Question

Factors that stimulate osteoclasts are

(A). PTH
(B). 1,25-dihydroxycholecalciferol
(C). TGF beta
(D). TNF

Choose the correct answer from the options given below:

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

Hint:

Remember that both PTH and Active Vitamin D function to increase blood calcium levels. They achieve this primarily by stimulating bone-resorbing osteoclasts to break down bone and release calcium into the bloodstream.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Osteoclasts are multinucleated giant cells responsible for bone resorption.
Their differentiation and activation are regulated by endocrine hormones, local growth factors, and cytokines.

Step 2: Detailed Explanation:
Let us evaluate the effect of each factor on osteoclasts:
- PTH (Parathyroid Hormone) (A): Binds to osteoblast receptors, triggering them to express RANKL, which strongly binds to RANK on osteoclast precursors to stimulate osteoclastogenesis and bone resorption. Thus, (A) stimulates osteoclasts.
- 1,25-dihydroxycholecalciferol (Active Vitamin D) (B): Synergizes with PTH to stimulate osteoclast differentiation and bone resorption to maintain calcium homeostasis. Thus, (B) stimulates osteoclasts.
- TGF-beta (C): Generally inhibits mature osteoclasts and promotes bone-building osteoblast activity. Thus, (C) does not stimulate osteoclasts.
- TNF (Tumor Necrosis Factor) (D): A pro-inflammatory cytokine that directly stimulates osteoclast differentiation and activity, accelerating bone loss. Thus, (D) stimulates osteoclasts.
Therefore, factors (A), (B), and (D) stimulate osteoclasts.

Step 3: Final Answer:
The correct option is 2, which corresponds to (A), (B) and (D) only.