Ossification and Bone Growth Flashcards
What is endochondral ossification and how does it help bones
Bone formation from a cartilage model
Typical of long bone formation
Permits stress to be handled during growth
Describe the process of the primary centre of ossification in endochondral ossification
Hyaline cartilage model forms in embryo. Capillaries invade perichondrium to form periosteum around centre of this model. Bone collar produced from osteoblasts in this periosteum. Chondrocytes in the middle of the diaphysis mature, hypertrophy and die.
Cartilage matrix calcifies and leaves spicules of calcified cartilage. Blood vessel from periosteum enters diaphysis through bony collar. Carries osteoblasts with it that lay down trabecular bone in place of calcified cartilage. This area of bone formation is called the primary centre of ossification.
Describe the process of the secondary centre of ossification in endochondral ossification
The later developing epiphyseal foci of ossification.
As hyaline cartilage of the epiphysis grows by appositional growth (at the surface) chondrocytes in its centre mature and start to die.
Calcification of this cartilage occurs. A blood vessels enters the degenerating hyaline cartilage and osteoblast activity replaces the calcified cartilage with bone
Describe what happens to the diameter and length of bones in postnatal bone growth
Bone shaft diameter increases by bone formation on outer/periosteal surface (appositional growth).
Long bones increase in length at the epiphyseal growth plate.
Epiphysis diameter growth occurs by adding cartilage to the outer surface and expansion of the secondary ossification centre
From the epiphysis to the diaphysis, name the morphologic zones seen during transition from cartilage to bone in the epiphyseal growth plate
- Reserve/Resting chondrocytes
- Proliferating chondrocytes
- Maturing/hypertrophying chondrocytes
- Calcification/dying chondrocytes
- Ossification - osteoblastic activity
Summarise bone growth as succinctly as possible but make sure you go through all the steps
- Cartilage Model
- Perichondrium -> periosteum
- Diaphysis chondrocytes mature, die and the cartilage matrix calcifies
- Vascularisation
- Osteoblasts replace calcified cartilage with bone - primary centre of ossification
- similar process at epiphyses at secondary centres of ossification
- Growth in diameter: appositional growth of compact bone at periosteal surface
- growth in length: occurs at epiphyseal growth plate via interstitial growth
What is intramembranous ossification and how does it happen
Bone formation within a fibrous membrane.
Within a fibrous CT membrane, mesenchymal cells cluster at multiple sites.
These cells differentiate into osteoblasts and secrete osteoid at these centres of ossification. The osteoid matrix is calcified. Further osteoblast activity = small trabeculae that fuse and form trabecular bone. Woven bone is remodelled into lamellar bone. Layer of compact bone eventually covers trabecular bone. Appositional growth permits increase in size.
What supplies the periosteum and outer compact bone of the diaphysis with blood
Periosteal arteries supply the periosteum and outer compact bone of the diaphysis through Volkmann’s and Haversian canals.
What supplies the diaphysial compact bone, trabecular bone and bone marrow with blood
Nutrient artery
What supplies the epiphyseal and metaphysical trabecular bone with blood
Epiphyseal and metaphysical arteries
How does bone remodelling happen
Osteoclasts resorb bone and osteoblasts produce new lamellar bone.
What can affect bone remodelling
Changing mechanical stresses
Demands of calcium homeostasis (parathyroid hormone, calcitonin fracture)
What types of cells are osteoclasts derived from
Monocyte/macrophage lineage
Can form from myeloid lineage or tissue macrophages
What is the lifespan of an osteoclast
<24hours
Are osteoclasts mono or multinuclear and why
Multi due to fusion of mononuclear precursors
