In human blood, calcium (Ca2+) concentration is regulated by vitamin D3. First vitamin D3 is converted to calcidiol (CD) in the liver. An elevated concentration of CD inhibits furhter conversion of vitamin D3. Next, CD is conceverted to calcitriol (CT) in the kidneys in a reaction tht requires parathyroid hormone (PTH). An elevated concentration of CT increases Ca2+ concentration, which in turn inhibits further release of PTH. See figure 1 According to Figure 3, the relative blood CT concentration is between 5 times normal and 6 times normal within which of the following blood Ca2+ concentration ranges?

Correct answer: A. 8mg/100 mL to 9mg/100 mL

  • A. 8mg/100 mL to 9mg/100 mL
  • B. 10mg/100 mL to 11 mg/100 mL
  • C. 11mg/100 mL to 12mg/100 mL
  • D. 13mg/100 mL to 14mg/100 mL

Explanation

Looking at figure 3, it is clear that only at blood Ca2+ concentration range of 8mg/100 mL to 9mg/100 mL, the relative blood CT concentration is between 5 times normal and 6 times normal.

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