parathyroid gland

The parathyroid glands are four tiny glands, located in the neck, that control the body’s calcium levels. Each gland is about the size of a grain of rice (weighs approximately 30 milligrams and is 3-4 millimeters in diameter). The parathyroids produce a hormone called parathyroid hormone (PTH). PTH raises the blood calcium level by:

breaking down the bone (where most of the body’s calcium is stored) and causing calcium release
increasing the body’s ability to absorb calcium from food
increasing the kidney’s ability to hold on to calcium that would otherwise be lost in the urine.
Normal parathyroid glands work like the thermostat in your home to keep blood calcium levels in a very tightly controlled range. When the blood calcium level is too low, PTH is released to bring the calcium level back up to normal. When the calcium level is normal or gets a little too high, normal parathyroids will stop releasing PTH. Proper calcium balance is crucial to the normal functioning of the heart, nervous system, kidneys, and bones.