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If enzymatic
digestion is accomplished by enzymes derived from cells other than the
dead or dying ones, the process is termed
heterolysis.
Here the
enzymes are derived from the lysosomes of cells such as neutrophil
polymorphonuclear leucocytes or mononuclear phagocytes (macrophages).
Heterolysis may
occur as a result of
endocytosis,
in the
course of which phagocytes ingest portions of dead or dying cells and
segregate them into phagocytic vacuoles
(phagosomes).
The lysosomes
of the phagocyte then fuse with the phagosomes to form secondary
lysosomes in which enzymatic digestion of all or part of the ingested
cell debris takes place.
However,
phagocytosis is not an absolute prerequisite for heterolysis and the
latter can take place as a result of the local release of lysosomal
enzymes by phagocytes.

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