Normally, blood glucose remains at fairly steady and predictable levels in a healthy individual at around 90 mg/dL. After a meal the level of glucose in your blood can increase quickly, to around 160 mg/dL, however this increase triggers beta cells of the pancreas to secrete insulin, a hormone that acts on the liver, telling it to remove glucose from the blood and store it as glycogen. This restores blood glucose back to steady levels of 90 mg/dL. If blood sugar drops, the pancreas responds by releasing a different hormone, called glucagon, from alpha cells that act on the liver, giving instructions to break down glycogen and liberate glucose from storage, returning it to the blood and once again restoring steady levels.
In this example of homeostatic regulation, which component is the effector?