Phagocytosis involves the sporadic engulfment of large extracellular particles by wrapping cytoskeletally supported pseudopodia around the particle and internalizing it into vacuoles called phagosomes. The phagosome then fuses with a lysosome, and the phagocytosed particle is digested in an oxidative burst (respiratory burst) by lysosomal enzymes. The respiratory burst produces toxic mediators of inflammation – nitric oxide, peroxides, and oxygen radicals.

In the case of complete destruction of phagocytosed matter, the hydrolyzed products are absorbed into the cytoplasm through the vacuolar wall, and the waste products are excreted from the cell. However, partial hydrolysis is a feature of phagocytosis/endocytosis performed by antigen presenting cells, which display epitope proteins – exogenous antigen or fragmented antigen from phagocytosed cells – on their surfaces.

Inflammatory response battles between phagocytes and pathogens produces pus.
Phagocytic cells include:
dendritic cells
polymorphonuclear lymphocytes (neutrophils, granulocytes)

Receptor-mediated endocytosis is a specialized form of phagocytosis that creates receptosomes. Cells invaginate proteins and other types of ligands that have attached to specific receptors on the plasma membrane.
1. First, the protein or ligand binds to a specific receptor, forming a coated pit ("coated pit endocytosis"). The coated pit is a specialized membranous region coated with clathrin, which provides stability and aids the transport process.
2. Next, the coated pit next forms a coated vesicle and, shedding its clathrin coat, joins with other coated pits to form a receptosome.

Pinocytosis is a continuous process in most cells. Pinocytosis is called "cellular drinking" and involves encysting small quantities of extracellular fluid (ESF). View animation - pinocytosis :

Circulating monocytes possess migratory, chemotactic, pinocytic, and phagocytic capabilities, and tissue macrophages trigger acquired immunity by capturing foreign (exogenous) antigens, which they ingest in cellular lysosomes and present to T lymphocytes, sensitizing the T cells to recognize the antigen.

In some instances, phagocytosis does not result in the destruction of phagocytozed bacteria – this mechanism is considered responsible for serial endosymbiosis. Endosymbiotic bacteria have been experimentally observed to undergo endosymbiotic gene transfer.

[] image_Paramecium feeding on hematococcus [] phagocytic embrace [] macrophage attacking bacterium [] sem Macrophage [] sem "walking macrophage" [] sem activated macrophage phagocytosing bacteria [] sem alveolar macrophage attacking E. coli Џ animation - phagocytosis Џ animated diagram - phagocytosis of bacterium Џ time-lapse movie - phagocytosis Џ animation - exocytosis Џ

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