Cells that promote bone resorption and remove old bone are called?

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

Answer: (C)

Bone remodeling relies on a balance between bone formation and bone resorption. The cells that promote resorption and remove old bone are osteoclasts. These are large, multinucleated cells derived from the macrophage lineage that attach to the bone surface and create a sealed zone. They secrete acid to dissolve the mineral component and proteolytic enzymes like cathepsin K to break down the organic matrix, forming resorption pits known as Howship’s lacunae. This resorption step clears old or damaged bone so osteoblasts can lay down new bone scaffolding. Osteoclast activity is tightly regulated by signaling pathways such as RANKL and osteoprotegerin, and hormones like PTH (which stimulates resorption) and calcitonin (which inhibits it). For contrast, osteoblasts build bone by producing osteoid that mineralizes, osteocytes are mature bone cells embedded in the matrix that help sense mechanical load, and chondrocytes are cartilage cells.