Glucose fuels your cellular powerhouses, providing the energy needed for your mental and physical functions. Your liver performs several critical roles in glucose metabolism, including sugar storage, release and production. Your liver's roles in glucose metabolism help ensure that your blood sugar level stays within a narrow normal range, regardless of when you last ate.
Storage
When you eat food containing glucose, it is absorbed from your intestines into your bloodstream. As your blood sugar level increases, your liver removes excess glucose from your bloodstream and converts it into a temporary storage form called glycogen. This process, called glycogenesis, helps keep your blood sugar level from getting too high and saves the sugar in a readily available form for future use. If you already have an adequate amount of stored glycogen, your liver transforms excess glucose into triglycerides, which are subsequently stored as fat. This is how excess sugar in your diet causes weight gain.
Release
As your blood sugar level begins to drop between meals or during sleep, your liver converts stored glycogen back into glucose and releases it into your bloodstream. This process, called glycogenolysis, helps prevent your blood sugar from dropping to an abnormally low level. The hormone glucagon, from your pancreas, triggers the breakdown of glycogen in your liver to maintain your blood glucose level.
Production
There are times when you body burns through its glycogen stores and needs more glucose. You may not realize that your liver can manufacture glucose from protein and fat precursors in such circumstances. This process, called gluconeogenesis, is vital during periods of extended physical activity, such as an endurance sports event, or if you are sick and unable to eat for a few days. Starvation, whether self-imposed or unintentional, also triggers liver glucose production.
If you enjoy endurance sports, you probably know that your glycogen stores become depleted within approximately two hours of ongoing, strenuous activity. That's when you "bonk" or "hit the wall." Carbohydrate-loading for a few days before an endurance event and taking in sugar during an event can temper the negative effects of glycogen depletion on your athletic performance.
Problems with Liver Glucose Metabolism
Because your liver is essential in the regulation of glucose metabolism, diseases that significantly impair liver function often cause problems with blood sugar regulation. For example, many people with cirrhosis of the liver--- caused by hepatitis B, hepatitis C, alcohol abuse or autoimmune disease --- develop high blood sugar levels, or hyperglycemia. With rapidly developing infectious or toxic liver diseases, low blood sugar levels, or hypoglycemia, may be life threatening.
References
- The Medical Biochemistry Page; Glycogen Metabolism; Michael W. King, Ph.D.; February 2011
- The Medical Biochemistry Page; Gluconeogenesis; Michael W. King, Ph.D.; February 2011
- Elmhurst College Virtual Chembook; Glycogenesis, Glycogenolysis, and Gluconeogenesis; Charles E. Ophardt, Ph.D.; 2003
- "Nutrition: Concepts and Controversies, 11th Edition"; Frances Sizer, M.S., R.D., Ellie Whitney, Ph.D.; 2008
- "Clinical Hepatology: Principles and Practice of Hepatobiliary Diseases"; Henryk Dancygier, M.D.; 2010
- "Insulin Resistance: A Clinical Handbook"; Andrew J. Krentz, M.D.; 2002
