Osteoclasts resorb bone in remodeling. Which cell type is responsible for this process?

• A. Osteocytes
• B. Osteoclasts
• C. Osteoblasts
• D. Chondrocytes

Answer: (B)

In bone remodeling, the resorption step is carried out by osteoclasts. These large, multinucleated cells originate from the monocyte/macrophage lineage and attach to the bone surface, forming a sealed resorption cavity. They dissolve mineral components with proton pumps to create an acidic environment and use proteolytic enzymes like cathepsin K to break down the organic matrix. Their activity is tightly regulated by signals such as RANKL from osteoblast-lineage cells and osteoprotegerin, with calcitonin providing inhibitory input. By contrast, osteocytes act as mechanosensors within bone, and osteoblasts are responsible for forming new bone matrix, while chondrocytes produce cartilage. Thus, osteoclasts are the cells specifically responsible for bone resorption.