GENERAL HISTOLOGY

Detailed explanation-1: -Osteoblasts penetrate the disintegrating cartilage and replace it with spongy bone. This forms a primary ossification center. Ossification continues from this center toward the ends of the bones. After spongy bone is formed in the diaphysis, osteoclasts break down the newly formed bone to open up the medullary cavity.

Detailed explanation-2: -A secondary ossification center will appear in each epiphysis (expanded end) of these bones at a later time, usually after birth. The primary and secondary ossification centers are separated by the epiphyseal plate, a layer of growing hyaline cartilage. This plate is located between the diaphysis and each epiphysis.

Detailed explanation-3: -The primary ossification center is the first place where the bone formation begins in the axle of a long bone or in the body of an irregular bone. Conversely, the secondary ossification center is the area of ossification that appears after the primary center of ossification at the epiphysis of edges of bones.