This cartilage covers the end of the bone and forms the articular cartilage. Deeper from the end between the epiphysis and diaphysis, some cartilage remains to form the epiphyseal plate. Osteoclasts in the diaphysis break down cartilage at the epiphyseal plate and osteoblasts invade and lay down spongy bone. When this occurs the epiphyseal plate will ossify and bone growth will stop. The periosteal cells continue to lay down bone on the outer surfaces of the shaft.
Bones continue to grow in thickness by the process of appositional growth.
Weight bearing activity and stress on bone causes small electrical fields to be generated by the minerals of the bone. This detected by the by the osteoblasts which migrate to lay down new bone in the stressed area. Unstressed bone will decrease in size, microgravity, bed rest. Bones of athletes tend to be bigger than those of non-athletes. Somatomedins act on the osteoprogenitor cells which form the osteoblasts.