Normal linear growth is regulated by the GH-IGF-1 axis: hypothalamic GHRH stimulates anterior pituitary growth hormone (GH) release, which acts on hepatocytes to produce insulin-like growth factor 1 (IGF-1). IGF-1 mediates long bone growth by stimulating chondrocyte proliferation at the epiphyseal growth plate. Growth hormone deficiency (GHD) results from pituitary pathology (tumors, surgery, radiation, congenital hypopituitarism) and presents with proportionate short stature, delayed bone age, and characteristic facial features (frontal bossing, midface hypoplasia). Failure to thrive (FTT) is weight < 5th percentile or crossing downward across two major percentile lines, most commonly caused by inadequate caloric intake rather than organic disease.