Alveolar Bone Flashcards
What is the composition of alveolar bone?
60% inorganic, 25% organic and about 15% water. Organic component is 90% type 1 collagen fibres and remaining 10% proteoglycans, glycoproteins, osteocalcins etc
What is the matrix of alveolar bone made up of?
Inorganic material and an organic matrix
Most of the collagen in alveolar bone can be considered as what?
Intrinsic collagen secreted by osteoblasts however collagen fibres inserted as Sharpey’s fibres can be considered as extrinsic collagen by adjacent fibroblasts.
Where are the hydroxyapatite crystallites distributed?
Within the spaces between, and on the surfaces of the collagen fibrils
How may bone be classified?
Compact (cortical) or cancellous according to its bone density
What is the difference between cancellous and cortical bone?
Cancellous bone has a lattice arrangement of the individual bony trabeculae that surround marrow. Cortical bone forms a dense, solid mass.
What are the parallel layers of lamellae called in compact bone?
Circumferential lamellae
What is a Haversian system?
Deep to the circumferential lamellae, lamellae are arranged as small concentric layers around a neurovascular canal with up to 20 concentric lamellae.
What can haemopoietic bone marrow cells in cancellous bone give rise to?
Mesenchymal cells - osteoblasts
Blood cell lineage - osteoclasts
How do Sharpey’s fibres enter the bone?
Perpendicular to the surface, less numerous but thicker than those at the cementum surface
What are trans alveolar fibres?
Sharpey’s fibres that enter the bone mesio-distally passing straight through to become continuous with similar fibres from the root of the adjacent tooth.
What are features of osteoblasts?
- Mesenchymal in origin
- Lie on surface of forming bone
- Secrete and mineralise organic matrix
- Incorporated into bone matrix as osteocytes
- Has numerous cell contacts with adjacent cells
- Have only one nucleus
What are features of osteocytes?
- Cells living in the bone itself
- Represent osteoblasts trapped in bone matrix
- Important function of osteoclast activation and is a mechanosensor in bone
- Mesenchymal in origin
What are features of osteoclasts?
- Removes mineral matrix then organic matrix after
- Secretes protons for a low pH
- Express receptors for hormones
- Multinucleated cells that resorb bone
- Haemopoietic in origin
- Rich in acid phosphatase
What is osteoid formed of?
Type 1 collagen fibrils and proteoglycans, glycoproteins and other proteins. (lag phase to make sure osteoid has matured enough to undergo mineralisation)
