Polymorphism

The lysosomes show polymorphism in different cell types, and even within a single cell. A mentioned previously, there are two basic types of lysosomes, the primary lysosomes and the secondary lysosomes. The latter are of three types, phaogsomes, residual bodies and autophagic vacuoles.

(1) The primary lysosome (storage granule) is formed either directly from the endoplasmic reticulum, or indirectly from the Golgi complex, by a process similar to budding. The enzymes of the primary lysosome are synthesized by the ribosomes. The primary lysosomes contain a definite enzyme type. It can secrete its enzymes outside the cell or store them.

(2) The phagosome is formed by phagocytosis or pinocytosis of foreign material. The phagosome associates with a primary lysosome and undergoes fusion to form the secondary lysosome. It shows a positive phosphates reaction.

(3) The residual body is the final particle containing indigestible material. It is formed when digestion is incomplete. In Amoeba and some other Protozoa the residual bodies are removed by defecation. The residual body may persist in the cell for a long period and may be important in the aging of the cell.

 (4) The autophagic vacuole or autophagosome is a lysosome containing some part of the cell in the process of digestion. Various cell organelles like mitochondria, endoplasmic reticulum, etc, may be found in the autophagic vacuoles. The autophagic voculaes are devices for achieving breakdown of parts of the cell without damages to the cell as a whole. These bodies, containing remnants of mitochondra, can be found in the liver cell during starvation.