Hormonal Effects on Bone Cells

This chapter focuses on the direct effects of systemic hormones on the skeleton. Parathyroid hormone increases bone formation and resorption by acting through receptors expressed in cells of the osteoblastic lineage, and exerts catabolic or anabolic effects depending on the mechanism of elevation (continuous or intermittent). The sex steroids, androgens and estrogens, protect the growing and mature skeleton through receptors expressed in osteoblasts, as well as in osteoclasts, by maintaining the balance between bone formation and resorption. Glucocorticoids, when present in excess due to endogenous elevation or to administration as immunosuppressant therapy, have deleterious effects on bone resulting from acceleration of bone resorption, inhibition of bone formation, and increased bone fragility. Other hormones, such as thyroid hormone, growth hormone, insulin, 1,25-dihydroxyvitamin D₃, and leptin affect bone development and homeostasis of the mature skeleton by acting on bone cells of both mesenchymal and hematopoietic lineages.