calcium levels in Mr. gallariani's blood are dropping to dangerously low levels . the hormon PTH is released and soon blood calcium level's begin to...

calcium levels in Mr. gallariani's blood are dropping to dangerously low levels . the hormon PTH is released and soon blood calcium level's begin to rise . shortly after ,PTH released slows. is this an example of a positive or negitive feedback mechanism ? what is the initial stimulus ?what is the result?