ʻO Gastrin, ka mea i kapa ʻia ʻo pepsin, he hormone gastrointestinal i hūnā nui ʻia e nā cell G o ka gastric antrum a me ka duodenum a he hana koʻikoʻi i ka hoʻoponopono ʻana i ka hana o ka digestive tract a me ka mālama ʻana i ke ʻano o ka digestive tract. Hiki i ka Gastrin ke hoʻoikaika i ka huna ʻana o ka ʻōpū o ka ʻōpū, hoʻomaʻamaʻa i ka ulu ʻana o nā cell mucosal gastrointestinal, a hoʻomaikaʻi i ka meaʻai a me ke koko o ka mucosa. I loko o ke kino kanaka, ʻoi aku ma mua o 95% o ka gastrin biologically active ka α-amidated gastrin, nona ka nui o nā isomers ʻelua: G-17 a me G-34. Hōʻike ka G-17 i ka ʻike kiʻekiʻe loa i ke kino o ke kanaka (ma kahi o 80%~90%). Hoʻomalu paʻa ʻia ka huna o G-17 e ka waiwai pH o ka gastric antrum a hōʻike i nā ʻano pane maikaʻi ʻole e pili ana i ka waikawa gastric.