At the cellular level the physiological affects of human growth hormone are mediated by?

Human growth hormone, also known as somatotropin is a 191 amino acid polypeptide with a molecular weight of 22,000 and is the major hormone regulating growth in humans. It is synthesized as a 28,000 Dalton precursor that is not biologically active. The gene for pre-growth hormone is found on chromosome 17. Growth hormone is pa of a family of hormones which include prolactin and human placental lactogen. Of the three only growth hormone has growth promoting activities. Growth hormone directly acts on cells a receptor signaling pathway to cause differentiation and the release of insulin-like growth factors ( IGFs). The IGF's promotes cell division. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 18. The Pituitary Gland. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds),Ganong's Review of Medical Physiology, 24e.