BONE FORMATION
PREOSTEOBLASTS
OSTEOBLASTS
OSTEOID
MINERALIZATION
OSTEOCYTES
WOVEN BONE
LAMELLAR BONE
BONE DEVELOPMENT
DIRECT (INTRAMEMBRANOUS)
INDIRECT (ENDOCHONDRAL)
PREOSTEOBLASTS
origin: mesenchymal cells
bone growth factors activate:
cytoplasm enlarges
secretory organelles develop
OSTEOBLASTS
endoplasmic reticulum, golgi apparatus active
secrete osteoid, mineral components:
collagen precursors: protofibrils
proteoglycans
alkaline phosphatase
growth factors
cadherins
"nucleating" factors
Ca, PO4 ions
gap junctions form between cells
OSTEOBLASTS (arrow) ON DEVELOPING BONE
ANATOMY AND NEUROBIOLOGY SLIDE COLLECTION similar to 8-2
OSTEOID FORMATION AND MINERALIZATION
Garant 8-18
BONE FORMATION SEQUENCE
first:
primary/woven/immature bone
replaced by:
secondary/lamellar/mature bone
WOVEN BONE
Ross 8-5
LAMELLAR BONE
BONE IN FRACTURE RECOVERY
collagen fibres in lamellar (L) and woven (W) regions
Stevens 13-11
Fitzgerald p 149
DIRECT BONE FORMATION - INTRAMEMBRANOUS
-many flat bones of skull
-bone forms directly from sheets of undifferentiated
mesenchyme cells
FETAL PIG HEAD
CORONAL SECTION
slide 308
skull developing
from mesenchyme
brain
pharynx
tongue
DEVELOPING FETAL SKULL: INTRAMEMBRANOUS BONE
FORMATION
slide 308
undifferentiated
mesenchyme
skull: compact bone
spongy bone
scalp
brain
INDIRECT BONE FORMATION
-most skeletal bones
-bones begin as cartilagenous models,
cartilage replaced with bone during development
BONE GROWTH AFTER FORMATION
INTERSTITIAL GROWTH
bone elongates at epiphysial plate
-more cartilage added along long axis
-replaced with new bone
APPOSITIONAL GROWTH
diameter enlarges: osteoblasts add more bone
to outside
-marrow cavity enlarges by osteoclast activity
-compact bone thickness to diameter ration
maintained during growth