Which statement is true about osteoclasts?

• A. They resorb bone
• B. They form new bone matrix
• C. They become osteoblasts
• D. They originate from chondrocytes

Answer: (A)

Bone remodeling hinges on osteoclasts removing old or damaged bone while osteoblasts lay down new bone. Osteoclasts are large, multinucleated cells that come from the hematopoietic lineage (monocyte/macrophage precursors) and form by fusing these precursors. Their primary job is to resorb bone: they attach to the mineralized surface, create a sealed specialized area, and secrete hydrogen ions to dissolve the mineral component and proteolytic enzymes like cathepsin K to break down the organic matrix. This activity forms Howship’s lacunae and releases calcium and phosphate into circulation, balancing bone formation by osteoblasts. In contrast, forming new bone matrix is the function of osteoblasts, not osteoclasts, and osteoclasts do not originate from chondrocytes (cartilage cells); chondrocytes are involved in cartilage, not the origin of bone-resorbing cells.