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calcium metabolism
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.
==Calcium location and quantity==
Calcium is the most abundant mineral in the human body. The average adult body contains in total approximately 1 kg, 99% in the skeleton in the form of calcium phosphate salts. The extracellular fluid (ECF) contains approximately 22 mmol, of which about 9 mmol is in the plasma.〔Diem k, Lenter C ''Scientific Tables'' (Seventh Edition). pp. 565, 653-654. Basle, Ciba-Geigy Limited.〕 Approximately 10 mmol of calcium is exchanged between bone and the ECF over a period of twenty-four hours. The concentration of calcium ions inside the cells (in the intracellular fluid) is 10,000 times lower than in the plasma (i.e. at <0.0002 mmol/L, compared with 1.4 mmol/L in the plasma).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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