Which cell type is primarily responsible for breaking down and remodeling the bone matrix?

Which cell type is primarily responsible for breaking down and remodeling the bone matrix?

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

Answer: (C)

Bone remodeling relies on removing old bone and replacing it with new, and the cells that carry out the resorption phase are osteoclasts. These large, multinucleated cells attach to the bone surface and create a sealed resorption compartment. They secrete acid to dissolve the mineral components and proteolytic enzymes, such as cathepsin K, to break down the organic matrix, forming small pits called Howship’s lacunae. This resorption prepares the surface for new bone formation by osteoblasts, and the process is tightly regulated by signaling from osteoblasts and osteocytes (for example, RANKL promotes osteoclast activity, while osteoprotegerin inhibits it). Meanwhile, osteoblasts later fill the resorption cavities with new bone matrix, and osteocytes act as mechanosensors within the bone. Chondrocytes, by contrast, are cartilage cells and do not drive the remodeling of mineralized bone.

Bone remodeling relies on removing old bone and replacing it with new, and the cells that carry out the resorption phase are osteoclasts. These large, multinucleated cells attach to the bone surface and create a sealed resorption compartment. They secrete acid to dissolve the mineral components and proteolytic enzymes, such as cathepsin K, to break down the organic matrix, forming small pits called Howship’s lacunae. This resorption prepares the surface for new bone formation by osteoblasts, and the process is tightly regulated by signaling from osteoblasts and osteocytes (for example, RANKL promotes osteoclast activity, while osteoprotegerin inhibits it). Meanwhile, osteoblasts later fill the resorption cavities with new bone matrix, and osteocytes act as mechanosensors within the bone. Chondrocytes, by contrast, are cartilage cells and do not drive the remodeling of mineralized bone.