A hormone that comes from the parathyroid glands is conveniently called a parathyroid hormone (PTH). So, we see that parathyroid hormone is defined as a hormone produced by the parathyroid glands that regulates the amount of calcium and phosphorus in the body.
Calcium is an important ion that has a wide variety of effects on the body. We usually think of calcium when we think of bone formation, but it's also important for proper muscle contraction and proper cell membrane permeability.
Phosphorus, like calcium, is needed for bone formation. Among other things, it combines with lipids to form a major structural component of all cell membranes, which we know as phospholipids.
Obviously, when we talk about bone formation, we're talking about our bony skeleton. It's easy to think of your skeleton as the part of your body that provides support and gives you your basic height and shape. What we don't always think about as quickly when we talk about the bony structures is that they hold a large reserve of calcium and phosphate.
These two minerals can be found floating around in your bloodstream. The amount that is in your blood at any given time needs to be closely regulated and maintained within a very narrow limit in order for your body to be in homeostasis, or internal balance.
If the body needs more of these minerals, it turns to the reserves found in the bony skeleton, and if there are too many of the minerals present in the blood, the minerals are deposited in the bone. Therefore, we see that bone is constantly being broken down and built up to keep the blood levels within a normal range. This is done through the action of osteoclasts and osteoblasts.
Bone is constantly built up and broken down to maintain blood levels of calcium and phosphorus.
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