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see endocytosisendocytosis
, in biology, process by which substances are taken into the cell. When the cell membrane comes into contact with a suitable food, a portion of the cell cytoplasm surges forward to meet and surround the material and a depression forms within the cell wall.
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A mechanism by which single cells of the animal kingdom, such as smaller protozoa, engulf and carry particles into the cytoplasm. It differs from endocytosis primarily in the size of the particle rather than in the mechanism; as particles approach the dimensions and solubility of macromolecules, cells take them up by the process of endocytosis.

Cells such as the free-living amebas or the wandering cells of the metazoa often can “sense” the direction of a potential food source and move toward it (chemotaxis). If, when the cell contacts the particle, the particle has the appropriate chemical composition, or surface charge, it adheres to the cell. The cell responds by forming a hollow, conelike cytoplasmic process around the particle, eventually surrounding it completely. Although the particle is internalized by this sequence of events, it is still enclosed in a portion of the cell's surface membrane and thus isolated from the cell's cytoplasm. The combined particle and membrane package is referred to as a food or phagocytic vacuole. See Vacuole

Ameboid cells of the metazoa also selectively remove foreign particles, bacteria, and other pathogens by phagocytosis. After the foreign particle or microorganism is trapped in a vacuole inside the macrophage, it is usually digested. To accomplish this, small packets (lysosomes) of lytic proenzymes are introduced into the phagocytic vacuole, where the enzymes are then dissolved and activated. See Lysosome



the engulfing and absorption of living and nonliving particles by unicellular organisms or specialized cells—phagocytes—in multicellular animals. Phagocytosis was discovered by E. Metchnikoff (I. I. Mechnikov), who traced its evolution and elucidated its function in the defense reactions of the higher animals and man, particularly those related to inflammation and immunity. The process plays a major role in the healing of wounds.

The ability to seize and digest particles, which is the basis of nutrition in primitive organisms, was gradually transferred in the course of evolution to certain specialized cells—initially to the digestive cells and later to some special cells in the connective tissues. In mammals and in man, the neutrophils (that is, micro-phages, or specialized leukocytes) and the reticuloendothelial cells are active phagocytes capable of being transformed into active macrophages. The neutrophils phagocytize small particles, such as bacteria, while macrophages can ingest such larger particles as dead cells and their nuclei and fragments. Marcrophages can also store the negatively charged particles of pigments and of colloidal substances. The ingestion of small colloidal particles is called ultraphagocytosis.

Phagocytosis—a process that requires the expenditure of energy—involves primarily the activity of the cell membrane and intracellular organoids, or lysosomes, which have a high content of hydrolytic enzymes. Phagocytosis proceeds in stages. After a phagocytable particle has attached itself to the cell membrane, an intracellular corpuscle, or phagosome, is formed by invagination of the membrane and the particle. Hydrolytic enzymes enter the phagosome from the surrounding lysosomes and digest the phagocytized particle. Depending on the particle’s physiochemi-cal properties, digestion may be complete or incomplete. In the latter case, a residual corpuscle is formed and may remain in the cell a long time.


Mechnikov, I. I. Izbrannye biologicheskie proizvedeniia. Moscow, 1950.
Zil’ber, L. A. Osnovy immunologii, 3rd ed. Moscow, 1958.



(cell and molecular biology)
A specialized form of macropinocytosis in which cells engulf large solid objects such as bacteria and deliver the internalized objects to special digesting vacuoles; exists in certain cell types, such as macrophages and neutrophils.
References in periodicals archive ?
The predominant fraction of phagocytized NPs at any long-term retention time point suggests that this reentrainment of the particles at the epithelial surface may be macrophage mediated; at least the very small fractions of free NPs in the BAL samples are suggesting this mechanism.
In contrast to SWCNTs, a similar dose of UfCB agglomerated particles, which are readily phagocytized by alveolar macrophages, did not produce lung fibrosis or granulomas (Shvedova et al.
Macrophages and blood monocytes did not exhibit detectable levels of EBOV GP by immunohistochemistry, except in rare cases in which macrophages contained antigen-positive granular material consistent with phagocytized cellular debris.
Dark field microscopy revealed large alveolar macrophages with phagocytized Ti[O.
1-4] Mineral dusts on the surface of the bronchial mucosa can be phagocytized by macrophages, which either are expelled by the mucociliary escalator or migrate through the epithelial barrier into the bronchial mucosa.
marinus cells are readily recognized and phagocytized by the hemocytes of the oyster; however, the hemocytes have little or no ability to destroy the ingested parasites, and may actually be instrumental in spreading the disease throughout the oyster (Perkins, 1976).
Helminthic parasites are too large to be phagocytized.
virginica granulocytes phagocytized significantly more parasites and fluorescent latex beads than C.
This process of phagocytosis of deposited particles takes place within a few hours, so by 6-12 hr after deposition essentially all of the particles are phagocytized by alveolar macrophages, to be cleared subsequently by the slow alveolar clearance mentioned above.
Alternatively, senescent hemocytes could be undergoing apoptosis during their transit in the connective tissue where apoptotic bodies are more easily phagocytized than in circulation.