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Insulin-like growth factor (IGF) is a group of growth-promoting peptides. Its secreting cells are widely distributed in human liver, kidney, lung, heart, brain, and intestine. The production of IGF-I is more dependent on GH, which has a strong growth-promoting effect and is an important growth factor in childhood. IGF-I synthesized in various tissues mostly exerts its growth-promoting effects in an autocrine or paracrine manner, while IGF-I synthesized by the liver enters the blood circulation and acts on target cells in an endocrine manner. The level of IGF-I in the body is regulated by GH. IGF- I also has a negative feedback regulation effect on GH secretion. IGF-II is more insulin-like and plays an important role in fetal growth. IGF receptors are divided into two types, namely, IGF-I receptor (IGF-I R) and IGF-II receptor (IGF-II R). The former is a tyrosine kinase-type receptor and is composed of two α subunits. The latter has no amino acid kinase activity.