Cells that form new bone by laying down osteoid are known as?

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

Answer: (A)

Bone formation starts with cells that lay down osteoid, the organic, nonmineralized matrix that will become bone. These cells are osteoblasts. They synthesize and secrete type I collagen and other proteins, forming the osteoid on bone surfaces such as the periosteum and endosteum. Once the osteoid becomes mineralized with calcium phosphate, it hardens into bone. Some osteoblasts remain on the surface to continue forming new bone, while others become embedded in the mineralized matrix and differentiate into osteocytes, which reside in lacunae and help regulate bone remodeling. In contrast, osteoclasts resorb bone, and chondroblasts form cartilage rather than bone. So the cells responsible for laying down osteoid and building new bone are osteoblasts.