The body has four parathyroid glands. They are small, pea-sized glands located in the neck just behind the butterfly-shaped thyroid gland. Two parathyroid glands lie behind each 'wing' of the thyroid gland. The parathyroid glands release a hormone called parathyroid hormone (Parathormone / PTH). PTH helps to control the levels of three minerals in the body; calcium, phosphorus and magnesium.
Parathormone (PTH) has a number of effects on the body:
It causes the release of calcium from bones.
It causes calcium to be absorbed (taken up into the blood) from the intestine.
It stops the kidneys from excreting calcium in the urine.
It causes the kidneys to excrete phosphate in the urine.
It increases blood levels of magnesium.
It is therefore clear that the consumption of minerals (Calcium, Magnesium and Phosphate) affects the level of PTH produced by the parathyroid.
When the calcium level is high in the bloodstream, the thyroid gland releases calcitonin. Calcitonin slows down the activity of the osteoclasts found in bone. This decreases blood calcium levels.
When calcium levels decrease in the bloodstream, this stimulates the parathyroid gland to release Parathormone (PTH). PTH encourages the normal process of bone breakdown (essential for maintenance and growth of the bone). This process of bone breakdown releases calcium in the bloodstream. These actions raise calcium levels and counteract the effects of calcitonin. By having two hormones with opposing actions, the level of calcium in the blood is carefully regulated.
Parathormone (PTH) also acts on the kidneys. Here it slows down the amount of calcium and magnesium filtered from the blood into the urine. Parathyroid hormone also stimulates the kidneys to make calcitriol, the active form of vitamin D. Calcitriol helps to increase the amount of calcium, magnesium and phosphorus absorbed from the intestines into the blood.
Deficiency of Parathormone results in abnormally low calcium levels in the blood (hypocalcemia). Excessive Parathormone leads to elevated calcium levels in the blood (hypocalcemia) and calcium deposition in cartilage.