Senescence - N. - Deterioration of health with age (put in contrast to "aging", which is very broad and just means continuing to live as time goes on).

Intrinsic - Adj. - Describes the cause of something being within it somehow.

Extrinsic - Adj. - Describes the cause of something being outside of it somehow.

Let's say we have two people, Anthony and Bella. Anthony has tragically inherited cancer from a recessive gene that got picked up somewhere along the way in his family's history. Bella has thankfully been born completely healthy with no issues to be addressed. While Anthony's cancer may not develop enough to kill him, it contributes to him having higher senescence, so it is more likely for his health to get worse as he gets older. Still, Anthony does end up dying from the cancer, making his cause of death intrinsic, since the cancer was in his genetics. Bella ends up also dying, but instead by severe head trauma in a rock-climbing accident, making her cause of death extrinsic, since the head trauma was caused by something outside of her body.