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1. Digestion:
Acid hydrolases of lysosomes can digest all types of macromolecules such as polysaccharides, proteins, nucleic acids.
2. Extracellular digestion:
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Some cells release lysosomal enzymes to the outside through exocytosis for digestion of extracellular materials, e.g., saprophytic fungi derive their nutrition by extracellular digestion. The osteoclasts of bone perform extracellular digestion of bone matrix during remodeling of bones.
3. Intracellular digestion:
Lysosomes take part in intracellular digestion through heterophagy & autophagy. Heterophagy is a regular feature of food digestion in protozoans, sponges & coelenterates. Autophagy or autolysis helps in degeneration of tadpole tail during metamorphosis, regression of uterus after delivery, regression of mammary glands after weaning etc. Both heterophagy & autophagy may occur simultaneously within the same lysosome called ambilysosome.
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4. Sperm penetration:
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Sperm acrosome is considered as a giant lysosome which release sperm lysins to dissolve the egg barriers during fertilization.
5. Thyroxin formation:
In thyroid, thyroglobulin is hydrolyzed by lysosomal enzymes to form thyroxin.
6. Starvation management:
During starvation, lysosomes provide nourishment by rapidly hydrolyzing the organic foods that stored in the cells. Extra nourishment may also be obtained by digesting some cellular organelles and cells.
7. Renewal of cells & organelles:
Lysosomes cause breakdown of ageing and worn out dead cells to make their component molecules available for the formation of new cells and organelles.
8. Initiation of mitosis:
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Lysosomes play important role in the initiation of mitotic cell division by overcoming agents that cause repression of mitosis.
9. Storage diseases:
These are the genetic diseases caused by accumulation of undigested materials due to deficiencies in single lysosomal enzymes. About 30 types of lysosomal storage diseases are known in human, e.g. Gaucher’s disease, Tay-Sach’s disease, Hunter’s syndrome etc.
10. Lung fibrosis:
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Inhalation of silica, asbestos, cotton fibers etc. attracts macrophages which release lysosomal enzymes to destroy the same. This promotes inflammation and fibrosis of lungs.
