In lysosomal digestion, residual bodies are vesicles containing indigestible materials.[1] Residual bodies are either secreted by the cell via exocytosis (this generally only occurs in macrophages), or they become lipofuscin granules that remain in the cytosol indefinitely. Longer-living cells like neurons and muscle cells usually have a higher concentration of lipofuscin than other more rapidly proliferating cells.
Book: Karp , Gerald . Cell and Molecular Biology: Concepts and Experiments . John Wiley & Sons . 2005 . Hoboken, NJ . 311–313 . 0-471-46580-1 .