What is an osteoblast?

• A. Bone-destroying cell
• B. Cartilage cell
• C. Cells that produce bone
• D. Inactive bone cell

Answer: (C)

Osteoblasts are the bone-forming cells. They synthesize the organic matrix of bone (the osteoid), mainly type I collagen, and secrete other proteins that set the stage for mineralization. They then promote deposition of calcium and phosphate to harden the matrix, creating new bone. These cells originate from mesenchymal stem cells on bone surfaces and can become embedded in the matrix to become osteocytes, or remain as active lining cells on the surface if not currently forming bone. They are not bone-destroying cells (that role belongs to osteoclasts) and they are not cartilage cells (which are chondrocytes). So the cells that produce bone best describe osteoblasts.