▪ Two processes happen here:
1. Interstitial growth of cartilage
2. Endochondral ossification
Growth at the Epiphyseal Plate
Cartilage grows from within at the
epiphyseal side of the epiphyseal plate
Interstitial growth of cartilage
- Mesenchymal cells differentiate into
chondroblasts - Chondroblasts build matrix and differentiate into
chondrocytes - Chondrocytes divide and spread apart
- Cartilage tissue grows from within
Interstitial Growth
(Cartilage)
Cartilage is replaced by bone on the
diaphyseal side of the epiphyseal plate
Endochondral ossification
A, B, C
Resting cartilage, Proliferating cartilage, Hypertrophic cartilage
D, E
Calcified cartilage
(will be replaced by bone),
Diaphysis (bone)
________ grows in length, but the thickness of the _____________
does not change during childhood
Diaphysis; epiphyseal plate
▪ Diaphyseal osteoclasts break down calcified cartilage
▪ Osteoblasts lay down spongy bone
▪ Chondrocytes continue to form cartilage matrix at the proliferating
cartilage region
▪ Growth in length stops when osteoclasts and osteoblasts work faster
than chondrocytes in the proliferating zone → epiphyseal plate closes
and becomes the epiphyseal line
Growth at the Epiphyseal Plate – Summary
▪ Epiphyseal plates _______ at the end of adolescence
▪ Age 18 (females)
▪ Age 21 (males)
close
- _________________ cells stop dividing and are replaced by bone
- Epiphyseal line forms
Epiphyseal cartilage
Interstitial _________
cannot occur after the
epiphyseal plate closes
growth
growth in width
Appositional Growth
Where do periosteal osteoblasts build bone?
Outer surface of bone
Periosteal osteogenic cells _________ into osteoblasts
___________ increase the _________ of the marrow cavity
Endosteal osteoclasts; diameter
During appositional growth….
Bone diameter, cortical width, and medullary cavity size increase
Osteons are added to the periosteal side of bone by the following steps:
1) Ridges in periosteum create groove for periosteal blood vessel
2) Periosteal ridges fuse, forming an endosteum-lined tunnel
3) Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon
4) Bone growth outward as osteoblasts in the periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels
▪ Bone diameter increases
▪ Cortical width increases
▪ Medullary cavity size increases
Appostitional Growth
a break in the continuity of bone rendering it structurally
incompetent
Fracture
Classification of fractures:
normal bone experiencing abnormal force
Traumatic
Classification of fractures:
abnormal bone experiencing normal forces
Pathologic
bone is only partially broken in continuity
Incomplete
incomplete fracture, which results in a bent bone in children and youths
greenstick fracture (remember it like glowstick)
loss of continuity
Complete
