1: Bone Flashcards
What are the main functions of the bone?
- Structural support (shape+muscle action)
- protection
- blood formation
- mineral storage site
What are the two mechanical properies of bone?
- Cable-like flexibility –>osteioid due to collagen fibres (resistant to tension)
- Pillar-like stiffness –> impregnation of collagen with hytroxyapatite –> complex calcium hydrophosphate (also causes resistance to compression
What is the structure of immature or healing bone?
Woven bone
–> quite irregular structure, not as stable
What is the normal structure of a bone in healthy adults?
Mature bone: Lamellar bone –>
organised and stable
Explain the different arrangements of lamellar bone
Arranges into
- Cortical bone (hard, outer part), compact lamellar bone
- Cancellous bone (spongy/ trabecular bone)
What is an osteon?
How is it organised
Small funtion al unit of bone–> organised as laminar organised cells around a centric canal that carries blood vessels
How does the organisation of spongey osteons differ from compact bone osteons?
They barely differ and have the same structure –> both Lamellar
but spongy part might be a bit smaller
Explain the structure of an osteocyte
It is a big cell with many connections to other cells (gap juctions) to share nutrients
Summarise the bony blood supply
A nutrient artery (middle part, but also epyphisis artery and veins) enters the bone through a nutrient canal
Bone is highly vascularised
How do you call the most outer part iof bone?
What is its function?
It is the periosteum
- Vascularised
- –> important in growth and repair
- good sensory supply (hurts when fractures)
Explain the developemnt of osteocytes
Develop from osteoblasts (that develop from osteogenic cell)
When do bones start to form?
When do they stop growing?
The skeleton starts to form at 6 weeks
Stops growing at Age 25
What are the two types of bone development?
- Intramembranous –> in existing vascular connective tissue
- Endochondral –> exisiting fetal cartilage models
Explain intramembranous formation of bone
- In existing vascular connective tissue
- Bone matrix (ostein) deposited around collagen
- Mineralises to form woven bone
- Remodels to lamellar bone
–> normally in flat bones
How does bone growth?
When bone growth it still needs to carry weight –> not ideal if that is the end of the bone
So:
- Shaft ossifies first, followed by epiphyses
- Growth continues by ossification at growing cartilage plate between them
- Growth cessation when cartilage growth ceases and plate is over-run by ossification
Explain endochrondal bone growht
Forms around existing fetal cartilage models
- Cartilage calcifies and chondrocytes (part of cartilage) die
- Periosteal osteoclasts cut channels for sprouting vessels
- Osteoblasts enter with vessels to build bone around them
Explain the structure and function of the epiphysal plate
It is a cartilage region between shaft and head of bone
–> Cartilage forms and gets ostefied (endochondral) –> enables bone growth
What happens to bone when it is used little and a lot?
Increases or decreases bulk and density in response to pattern of use
- But: when less used: loss of bone mass (ISS)
What shows that bone is an adaptable structure?
- Can grow
- changes density with use
- can remoddel depending on pattern of use
- ability to repair
What is the role in osteocytes in bone repair?
•Osteocytes maintain matrix but can activate osteoblasts for new bone building
How does bone grows in diameter?
When does this happens?
Periosteum is activated to become osteoblasts
Expalint the process of bone healing
- Haematoma
- becomes infiltrated by fibrous matrix and invaded by cartilage/bone progenitors
- Blood vessels invade damaged structure
- Woven bone is forming
- Remoddeling in lamellar bone
What happens to the bone at high calcium levels?
Calcitonin released by parafollicular thyroid cells;
- Inhibition of breakdown of bone matrix by osteoclasts
- Promotion of Ca2+ uptake into bone matrix
What happens to bone at low Ca2+ levels?
Parathyroid Hormone (PTH) released
- Promote osteoclast bone resorption
- increases Ca2+ re-absorption by the kidneys + intestine
