Question

The hormone that promotes the activation of calciferol into calcitriol is:

• A. Thymosins
• B. Aldosterone
• C. Somatostatin
• D. Parathyroid hormone

Hint:

PTH is the primary hypercalcemic hormone.
It elevates blood calcium by bone resorption, decreasing calcium excretion in kidneys, and promoting calcitriol synthesis to increase calcium absorption in the gut.

Answer 1

The Correct Option is D

Step 1: Track the vitamin D activation pathway.
Vitamin D from skin or diet is first hydroxylated in the liver, then it needs one more hydroxylation step in the kidney to become the active hormone calcitriol.
Step 2: Ask what drives that final kidney step.
The enzyme doing this last conversion, 1-alpha-hydroxylase, is not switched on randomly, it responds to the body's calcium status.
Step 3: Identify the trigger hormone.
When blood calcium drops, the parathyroid glands release parathyroid hormone, which directly activates that kidney enzyme, boosting calcitriol production and calcium absorption.
Final answer: Option 4, Parathyroid hormone.