Growth hormone is synthesized primarily by somatotropin in the anterior pituitary and stored in secretory granules. GH is a pleiotropic cytokine that exerts its biological effects by binding to transmembrane GH receptors present in many cell types. hGH stimulates hepatic insulin-like growth factor-1 and mobilizes fatty acids from fat deposits to the liver. GH can act directly or indirectly through IGF-1 on B cells, T cells, NK cells, macrophages, and neutrophils to exert immunomodulatory activity. Insufficient secretion of hGH results in dwarfism in children, and excessive secretion results in gigantism in children or acromegaly in adults.