In a coupled process, bone is resorbed through the action of osteoclasts which are large multinucleated cells derived from monocyte/macrophage lineage. The most characteristic feature of monocytes is the ruffled border of finger-shaped projections of cell membrane that mediate the resorption of calcified bone matrix. The mineral content of the matrix is first dissolved in the acidic environment of the ruffled border and the remaining protein components of the matrix (primarily collagen) are then degraded by proteolytic enzymes secreted into the resorption space. The result is the dissolution of the bony matrix of the trabeculae to form a cavity or lacuna.