Why do bones become osteoporotic in some people? (What, specifically, is happening in
the bones themselves?)

Osteoporosis is a term that describes the loss of calcium from bones resulting in bones that are thin. Since parathyroid hormone (PTH) removes calcium from bones (that is what it does), all patients with a parathyroid problem will eventually develop thin bones. Bones with osteoporosis due to parathyroid problems can ache and hurt because the PTH is actively destroying the bone. Bones with osteoporosis are fragile bones which are much more susceptible to fractures and breaks.

As you age, your body may reabsorb calcium and phosphate from your bones instead of keeping these minerals in your bones. This makes your bones weaker. A major risk is not having enough calcium to build new bone tissue.