When levels of blood calcium decrease parathyroid hormone is
     When levels of blood calcium decrease, parathyroid hormone is released from the four nodular parathyroid glands located on the posterior thyroid decrease reabsorption Parathyroid hormone causes an increase in the number of osteoclasts and greater rates of bone resorption increase at the level of the kidney, parathyroid hormone will decrease the amount of calcium excreted by increasing reabsorption from the kidney tubules. osteoblasts calcitriol to calcitriol Parathyroid hormone increases the renal conversion of calcitriol to calcitriol which secondarily works to increase calcium levels in the blood osteogenic stem cells osteocytes inhibition of by parathyroid hormone occurs as a result of a decreased production of organic matrix osteoclasts As a result of direct actions on the target cells of the bone and kidneys along with an indirect action on the small intestine (calcitriol parathyroid hormone works to increase blood calcium levels calcitriol to calcitriol 
  
  Solution
Parathyroid hormone increases the renal conversion of \'calcidiol to calcitriol\', which secondarily works to increase calcium levels in blood. (Calcitriol increases absorption of calcium from GI tract. It also increases renal calcium absorption and release of calcium from bones. All this ultimately results in increase of calcium levels in blood.)

