Which cell resorbs bone by secreting acids and proteolytic enzymes?

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

Answer: (C)

Osteoclasts resorb bone by secreting acids and proteolytic enzymes. These multinucleated cells attach to bone and create a sealed resorption lacuna. They pump hydrogen ions into this space to acidify it, dissolving the mineral component of bone, while proteolytic enzymes such as cathepsin K break down the organic matrix like collagen. This coordinated attack removes bone tissue and releases minerals into the bloodstream. Osteoclast activity is balanced by signals from other bone cells, but the actual resorption is carried out by osteoclasts. In contrast, osteocytes are mature bone cells embedded in the matrix, osteoblasts build new bone, and chondrocytes are cartilage cells.