Cellular autophagy. Illustration showing the stages of the mechanism by which cells remove unnecessary or dysfunctional cellular components, known as autophagy (autophagocytosis). During this process (from top), the target organelles are isolated from the rest of the cell within a double-membrane vesicle called an autophagosome. This then fuses with a lysosome (orange spheres). The contents of the lysosome then degrade the target organelles and their constituents are recycled.