p r o c e ss
diagram
E ndochondral ossification • Figure 5.3
Most bones in the body are formed through endochondral ossification, replacing
cartilage with bone.
Proximal
epiphysis
Diaphysis
Distal
epiphysis
Perichondrium
Hyaline
cartilage
Chondroblasts
Uncalcified
extracellular
matrix
Calcified
extracellular
matrix
Periosteum
Nutrient
- g M -
-------- - Primary,
A M E r;
ossification
artery
S
\ W
center
Spongy
bone
Development of cartilage model:
• Mesenchymal cells cluster and
differentiate into
chondroblasts
• Chondroblasts secrete
hyaline cartilage
Perichondrium
(a membrane)
forms around the cartilage
Growth of cartilage model:
• Chondroblasts differentiate
into
chondrocytes
• Chondrocytes in the middle
grow and surrounding matrix
calcifies
• Inner chondrocytes die and
form spaces (lacunae)
Development of
primary
ossification center:
• Nutrient artery penetrates the center of
the cartilage model
• Osteogenic cells in perichondrium differentiate
into osteoblasts
• Perichondrium forms bone and becomes
periosteum
• In primary ossification center, cartilage breaks
down, blood vessels expand, and osteoblasts
deposit bone over cartilage remnants
Uncalcified
extracellular
matrix
Calcified
extracellular
matrix
Periosteum
Medullary
(marrow) cavity
Nutrient
artery and vein
^
Q Development of medullary cavity:
• Primary ossification center grows
toward ends
• Osteoclasts break down some
spongy bone trabeculae,
leaving a marrow cavity
• Most of the diaphysis wall
becomes compact bone
Development of secondary
ossification centers:
• Blood vessels enter epiphyses
and form secondary ossification
centers
• Secondary ossification
proceeds outward
• No cavities form
Articular
cartilage
Spongy
bone
Epiphyseal
plate
Formation of
articular
cartilage
and epiphyseal plate:
• Hyaline cartilage at ends become
articular cartilage
• Hyaline cartilage remaining between
the ossification centers (diaphysis and
epiphyses) becomes epiphyseal
growth plate
118
CHAPTER 5
The Skeletal System
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