The mammalian skeletal system has evolved over hundreds of millions of years. When functioning properly, it has the ability to repair broken bones and act as a reservoir for calcium and phosphates ions; when it is not, conditions such as osteoporosis can develop. Of the many skeletal cells, osteoclasts and osteoblasts are responsible for resorption and bone formation. A hormone that directly and indirectly affects the dynamics of osteoblasts and osteoclasts is a 84 amino acid polypeptide named parathyroid hormone or PTH and is secreted by the parathyroid glands.
Source: Encyclopedia Britannica
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