I-Gastrin, ekwabizwa ngokuba yi-pepsin, i-hormone ye-gastrointestinal efihliweyo ngokukodwa kwiiseli ze-G ze-antrum ye-gastric kunye ne-duodenum kwaye idlala indima ebalulekileyo ekulawuleni umsebenzi wokugaya ukutya kunye nokugcina isakhiwo esicacileyo sendlela yokugaya. I-Gastrin inokukhuthaza ukukhutshwa 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.