primary ossification center

A primary ossification center is the first area of a bone to start ossifying.

Endochondral ossification begins with points in the cartilage called "primary ossification centers."

Next, the chondrocytes cease to divide and begin to hypertrophy (enlarge), much like they do in the primary ossification center of the fetus.

The blood vessels stimulate a primary ossification center to grow - this is the place where bone tissue will begin to take the place of cartilage.

NOTE: most other bones (e.g. vertebrae) also have primary ossification centres and bone is laid down in a similar manner.

Periosteal buds carry mesenchyme and blood vessels in and the process is similar to that occurring in a primary ossification center.

Secondary ossification centers develop to form bone, although unlike with the primary ossification center, spongy bone stays at the center of epiphyses instead of marrow.

A secondary ossification center is the area of ossification that appears after the primary ossification center has already appeared - most of which appear during the postnatal and adolescent years.