Phagocytosis is the process by which a cell engulfs solid material. The molecule is then internalized in a vesicle of plasma membrane (phagosome) which fuses with a lysosome for destruction, any undigested remains of the molecule (eg. bacterium) are removed by exocytosis and the products of digestion are absorbed into the cytoplasm. It occurs in the immune system, and is carried out by phagocytes such as macrophages which are involved in the innate immune response .
The process of phagocytosis involves the macrophage beginning to encase the pathogen or substance via endocytosis. Once the macrophage has engulfed the substance, a phagosome is formed containning the substance. The substance is then broken down by the fusion of the phagocytic vesicle (phagosome) and the lysosome vesicles which contain oxidase and proteases, this process is called phagolysosome. 
- ↑ http://www.ncbi.nlm.nih.gov/pubmed/10358769
- ↑ Jeff Hardin, Gregory Bertoni, Lewis J. Kleinsmith (2012) Becker's World of the Cell, Eighth Edition
- ↑ http://courses.washington.edu/conj/bloodcells/phagocytosis.htm