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KNES 363 > Bone (re)modelling dynamics > Flashcards

Bone (re)modelling dynamics Flashcards

1
Q

what are the 4 types of bone cells

A

osteoclasts
osteoblasts
osteocytes
bone lining cell

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2
Q

what is the function of osteoclasts

A

reabsorb/break down bone

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3
Q

what are osteoclast cells

A

multinucleated cells
formed by fusion of monocytes originated in bone marrow

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4
Q

what is the function of osteoblasts

A

form bone
(blasts are builders)

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5
Q

what are osteoblast cells

A

mononuclear cells that produce osteoid
formed from mesenchymal stem cells from the bone marrow

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6
Q

what is osteoid

A

organic component of bone tissue

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7
Q

what cell are osteoclasts closely related to

A

macrophages - migrate through all tissues and remove debris adn pathological material

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8
Q

what cell are osteoblasts closely related to

A

fibroblasts - produce structural molecules in other tissue

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9
Q

how fast do osteoclasts work

A

move at 10s of microns per day

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10
Q

what is the process that osteoclasts use to reabsorb bone

A
  1. demineralise bone with acids
  2. dissolve collagen with enzymes
    (2 step process for 2 main parts of bone)
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11
Q

how fast do osteoblasts work

A

move at ~1 micron per day
(10x slower than clasts)

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12
Q

what are bone lining cells

A

osteoblasts that escape from osteoid and live on the surface of the bone

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13
Q

what is the function of bone lining cells

A

doesn’t do much
- believed to sense loading

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14
Q

what are osteocytes

A

osteoblasts that have become buried in bone (can also be considered a bone forming cell)
- very large SA in bone

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15
Q

where are osteocytes found

A

sit in lacunae (~15000 lacunae per mm3)
communicate with each other via dendritic processes called canaliculi

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16
Q

what is the function of osteocytes

A

mechanosensitive cells (respond to stress and strain)
primarily responsible for planning / orchestrating bone remodelling and adaptation

17
Q

what is bone modelling

A

independent action of osteoclasts and osteoblasts on different surface (not acting in unison together)

18
Q

what is the function of bone modelling

A

produce large scale changes in bone size and shape

19
Q

when is bone modelling the most active

A

during growth and development
- never goes away but easier to do large scale changes during development so declines with age

20
Q

what is bone remodelling

A

coupled seqeuntial action of clasts and blasts
(removes a small portion of bone and replaces with newly formed bone)

21
Q

what is the function of bone remodelling

A

to have small local changes in bone
(doesn’t influence bone size and shape)
- removes boen damage and mechanically “fine tunes” the skeleton to best resist laod

22
Q

when does bone remodelling occur

A

occurs throughout life but decreases after growth

23
Q

where does bone remodelling occur

A

can only happen on a surface

24
Q

how does remodelling occur in trabecular bone

A

clasts make divet in bone surface and blasts fill it in
(way more common and faster than cortical)

25
Q

how much bone remodelling occurs in trabecular bone

A

about 25% new per year

26
Q

how does remodelling occur in cortical bone

A

clasts make a cave in teh bone and blasts fill in behind them
- requires a blood vessel
- much slower than trabecular bone

27
Q

what is a BMU

A

basic multicellular unit
- anytime clasts and blasts are working together

28
Q

how fast is remodelling accomplished by BMUs

A

about 40 microns per day

29
Q

what are the three steps in the ARF seqeunce of BMU remodelling

A
  1. activation
  2. reabsorption
  3. formation
30
Q

explain the activation stage of BMU remodelling (process and time)

A
  • differentiation of precursor cells to produce osteoclasts
  • 3 days
31
Q

explain the reabsorption stage of BMU remodelling (process and time)

A
  • osteoclasts start to reabsorb bone (abotu 40 microns per day)
  • 30 days
32
Q

explain the formation stage of BMU remodelling (process and time)

A
  • osteoblasts appear and begin to refill (leave vascular loop to support metabolism of the BMY and carry nutrients)
  • 3 months
33
Q

how long does the whole process of BMU remodelling take

A

10-12 months total
(can take another 6 months after formation stage to be fully mineralised)

34
Q

why does BMU activation rise around 55yo

A

loss of estorgen leads to no inhibiton of osteoclasts and reabsorption

KNES 363 (19 decks)

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