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Which one of the following hormones increases the blood calcium level in the human body?

A
  

Calcitonin

B
  

Parathormone

C
  

Thyroxin

D
  

Vasopressin

Correct Answer: B

Parathormone

Parathormone (PTH), secreted by the parathyroid glands — four small glands sitting behind the thyroid in the neck — is the principal hormone responsible for raising blood calcium levels in the human body. When calcium drops below normal range, PTH is immediately released into the bloodstream and actively works on three major target sites to restore the balance.

  • Bones: Stimulates osteoclasts to break down bone tissue, releasing stored calcium directly into the bloodstream
  • Kidneys: Promotes calcium reabsorption from filtered blood and reduces phosphate retention in urine
  • Intestines: Activates Vitamin D, which significantly enhances dietary calcium absorption
  • Calcitonin: Works completely opposite to PTH by actively lowering blood calcium levels
  • Thyroxin: Primarily regulates basal metabolic rate, plays no direct role in calcium regulation
  • Vasopressin (ADH): Controls water reabsorption in kidneys, entirely unrelated to calcium balance

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