In most higher animal cells, phagocytosis is a protective measure, not a means of eating. Higher animals have some specialized phagocytes, including macrophages and neutrophils. They ingest and destroy infected bacteria, viruses, damaged cells and aging red blood cells through phagocytosis.
Phagocytosis is one of the oldest and most basic defense mechanisms of living things. There is no specificity for the destroyed object, which is called nonspecific immunity in immunology. Neutrophils and monocytes have strong phagocytic ability, eosinophils have strong migratory ability, but their phagocytic ability is weak. White blood cells can seep out of blood vessels through the endothelial space of capillaries and swim in the tissue space.
The phagocytosis of infected virus, bacteria or other particles by cells is called heterogeneous phagocytosis. The phagocytosis of lysosomes means that foreign harmful substances are swallowed into cells, that is, phagocytes wrapped in membranes are formed, and primary lysosomes quickly fuse with phagocytes to form secondary lysosomes. At this time, the substrate in lysosome is taken from outside the cell, so it is a heterophilic lysosome.
In heterophilic lysosomes, phagocytes are hydrolyzed by enzymes; After hydrolysis, those soluble small molecules can enter the cytosol through lysosomal membrane and be reused by cells or discharged as waste. Therefore, the phagocytosis of lysosomes can protect cells from infection by bacteria and viruses, which is necessary for cell defense function.
Multicellular animals have specialized phagocytes, namely macrophages and neutrophils, which play a protective and defensive role in the body.