PTHrP exerts its effects on bone and kidney by which combination?

• A. Decreases osteoclast activity and decreases renal calcium reabsorption
• B. Increases osteoclast activity and increases renal calcium reabsorption with phosphate excretion
• C. Increases bone formation and increases phosphate reabsorption
• D. Suppresses PTH secretion

Answer: (B)

PTHrP mimics PTH in how it acts on bone and kidney, mobilizing calcium to raise serum calcium. In bone, it stimulates osteoblast-lineage cells to produce RANK-L, which promotes osteoclast formation and bone resorption. That process releases calcium (and phosphate) from bone into the bloodstream. In the kidney, PTHrP increases calcium reabsorption in the distal tubule, helping conserve calcium, and it promotes phosphate excretion by reducing phosphate reabsorption in the proximal tubule. So the combined effect is more osteoclast-driven bone resorption and greater renal calcium reabsorption with phosphate excretion.