Problem:

I am reading about atrophy and I am thinking to which processes the phrase cells eating themselves refer to.

Cells need something to survive these difficult times. To decrease protein synthesis to survive. If insufficient, cells start to eat themselves. Then, ubiquitine-proteosome pathway and autophagy pathway.

I am not sure if it is only apoptosis. It can refer here to longer cascade. I think it can at least refer to autophagy where one cell degrades its components.

Required:

Question: Which processes does the phrase cells eating themselves include?

Does anybody know any source of this kind?