Lastly, parathyroid hormone increases calcium reabsorption and reduces the reabsorption of phosphate from the kidneys, so more phosphate is excreted through the urine.
Parathyroid hormone is produced by the parathyroid glands in response to low serum calcium, and it increases bone resorption to release calcium into the bloodstream.
Less calcium entering the blood is the most common cause and can be due to hypoparathyroidism, or lower levels or lower activity of parathyroid hormone.
Also, people with the genetic disease DiGeorge syndrome, often born with parathyroid glands that are too small and can't produce enough parathyroid hormone.
Now, even though parathyroid hormone stimulates bone resorption, it's been found that intermittent injections with teriparatide activates osteoblasts more than osteoclasts, therefore increasing bone formation.