In bone remodeling, which cell type is primarily responsible for bone resorption?

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

Answer: (C)

Bone remodeling relies on coordinated resorption and formation, and the primary cell responsible for bone resorption is the osteoclast. Osteoclasts are large, multinucleated cells derived from the hematopoietic lineage that attach to the mineralized surface and create a sealed zone. They secrete acid and proteolytic enzymes at the ruffled border to dissolve hydroxyapatite and break down the organic matrix, forming resorption pits known as Howship’s lacunae. This resorption clears old or damaged bone so osteoblasts can lay down new bone matrix to fill the space. Signals from osteoblasts, such as RANKL, stimulate osteoclast formation and activity, with osteoprotegerin acting as a decoy receptor to modulate this process. In contrast, osteocytes act as mechanosensors and regulators rather than resorbers; osteoblasts are the cells that form new bone, and chondrocytes are cartilage cells, not part of the bone remodeling resorption phase.