insulin-like growth factor

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insulin-like growth factor (IGF) Any of certain polypeptides (see growth factor) that are structurally similar to the hormone insulin and promote division and growth of cells. There are two principal types: IGF-I (somatomedin C) and IGF-II (somatomedin A). Growth hormone stimulates the liver to release IGF-I, which circulates in the bloodstream bound to several specific IGF-binding proteins. IGF-I is also produced locally in various tissues, including kidney, muscle, bone, and the gastrointestinal tract.