The sole purpose of the parathyroid glands is to control calcium within the blood in a very tight range between 8.5 and 10.5. In doing so, parathyroid glands also control how much calcium is in the bones, and therefore, how strong and dense the bones are. Although the parathyroid glands are intimately related to the thyroid gland anatomically, they have no related function. The thyroid gland regulates the body’s metabolism and has no effect on calcium levels while parathyroid glands regulate calcium levels and have no effect on metabolism. Calcium is the primary element which causes muscles to contract. Calcium levels are also very important to the normal conduction of electrical currents along nerves. Knowing these two major functions of calcium helps explain why people can get a tingling sensation in their fingers or cramps in the muscles of their hands when calcium levels drop below 8.5 (like immediately after a successful parathyroid operation). Likewise, too high a calcium level can cause a person to feel run down, cause them to sleep poorly, make them more irritable than usual, and even cause a decrease in memory.
Even though half of patients with this hyperparathyroidism (Parathyroid Disease) will state that they feel just fine, after a successful parathyroid operation more than 85 percent of these patients will claim to "feel much better"! Some say its like "someone turned the lights on".
Although the four parathyroid glands are quite small, they are very vascular. This suits them well since they are required to monitor the calcium level in the blood 24 hours a day. As the blood filters through the parathyroid glands, they detect the amount of calcium present in the blood and react by making more or less parathyroid hormone (PTH). When the calcium level in the blood is too low, the cells of the parathyroids sense it and make more parathyroid hormone. Once the parathyroid hormone is released into the blood, it circulates to act in a number of places to increase the amount of calcium in the blood (like removing calcium from bones). When the calcium level in the blood is too high, the cells of the parathyroids make less parathyroid hormone (or stop making it altogether), thereby, allowing calcium levels to decrease. This feed-back mechanism runs constantly, thereby maintaining calcium (and parathyroid hormone) in a very narrow "normal" range.
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