Ghrelin is a 27 or 28 residue long peptide that is the ligand of Growth hormone secretagogue receptor type 1 (GHSR). O-octanoylation or O-decanoylation is essential for ghrelin activity. GHSR activation induces the release of growth hormone from the pituitary. It has an appetite-stimulating effect, induces adiposity and stimulates gastric acid secretion. Involved in growth regulation.