American Board of Orthodontics (ABO) 2025 – 400 Free Practice Questions to Pass the Exam

Osteoclasts are specialized cells responsible for the resorption of bone tissue, a critical process in bone remodeling and maintenance. They are derived from the monocyte/macrophage lineage, which means they originate from hematopoietic stem cells in the bone marrow. This lineage produces monocytes that migrate into tissues and differentiate into macrophages, and these macrophages further differentiate into osteoclasts in the presence of specific factors such as RANKL (Receptor Activator of Nuclear Factor Kappa-Β Ligand) and macrophage colony-stimulating factor (M-CSF).

In contrast to the other options, mesenchymal stem cells are primarily responsible for forming osteoblasts and chondrocytes but do not differentiate into osteoclasts. Chondrocytes are specialized cells found in cartilage tissue and do not contribute to the formation of osteoclasts. Osteoprogenitor cells are stem cells that give rise to osteoblasts and are involved in the formation of new bone tissue rather than its resorption. Thus, the correct understanding is that osteoclasts arise specifically from the monocyte/macrophage lineage, which is essential for their formation and function in the skeletal system.