glycogen, starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals. Chemically it is a highly branched condensation polymer of glucose; it is readily hydrolyzed to glucose. Glycogen is formed by the liver from glucose in the bloodstream and is stored in the liver; conversion of glucose to glycogen (glycogenesis) and hydrolysis of glycogen to glucose (glycogenolysis) together are the usual mechanism for maintenance of normal levels of blood sugar. Glycogen is also produced by and stored in muscle cells; during short periods of strenuous activity, energy is released in the muscles by direct conversion of glycogen to lactic acid. During normal activity, energy is released by metabolic oxidation of glucose to lactic acid.

or glycogenosis

Any of numerous types of hereditary enzyme deficiency resulting in altered metabolism of glycogen. The problems are classified in two groups, those affecting the liver and those involving striated muscle, both primary glycogen storage sites. Symptoms in the liver group range from symptomatic hypoglycemia with ketosis to asymptomatic liver enlargement (hepatomegaly). In the muscle group, they range from weakness and cramps to fatal heart enlargement.

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Principal storage carbohydrate of animals, occurring primarily in the liver and resting muscles. It is also found in various bacteria, fungi, and yeasts. Glycogen is a branched polysaccharide, a long chain of glucose units, into which it is broken down when energy is needed.

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