What Is the Role of the Liver in Maintaining the Glucose Concentration of the Blood?
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The liver is the second-largest organ of the human body, after the skin. It is the heaviest gland, weighing about three pounds in the average adult. Usually located on the right side of the abdomen, it works with the pancreas and the intestines during food digestion and absorption. The liver is responsible for numerous vital functions, including carbohydrate metabolism. As a major filter of the nutrient-rich blood coming from the digestive tract, the liver is particularly important in maintaining the glucose concentration of the blood within a healthy range.
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The liver plays an important role in maintaining blood sugar levels through such mechanisms as glycogen storage, lipogenesis, glycogen breakdown, gluconeogenesis and the conversion of other sugars into glucose.
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Mechanisms
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After a carbohydrate-rich meal, the liver receives glucose via the hepatic portal vein. The liver cells absorb most of that glucose and convert it into glycogen, the storage form of glucose. This is glycogenesis, a process whereby the liver removes excess glucose from the blood. Excess glucose can also be processed and stored in the form of fats through lipogenesis.
When blood sugar levels fall, the liver breaks down the glycogen stored within its cells, converts it back into glucose and releases it into the bloodstream. Through this process, called glycogenolysis, the liver provides the body with a continual supply of glucose during short-term fasts.
During a prolonged fast, liver glycogen is used up, and other sources of blood glucose are needed. The liver and the kidneys are able to synthesize glucose from amino acids, glycerol or lactic acid. This process is called gluconeogenesis.
Depending on the body's needs and carbohydrate availability in the diet, the liver can also convert other types of sugars--such as fructose, sucrose and galactose--into glucose. This conversion allows the blood glucose concentration to remain within a range that contributes to normal body function.
Considerations
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The liver acts as a glucose buffer, which means that it helps maintain blood glucose concentration close to the normal range of 80 to 120 mg/dL (milligrams of glucose per deciliter of blood). This makes it an essential organ because hyperglycemia (high blood sugar) and hypoglycemia (low blood sugar) can both be harmful to the body. While excess blood glucose often causes such early symptoms as increased thirst, headaches or frequent urination, a 2006 study appearing in Diabetes Journal indicates that chronic hyperglycemia accelerates plaque formation in blood vessels, thus increasing the risk of vascular accidents. Low blood glucose can also be dangerous because certain organs, such as the brain, require glucose to function.
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References
- Gastrointestinal Physiology; Functional Anatomy of the Liver and Biliary System (Chapter 10); Kim E. Barrett; 2006
- Lippincott's Illustrated Reviews: Biochemistry; Pamela Champe, Ph.D, Richard Harvey, Ph.D. & Denise Ferrier, Ph.D.; 2005
- Diabetes Journal (Vol. 55); Effects of Hyperglycemia and Hyperinsulinemia on Circulating Tissue Factor Pro-coagulant Activity and Platelet CD40 Ligand; Vijender R. Vaidyula et al; January 2006
Resources
- Photo Credit Image courtesy of Wikimedia Commons
