Which bone cell is primarily responsible for bone formation and expresses alkaline phosphatase?

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

Answer: (B)

Osteoblasts drive bone formation. They synthesize the organic bone matrix (osteoid), primarily type I collagen, and secrete alkaline phosphatase, an enzyme that promotes mineralization by increasing local phosphate availability. Alkaline phosphatase activity is a hallmark of active osteoblasts and supports the deposition of hydroxyapatite in the matrix. While some osteoblasts become embedded as osteocytes to maintain bone tissue, the cells primarily responsible for forming new bone and expressing alkaline phosphatase are osteoblasts. In contrast, osteoclasts resorb bone, osteocytes maintain mature bone, and osteoprogenitor cells are precursors that differentiate into osteoblasts.