Multiple choice

Which of the following statements regarding calcium and phosphate ions in the body is INCORRECT?

  1. Calcium is the major cation in extracellular fluid.

  2. A rise in plasma calcium levels can cause precipitation of calcium phosphate.

  3. Intracellular calcium concentration is tightly regulated.

  4. The calcium in plasma also exists as complexes with other ions such as phosphate.

  5. A rise in plasma phosphate levels can cause precipitation of calcium phosphate.
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A Correct answer
Explanation

Calcium is the major divalent cation in the body. But most of this calcium is present in bone. Sodium is the major cation in extracellular fluid. In extracellular fluid, the concentration of sodium is around 135-145mMol/l whereas the concentration of calcium is around 2.25mM, of which about half is protein bound.

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