STAGE 1: A fetus skeleton is formed of cartilage.
STAGE 2: Around the cartilage periosteal develops. Blood, nutrients and minerals are transported to the middle of the bone. The primary ossification centre develops, where osteoblast cells start to build the diaphysis structure.
STAGE 3: The bone continues to develop and the primary ossification centre divides. Growth continues from the secondary ossification sites located at either end of the diaphysis. These are the epiphyseal growth plates where bone growth occurs during childhood and adolescence.
STAGE 4: At the final stage the growth plates ossify and then become epiphyseal lines (this occurs around the age of 21). After this point the bones will not grow in length, but throughout lifetime bones renew themselves.