Gastrin, izwi kandi ku izina rya pepsin, ni imisemburo ya gastrointestinal ahanini isohorwa na G selile ya antric gastrum na duodenum kandi igira uruhare runini muguhuza imikorere yinzira yigifu no gukomeza imiterere yimitsi yigifu. Gastrin irashobora guteza imbere aside gastricike, ikorohereza imikurire ya gastrointestinal mucosal selile, kandi igateza imbere imirire no gutanga amaraso ya mucosa. Mu mubiri w'umuntu, ibice birenga 95% bya gastrine ikora mubuzima ni α-amidated gastrine, irimo ahanini isomeri ebyiri: G-17 na G-34. G-17 yerekana ibintu byinshi mumubiri wabantu (hafi 80% ~ 90%). Ibanga rya G-17 rigenzurwa cyane nagaciro ka pH ya antrum gastric kandi ikerekana uburyo bubi bwo gutanga ibitekerezo ugereranije na acide gastric.