Which statement about osteoclasts is correct?

Which statement about osteoclasts is correct?

• A. It dissolves bone and forms new marrow
• B. It forms osteoblasts directly
• C. It transcribes collagen genes
• D. It secretes acids and proteolytic enzymes to dissolve mineralized bone

Answer: (D)

Osteoclasts are the bone-resorbing cells in the remodeling unit. They attach to the bone surface and create a sealed resorption lacuna where they work with a ruffled border. In this space they pump hydrogen ions to create an acidic environment and release proteolytic enzymes, such as cathepsin K, to break down the organic matrix (mainly collagen) and dissolve the mineral crystals. This combination of mineral dissolution by acid and matrix degradation by enzymes is how mineralized bone is resorbed. The other options describe functions of different cells or processes: forming marrow is not done by osteoclasts, they do not directly form osteoblasts, and transcription of collagen genes is a activity of osteoblasts, not osteoclasts.

Osteoclasts are the bone-resorbing cells in the remodeling unit. They attach to the bone surface and create a sealed resorption lacuna where they work with a ruffled border. In this space they pump hydrogen ions to create an acidic environment and release proteolytic enzymes, such as cathepsin K, to break down the organic matrix (mainly collagen) and dissolve the mineral crystals. This combination of mineral dissolution by acid and matrix degradation by enzymes is how mineralized bone is resorbed. The other options describe functions of different cells or processes: forming marrow is not done by osteoclasts, they do not directly form osteoblasts, and transcription of collagen genes is a activity of osteoblasts, not osteoclasts.