The human body has four parathyroid glands that all do the same thing - regulate calcium levels in the blood. The glands are located right behind the thyroid gland but actually have nothing to do with the thyroid gland itself. Location is the reason that the two sets of glands are named similarly (para means around) -so a parathyroid is one of four small glands that are near the thyroid. 

How does the normal parathyroid gland work?

The parathyroid glands monitor the blood and adjust the amount of PTH (parathyroid hormone) produced to keep calcium levels in a very tight range. The normal adult has calcium levels that are almost always between 9.0 and 9.5. Teenagers have slightly higher calcium levels. When calcium levels are low, the four parathyroid glands produce more PTH to increase the blood levels until normal levels are achieved. If the calcium level is too high, the four parathyroid glands will produce less PTH, allowing blood levels to decrease into the normal range. 

What does the abnormal parathyroid gland do?

An abnormal parathyroid gland will produce PTH levels that are inappropriate for the level of blood calcium. In most cases, this means that high calcium levels are seen with high PTH levels. This is the easiest situation to diagnose as laboratory testing gives you the answers in a straightforward way. In some cases, there may be elevated calcium levels but normal PTH levels. This may also reflect a bad parathyroid gland as PTH levels should be low when calcium levels are high. This is called a negative feedback loop and frequently bad glands lack proper control and overproduce. 

Where does the excess calcium in the blood come from?

Chronically elevated calcium levels are bad for a variety of reasons. See my parathyroid symptoms page to see what excess calcium can produce. One of the major problems with excess calcium is that the body can't get enough calcium from the diet to keep up with the demands of an abnormally elevated PTH. So where does the extra calcium come from? From your bones! Yes, high PTH will cause the bones to loose valuable calcium deposits. Eventually, the bones will loose enough calcium to produce reduced density on scans and bones weak enough to fracture! All of this can be avoided with simple removal of the offending parathyroid gland(s). Osteopenia (loss of calcium that is mild) leads to osteoporosis (severe loss of bone density) in 100% of patients with an abnormal parathyroid. The body simply can't fight the effects of elevated PTH and the longer PTH is elevated - the more problems that occur.