Bone Growth Flashcards
Describe the formation of the cartilage callus in endochondral bone ossification.
Endochondral ossification begins when mesenchymal cells crowd together in the shape of a future bone and develop into chondroblasts which secrete an ECM to forma hyaline cartilage model of the future bone
Surrounding mesenchymal cells then condense to form the outer perichondrium
The chondroblasts become encased in the secreted ECM and differentiate into chondrocytes
These chondrocytes undergo continual cell proliferation to cause interstitial growth
As the cartilage model grows, centra chondrocytes hypertrophy and the surrounding ECM calcifies
This prevents the diffusion if nutrients so that the encased chondrocytes die
Describe the formation of the primary ossification centre during endochondral bone growth
A growing nutrient artery will grow through a small hole in the cartilage model called the nutrient foramen and grow into the central region of the cartilage model
This stimulates osteoprogenitor cells in the pericondrium to differentiate into osteoblasts which eventually form the periosteum
As periosteal capillaries grow into the calcified cartilage and chondrocytes hypertrophy and die a primary ossification centre grows within the shaft of the bone
Osteoblatsts graduallu replace the calcified cartilage matrix and begin to secrete osteoid
Invading osteoclasts break down some of the central trabecular bone to form medullary cavities
The surrounding bone is replaced with compact bone
Describe the development of the secondary ossification centre in endochondral bone formation
Branches of the epiphyseal arteries invade the epiphysis inducing the development of a secondary ossification centre where cartilage is replaced by bone but no medullary cavity is formed
What is appositional growth?
Growth which increases the girth or width
What is interstitial growth?
Increase in length such as what happens with the growth plate cartilage model
What is endochondral ossification?
The formation of bone where a cartilage model is first laid down as a precursor to bone
What is intramembranous ossification?
The formation of bone where cartilage is not involved and there is instead a condensation of mesenchyme straight to bone
Appositional growth occurs by what tyoe of ossification?
Intramembranous ossification
When does the physis of long bones close?
Puberty
