Osteoblasts and osteoclasts are types of cells the human body uses to repair broken bones. Osteoclasts break down old bone tissue allowing osteoblasts to replace it with new material. Together, these cells facilitate bone mending and bone growth.
Osteoblasts are single nuclei cells that operate in groups to form bone. They produce calcium and phosphate mineral deposits that form a very dense, hard shell around a bone fracture. The shell is known as a bone callus and lasts for three to four months.
Osteoclasts break down the mineral deposits from the osteoblasts by releasing acid and collagenase enzymes. The broken down material is then released into the bloodstream. The process of bone repair takes months. Osteoblasts and osteoclasts continually work to rebuild fractured bone until it is completely healed.