endocytosis). See opsonization, phagocyte … Dictionary of molecular biology
phagocytosis — noun The process where a cell incorporates a particle by extending pseudopodia and drawing the particle into a vacuole of its cytoplasm … Wiktionary
phagocytosis — fÃ¦gÉ™saÉª tÉ™ÊŠsÉªs n. destruction by white cells, destruction by phagocytes … English contemporary dictionary