Calcium metabolism refers to all the movements (and how they are regulated) of calcium atoms and ions into and out of various body compartments, such as the gut, the blood plasma, the interstitial fluids which bathe the cells in the body, the intracellular fluids, and bone. An important aspect, or component, of calcium metabolism is
plasma calcium homeostasis, which describes the mechanisms whereby the concentration of
calcium ions in the
blood plasma is kept within very narrow limits. Derangements of this mechanism lead to
hypercalcemia or
hypocalcemia, both of which can have important consequences for health. In humans, when the blood plasma ionized calcium level rises above its set point, the
thyroid gland releases
calcitonin, causing the plasma ionized calcium level to return to normal. When it falls below that set point, the
parathyroid glands release
parathyroid hormone (PTH), causing the plasma calcium level to rise.