Calcium metabolism Calcium metabolism Calcium metabolism refers to the movements and regulation of calcium ions (Ca) "in" and "out" of various body compartments, such as the gastrointestinal tract, the blood plasma, the extracellular and intracellular fluids, and bone tissue. An important aspect of calcium metabolism is plasma calcium homeostasis, the regulation of calcium ions in the blood plasma within narrow limits. In this process, bone tissue acts as a calcium storage center for deposits and withdrawals as needed by the blood, via continual bone remodeling. Derangement of this mechanism leads to hypercalcemia or hypocalcemia, both of which can have consequences for health.
Calcium metabolism excretion of calcium is relatively modest (about 5 mmol/day) in comparison to what can be excreted via the feces (15 mmol/day). The plasma ionized calcium concentration is regulated within narrow limits (1.3–1.5 mmol/L). This is achieved by both the parafollicular cells of the thyroid gland, and the parathyroid glands constantly sensing (i.e. measuring) the concentration of calcium ions in the blood flowing through them. When the concentration rises the parafollicular cells of the thyroid gland increase their secretion of calcitonin (a proteinaceous hormone) into the blood. At the same time the parathyroid glands reduce their rate of parathyroid hormone (or