Gastrin, wanda kuma aka sani da pepsin, shine hormone na ciki wanda aka fi sani da G cell na antrum na ciki da duodenum kuma yana taka muhimmiyar rawa wajen daidaita aikin tsarin narkewa da kuma kiyaye tsarin tsarin narkewa. Gastrin na iya inganta haɓakar acid na ciki, sauƙaƙe haɓakar ƙwayoyin mucosal na ciki, da inganta abinci mai gina jiki da samar da jini na mucosa. A cikin jikin mutum, fiye da 95% na gastrin mai aiki na halitta shine gastrin α-amidated, wanda galibi ya ƙunshi isomers guda biyu: G-17 da G-34. G-17 yana nuna mafi girman abun ciki a jikin mutum (kimanin 80% ~ 90%). Sirrin G-17 ana sarrafa shi ta hanyar ƙimar pH na antrum na ciki kuma yana nuna tsarin amsa mara kyau wanda ya danganta da acid na ciki.