Regulation of Blood Sugar - this a negative feedback loop controlled by two antagonistic hormones.
Insulin converts glucose into glycogen and lowers blood sugar; Glucagon converts stored glycogen into glucose causing an increase in blood sugar.
Regulation of blood sugar follows a number of steps:
Step 1: Low levels of blood sugar stimulate the secretion of glucagon.
Step 2: Increased glucagon causes stored glycogen in the liver to be converted into glucose for release into the blood stream.
Step 3: As blood sugar levels rise the glucagon stops but high blood sugar levels result in the release of insulin.
Step 4: Increased insulin levels cause the intake of glucose into muscle cells and convert excess glucose into glycogen for storage in the liver.
Step 5: When blood sugar levels drop the cycle starts again.
To learn more, see Boundless.com's Hormonal Regulation of Metabolism.