in ▁in ▁response ▁to ▁the ▁presence ▁of ▁food ▁in ▁the ▁st om ach . ▁Le pt in ▁has ▁been ▁found ▁in ▁the ▁pe ps in ogen ▁gran ules ▁of ▁chief ▁cells . ▁ ▁G astr ic ▁pit ▁cells ▁are ▁replaced ▁every ▁ 2 – 4 ▁days . ▁This ▁high ▁rate ▁of ▁turn over ▁is ▁a ▁protect ive ▁mechanism ▁designed ▁to ▁protect ▁the ▁ep ith el ial ▁l ining ▁of ▁the ▁st om ach ▁from ▁both ▁the ▁prote ol yt ic ▁action ▁of ▁pe ps in ▁and ▁the ▁acid ▁produced ▁by ▁par iet al ▁cells . ▁G astr ic ▁chief ▁cells ▁are ▁much ▁longer ▁lived ▁and ▁are ▁believed ▁to ▁differenti ate ▁from ▁stem ▁cells ▁located ▁higher ▁in ▁the ▁g astr ic ▁unit ▁in ▁the ▁is th mus . ▁▁ ▁These ▁stem ▁cells ▁differenti ate ▁into ▁m uc ous ▁neck ▁cells ▁in ▁the ▁is th mus ▁and ▁transition ▁into ▁chief ▁cells ▁as ▁they ▁migr ate ▁towards ▁the ▁base . ▁Since ▁the ▁m uc us ▁neck ▁cells ▁do ▁not ▁divide ▁as ▁it ▁becomes ▁a ▁chief ▁cell ▁this ▁process ▁is ▁known ▁as ▁trans d iffer enti ation . ▁The ▁gene ▁M ist 1 ▁has ▁been ▁shown ▁to ▁reg ulate ▁m uc us ▁neck ▁cell ▁to ▁chief ▁cell ▁trans d iffer enti ation ▁and ▁plays ▁a ▁role ▁in ▁the ▁normal ▁development ▁of ▁the ▁chief ▁cell ▁organ elles ▁and ▁structures . ▁ ▁The ▁par ath y roid ▁chief ▁cell ▁is ▁the ▁primary ▁cell ▁of ▁the ▁par ath y roid ▁g land . ▁It ▁produces ▁and ▁secre tes ▁par ath