MS System - Bones Flashcards
What is bone?
- Collagen fibre framework
- In a mucopolysaccharide-rich gel
- Hardened by hydroxyapatite crystals
Epiphysis
- where
- structure
- function
- Top of bone
- Top = articular surface w hyaline cartilage
- Movement, stability
Diaphysis
- where
- structure
- function
- Middle of bone
- Outside = compact bone, inside = hollow cylinder (bone marrow)
- Where blood vessels enter
Metaphysis
- where
- structure
- function
- Between epiphysis & diaphysis
- Plates of hyaline cartilage
- Region of growth
Cancellous (trabecular) bone
- where
- structure
- function x2
- Both ends
- Porous, open structure
- Supporting strength
- Site of haemopoiesis
Cortical (compact) bone
- where
- structure
- function
- Outside (forms shaft)
- Solid, compact
- stiffness, strength
Periosteum
- where
- structure
- Outside of diaphysis
- Compact bone
Trabeculae
Laid along lines of stress:
- Allows distribution of stress
- High SA for metabolism
Loss of trabecular due to…
If bones aren’t stressed –> bones remodel –> lose trabeculae
Haversian Canals
Blood vessels along the LONG axis
Volkmann’s Cannals
Blood vessels along the PERPENDICULAR axis
Lamellae
- what
- where
- Concentric circles around vessels
- Mainly in cortical bone
Lamellae & osteocytes
Most cells are in v close contact to blood vessels, BUT osteocytes aren’t –> finger-like projections
Cancellous bone & lamellae
- SO?
- Less lamellar layers
SO - Less dense & coordinated –> weaker
Bone matrix components x3
- Collagen (organised arrangement)
- Hydroxyapatite
- Water
What is hydroxyapatite?
Precipitated calcium phosphate crystals
Osteoblasts
- function
- structure
- extra
- Bone builders
- Mononucleate
- Deposit collagen –> then hydroxyapatite
Osteoclasts
- function
- structure
- extra
- Bone chewers
- Multinucleate
- Reabsorb bone by demineralisation:
- forms ‘sealing zone’ –> protons & hydrolytic enzymes –> breaks down bone matrix –> releases Ca
Osteocytes
- function x2
- formed
- Maintain matrix
- Relatively inactive
- Osteocytes become entombed in matrix/lacunae
Osteoprogenitors
- where
- function
- Line bone surface
- Stem cells –> form osteoblasts
Formation of woven bone
- when damaged…
- then…
- over time…
- Periosteum = damaged –> sends signals –> increased blood flow, inflammation
- Callus formation –> osteoblasts form ‘woven bone’ = weak
- Lamellular bone laid down
Lamellular bone = stronger than woven bone as…
Woven bone –> collagen fibres = irregular
Lamellular bone –> collagen fibres = in sheets
Wolff’s Law
Bone adapts to the load under which it is placed
Bone remodelling/straightening
Side with more pressure remodels more –> bone can straighten
Calcitonin
Less osteoclast activity –> lower blood Ca levels
PTH
Parathyroid hormone
More ostoaclast activity –> releases Ca
Bone remodelling (4 steps)
1) Quite (quiescence)
2) Osteoclasts –> demineralisation
3) Osteoprogenitors –> differentiate to osteoblasts
4) Osteoblasts –> lay down new bone
Bone mass & menopause
Decreases faster –> as less oestrogen = more bone ‘chewing’
Chondroblasts
Form cartilage
Chondroclasts
Remove cartilage
Ossification
The process where cartilage is replaced by bone
Centres of ossification:
- primary
- secondary
- Diaphysis
- Epiphysis
Epiphyseal plate
- what
- where
- structure
- Growth plate
- Between epiphysis & diaphysis
- Made of cartilage
Growth stops when…
Epiphysis & diaphysis fuse
normally end of puberty
Ossification process (5 steps)
1) Resting zone
- Chondroblasts lay down cartilage (by epiphysis)
2) Growth zone
- Chondroblasts –> mitosis
3) Hypertrophic zone
- Differentiate –> chondrocytes = swell (increase cytoplasm)
4) Calcification zone
- Swelling –> mineralisation
5) Ossification zone
- Disorganised bone from mineralisation = remodelled
