Which cell is primarily responsible for bone resorption during remodeling?

• A. Osteoblast
• B. Osteocyte
• C. Osteoclast
• D. Chondrocyte

Answer: (C)

Bone resorption during remodeling is carried out primarily by osteoclasts. These large, multinucleated cells attach firmly to the bone surface and create a sealing zone, forming a resorption pit known as a Howship’s lacuna. They dissolve mineral with acid secretion and break down organic matrix with proteolytic enzymes such as cathepsin K. This resorptive activity is tightly regulated by signals like RANKL (from osteoblast lineage cells) and its decoy receptor osteoprotegerin, with hormones such as parathyroid hormone promoting resorption and calcitonin inhibiting it. After resorption, osteoblasts come in to lay down new bone matrix, continuing the remodeling cycle. Osteoblasts build bone, osteocytes are mature cells embedded in bone that sense mechanical load and help regulate remodeling, and chondrocytes are cartilage cells, not directly involved in bone resorption.