Schematic diagram of current understanding of extrinsic and intrinsic apoptosis pathways. The prototypical receptor of the extrinsic pathway is FAS. It recruits the adaptor FADD and the procaspases 8 and 10 on ligation. The caspases are then cleaved to further activate other downstream caspases, leading to cell death. The intrinsic pathway is controlled by proteins of the BCL2 family and triggered by stimuli, such as DNA damage and growth factor withdrawal. These stimuli ultimately lead to activation of caspase 9 and downstream effecter caspases. There is a crosstalk between the 2 pathways in some cell types.