Chapter 9 - Calcium-Regulating Hormones: Vitamin D, Parathyroid Hormone, Calcitonin, and Fibroblast Growth Factor 23

Abstract

This chapter focuses on four hormones: parathyroid hormone (PTH), calcitonin (CT), a steroid hormone metabolically produced from vitamin D3, namely 1α,25(OH)2-vitamin D3 [1α,25(OH)2D3] and fibroblast growth factor 23 (FGF23). Historically, the first three have been intimately involved in calcium and phosphate homeostasis. However, as a consequence of major advances in biological research over the past 30 years, these four hormones have been discovered to have many additional assignments. For optimal growth and function, organisms with a skeleton require an adequate supply of calcium and phosphate to meet both their structural and metabolic needs. These higher organisms must be dietarily supplied with calcium and phosphate on a regular basis. The plasma concentrations of these substances are maintained within a surprisingly narrow limit by an endogenous hormonal control mechanism. The maintenance of calcium and phosphate homeostasis involves the delicate and coordinated interrelationships of absorption by the intestine, accretion by bone osteoblasts and reabsorption by bone osteoclasts, and renal tubular reabsorption and/or urinary excretion of calcium and phosphate by the kidney. This chapter discusses the details of related anatomy, processes, and hormonal mechanisms.