Ca+2

More Specific Terms

The average adult body contains 1 kg of Ca+2, 99% of which is deposited in bone in the form of hydroxyapatite. The remainder is found in soft tissues & the extracellular space.

normal serum concentration of Ca+2 is 9.0-10.5 mg/dL (2.2-2.6 mmol/L) with 50-60% bound to serum protein or complexed with citrate or phosphate
free or ionized Ca+2 is biologically active
plasma ionized Ca+2 (~ 1 mmol/L) is regulated under tight control by PTH, 1,25-(OH)2 vit D3, & to a lesser extent calcitonin, varying < 0.1 mg/dL under normal conditions
a Ca+2 sensing receptor is expressed on parathyroid cells, renal tubular cells & others & serves to monitor ionized Ca+2 concentrations

intracellular Ca+2 is present in much lower concentrations than extracellular Ca+2 (2-4 orders of magnitude lower), except for intracellular compartmentalized stores of Ca+2 in the endoplasmic reticulum & mitochondria
intraneuronal Ca+2 is typically 100 nM (0.1 mM)

normal dietary Ca+2 varies between 400-1500 mg/day
150-200 mg is excreted in the urine
~500 mg is deposited in & released from bone each day from bone remodeling
bone serves as a reservoir for extracellular Ca+2 in the face of diminished dietary supply
diminished intake of Ca+2 stimulates production of PTH by the parathyroid thus enhancing bone resorption, renal tubular reabsorption of Ca+2, & 1,25-(OH)2 vit D3 production by the kidney which in turn stimulates Ca+2 absorption from the intestine
excess absorbed Ca+2 is excreted in the urine as a result of diminished levels of PTH
see calcium carbonate for calcium supplementation

PubChem: 271
PubChem: 272
Kegg: [1]

Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998
Prescriber's Letter 14(3): 2007 Calcium and Vitamin D Supplementation: Who Needs It? Detail-Document#: [2] (subscription needed) [3]
Calcium: NIH Institute and Center Resources [4]

Ca+2