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What percentage of total body calcium is ionized?

A. 10%

B. 20%

C. 40%

D. 60%

E. 80%

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The answer is C. Plasma Ca2+ is maintained at a concentration of 9 to 10.5 g/dL (2.2 to 2.4 mmol/L) as total calcium, with approximately 40% of this value comprising the protein-bound nonfiltratable fraction, and 10% is chelated. Ionized calcium accounts for 47% of the total circulating Ca2+ and ranges from 4 to 5 mg/dL (1.0 to 1.25 mmol/L) . The extent of protein binding per deciliter of plasma is approximately 0.8 mg of Ca2+ for every 1 g of albumin and 0.16 mg for each 1 g of globulin. Furthermore, a threefold increase in serum phosphate or sulfate concentration results in a 10% decrease in serum Ca2+ concentration. In addition, the binding of Ca2+ to albumin is pH-dependent between pH 7 and 9. An acute increase or decrease in the pH by 0.1 units results in an increase or a decrease, respectively, of proteinbound Ca2+ of 0.2 mg/dL (0.05 mmol/L).

Notes

Keywords

Water, volume, and blood composition

Homeostasis functions (Renal/Urinary)

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