Bone histogenesis Flashcards
What bones form via intramembranous ossification?
Flat bones of the skull and face (e.g. mandible and clavicle)
What is endochondral osteogenesis?
Cartilage provides a provisional matrix to be eroded and replaced with mature bone
What are the steps of intramembranous bone formation?
- Formation of well-vascularized connective tissue
- Transformation of mesenchymal cells to basophilic osteoblasts (bone blastema)
producing an eosinophilic osteoid matrix - Modeling/shaping of bone as fetus grows (osteoclasts/osteoblasts)
How will bone stain?
Eosinophilic
How will calcified cartilage stain?
Basophilic
What are the 2 phases of bone formation?
- Matrix (osteoid) formation
2. Mineralization
What is the osteoid seam?
The layer between osteoblasts and mineralized matrix.
What is the name of the first bone to appear? What replaces it?
Woven, primary bone.
Later replaced by lamellar, secondary bone.
How does primary bone differ from secondary bone?
Less mineralized, more cellular than mature bone
Grows more rapidly
What are the steps of endochondral bone formation?
- Hypertrophy of chondrocytes in the central portion: matrix vesicles and type X collagen
- Formation of the bone collar between the periosteum and the bone shaft
- Calcification and condensing of cartilage matrix -> apoptosis of chondrocytes -> calcified cartilage
- Invasion of blood vessels (periosteal/osteogenic bud) OPCs and HPCs form the primary ossification center
- OPCs differentiate into osteoblasts, lay down bone matrix on calcified cartilage scaffoldC
How do chondrocytes lead to their own death?
Secrete pyrophosphatase and alkaline phosphatase which increase overall posphate ions.
What do matrix vesicles do?
Form mineral crystals in endochondral bone mineralization
What does type X collagen do?
Binds mineral crystals together in endochondral bone mineralization.
Can secondary centers of ossification occur?
Postnatally in long bones
What is the epiphyseal plate?
The region of hyaline cartilage remaining between the primary and secondary centers.