Question

Which of these is/are correct for calcium metabolism?

(A). Calcitriol facilitates the absorption of calcium from intestine.
(B). PTH enhances calcium transport from intestine by enhancing 1\(\alpha\)-hydroxylase activity.
(C). Lysine and arginine amino acids enhance calcium absorption.
(D). Calcitonin enhances calcium reabsorption from kidneys.

Choose the correct answer from the options given below:

• A. (B) and (D) only.
• B. (C) and (D) only.
• C. (A), (B) & (C).
• D. (A) and (B) only.

Hint:

Remember:
- PTH and Calcitriol act to raise blood calcium levels (calcium absorption and reabsorption).
- Calcitonin acts to lower blood calcium levels (calcium excretion and bone deposition).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Calcium homeostasis is regulated by endocrine feedback loops involving Parathyroid Hormone (PTH), Calcitriol (active Vitamin D), and Calcitonin, alongside dietary factors that influence absorption in the gut.

Step 2: Detailed Explanation:
Let us evaluate each statement:
- Statement (A): Calcitriol (\(1,25\text{-}(\text{OH})_2\text{D}_3\)) increases the synthesis of calbindin (calcium-binding protein) in intestinal enterocytes, directly facilitating calcium absorption. Thus, (A) is correct.
- Statement (B): Parathyroid Hormone (PTH) stimulates the renal 1\(\alpha\)-hydroxylase enzyme, which converts inactive \(25\text{-}(\text{OH})\text{D}_3\) to active calcitriol. Calcitriol then increases calcium absorption in the intestine. Thus, PTH indirectly enhances intestinal calcium absorption. Thus, (B) is correct.
- Statement (C): Basic amino acids, especially lysine and arginine, increase the solubility of calcium salts in the gut, enhancing its absorption. Thus, (C) is correct.
- Statement (D): Calcitonin functions to lower blood calcium levels. It inhibits renal reabsorption of calcium, increasing calcium excretion in urine. Thus, (D) is incorrect.
Therefore, statements (A), (B), and (C) are correct.

Step 3: Final Answer:
The correct option is 3, which corresponds to (A), (B) & (C).