Bone Flashcards
What are the functions of bones?
Weight bearing / support
Mineral store
Protection
Blood formation
What is the hard bone found on the outside of the bone?
Cortical
What is the spongy bone called?
Trabecular
What is the cavity in the bone called?
Medullary cavity
How is compact bone organised?
Compact structures called osteons or haversian systems
What type of canals exist in haversian systems?
Central haversion canal and horizontal perforating / volkmann’s canals
What can be found around a haversian canal?
Osteocytes and concentric rings of bone matrix (lamellae) around the haversion canal
How does density differ between spongy bone and dense bone?
Spongy bone is much less dense
What does spongy bone consist of?
Network of lamellated trabeculae (a network of intercommunicating spaces)
What is the direction of the trabeculae dependant on?
The main direction of mechanical forces
What are the six types of bones?
Flat bone, Sutural bone, Irregular bone, Long bone, short bone, sesamoid bone
What are the two types of bone formation?
Endochronal (most common type including long bone growth)
Intramembranous (Flat bones of the skull, mandible, maxilla, clavicles)
What are the stages of endochronal ossification?
Bone forms as cartilage 'model' first Blood vessels invade the cartilage Cartilage is replaced with bone Cartilage remains in the epiphyseal growth plate Growth plate eventually ossifies
Describe the stages of intramembranous ossification
No cartilagenous phase!
Mesenchymal cells develop into osteoprogenitor cells that mature into osteoblasts that start depositing bone.
Residual mesenchymal cells develop blood vessels and bone marrow
This bone formation also occurs in adult cortical bone
What makes up bone cells?
Osteoblasts, osteocytes and osteoclasts
What makes up the extracellular matrix?
45% hydroxyapatite crystals
35% collagen type 1
20% Water
What properties does the hydroxyapatite confer?
Make bones stiff and able to support structures
High strength under compression
What properties does collagen give to the bone?
Gives the bones some flexibility and reduces the risk of fracture
High strength under tension
What ways is bone considered dynamic?
Fracture healing and bone density adaptation to high stress (sports)
What is responsible for the bone turnover/remodelling?
Osteoclasts breaking down old bone
Osteoblasts building new bone
What type of membranes exist in the bone?
Periosteum and endosteum
Where are the osteoblasts created by the osteopreginitor cells?
Periosteum and endosteum
What is the function of an osteoblast?
Produces bone matrix and initiates calcification
What is osteoid?
Unmineralised matrix
When does an osteoblast become an osteocyte?
Once it is surrounded by matrix
What is an osteocyte?
Mature bone found inside lacunae (cavity within bone)
What are canaliculi?
Connect lacunae to each other - allows communication between cells
What are osteoclasts?
Multinucleate cells derived from monocytes/ macrophages
What is the function of osteoclasts
resorb bone matrix
What does the extracellular matrix consist of?
Mainly minerals, protein, collagen and water
Describe the fibres in the extracellular matrix
Mostly modified type 1 collagen fibres
Strongly cross linked and large gaps within the fibres
Gaps provide space for hypoxyapatite crystals
Collagen fibre formation is linked to mechanical forces
What diseases can result when resorption is greater than formation?
Osteoporosis and pagets disease
What disease results from a decrease in bone resorption?
Osteopetrosis
Why is there a loss of bone mass in women after the menopause?
Less oestrogen - confers an inhibitory effect on bone breakdown
What is responsible for bone density?
Genes and the environment
What is good for increasing bone mineral density?
Resistance and high impact sports
