Programmed cell death. Animation of programmed cell death, or apoptosis, in three cells. Apoptosis occurs when a cell becomes old or damaged. The cell becomes spherical as its cytoskeleton is digested, and blebs (vesicles) form on its surface. Eventually the cell breaks into several vesicles, now known as apoptotic bodies, and is phagocytosed (engulfed and digested) by specialist cells. The breakdown into vesicles prevents the leakage of potentially toxic or immunogenic substances from the cell.