A. Osteoclasts are bone cells that break down bone tissues. As a result, these cells are required for appropriate remodelling, repair, and maintenance of bone tissues. Also, osteoclasts are involved in the resorption of bones regulating calcium concentration in the blood serum.
B. Intramembranous ossification is a process of formation of flat bones (i.e., skull bones) from fibrous membranes. Osteoclasts provide the modification and remodelling of the calcified flat bones controlling their thickening. When osteoblasts form osteoid, some of them are embedded in their matrix and are transformed into oocytes after mineralization. Osteoclasts remove the mineralized matrix and enabled the formation of new osteoid osteoblasts. The defect of osteoclasts during fetal development leads to the formation of bones of abnormal shape and development of bones artefacts (i.e., abnormal thickening).