Ossification
Formation of bone tissue.
Intramembranous Ossification
Flat bones form directly from connective tissue (like skull).
Endochondral Ossification
Long bones form by replacing cartilage with bone.
Primary Ossification Center
Forms in the shaft (diaphysis).
Secondary Ossification Center
Forms at the ends (epiphyses).
Growth Plate (Epiphyseal Plate)
Zone where bone grows in length.
Five Zones of Growth Plate
Resting → Proliferation → Hypertrophy → Calcification → Ossification.
(Mnemonic: R-P-H-C-O)
Appositional Growth
Bone grows thicker by adding layers under the periosteum.
Epiphyseal Line
What the growth plate becomes after growth stops.
Bone Length Stops When…
Girls: growth plates usually CLOSES by 16–18 years
Boys: growth plates usually CLOSES by 18–21 years
By age 30: fully CLOSED for both sexes
