What are the types of apoptotic signaling pathways?

There are two major apoptotic signaling pathways for inducing cell death: extrinsic signaling and intrinsic signaling pathways. The extrinsic signaling pathway involves death receptors that lead to the creation of the death-inducing signaling complex (DISC). Intrinsic signaling mainly occurs through mitochondria which leads to the creation of the apoptosome. The formation of the apoptosome or DISC activates initiator and common effector caspases that carry out the process of apoptosis. The extrinsic pathway starts outside a cell, when circumstances in the environment determine that a cell must die.  In contrast, intrinsic pathways begin when an injury happens within the cell. For example, stresses like DNA damage, hypoxia, and oncogenes can activate intrinsic apoptotic pathways. p53 detects cellular stress and is a crucial activator of the intrinsic pathway.