Final answer:
A fetus will begin with a primary ossification center for each bone during development, and secondary ossification centers appear after birth. Ossification at these centers leads to bone formation at the ends of the bone, separated by the epiphyseal plate that allows for continued growth in childhood and adolescence.
Step-by-step explanation:
The number of ossification centers present at birth varies, but primary ossification begins during fetal development. Secondary ossification centers form after birth, and the ossification from these centers eventually forms the ends of the bones. There is expected to be at least one primary ossification center in the middle of long bones with additional secondary ossification centers appearing postnatally in the bone's epiphyses.
Endochondral ossification, which is the process where a cartilage model is turned into bone, begins with a primary ossification center. This ossification creates the midsection or diaphysis of the bone during fetal development. Later on, usually after birth, the secondary ossification centers develop at the ends of the bones (epiphyses).
Childhood and adolescence are marked by the presence of an epiphyseal plate between the primary and secondary ossification centers, which signifies continued bone growth. Eventually, the epiphyseal plates will disappear as one reaches skeletal maturity, and the separate bony components fuse to form a single, adult bone.