Bones Flashcards
Describe the structure of compact bone
Organised into circular structures called osteons/Haversian systems
What structure lies in the middle of an osteon ?
Haversian canal
The less dense bone is known as what?
Spongey (trabecular) bone
Describe the structure of trabecular bone
Network of lamellate trabeculae filled with bone marrow (no Haversian systems)
Orientation of trabeculae serves what physiology?
Directions of main mechanical stress
What permeates the trabecular bone?
Blood vessels
What are the names of the two membranes of bones?
Periosteum and endosteum
What three specialised cell types make up bone?
Osteocytes, osteoblasts and osteoclasts
What is an osteocyte?
Mature bone cells found in lacunae (natural depressions)
What is the function of an osteocyte?
Not well understood - its suggested that they may maintain the bone matrix and sense mechanical forces
What channels allow communication between bone cells?
Canaliculi connect lamellae to each other
What is an osteoblast?
Immature bone cell created from osteoprogenitor cells in periosteum and endosteum
What are the functions of osteoblasts?
Produces bone matrix and initiates calcification
Unmineralised bones matrix is also known as what?
Osteoids
When do osteoblasts become osteocytes?
When the bone matrix is fully developed
What is an osteoclast?
Multinucleate cells derived from monocytes/macrophages
Where are osteoclasts found?
Bone surface
What do osteoclasts look like?
Large cells with ‘ruffled’ edge
What do osteoclasts do?
Reabsorb bone matrix
Where are the structure called where osteoclasts arefound?
Howships’ lacunae (pits on surface of bone)
Describe the extracellular matrix of bone
- 45% Hydroxyapatite crystals (complex calcium phosphate crystal)
- 35% collagen
- 20% water
What is the special feature of collagen found in bone?
- Modified Type I collagen fibres have strong covalent cross links which leave large gaps for hydroxyapatite crystals
- Collagen fibre orientation linked to mechanical forces
What two types of bone formation are there?
Endochondral and intramembranous
Which is the most common type of bone formation?
Endochondral
Describe the process of endochondral ossification (bone synthesis)
- Bone forms a cartilage ‘model’ first
- Blood vessels invade cartilage
- Cartilage replaced with bone
- Cartilage remains in epiphyseal growth plate - eventually ossifies
What is the key difference between endochondral and intramembranous bone development?
Intramembranous bone development has no cartilaginous phase
Describe intramembranous ossification
Mesenchymal cells develop osteoprogenitor cells that develop into osteoblasts that start depositing bone
What happens to residual mesenchymal cells?
They develop into blood vessels and bone marrow
Healthy bone is a balance of what processes?
Removal and formation
Describe the process of bone turnover
- Osteoclasts breakdown old bone
- Osteoblasts build new bone
- Repeat
What are the functions of bones?
- Weight baring
- Protection
- Mineral store
- Blood formation
Weight baring functions are achieved how?
Minerals make bone stiff (High strength under compression) and collagen gives bone flexibility and reduces risk of fracture (high tensile strength)
Name the six types of bone
- Flat bone
- Sutural bone
- Irregular bone
- Short bone
- Sesamoid bone
- Long bone
What is osteoporosis?
Occurs when the process of reabsorption is greater than the process of formation - this results in bone degradation
Paget’s Disease
Increased reabsorption/formation - causing massive irregularity in bone structure
Osteopetrosis
Decreased reabsorption of bone
What factors can regulate density of bone?
- Weightlessness - can cause serious loss of bone density
- Athleticism - higher bone density
- Resistance and high impact sports are effective at maintaining bone density
