Which cells build or replace bone tissue?

• A. Osteoclasts
• B. Bone densitometry
• C. Osteoblasts
• D. Bone mineral density (BMD)

Answer: (C)

The main concept is bone formation by specialized cells that synthesize and deposit new bone tissue. Osteoblasts are the bone-forming cells. They produce the organic matrix (osteoid), primarily collagen, and then promote mineralization to convert that matrix into hard bone. As they lay down new bone, they help replace old tissue during growth, remodeling, and fracture repair. Some osteoblasts become osteocytes embedded within the bone to help maintain it, while others become lining cells on the bone surface.

Osteoclasts, by contrast, resorb bone, breaking it down rather than building it up. The other terms refer to measurements or techniques for assessing bone density, not to cells involved in bone synthesis. So osteoblasts are the cells that build or replace bone tissue.