TY - CHAP M1 - Book, Section TI - Disorders of the Parathyroid Gland and Calcium Homeostasis A1 - Potts, Jr., John T. A1 - Jüppner, Harald W. A2 - Jameson, J. Larry A2 - Fauci, Anthony S. A2 - Kasper, Dennis L. A2 - Hauser, Stephen L. A2 - Longo, Dan L. A2 - Loscalzo, Joseph PY - 2018 T2 - Harrison's Principles of Internal Medicine, 20e AB - The four parathyroid glands are located posterior to the thyroid gland. They produce parathyroid hormone (PTH), which is the primary regulator of calcium physiology. PTH acts directly on bone, where it induces calcium release, and on the kidney, where it enhances calcium reabsorption in the distal tubules, and in the proximal renal tubules the synthesis of 1,25-dihydroxyvitamin D (1,25[OH]2D), a hormone that increases gastrointestinal calcium absorption. Serum PTH levels are tightly regulated by a negative feedback loop. Calcium, acting through the calcium-sensing receptor (CaSR), and vitamin D, acting through its nuclear receptor, reduce PTH release and synthesis. Additional evidence indicates that fibroblast growth factor 23 (FGF23), a phosphaturic hormone, can suppress PTH secretion. Understanding the hormonal pathways that regulate calcium levels and bone metabolism is essential for effective diagnosis and management of a wide array of hyper- and hypocalcemic disorders. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/03/29 UR - accesspharmacy.mhmedical.com/content.aspx?aid=1172536427 ER -