An osteoclast (from the Greek words for "bone" and "broken") is a type of bone cell that removes bone tissue by removing its mineralized matrix. This process is known as bone resorption. Osteoclasts and osteoblasts are instrumental in controlling the amount of bone tissue: osteoblasts form bone, osteoclasts resorb bone. Osteoclasts are formed by the fusion of cells of the monocyte-macrophage cell line. Osteoclasts are characterized by high expression of tartrate resistant acid phosphatase (TRAP) and cathepsin K.
Morphology
An osteoclast is a large cell that is characterized by multiple nuclei and a cytoplasm with a homogeneous, "foamy" appearance. This appearance is due to a high concentration of vesicles and vacuoles. At a site of active bone resorption, the osteoclast forms a specialized cell membrane, the "ruffled border", which touches the surface of the bone tissue.
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