Ossification starts from before birth. Growth ceases during
adolescence to adulthood. After growth ceases, you don't get taller
but bone still remodels.
Mesenchymal condensation occurs in area where cartilage
formation is to take place, pre chondroblasts proliferate to form
mass in cartilage
Condensed mesenchymal cells become round and secrete basophilic
ECM.
Cells differentiate into chondroblasts and produce ECM.
Cartilage model surrounded by perichondrium
Bone growth:
Mesenchymal cells that undergo intramembranous ossification or
transform into cartilage which undergo endochondral
ossification.
Intramembranous ossification:
1.Mesenchymal condensation occurs and cells become small,
spindle shaped with parallel orientation.
2.Mesenchymal cells produce collagen
3.Some cells differentiate into osteoblasts
4.Osteoblasts produce ECM called osteoid
5. Become highly vascular
6. Osteoblasts trigger deposition of Ca salts
7. Osteoblasts trapped in matrix become osteoclasts
8. Centre of ossification established. Layer of vascular
mesenchyme condenses on bone( periosteum).
9. Inner periosteum cells differentiate into osteoblasts which
lay down bone as parallel plates or lamellae.
Endochondral ossification-Most bones.
1. Mesenchymal condensation occurs in area where bone
formation is taking place, cells proliferate to form a mass in
shape of future bone.
2.Condensed mesenchymal cells become round and secrete
basophilic ECM substance cells.
3. The cells differentiate into chondroblasts and produce
ECM
4.Catilage model surrounded by perichondrium.
5. Week 8 ossification occurs in middle of shaft
6.Cartilage cells in middle shaft enlarge and calcium salts are
deposited in the matrix.
7.Calcification inhibit nutrient diffusion so cartilage cells
degenerate, leaving large spaces. At the same time, cells of
perichondrium become active and become osteoblasts( now periosteum)
and start laying down compact bone.
8. Vascular tissue invades areas of calcified matrix, bringing
in chondroclasts and osteoblasts.
9. Chondroclasts break down lacunawalls and osteoblasts lay down
bone in these spaces and primary centre of ossification
established.
From UTAS notes: This is not a comprehensive guide, its my
summary.