Aim: How can we describe the steps of
endochondral ossification?
DO NOW:
Review
HWEndochondral
ossification due
tomorrow
Review packet due on
Thursday
Test on
Friday
Bone Formation and Growth
• Bone Development
– Human bones grow until about age 25
– Osteogenesis
• Bone formation
– Calcification
• The process of depositing calcium salts
• Occurs during bone ossification and in other tissues
Bone Formation and Growth
• Bone Development
– Ossification
• The process of replacing other tissues with bone
• The two main forms of ossification are
– intramembranous ossification
– endochondral ossification
Literacy Activity-Pair and Share
Define Endochondral ossification
• Endochondral Ossification
– Ossifies bones that originate as hyaline cartilage
– Occurs in most bones of the body
Explain the events of the cartilage
model.
• Cartilage expands and chondrocytes enlarge then die and
disintegrate leaving cavities within cartilage
• Blood vessels grow into perichondrium (surface of
cartilage)
• Osteoprogenitor cells differentiate into osteoblasts ,
which start to lay down matrix.
Define primary ossification center.
Where is it located and briefly describe the events that take place there?
› Occurs in the diaphysis
› Bone Development begins in the Primary
Ossification Center- Spongy Bone
 No Medullary Cavity
› Development of medullary Cavity due to
osteoclasts
› Growth continues in length(interstitial growth)
and diameter(appositional growth)
Define secondary ossification.
Where is it located and briefly describe the events that take place
there?
• Capillaries and osteoblast migrate into the
epiphyses creating secondary ossification
centers.
– The epiphyses becomes filled with spongy bone
– Articular cartilage- remnants of cartilage
• Prevents bone to bone contact within joint
Explain the significance of the
epiphyseal plate.
• Epiphyseal cartilage (plate) separates epiphysis and
diaphysis.
• Remains cartilage until growth ends
• Epiphyseal Lines
– When long bone stops growing, after puberty
• Epiphyseal cartilage disappears
• Is visible on X-rays as an epiphyseal line
Bone Formation and Growth
Figure 6–11 Bone Growth at an Epiphyseal Cartilage.
B
A
C
E
F
D
Endochondral Bone
Intramembranous Ossification
– bones such as mandible (lower jaw)
– Clavicle (collarbone)
– Soft Spots
Bone Formation and Growth
Figure 6–12 Intramembranous Ossification.
Bone Formation and Growth
Ossification
• Ossification
Summary
1. The ______________________ nutrient artery penetrates
the _____________________, which is converted to the
___________________ of bone.
2. Primary ossification begins in the
__________________________ of bone.
3. Secondary ossification takes place in the
_______________________.
True or False
4. Intramembranous ossification forms long bones.
5. Endochondral ossification does not begin with mesenchymal
cells.
6. Spongy bone is laid down before compact bone during
ossification.
Bone Formation and Growth
• Epiphyseal Lines
– When long bone stops growing, after puberty
• Epiphyseal cartilage disappears
• Is visible on X-rays as an epiphyseal line
• Mature Bones
– As long bone matures
• Osteoclasts enlarge medullary (marrow) cavity
• Osteons form around blood vessels in compact bone
Bone Formation and Growth
Figure 6–10 Endochondral Ossification.
Bone Formation and Growth
5
6
4
1
2
3
Perichondrium
Perichondrium
Proximal
epiphysis
Proximal
epiphysis
Uncalcified
Uncalcified
matrixmatrix
Hyaline Hyaline
cartilage cartilage
Periosteum
Periosteum
Uncalcified
Uncalcified
matrix matrix
Diaphysis
Diaphysis
Distal
epiphysis
Distal
epiphysis
CalcifiedCalcified
matrix matrix
Calcified
Calcified
matrixmatrix
Periosteum
Periosteum
Primary
Primary
(covering
ossification
ossification (covering
compact
compact
bone)bone)
center
center
Medullary
Medullary
Spongy
Spongy
cavitycavity
bone
bone
Nutrient
Nutrient
artery
artery
Nutrient
Nutrient
arteryartery
and vein
and vein
of
of
1 Development
1 Development
cartilage model
cartilage model
of
of
2 Growth
2 Growth
cartilage
cartilage
modelmodel
33 Development
Development of
of
primary
primary ossification
ossification
center
center
4 Development
4 Development
of
of
the medullary
the medullary
cavity
cavity
Articular cartilage
Secondary
ossification
center
Epiphyseal
Epiphyseal
artery
artery
andand
vein
vein
Secondary
ossification
center
Spongy bone
Uncalcified
Uncalcified
matrix
matrix
Epiphyseal plate
Nutrient
Nutrient
artery and vein
artery and vein
5 Development
5 Development
of secondary
of secondary
ossification
ossification
center center
6 Formation of articular cartilage
and epiphyseal plate
Bone Formation and Growth
Steps of Endochondral ossification
• Step 1
• Chondrocytes (cartilage cells)increase in size
• Chondrocytes die
• Step 2
• Blood vessels grow into perichondrium
(surface of cartilage)
• Cells of perichondrium convert to
osteoblasts.
• Osteoblasts convert perichondrium to
periosteum
Steps of Endochondral ossification
Step 3
› Blood vessel penetration
› Fibroblast
Osteoblast
› Bone Development begins in the center
 Primary Ossification Center- Spongy Bone
 No Medullary Cavity
Step 4
› Development of medullary Cavity
› Growth continues in length(interstitial
growth) and diameter(appositional growth)
Steps of Endochondral ossification
• Step 5
– Capillaries and osteoblast migrate into the
epiphyses creating secondary ossification
centers.
• Step 6
– The epiphyses becomes filled with spongy
bone
– Articular cartilage- remnants of cartilage
• Prevents bone to bone contact within joint
– Epiphyseal cartilage (plate) separates
epiphysis and diaphysis.
Growth in Length- Interstitial Growth
• The growth in length of long
bones involves two major
events:
– 1) Growth of cartilage on
the epiphyseal plate
– 2) Replacement of cartilage
by bone tissue in the
epiphyseal plate
Copyright 2009, John Wiley & Sons, Inc.
Bone Formation and Growth
• Appositional growth
– Compact bone thickens and strengthens long
bone with layers of circumferential lamellae
Endochondral Ossification
Bone Formation and Growth
• Epiphyseal Lines
– When long bone stops growing, after puberty
• Epiphyseal cartilage disappears
• Is visible on X-rays as an epiphyseal line
• Mature Bones
– As long bone matures
• Osteoclasts enlarge medullary (marrow) cavity
• Osteons form around blood vessels in compact bone