Lastly, parathyroid hormone increases calcium reabsorption and reduces the reabsorption of phosphate from the kidneys, so more phosphate is excreted through the urine.
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.
Related to this is pseudohyporparathyroidism, which is where the kidneys simply don't respond to parathyroid hormone because of a genetic defect in the parathyroid hormone receptor.
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.
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.
This can result in conditions like primary hyperparathyroidism which result in too much parathyroid hormone, which leads to excess phosphate being excreted in the urine.
Parathyroid hormone is secreted in response to low blood calcium levels, and it stimulates the resorption of calcium and a small amount of phosphate from the bone and into the bloodstream.
If calcium levels fall, the four parathyroid glands buried within the thyroid gland release parathyroid hormone which frees up both calcium and phosphate ions from the bones.
Bone remodelling as a whole is highly dependent on serum calcium levels, which, in turn, are kept in the normal range by a balance between parathyroid hormone, or PTH, calcitonin and vitamin D.