Calcium balance. Dietary intake of calcium averages 1 g/d and is a critical determinant of calcium homeostasis. A small fraction is absorbed in the intestinal tract, and this is significantly enhanced by vitamin D. Calcium in bone is distributed in a readily exchangeable pool and a stable pool. The readily exchangeable pool is involved in maintaining Ca2+ plasma levels. The stable Ca2+ pool is involved in bone remodeling. Virtually all filtered Ca2+ is reabsorbed, and approximately 40% of the Ca2+ that is reabsorbed is under hormonal regulation by PTH. ECF, extracellular fluid; PTH, parathyroid hormone. Source: Chapter 5. Parathyroid Gland and Ca2+ and PO4- Regulation, Endocrine Physiology, 4e Citation: Molina PE. Endocrine Physiology, 4e; 2013 Available at: https://accessmedicine.mhmedical.com/DownloadImage.aspx?image=/data/Books/moli4/moli4_c005f008.png&sec=42540997&BookID=507&ChapterSecID=42540505&imagename= Accessed: December 27, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved