1. Membrane-bound vesicles 0.2-0.5§­ in diameter, containing hydrolytic enzymes.
  2. Active intracellular digestion of ingested materials (phagocytosis) or normal cellular organells (autophagy)
  3. Synthesized in RER, transfered and packed in Golgi apparatus as primary lysosomes containing inactive enzymes.
  4. Secondary lysosomes, vacuolar structure engaged in current or past digestive activity, autophagic and heterophagic vacuoles, residual bodies, lipofuscin pigment.
  5. Inborn lysosomal diseases, congenital absence of one of lysosomal enzymes.