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What percentage of total body calcium is ionized?

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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) [1] . 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).[2]

Notes

  1. J Clin Invest. 1970;49(2):318–334[1]
  2. JASN July 2008 vol. 19 no. 7 1257-1260 [2]

Keywords

Water, volume, and blood composition
Homeostasis functions (Renal/Urinary)



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This is a paragraph with several references that I would like to practice using.

According to scientists, the Sun is pretty big.[1] The Moon, however, is not so big.[2]

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  1. E. Miller, The Sun, (New York: Academic Press, 2005), 23-5.
  2. R. Smith, "Size of the Moon", Scientific American, 46 (April 1978): 44-6.


This is an example of multiple references to the same footnote.[1]

Such references are particularly useful when citing sources, if different statements come from the same source.[1] Any reused tag should not contain extra content, that will spawn an error. Only use empty tags in this role.

A concise way to make multiple references is to use empty ref tags, which have a slash at the end. Although this may reduce redundant work, please be aware that if a future editor removes the first reference, this will result in the loss of all references using the empty ref tags.[1]

Notes

  1. 1.0 1.1 1.2 Remember that when you refer to the same footnote multiple times, the text from the first reference is used.

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