Abstract: Objective Autophagy is a process by which cells phogocytize intracellular cytoplasm or organelles when cells are stimulated and cargoes are eventually degraded in lysosomes. According to the ways in which cargoes are transported into lysosomes, types of autophagy are divided into macroautophagy, microautophagy and chaperone-mediated autophagy. In macroautophagy, the autophagosome precursor wraps cytoplasm or organelles to form an autophagosome. Then the autophagosome fuses with the lysosome forming the autophagolysosome. The cargoes are degraded in lysosome. In microautophagy, the lysosome engulfs cytoplasm, organelles or nucleus directly through invagination of the lysosomal membrane and formation of the autophagosome. Finally, the contents of the autophagosome are digested by lysosomal enzymes. In chaperonemediated autophagy, cytosolic proteins are translocated into the lysosome by lysosomal membrane receptor. Autophgy is evolutionarily conserved from yeasts to mammalian cells and plays important roles in tolerating starvation and ischemia, cleaning the senescent organelles, eliminating bacteria and foreign matters, maintaining cellular activities and extending longevity. Autophagic activities are regulated by autophagic genes. Deletion or dysfunction of autophagic genes may result in some diseases. Elucidating the processes of autophagy, autophagic structures and their functions is helpful for exploring mechanisms of roles of autophagy in physiological and pathological processes. This review focuses on morphological characteristics of the autophagic structures and functional implications of these structures.

Key words: Autophagy, Macroautophagy, Microautophagy, Chaperonemediated autophagy, Lysosome