General principles of glucose homeostasis
- Glucose is derived from dietary carbohydrates, glycogenolysis (breakdown of glycogen, which is a storage form of glucose), and gluconeogenesis (formation of glucose by the liver). Insulin, glucagon, and other hormones maintain normal plasma glucose levels.
- High glucose stimulates insulin production.
- Insulin enhances glucose uptake, use, and storage.
- As a result, blood glucose returns to normal.
- Fasting lowers blood glucose and insulin. It also results in the release of counter-regulatory hormones (i.e., glucagon, epinephrine, cortisol, and growth hormone).
- These hormones limit glucose use and stimulate hepatic glucose production.
- In addition, lack of insulin causes lipolysis in adipose tissue, proteolysis in muscle, and ketosis in the liver. Ketones are an alternative energy source and its formation is glucagon dependent
