Figure 1. Schematic of the growth hormone - insulin-like growth factor-1 axis in human growth. Growth hormone secretion produces insulin-like growth factor-1 in the liver and at the local target tissue, such as the growth plate. Growth hormone also regulates the expression of insulin-like growth factor binding proteins and insulin-like growth factor acid labile subunit from the liver. Insulin-like growth factor-1 circulates bound to insulin-like growth factor binding proteins and insulin-like growth factor acid labile subunit in serum. Free insulin-like growth factor-1 liberated from insulin-like growth factor binding proteins is the active form of the hormone IGF-1: insulin-like growth factor-1, IGFBP: insulin-like growth factor binding protein, GH: growth hormone, GHRH: growth hormone-releasing hormone, IGFALS: insulin-like growth factor acid labile subunit.
