Figure 4

Outline of endocrine, autocrine and paracrine GH-IGF-SST system in human adult life. At the whole organism level, circulating IGF1 is mainly produced in the liver and IGF1 levels are under the control of GH. In turn, GH is regulated by SST and GHRH. IGF1 is usually delivered by circulation but it can also be produced in an autocrine or paracrine manner.