A normal blood Ca2+ concentration is critically important for contraction of muscles and maintenance of proper membrane permeability. Parathyroid hormone promotes an elevation in blood Ca2+ by stimulating resorption of the calcium phosphate crystals from bone and renal excretion of phosphate. A derivative of vitamin D produced in the body, 1,25-dihydroxyvitamin D3, promotes the intestinal absorption of calcium and phosphate.
The calcium and phosphate concentrations of plasma are affected by bone formation and resorption, intestinal absorption of Ca2+ and PO43-, and urinary excretion of these ions. These processes are regulated by parathyroid hormone, 1,25-dihydroxy vitamin D3, and calcitonin, as summarized in table 19.7.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.