Which cells build the collagen matrix for mineralization in bone formation?

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

Answer: (A)

In bone formation, the building of the collagen matrix happens first. Osteoblasts are the cells that synthesize and secrete osteoid, the organic scaffold rich in type I collagen and other matrix proteins. This collagen-rich osteoid provides the framework onto which calcium and phosphate crystallize as hydroxyapatite, mineralizing the matrix and giving bone its strength. Osteoblasts originate from mesenchymal stem cells and line bone surfaces; as they become embedded in the matrix, some differentiate into osteocytes, which help maintain and regulate the bone. In contrast, osteoclasts resorb bone, osteocytes are mature, embedded cells that maintain the matrix, and chondrocytes produce cartilage (a template in endochondral ossification, not the direct collagen scaffold for the mineralizing bone in this context).