Which bone cell forms the mineralized bone matrix?

• A. Osteoclasts
• B. Osteoprogenitor cells
• C. Osteocytes
• D. Osteoblasts

Answer: (D)

During bone formation and remodeling, the mineralized bone matrix is produced by osteoblasts. These cells line bone surfaces and secrete osteoid, the organic matrix rich in type I collagen and non-collagenous proteins. The osteoid is then mineralized as calcium phosphate is deposited to form hydroxyapatite crystals, hardening the matrix. The enzyme alkaline phosphatase from osteoblasts helps drive this mineralization process. As osteoblasts lay down matrix, some become embedded in it and differentiate into osteocytes, which remain within the bone and help maintain and regulate the mature matrix. Osteoclasts resorb bone, and osteoprogenitor cells are precursors that can become osteoblasts but do not themselves form the mineralized matrix. So the cell that forms the mineralized bone matrix is the osteoblast.