I-Gastrin, eyaziwa ngokuba yi-pepsin, i-hormone yesisu ekhutshwe ngokukodwa yi-G iiseli ze-antrum ye-gastric kunye ne-duodenum kwaye idlala indima ebalulekileyo ekulawuleni umsebenzi wokugaya ukutya kunye nokugcina isakhiwo esicacileyo sendlela yokugaya.I-Gastrin inokukhuthaza ukukhuselwa kwe-asidi yesisu, iququzelele ukukhula kweeseli ze-mucosal zesisu, kunye nokuphucula ukutya kunye nokunikezelwa kwegazi kwe-mucosa.Emzimbeni womntu, ngaphezu kwe-95% ye-gastrin ye-biologically esebenzayo yi-α-amidated gastrin, equkethe i-isomers ezimbini: i-G-17 kunye ne-G-34.I-G-17 ibonisa umxholo ophezulu emzimbeni womntu (malunga ne-80% ~ 90%).Imfihlo ye-G-17 ilawulwa ngokungqongqo ngexabiso le-pH ye-antrum yesisu kwaye ibonisa indlela yempendulo engalunganga enxulumene ne-asidi yesisu.