Defining set points isn't easy. The general observation is that cybernetic principles provide a useful model for various body processes.

Blood pressure get's for example regulated in a complex way but we have no real way to read the set point for it from the body or change the set point. It simply stored somewhere in the brain.

If you are looking at any body parameter where it's important that it stays within a certain range it's a good guess that the body uses cybernetic principles to regulate it.