ABSTRACT
Nature shows us often a basic framework for the control of complicated biological systems which is refined by the addition of nuance to the specific need of one element. There is a direct analogy between the interrelated systems of phosphorus, parathormone, and 1,25(OH)2D3 and that observed between potassium, renin, and aldosterone. Each homeostatic system involves ions, peptides, and steroid hormones and each of the systems is interrelated within itself with negative feedback loops at the levels of end-organ of production and of biological action. Many of the themes discussed below are similar in design elements between these two diverse biologic systems, and that discussed in this chapter also presents unique features. Let us begin our journey into the labyrinth of mineral metabolism by discussing the multiorgan control of vitamin D metabolism.
