Bone Development + Ossification Flashcards
What are the 2 main “layers” of the periosteum?
1 - fibrous (collagen fibres and fibroblasts)
2 - makes osteoblasts
> upper is osteoprogenitors
> lower is osteoblasts
What causes the scalloped appearance of the periosteum?
Sub-periosteal bone remodelling
Why are osteoclasts multinucleated?
Cell fusion
What is the function of the sealing/clear zone of an osteoclast and how can you identify it?
Allows attachment
No organelles
Why does an osteoclast have a ruffled border?
Increases surface area for proton and chloride ion channels for acidification
What are osteoclasts found sitting in?
Howship’s lacunae
What is intramembraneous ossification (briefly)?
Bone formed directly from precursors
What bones are formed from intramembraneous ossification?
Flat bones of skull, calvaria
Describe the process of intramembraneous ossification
Formation of periosteum then differentiation to osteoblasts to deposit matrix for mineralisation
Vascularisation and continued growth and remodelling
What is endochondral ossification (briefly)?
Bone formed via a cartilage intermediate
What bones are formed from endochondral ossification?
Long bones
Vertebrae
Describe the process of endochondral ossification
- Formation of cartilage model by chondroblasts which calcifies
- Formation of bony collar around diaphysis (periosteum)
- Capillary invasion to form primary ossification centre in diaphysis
- Invasion of capillaries in epiphyses to form secondary ossification centres
What is the area between the primary and secondary ossification centres called?
Epiphyseal growth plate
What type of collagen does the perichondrium produce?
Type I
What type of collagen do chondrocytes produce?
Type II
What does the epiphyseal growth plate become when growth ends?
Epiphyseal line
What are the zones of the epiphyseal growth plate (from epiphysis to diaphysis)?
Resting zone
Proliferative zone
Hypertrophic zone
Calcification/ossification zone/primary spongiosa
What is the resting zone of the epiphyseal growth plate?
Resting chondrocytes in cartilage matrix
What happens in the proliferative zone of the epiphyseal growth plate?
Chondrocytes expand, stretch and divide (pancakes)
What happens in the hypertrophic zone of the epiphyseal growth plate?
Huge chondrocytes start to atrophy and die off and cartilage starts to become calcified
What happens in the calcification zone of the epiphyseal growth plate?
Cartilage acts as scaffolding for bone matrix deposition (alveolar bone)
What is the secondary spongiosa?
Mature lamellar bone with no cartilage (after primary spongiosa)
What are the two types of bone growth?
Appositional
Interstitial
Where does appositional growth occur?
Bone and cartilage
Where does interstitial growth occur?
Cartilage only
What is appositional growth?
Matrix deposition upon pre-existing matrix
What is interstitial growth?
Matrix deposition from within a matrix
What is the lineage of a lining cell?
Mesenchymal stem cell | Chondro-osteo precursor | Osteoprogenitor | Osteoblast | Lining cell
What is the lineage of an osteocyte?
Mesenchymal stem cell | Chondro-osteo precursor | Osteoprogenitor | Osteoblast | Osteocyte
What is the lineage of a chondrocyte?
Mesenchymal stem cell | Chondro-osteo precursor | Chondroprogenitor | Chondrocyte
What other (non-bone) cells are formed from mesenchymal stem cells?
Muscle cells
Adipocytes
Fibroblasts
What is the lineage of an osteoclast?
Haematopoietic stem cell | Macrophage/osteoclast precursor | Osteoclast precursor | Osteoclast
What other (non-bone) cell-types are formed from haematopoietic stem cells?
Myeloid
Lymphoid
(Macrophage)
