Lecture 3 - Bone And Tooth Structure Flashcards
Bone mineral is
Calcium and phosphate laid down as hydroxyapetite crystal
- gives compressive strength
What has a high proportion of trabecular bone
Spine + pelvis
What has a high proportion of cortical bone
Bones of arm, femur
Bone matrix composition
COLLAGEN
- gives tensile strength
- type I
NON COLLAGENOUS PROTEINS
- alkaline phosphatase
- proteoglycans
- growth factors in bone matrix
BONE MINERAL
Osteoblasts
- bone forming cells
- line bone surface
- active synthesis of matrix
- involved in mineralisation
Lining cells
- flattened osteoblasts lining bone surface
Osteocytes
- osteoblasts embedded in bone matrix
- connected by canaliculae
- involved in sensing mechanical forces
- make up 90% of bone cells and are long lived
Bone resorbing cells: osteoclasts
- multinucleated giant cells
- secrete acid and proteolytic enzymes
- dissolve mineral and degrade protein
- release embedded growth factors
Activity of osteoblasts or osteoclasts depends on
- number of cells formed
- activity of cells
- lifespan of cells
3 reasons why bone turnover happens
- shape changes of bone
- in response to changing load
- repair of microdamage
Osteoclast induced osteoblast differentiation
Osteoclast release TGFb, BMP and IGF during resorption, which induces chemotaxis, proliferation and differentiation of osteoblasts, leading to mineralization
Osteoblast-induced osteoclast differentiation
Osteoblast express RANK-L on their surface
- binds to RANK ligand on a preosteoclast
- this interaction results in osteoclast differentiation
- osteoblasts can also produce osteoprotegerin to prevent this interaction
Tooth specialized cells
- Ameloblast: lay down enamel, very dense matrix resistant to acid attack. Closely packed collagen and HAP crystals
- Odontoblasts: lay down dentine. Collagen fibres in dentine extend to alveolar bone
- osteoblasts and osteoclasts involved in alveolar bone remodeling
Caries
Bacteria + food -> anaerobic acid release -> dissolves mineral
- also proteolytic enzymes -> break down matrix
Assessing bone: bone densitometry
- assume normal mineralisation
- no osteophytes
- consider aortic calcification
Other methods of assessing bone
- ultrasound
- bone biopsy - very invasive
- other: bone quality - microarchitecture/fractures/ cell death/ rates of bone turnover
Osteoporosis
- low trauma fracture
- bone mineral density
T score and Z score
- T score: compared with mean peak bone mass - assesses what is desirable, used to assess fracture risk
- Z score: compared with age and gender matched controls - assesses what is expected. USed to determine if bone mass is unusually low
T score and disease category
Normal: -1 and above
Osteopenia: -1- - 2.5
Osteroporosis:
