Bone Formation and Growth

Ossification

the replacement of other tissues with bone

calcification

the deposition of calcium salts

Endochondral Ossification

replaces existing cartilage with bone

Intramembranous Ossification

replaces mesenchyme tissue with bone

Step 1 of Endochondral Ossification:

chondrocytes and lacunae expand and calcify in what will be the future diaphysis; the chondrocytes die and leave a space behind

Step 2 of Endochondral Ossification:

blood vessels grow into the perichondrium around shaft; cells differentiate into osteoblasts and calcify surface

Step 3 of Endochondral Ossification:

capillaries and fibroblasts migrate into the interior; fibroblasts differentiate into osteoblast and begin producing spongy bone at new primary ossification center

Step 4 of Endochondral Ossification:

osteoclasts remodel spongy bone into a medullary cavity; outer layer remodeled into compact bone

Step 5 of Endochondral Ossification:

capillaries and fibroblasts migrate into epiphyses; where secondary ossification centers are then created

Step 6 of Endochondral Ossification:

the epiphyses fill with spongey bone; only the articular and epiphyseal zones of cartilage remain

articular cartilage

the surface exposed to joint cavity

epiphyseal cartilage

space at metaphysis; bones elongate from this region until puberty is over

Step 7 of Endochondral Ossification:

the epiphysial cartilage zone keeps producing cartilage and converting it into osteoblasts, elongating the shaft, until the space closes

Step 1 of Intramembranous Ossification

mesenchymal cells cluster and secrete minerals that calcify into osteoid, and differentiate into osteoblasts

Step 2 of Intramembranous Ossification

osteoid is calcified to form spicules

spicules

small shards of bone inside the tissue

Step 3 of Intramembranous Ossification

blood vessels grow into the tissue; spicules connect to form a branching network around the blood vessels

Step 4 of Intramembranous Ossification

spongy bone is formed by osteoblasts

Step 5 of Intramembranous Ossification

spongy bone near the surface is remodeled into compact bone; connective tissue and osteoblast at the surface become periosteum