Calciotropic Hormones and Calcium Homeostasis

Calcium (Ca) and phosphate (Pi) are critical to human physiology and are also needed for skeletal mineralization. They are essential to many vital physiological processes (Masi et al., Osteoporos Int. 2015;26(10):2529–58; 2015; Berndt et al., Am J Physiol Renal Physiol. 289:1170–82; 2005), and their regulation involves a concerted action among the digestive system, kidneys, and skeleton via the action of calciotropic hormones (Masi et al., Osteoporos Int. 2015;26(10):2529–58; 2015). An understanding of Ca and Pi metabolism is required for the clinician to evaluate disorders of the levels of calcium and phosphorus, as well as metabolic skeletal disorders (Joseph et al., Calcium and phosphate homeostasis; 2018). Alteration of Ca and Pi homeostasis involves many organs as skeleton, parathyroids, gastrointestinal (GI) tract, and kidneys. Parathyroid hormone (PTH), vitamin D [25 hydroxyvitamin D3: 25(OH) D3 and 1,25-dihydroxyvitamin D3: 1,25(OH)2D3], and calcitonin (CT) are involved in the regulation of Ca and Pi homeostasis. The present chapter shows the regulation of Ca homeostasis by calciotropic hormones.