Illustration of insulin-like growth factor 1 (IGF1) in a ternary complex with IGF-binding protein 3 (IGFBP3) and acid-labile subunit (ALS). IGFs are polypeptides that are similar in their molecular structure to insulin. IGF1 is mainly secreted by the liver as a result of stimulation by growth hormone. In addition to acting in a similar way to insulin, IGF1 can also regulate cell growth and development, especially in nerve cells, as well as cellular DNA synthesis. It plays an important role in growth and development throughout childhood and into adulthood. IGF1 bound in a ternary complex is protected from degradation and so has a greatly extended serum half-life.